Understanding the effects of land use changes on the spatiotemporal variation of soil organic carbon （SOC） can provide guidance for low carbon and sustainable agriculture. In this paper, based on the large-scale dat...Understanding the effects of land use changes on the spatiotemporal variation of soil organic carbon （SOC） can provide guidance for low carbon and sustainable agriculture. In this paper, based on the large-scale datasets of soil surveys in 1982 and 2009 for Pinggu District -- an urban-rural ecotone of Beijing, China, the effects of land use and land use changes on both temporal variation and spatial variation of SOC were analyzed. Results showed that from 1982 to 2009 in Pinggu District, the following land use change mainly occurred： Grain cropland converted to orchard or vegetable land, and grassland converted to forestland. The SOC content decreased in region where the land use type changed to grain cropland （e.g., vegetable land to grain cropland decreased by 0.7 g kg-1; orchard to grain cropland decreased by 0.2 g kg-l）. In contrast, the SOC content increased in region where the land use type changed to either orchard （excluding forestland） or forestland （e.g., grain cropland to orchard and forestland increased by 2.7 and 2.4 g kg-1, respectively; grassland to orchard and forestland increased by 4.8 and 4.9 g kg-1, respectively）. The organic carbon accumulation capacity per unit mass of the soil increased in the following order： grain cropland soil〈vegetable land/grassland soil〈orchard soil〈forestland soil. Therefore, to both secure supply of agricultural products and develop low carbon agriculture in a modern city, orchard has proven to be a good choice for land using.展开更多
With a warming climate,temperature extremes have been a main global issue in recent decades due to their potential influence on the sustainable development of human life and natural ecosystems.In this study,12 indicat...With a warming climate,temperature extremes have been a main global issue in recent decades due to their potential influence on the sustainable development of human life and natural ecosystems.In this study,12 indicators of extreme temperature events are used to evaluate the spatiotemporal distribution,periodic structure and teleconnections with large-scale atmospheric circulation in Xinjiang,Northwest China by combining wavelet coherence(WTC) analysis based on continuous wavelet transform(CWT) analysis with the sequential Mann-Kendall test.We find that over the past six decades,the climate in Xinjiang has become warmer and has suffered from increases in the frequency of warm extremes and decreases in the frequency of cold extremes.Warm extremes have mainly occurred in the southern Tianshan Mountains surrounding the Tarim Basin and western part of the Taklamakan Desert,and cold extremes have primarily occurred in the southwestern Altai Mountains and northern foot of the Tianshan Mountains.Extreme temperature events,including warm extremes,cold extremes,and other temperature indices,have significant interannual variability,with the main oscillation periods at smaller(2–4-year band),intermediate(4–7-year band),and greater time scales in recent decades.Furthermore,cold-extreme indices,including frost days,cool days,and cool nights all show a clear changepoint during 1990–1997 at the 95% confidence level,and both ice days and cold spell duration indicator have a potential changepoint during 1981–1986.However,the changing points for warmextreme indices are detected during 1992–1998.The temperature variables are significantly correlated with the EI Ni?o-Southern Oscillation(ENSO) and Arctic Oscillation(AO),but less well correlated with the Pacific Decadal Oscillation(PDO).The phase difference in the WTC spectra is not uniform between temperature extremes and climatic oscillations.Our findings will have important implications for local governments in taking effective measures to mitigate the potential effects of regional climate warming due to human activities in Xinjiang.展开更多
Soil erosion is a prominent environmental problem in karst regions.Exploring the spatiotemporal variability of soil erosion and the factors that influence soil erosion is of great significance for regional soil erosio...Soil erosion is a prominent environmental problem in karst regions.Exploring the spatiotemporal variability of soil erosion and the factors that influence soil erosion is of great significance for regional soil erosion prevention and control.However,the mechanisms influencing the characteristic features of the karst basins,such as bedrock exposure and lithology,still need to be further explored.This study used GIS technology,the Revised Universal Soil Loss Equation model,Getis–Ord Gi*,and partial least squares regression(PLSR)to identify the dominant factors influencing soil erosion and the spatiotemporal variability of soil erosion in 31 sub-basins of the Dabang River Basin(DRB),a typical karst area of Southwest China,from 2010 to 2020.The results indicated that soil erosion in the DRB from 2010 to 2020 was generally decreasing,the mean soil erosion in the DRB in 2010,2015 and 2020 was 18.46,16.51 and 15.29 t ha^(-1)a^(-1),respectively.During the study period,the area of slight erosion increased by 26.39%(706.54 km^(2)),while severe erosion enlarged by 26.36 km^(2).Spatially,the DRB was primarily affected by medium and slight soil erosion.The hot spot areas of soil erosion(key control areas)were mainly concentrated in the central and southern parts of the basin,decreasing each year,and the area of soil erosion hot pots has decreased from 43.22%to 20.60%.PLSR decoupling results show that elevation,bedrock exposure,land use type,interbedded limestone and clastic rock,and vegetation coverage were identified as the key variables affecting soil erosion,explaining 52.8%of soil erosion variability,with a high value of the Variable Importance on Projection(VIP)more than 1.These results can be used as a reference for comprehensive control of soil erosion and water loss in the basin.展开更多
The complex spatiotemporal vegetation variability in the subtropical mountain-hill region was investigated through a multi-level modeling framework. Three levels - parcel, landscape, and river basin levels- were selec...The complex spatiotemporal vegetation variability in the subtropical mountain-hill region was investigated through a multi-level modeling framework. Three levels - parcel, landscape, and river basin levels- were selected to discover the complex spatiotemporal vegetation variability induced by climatic, geomorphic and anthropogenic processes at different levels. The wavelet transform method was adopted to construct the annual maximum Enhanced Vegetation Index and the amplitude of the annual phenological cycle based on the 16-day time series of a5om Moderate Resolution Imaging Spectroradiometer Enhanced Vegetation Index datasets during 2OOl-2OlO. Results revealed that land use strongly influenced the overall vegetation greenness and magnitude of phenological cycles. Topographic variables also contributed considerably to the models, reflecting the positive influence from altitude and slope. Additionally, climate factors played an important role： precipitation had a considerable positive association with the vegetation greenness, whereas the temperature difference had strong positive influence on the magnitude of vegetation phenology. The multilevel approach leads to a better understanding of the complex interaction of the hierarchical ecosystem, human activities and climate change.展开更多
Well-mixed zone models are often employed to compute indoor air quality and occupant exposures.While effective,a potential downside to assuming instantaneous,perfect mixing is underpredicting exposures to high intermi...Well-mixed zone models are often employed to compute indoor air quality and occupant exposures.While effective,a potential downside to assuming instantaneous,perfect mixing is underpredicting exposures to high intermittent concentrations within a room.When such cases are of concern,more spatially resolved models,like computational-fluid dynamics methods,are used for some or all of the zones.But,these models have higher computational costs and require more input information.A preferred compromise would be to continue with a multi-zone modeling approach for all rooms,but with a better assessment of the spatial variability within a room.To do so,we present a quantitative method for estimating a room’s spatiotemporal variability,based on influential room parameters.Our proposed method disaggregates variability into the variability in a room’s average concentration,and the spatial variability within the room relative to that average.This enables a detailed assessment of how variability in particular room parameters impacts the uncertain occupant exposures.To demonstrate the utility of this method,we simulate contaminant dispersion for a variety of possible source locations.We compute breathing-zone exposure during the releasing(source is active)and decaying(source is removed)periods.Using CFD methods,we found after a 30 minutes release the average standard deviation in the spatial distribution of exposure was approximately 28%of the source average exposure,whereas variability in the different average exposures was lower,only 10%of the total average.We also find that although uncertainty in the source location leads to variability in the average magnitude of transient exposure,it does not have a particularly large influence on the spatial distribution during the decaying period,or on the average contaminant removal rate.By systematically characterizing a room’s average concentration,its variability,and the spatial variability within the room important insights can be gained as to how much uncertainty is introduced into occupant exposure predictions by assuming a uniform in-room contaminant concentration.We discuss how the results of these characterizations can improve our understanding of the uncertainty in occupant exposures relative to well-mixed models.展开更多
Implementing hardware primitives into cryptosystem has become a new trend in electronic community.Memristor,with intrinsic stochastic characteristics including the switching voltages,times and energies,as well as the ...Implementing hardware primitives into cryptosystem has become a new trend in electronic community.Memristor,with intrinsic stochastic characteristics including the switching voltages,times and energies,as well as the fluctuations of the resistance state over time,could be a naturally good entropy source for cryptographic key generation.In this study,based on kinetic Monte Carlo Simula-tion,multiple Artificial Intelligence techniques,as well as kernel density map and time constant analysis,memristive spatiotemporal variability within graphene based conductive bridging RAM(CBRAM)have been synergistically analyzed to verify the inher-ent randomness of the memristive stochasticity.Moreover,the ran-dom number based on hardware primitives passed the Hamming Distance calculation with high randomness and uniqueness,and has been integrated into a Rivest-Shamir-Adleman(RSA)cryptosystem.The security of the holistic cryptosystem relies both the modular arithmetic algorithm and the intrinsic randomness of the hardware primitive(to be more reliable,the random num-ber could be as large as possible,better larger than 2048 bits as NIST suggested).The spatiotemporal-variability-based random number is highly random,physically unpredictable and machinelearningattack resilient,improving the robustness of the entire cryptosystem.展开更多
This study was used oceanographic database in the Sea of Okhotsk between the period from 1929 to 2020(131286 stations).The paper used gas hydrate dissociation parameters for the“pure methane-seawater”system obtained...This study was used oceanographic database in the Sea of Okhotsk between the period from 1929 to 2020(131286 stations).The paper used gas hydrate dissociation parameters for the“pure methane-seawater”system obtained in the study by Dickens GR and Quinby-Hunt MS.The results have elucidated the spatiotemporal variability of distribution of such parameters at the upper boundary of the gas hydrate stability zone(GHSZ)as water temperature,salinity,and top depth of the stability zone.As the study has shown(based on average long-term spatial distributions),the minimum temperature and depth values of the GHSZ upper boundary in the Sea of Okhotsk occur off the western and southwestern parts of the water area.The maximum temperature and depth values of the GHSZ upper boundary are typical of the southeastern sea area and over the Kamchatka Peninsula slope.This study has also identified an area,where there are no thermobaric conditions for the emergence and stable existence of methane hydrates in the water column.The results presented agree well with the materials of observations conducted during expeditions and the previous data of predictive simulations for the Sea of Okhotsk.展开更多
Fire-induced forest loss has substantially increased worldwide over the last decade.In China,the connection between forest loss and frequent fi res on a national scale remains largely unexplored.In this study,we used ...Fire-induced forest loss has substantially increased worldwide over the last decade.In China,the connection between forest loss and frequent fi res on a national scale remains largely unexplored.In this study,we used a data set for a time-series of forest loss from the Global Forest Watch and for a MODIS-derived burned area for 2003–2015 to ascertain variations in forest loss and to explore its relationship with forest fi res(represented by burned areas)at the country-and forest-zone levels.We quantifi ed trends in forest loss during 2003–2015 using linear regression analysis and assessed the relation between forest loss and burned areas using Spearman’s correlation.Forest loss increased signifi cantly(264.8 km 2 a−1;R 2=0.54,p<0.01)throughout China,with an average annual increase of 11.4%during 2003–2015.However,the forest loss trend had extensive spatial heterogeneity.Forest loss increased mainly in the subtropical evergreen broadleaf forest zone(315.0 km 2 a−1;R 2=0.69,p<0.01)and tropical rainforest zone(38.8 km 2 a−1;R 2=0.66,p<0.01),but the loss of forest decreased in the cold temperate deciduous coniferous forest zone(−70.8 km 2 year−1;R 2=0.75,p<0.01)and the temperate deciduous mixed broadleaf and coniferous forest zone(−14.4 km 2 a−1;R 2=0.45,p<0.05).We found that 1.0%of China’s area had a signifi cant positive correlation(r≥0.55,p<0.05)with burned areas and 0.3%had a signifi cant negative correlation(r≤−0.55,p<0.05).In particular,forest loss had a signifi cant positive relationship with the burned area in the cold temperate deciduous coniferous forest zone(16.9% of the lands)and the subtropical evergreen broadleaf forest zone(7.8%).These results provide a basis for future predictions of fi re-induced forest loss in China.展开更多
The accurate assessment of the spatiotemporal changes in soil nutrients influenced by agricultural production provides the basis for development of management strategies to maintain soil fertility and balance soil nut...The accurate assessment of the spatiotemporal changes in soil nutrients influenced by agricultural production provides the basis for development of management strategies to maintain soil fertility and balance soil nutrients. In this paper, we combined spatial measurements from 2 157 soil samples and geostatistical analysis to assess the spatiotemporal changes in soil organic carbon （SOC）, total nitrogen （TN）, available phosphorus （AP） and available potassium content （AK） from the first soil survey （in the 1980s） to the second soil survey （in the 2000s） in the Taihu region of Jiangsu Province in China. The results showed that average soil nutrients in three soil types all exhibited the increased levels in the 2000s （except for AK in the yellow brown soil）. The standard deviation of soil nutrient contents increased （except for TN in the paddy soil）. Agricultural production in the 20 years led to increases in SOC, TN, AP and AK by 74, 82, 89 and 65%, respectively, of the Taihu areas analyzed. From the 1980s to 2000s all the nugget/sill ratios of soil nutrients indices were between 25 and 75% （except for AK in the yellow brown soil in the 2000s）, indicating moderate spatial dependence. The ratio of AP in the yellow brown soil in the 2000s was 88.74%, showing weak spatial dependence. The spatial correlation range values for SOC, TN, AP and AK in the 2000s all decreased. The main areas showing declines in SOC, TN and AP were in the northwest. For AK, the main region with declining levels was in the east and middle of western areas. Apparently, the increase in soil nutrients in the Taihu region can be mainly attributed to the large increase in fertilizer inputs, change in crop systems and enhanced residues management since the 1980s. Future emphasis should be placed on avoiding excess fertilizer inputs and balancing the effects of the fertilizers in soils.展开更多
The spatial and temporal variability of primary productivity in the China seas from 2003 to 2005 was estimated using a size-fractionated primary productivity model. Primary productivity estimated from satellite-derive...The spatial and temporal variability of primary productivity in the China seas from 2003 to 2005 was estimated using a size-fractionated primary productivity model. Primary productivity estimated from satellite-derived data showed spatial and temporal variability. Annual averaged primary productivity levels were 564.39, 363.08, 536.47, 413.88, 195.77, and 100.09 gCm2a1 in the Bohai Sea, northern Yellow Sea （YS）, southern YS, northern East China Sea （ECS）, southern ECS, and South China Sea （SCS）, respectively. Peaks of primary productivity appeared in spring （April-June） and fall （October and November） in the northern YS, southern YS, and southern ECS, while a single peak （June） appeared in the Bohai Sea and northem ECS. The SCS had two peaks in primary productivity, but these peaks occurred in winter （January） and summer （August）, with the winter peak far higher than the summer peak. Monthly averaged primary productivity values from 2003 to 2005 in the Bohai Sea and southern YS were higher than those in the other four seas during most months, while those in the southem ECS and SCS were the lowest. Primary productivity in spring （March-June in the southern ECS and April-July in the other five areas） contributed approximately 41% on average to the annual primary productivity in all the study seas except the SCS. The largest interannual variability also occurred in spring （average standard deviation = 6.68）, according to the satellite-derived estimates. The contribution during fall （October-January in the southern ECS and August-November in the other five areas） was approximately 33% on average; the primary productivity during this period also showed interannual variability. However, in the SCS, the winter （December-March） contribution was the highest （about 42%）, while the spring （April-July） contribution was the lowest （28%）. The SCS did share a feature with the other five areas： the larger the contribution, the larger the interarmual variability. Spatial and temporal variability of satellite-derived ocean primary productivity may be influenced by physicochemical environmental conditions, such as the chlorophyll-a concentration, sea surface temperature, photosynthetically available radiation, the seasonally reversed monsoon, river discharge, upwelling, and the Kuroshio and coastal currents.展开更多
It is essential to minimize soil quality degradation in sloping agricultural fields through stabilization and improvement of soil hydraulic properties using sustainable soil management.This study aimed to analyze the ...It is essential to minimize soil quality degradation in sloping agricultural fields through stabilization and improvement of soil hydraulic properties using sustainable soil management.This study aimed to analyze the impact of different tillage practices,including conventional tillage(CT),minimum tillage(MT),and zero tillage(ZT),on soil hydraulic conductivity in a sloping agricultural field under maizeewheat rotation.The results showed that the highest runoff volume(257.40 m3),runoff coefficient(42.84%),and soil loss(11.3 t)were observed when the CT treatment was applied.In contrast,the lowest runoff volume(67.95 m3),runoff coefficient(11.35%),and soil loss(1.05 t)were observed when the ZT treatment was adopted.The soil organic carbon and aggregate mean weight diameter were found to be significantly greater(with mean values of 0.79%and 1.19 mm,respectively)with the ZT treatment than with the CT treatment.With the tilled treatments(CT and MT),substantial changes in the saturated soil hydraulic conductivity(ks),near-saturated soil hydraulic conductivity(k),and water-conducting porosity(ε)were observed between two crop seasons.These three soil parameters were significantly higher in the period after maize harvesting than in the wheat growing period.In contrast,no significant difference in these soil parameters was found when the untilled treatment(ZT)was carried out.With regard to the slope positions,ks,k,andεshowed different behaviors under different treatments.The toe slope position showed significantly lower ks andεvalues than the summit and middle slope positions.Of the evaluated tillage practices,ZT was found to be the most promising means to improve the soil hydro-physical properties and effectively reduce surface runoff and soil erosion.展开更多
This paper analyzes the differences in the characteristics and spatio–temporal variabilities of summertime rainfall and water vapor transport between the East Asian summer monsoon（EASM） and South Asian summer mons...This paper analyzes the differences in the characteristics and spatio–temporal variabilities of summertime rainfall and water vapor transport between the East Asian summer monsoon（EASM） and South Asian summer monsoon（SASM） systems. The results show obvious differences in summertime rainfall characteristics between these two monsoon systems. The summertime rainfall cloud systems of the EASM show a mixed stratiform and cumulus cloud system, while cumulus cloud dominates the SASM. These differences may be caused by differences in the vertical shear of zonal and meridional circulations and the convergence of water vapor transport fluxes. Moreover, the leading modes of the two systems＇ summertime rainfall anomalies also differ in terms of their spatiotemporal features on the interannual and interdecadal timescales. Nevertheless, several close links with respect to the spatiotemporal variabilities of summertime rainfall and water vapor transport exist between the two monsoon systems. The first modes of summertime rainfall in the SASM and EASM regions reveal a significant negative correlation on the interannual and the interdecadal timescales. This close relationship may be linked by a meridional teleconnection in the regressed summertime rainfall anomalies from India to North China through the southeastern part over the Tibetan Plateau, which we refer to as the South Asia/East Asia teleconnection pattern of Asian summer monsoon rainfall. The authors wish to dedicate this paper to Prof. Duzheng YE, and commemorate his 100 thanniversary and his great contributions to the development of atmospheric dynamics.展开更多
Rivers are progressively being exposed to increased anthropogenic pollution stresses that are undermining their designated uses and affecting sensitive coastal areas. In this study, three adjacent eastern Mediterranea...Rivers are progressively being exposed to increased anthropogenic pollution stresses that are undermining their designated uses and affecting sensitive coastal areas. In this study, three adjacent eastern Mediterranean coastal rivers, Ibrahim, Kaleb and Beirut, were evaluated. Water quality samples were collected in dry and wet seasons from different sampling sites along the river from the source to the outlet which represent a gradient of increased urbanization. The spatiotemporal variability of the physio-chemical properties, heavy metals (Zn, Pb, Cu, Cr, and Cd) and organic matter (DOC) were statistically analyzed to better understand the contribution of point and nonpoint pollution sources. The three rivers (Beirut, Kaleb and Ibrahim) show a similar behavior in calcium and carbonate alkalinity due to the carbonate mineral weathering effect, so they are of calcium bicarbonate type due to their calcareous geological nature. The speciation of anions was affected by temporal variation. Moreover, it is obvious that the Beirut River has a different behavioral characteristic where the water is a sulfate type water with a preferable metal-OM complexation mainly with lead, zinc and copper, whereas Kaleb and Ibrahim are considered to be of a nitrate phosphate type with a preferable metal inorganic complexation, especially copper, that has a consistent behavior in both types of waters. This difference is attributed to the urbanization effect highly impacting the Beirut River.展开更多
Owing to the vast territory of China and strong regional characteristic of ozone pollution,it＇s desirable for policy makers to have a targeted and prioritized regulation and ozone pollution control strategy in China ...Owing to the vast territory of China and strong regional characteristic of ozone pollution,it＇s desirable for policy makers to have a targeted and prioritized regulation and ozone pollution control strategy in China based on scientific evidences. It＇s important to assess its current pollution status as well as spatial and temporal variation patterns across China.Recent advances of national monitoring networks provide an opportunity to insight the actions of ozone pollution. Here, we present rotated empirical orthogonal function（REOF）analysis that was used on studying the spatiotemporal characteristics of daily ozone concentrations. Based on results of REOF analysis in pollution seasons for 3 years＇ observations, twelve regions with clear patterns were identified in China. The patterns of temporal variation of ozone in each region were separated well and different from each other, reflecting local meteorological, photochemical or pollution features. A rising trend in annual averaged Eight-hour Average Ozone Concentrations（O3-8 hr） from 2014 to 2016 was observed for all regions, except for the Tibetan Plateau. The mean values of annual and 90 percentile concentrations for all 338 cities were 82.6 ± 14.6 and 133.9 ± 25.8 μg/m3,respectively, in 2015. The regionalization results of ozone were found to be influenced greatly by terrain features, indicating significant terrain and landform effects on ozone spatial correlations. Among 12 regions, North China Plain, Huanghuai Plain, Central Yangtze River Plain, Pearl River Delta and Sichuan Basin were realized as priority regions for mitigation strategies, due to their higher ozone concentrations and dense population.展开更多
The hydrogen isotope composition of leaf wax n-alkanes (δ2Halk) has been used to reconstruct hydroclimate conditions, yet the factors that influence it are not fully understood, particularly the control of soil pore ...The hydrogen isotope composition of leaf wax n-alkanes (δ2Halk) has been used to reconstruct hydroclimate conditions, yet the factors that influence it are not fully understood, particularly the control of soil pore water δ2H. This study monitored the temporal and vertical variations of peat pore water δ2H (δ2H_(pw)) from 2015 to 2019 in the Dajiuhu peatland, central China. Results showed that δ2H_(pw) was highly variable in the surface layers (0−10 cm;avg. −47‰, 1σ = 11‰) and remained almost constant in deeper depths (below 50 cm;avg. −56‰, 1σ = 2‰). The δ2H_(pw) of the 0−10 cm layer was strongly correlated with the preceding month’s precipitation δ2H (δ2Hp) in the adjacent area (r = 0.7, p < 0.01), indicating that δ2Hp is the main factor affecting the temporal variations of δ2H_(pw) in the upper layers. Moreover, the surface (0−10 cm) peat pore water slightly deviated from the local meteoric water line, suggesting that evaporation may also have an effect on the δ2H_(pw). These findings emphasize the importance of precipitation isotope composition in interpreting the δ2Halk in peat deposits under subtropical climates.展开更多
The Songhua River Basin(SRB),ranking third largest in China in terms of both runoff volume and basin area,has experi-enced frequent disasters and drastic changes in runoff since the early 20th century.Many studies hav...The Songhua River Basin(SRB),ranking third largest in China in terms of both runoff volume and basin area,has experi-enced frequent disasters and drastic changes in runoff since the early 20th century.Many studies have analyzed the causes of runoff re-duction;however,the spatiotemporal differences in runoff contributions and their underlying mechanisms remain poorly understood,which are crucial for regional water resources management and effective utilization.This study used the Mann-Kendall rank correlation trend test,continuous wavelet analysis,cumulative anomaly,and the slope change ratio of cumulative quantities(SCRCQ)method to explore the runoff changes characteristics and spatiotemporal differences of the contributions of climate change and human activities to runoff changes across three sub-basins of the SRB.The results show that:1)runoff from 1955 to 2022 in all the three sub-basins exhibit a statistically significant decreasing trend at 0.05 significant level.2)Four abrupt change points in runoff were detected in Nenjiang River Basin(NRB)and the mainstream of the SRB(MSRB),whereas only two change points in the Second Songhua River(SSRB).3)Runoff and precipitation series of the NRB and MSRB exhibit similar multi-timescale cycle characteristics with the most dominated cycles of 45-58 yr.In contrast,it is 12-18 yr for SSRB.4)Anthropogenic activities are the primary factor leading to in the reduction of runoff in NRB(74.33%-91.67%)and MSRB(50.11%-102.12%),whereas it is only 5.38%-33.12%in SSRB.This is attributed to the uneven distribution of regional climate and human activities in the entire SRB.5)With the growing demand for water diversion for agri-cultural irrigation,anthropogenic activities in the NRB and MSRB have increased.However,the opposite is found in SSR,where the in-creased influence of precipitation on runoff and water conservation policies are identified.展开更多
Background Understanding of mosquito spatiotemporal dynamics is central to characterize candidate field sites for the sterile insect technique(SIT)testing,and is critical to the effective implementation and evaluation...Background Understanding of mosquito spatiotemporal dynamics is central to characterize candidate field sites for the sterile insect technique(SIT)testing,and is critical to the effective implementation and evaluation of pilot sterile male release programs.Here,we present a detailed description of Aedes albopictus(Skuse)egg-laying activity over a 6-year period in urban areas identified as potential SIT testing sites on Reunion Island.Method Weekly entomological collections using ovitraps were carried out in residential and adjacent uninhabited habitats in two urban areas,Duparc and Bois Rouge,in the municipality of Sainte Marie,Reunion Island.Time-series data incorporating the frequency of positive ovitraps and the total number of eggs/ovitrap recorded each time at each locality during the study period from May 2013 to December 2018 were analyzed with multifaceted statistical approaches including descriptive statistics and spatiotemporal analyses incorporating the role of climatic factors on overall ovitrap productivity.Results During the ovitrap survey,the proportion of egg-positive ovitraps differed among study sites(χ2=50.21,df=2,P<0.001),being relatively lower in Duparc(89.5%)than in Bois-Rouges(95.3%)and the adjacent buffer zone(91.2%).Within each neighborhood,Ae.albopictus egg abundance varied by month in a roughly seasonal pattern marked by a single peak occurring more regularly February each year,a decline at the onset of the austral winter in July,followed by a period of lower ovitrap productivity in August and September.Fluctuation in both positivity rate and eggs densities per ovitraps were related to annual and seasonal variations in local temperature and rainfall(P<0.001 in all cases).The spatial analysis also captured substantial between-and within-habitats heterogeneity,whereby the overall ovitrap productivity was higher in residential areas than in the buffer zone.Conclusions Collectively,these results reveal that the distribution of Ae.albopictus oviposition activity is shaped by local habitat heterogeneity and seasonal climatic factors.Overall,this study provides baseline insights into the reproductive dynamics of Ae.albopictus,which would assist in planning locally tailored SIT interventions,while addressing concerns related to focal areas of high egg-laying intensity and potential immigration of females from natural areas.展开更多
In this study,we employ advanced data-driven techniques to investigate the complex relationships between the yields of five major crops and various geographical and spatiotemporal features in Senegal.We analyze how th...In this study,we employ advanced data-driven techniques to investigate the complex relationships between the yields of five major crops and various geographical and spatiotemporal features in Senegal.We analyze how these features influence crop yields by utilizing remotely sensed data.Our methodology incorporates clustering algorithms and correlation matrix analysis to identify significant patterns and dependencies,offering a comprehensive understanding of the factors affecting agricultural productivity in Senegal.To optimize the model's performance and identify the optimal hyperparameters,we implemented a comprehensive grid search across four distinct machine learning regressors:Random Forest,Extreme Gradient Boosting(XGBoost),Categorical Boosting(CatBoost),and Light Gradient-Boosting Machine(LightGBM).Each regressor offers unique functionalities,enhancing our exploration of potential model configurations.The top-performing models were selected based on evaluating multiple performance metrics,ensuring robust and accurate predictive capabilities.The results demonstrated that XGBoost and CatBoost perform better than the other two.We introduce synthetic crop data generated using a Variational Auto Encoder to address the challenges posed by limited agricultural datasets.By achieving high similarity scores with real-world data,our synthetic samples enhance model robustness,mitigate overfitting,and provide a viable solution for small dataset issues in agriculture.Our approach distinguishes itself by creating a flexible model applicable to various crops together.By integrating five crop datasets and generating high-quality synthetic data,we improve model performance,reduce overfitting,and enhance realism.Our findings provide crucial insights for productivity drivers in key cropping systems,enabling robust recommendations and strengthening the decision-making capabilities of policymakers and farmers in datascarce regions.展开更多
In order to provide scientific support to policy makers in the regulation of PM2.5 pollution in China, it is important to accurately assess the current status, spatiotemporal characteristics and regionalization data f...In order to provide scientific support to policy makers in the regulation of PM2.5 pollution in China, it is important to accurately assess the current status, spatiotemporal characteristics and regionalization data for this air pollutant. An analysis of the pollution status of PM2.5 was conducted using daily averaged mass concentration data recorded in 74 cities in 2013 and 161 cities in 2014. The rotated empirical orthogonal function(REOF) method was applied to analyze this data. Results showed that the average annual PM2.5 concentration in urban areas of China is 62.2±21.5 ?g/m3, and that the distribution is spatially heterogeneous. The North China Plain, middle and lower Yangtze River Plain, Sichuan Basin and Guanzhong Plain had relatively high annual PM2.5 concentrations compared with the southeast coastal region, the Tibetan Plateau and the Yungui Plateau. PM2.5 mass concentrations tended to be higher in winter than in summer, however, the data for many cities showed a small peak in concentrations from May to July. An analysis of the spatial correlation of PM2.5 indicated a significant influence of topographic conditions. A lower correlation was observed where terrain features varied greatly. Based on the results of the REOF analysis and topographic characteristics, ten regions were identified in mid-eastern China, which could be considered as basic pollution prevention divisions for PM2.5; these include the North China Plain region, Pearl River Delta region, Jianghuai Plain region, middle Yangtze River Plain region, Northeast Plain region, Jiangnan coastal region, Sichuan Basin region, Qiantao Plain region, Guanzhong-Central Plain region and Yungui Plateau region. Seasonal variations in the regionalization data were observed, especially for the North China Plain and Pearl River Delta regions. Among the ten regions identified in this study, the North China Plain, Guanzhong-Central Plain, middle Yangtze River Plain and Jianghuai Plain had relatively high PM2.5 mass concentrations in comparison with the others. Therefore, these regions should be considered as the key regions to target in developing PM2.5 pollution prevention strategies. This study improves the present understanding of the spatial distribution, seasonal changes and regional status of PM2.5 pollution in China and helps establish possible control strategies for the reduction of this air pollutant.展开更多
Soil moisture is an essential climate variable(ECV) concerned widely. Due to its high spatial variability, it is costly to measure soil moisture at tens of kilometers scale. In this study, a ten-year(2002–2011) daily...Soil moisture is an essential climate variable(ECV) concerned widely. Due to its high spatial variability, it is costly to measure soil moisture at tens of kilometers scale. In this study, a ten-year(2002–2011) daily soil moisture dataset at 0.25° spatial resolution for Chinese mainland was produced through assimilating the Advanced Microwave Scanning Radiometer for Earth Observing System(AMSR-E) brightness temperature(TB) data into a land surface model(LSM). The obtained soil moisture data was evaluated against soil moisture-measuring networks deployed in two wet areas and one dry area of the Tibetan Plateau.The results show that for the wet areas the accuracy of the soil moisture product obtained from the assimilation is considerably higher than that of both AMSR-E official soil moisture products and land surface simulation results, and for the dry area their accuracy is comparable to each other. The spatial pattern of the soil moisture from the new product is consistent with that of soil porosity from an independent survey-based dataset, further confirming the credibility of the new product. According to this product, the transition regions in China show stronger seasonal variation of soil moisture than dry and wet regions, and drier regions have stronger inter-annual variability of soil moisture than wetter regions, particularly during transitional seasons(spring and autumn). The soil moisture product is accessible at the National Tibetan Plateau Data Center.展开更多
基金supported by the Hundred Talent Program of the Chinese Academy of Sciences(Huang Wenjiang)the Innovation“135”Program from Chinese Academy of Sciences(Y3SG0100CX)the Science&Technology Basic Research Program of China(2014FY210100)
文摘Understanding the effects of land use changes on the spatiotemporal variation of soil organic carbon （SOC） can provide guidance for low carbon and sustainable agriculture. In this paper, based on the large-scale datasets of soil surveys in 1982 and 2009 for Pinggu District -- an urban-rural ecotone of Beijing, China, the effects of land use and land use changes on both temporal variation and spatial variation of SOC were analyzed. Results showed that from 1982 to 2009 in Pinggu District, the following land use change mainly occurred： Grain cropland converted to orchard or vegetable land, and grassland converted to forestland. The SOC content decreased in region where the land use type changed to grain cropland （e.g., vegetable land to grain cropland decreased by 0.7 g kg-1; orchard to grain cropland decreased by 0.2 g kg-l）. In contrast, the SOC content increased in region where the land use type changed to either orchard （excluding forestland） or forestland （e.g., grain cropland to orchard and forestland increased by 2.7 and 2.4 g kg-1, respectively; grassland to orchard and forestland increased by 4.8 and 4.9 g kg-1, respectively）. The organic carbon accumulation capacity per unit mass of the soil increased in the following order： grain cropland soil〈vegetable land/grassland soil〈orchard soil〈forestland soil. Therefore, to both secure supply of agricultural products and develop low carbon agriculture in a modern city, orchard has proven to be a good choice for land using.
基金supported by the National Natural Science Foundation of China (No.41672246)the Fundamental Research Funds for the Central Universities,China University of Geosciences (Wuhan)(No.1910491T05)。
文摘With a warming climate,temperature extremes have been a main global issue in recent decades due to their potential influence on the sustainable development of human life and natural ecosystems.In this study,12 indicators of extreme temperature events are used to evaluate the spatiotemporal distribution,periodic structure and teleconnections with large-scale atmospheric circulation in Xinjiang,Northwest China by combining wavelet coherence(WTC) analysis based on continuous wavelet transform(CWT) analysis with the sequential Mann-Kendall test.We find that over the past six decades,the climate in Xinjiang has become warmer and has suffered from increases in the frequency of warm extremes and decreases in the frequency of cold extremes.Warm extremes have mainly occurred in the southern Tianshan Mountains surrounding the Tarim Basin and western part of the Taklamakan Desert,and cold extremes have primarily occurred in the southwestern Altai Mountains and northern foot of the Tianshan Mountains.Extreme temperature events,including warm extremes,cold extremes,and other temperature indices,have significant interannual variability,with the main oscillation periods at smaller(2–4-year band),intermediate(4–7-year band),and greater time scales in recent decades.Furthermore,cold-extreme indices,including frost days,cool days,and cool nights all show a clear changepoint during 1990–1997 at the 95% confidence level,and both ice days and cold spell duration indicator have a potential changepoint during 1981–1986.However,the changing points for warmextreme indices are detected during 1992–1998.The temperature variables are significantly correlated with the EI Ni?o-Southern Oscillation(ENSO) and Arctic Oscillation(AO),but less well correlated with the Pacific Decadal Oscillation(PDO).The phase difference in the WTC spectra is not uniform between temperature extremes and climatic oscillations.Our findings will have important implications for local governments in taking effective measures to mitigate the potential effects of regional climate warming due to human activities in Xinjiang.
基金supported by National Natural Science Foundation of China(32060372,32360421)Guizhou Science and Technology Department(Qian Ke He Ji Chu ZK-[2023]Key 029Qiankehe Zhicheng[2021]Yiban462)。
文摘Soil erosion is a prominent environmental problem in karst regions.Exploring the spatiotemporal variability of soil erosion and the factors that influence soil erosion is of great significance for regional soil erosion prevention and control.However,the mechanisms influencing the characteristic features of the karst basins,such as bedrock exposure and lithology,still need to be further explored.This study used GIS technology,the Revised Universal Soil Loss Equation model,Getis–Ord Gi*,and partial least squares regression(PLSR)to identify the dominant factors influencing soil erosion and the spatiotemporal variability of soil erosion in 31 sub-basins of the Dabang River Basin(DRB),a typical karst area of Southwest China,from 2010 to 2020.The results indicated that soil erosion in the DRB from 2010 to 2020 was generally decreasing,the mean soil erosion in the DRB in 2010,2015 and 2020 was 18.46,16.51 and 15.29 t ha^(-1)a^(-1),respectively.During the study period,the area of slight erosion increased by 26.39%(706.54 km^(2)),while severe erosion enlarged by 26.36 km^(2).Spatially,the DRB was primarily affected by medium and slight soil erosion.The hot spot areas of soil erosion(key control areas)were mainly concentrated in the central and southern parts of the basin,decreasing each year,and the area of soil erosion hot pots has decreased from 43.22%to 20.60%.PLSR decoupling results show that elevation,bedrock exposure,land use type,interbedded limestone and clastic rock,and vegetation coverage were identified as the key variables affecting soil erosion,explaining 52.8%of soil erosion variability,with a high value of the Variable Importance on Projection(VIP)more than 1.These results can be used as a reference for comprehensive control of soil erosion and water loss in the basin.
基金supported by the National Natural Science Foundation of China (NSFC) (Grant No. 41071267)Scientific Research Foundation for Returned Scholars ([2012]940)Ministry of Education of China, and the Science Foundation of Fujian Province (Grant Nos. 2012I0005, 2012J01167)
文摘The complex spatiotemporal vegetation variability in the subtropical mountain-hill region was investigated through a multi-level modeling framework. Three levels - parcel, landscape, and river basin levels- were selected to discover the complex spatiotemporal vegetation variability induced by climatic, geomorphic and anthropogenic processes at different levels. The wavelet transform method was adopted to construct the annual maximum Enhanced Vegetation Index and the amplitude of the annual phenological cycle based on the 16-day time series of a5om Moderate Resolution Imaging Spectroradiometer Enhanced Vegetation Index datasets during 2OOl-2OlO. Results revealed that land use strongly influenced the overall vegetation greenness and magnitude of phenological cycles. Topographic variables also contributed considerably to the models, reflecting the positive influence from altitude and slope. Additionally, climate factors played an important role： precipitation had a considerable positive association with the vegetation greenness, whereas the temperature difference had strong positive influence on the magnitude of vegetation phenology. The multilevel approach leads to a better understanding of the complex interaction of the hierarchical ecosystem, human activities and climate change.
基金supported in parts by the U.S.Defense Threat Reduction Agency and performed under U.S.Department of Energy Contract No.DE-AC02-05CH11231.
文摘Well-mixed zone models are often employed to compute indoor air quality and occupant exposures.While effective,a potential downside to assuming instantaneous,perfect mixing is underpredicting exposures to high intermittent concentrations within a room.When such cases are of concern,more spatially resolved models,like computational-fluid dynamics methods,are used for some or all of the zones.But,these models have higher computational costs and require more input information.A preferred compromise would be to continue with a multi-zone modeling approach for all rooms,but with a better assessment of the spatial variability within a room.To do so,we present a quantitative method for estimating a room’s spatiotemporal variability,based on influential room parameters.Our proposed method disaggregates variability into the variability in a room’s average concentration,and the spatial variability within the room relative to that average.This enables a detailed assessment of how variability in particular room parameters impacts the uncertain occupant exposures.To demonstrate the utility of this method,we simulate contaminant dispersion for a variety of possible source locations.We compute breathing-zone exposure during the releasing(source is active)and decaying(source is removed)periods.Using CFD methods,we found after a 30 minutes release the average standard deviation in the spatial distribution of exposure was approximately 28%of the source average exposure,whereas variability in the different average exposures was lower,only 10%of the total average.We also find that although uncertainty in the source location leads to variability in the average magnitude of transient exposure,it does not have a particularly large influence on the spatial distribution during the decaying period,or on the average contaminant removal rate.By systematically characterizing a room’s average concentration,its variability,and the spatial variability within the room important insights can be gained as to how much uncertainty is introduced into occupant exposure predictions by assuming a uniform in-room contaminant concentration.We discuss how the results of these characterizations can improve our understanding of the uncertainty in occupant exposures relative to well-mixed models.
基金This study was supported by grants from National Nat-ural Science Foundation of China(62174008)Beijing Municipal Education Commission(KZ202110005001)+1 种基金the Ministry of Science and Technology,Taiwan,China(MOST 111-2119-M-492-002-MBK,MOST 111-2622-8-182-001-TS1,MOST 109-2221-E-182-013-MY3,and MOST 110-2221-E-182-043-MY3)the Chang Gung Memorial Hospital(CORPD2J0073).
文摘Implementing hardware primitives into cryptosystem has become a new trend in electronic community.Memristor,with intrinsic stochastic characteristics including the switching voltages,times and energies,as well as the fluctuations of the resistance state over time,could be a naturally good entropy source for cryptographic key generation.In this study,based on kinetic Monte Carlo Simula-tion,multiple Artificial Intelligence techniques,as well as kernel density map and time constant analysis,memristive spatiotemporal variability within graphene based conductive bridging RAM(CBRAM)have been synergistically analyzed to verify the inher-ent randomness of the memristive stochasticity.Moreover,the ran-dom number based on hardware primitives passed the Hamming Distance calculation with high randomness and uniqueness,and has been integrated into a Rivest-Shamir-Adleman(RSA)cryptosystem.The security of the holistic cryptosystem relies both the modular arithmetic algorithm and the intrinsic randomness of the hardware primitive(to be more reliable,the random num-ber could be as large as possible,better larger than 2048 bits as NIST suggested).The spatiotemporal-variability-based random number is highly random,physically unpredictable and machinelearningattack resilient,improving the robustness of the entire cryptosystem.
基金the POI FEB RAS,entitled“Study of the Structure and Dynamics of World’s Oceans Waters in Conditions of Current Climate Change”(reg.no.124022100079-4).
文摘This study was used oceanographic database in the Sea of Okhotsk between the period from 1929 to 2020(131286 stations).The paper used gas hydrate dissociation parameters for the“pure methane-seawater”system obtained in the study by Dickens GR and Quinby-Hunt MS.The results have elucidated the spatiotemporal variability of distribution of such parameters at the upper boundary of the gas hydrate stability zone(GHSZ)as water temperature,salinity,and top depth of the stability zone.As the study has shown(based on average long-term spatial distributions),the minimum temperature and depth values of the GHSZ upper boundary in the Sea of Okhotsk occur off the western and southwestern parts of the water area.The maximum temperature and depth values of the GHSZ upper boundary are typical of the southeastern sea area and over the Kamchatka Peninsula slope.This study has also identified an area,where there are no thermobaric conditions for the emergence and stable existence of methane hydrates in the water column.The results presented agree well with the materials of observations conducted during expeditions and the previous data of predictive simulations for the Sea of Okhotsk.
基金We are grateful to Zhihua Liu for his constructive comments to improve the manuscript.
文摘Fire-induced forest loss has substantially increased worldwide over the last decade.In China,the connection between forest loss and frequent fi res on a national scale remains largely unexplored.In this study,we used a data set for a time-series of forest loss from the Global Forest Watch and for a MODIS-derived burned area for 2003–2015 to ascertain variations in forest loss and to explore its relationship with forest fi res(represented by burned areas)at the country-and forest-zone levels.We quantifi ed trends in forest loss during 2003–2015 using linear regression analysis and assessed the relation between forest loss and burned areas using Spearman’s correlation.Forest loss increased signifi cantly(264.8 km 2 a−1;R 2=0.54,p<0.01)throughout China,with an average annual increase of 11.4%during 2003–2015.However,the forest loss trend had extensive spatial heterogeneity.Forest loss increased mainly in the subtropical evergreen broadleaf forest zone(315.0 km 2 a−1;R 2=0.69,p<0.01)and tropical rainforest zone(38.8 km 2 a−1;R 2=0.66,p<0.01),but the loss of forest decreased in the cold temperate deciduous coniferous forest zone(−70.8 km 2 year−1;R 2=0.75,p<0.01)and the temperate deciduous mixed broadleaf and coniferous forest zone(−14.4 km 2 a−1;R 2=0.45,p<0.05).We found that 1.0%of China’s area had a signifi cant positive correlation(r≥0.55,p<0.05)with burned areas and 0.3%had a signifi cant negative correlation(r≤−0.55,p<0.05).In particular,forest loss had a signifi cant positive relationship with the burned area in the cold temperate deciduous coniferous forest zone(16.9% of the lands)and the subtropical evergreen broadleaf forest zone(7.8%).These results provide a basis for future predictions of fi re-induced forest loss in China.
基金the funding support from the New Century Exceptional Talent Program of China(NCET-08-0797)the National High-Tech Research and Development Program of China(2013AA100404)+2 种基金the National Basic Research Program of China(2009CB118608)the CSIRO-Chinese Ministry of Education(MOE)PhD Research Fellowship Programthe Priority Academic Program Development of Jiangsu Higher Education Institutions,China
文摘The accurate assessment of the spatiotemporal changes in soil nutrients influenced by agricultural production provides the basis for development of management strategies to maintain soil fertility and balance soil nutrients. In this paper, we combined spatial measurements from 2 157 soil samples and geostatistical analysis to assess the spatiotemporal changes in soil organic carbon （SOC）, total nitrogen （TN）, available phosphorus （AP） and available potassium content （AK） from the first soil survey （in the 1980s） to the second soil survey （in the 2000s） in the Taihu region of Jiangsu Province in China. The results showed that average soil nutrients in three soil types all exhibited the increased levels in the 2000s （except for AK in the yellow brown soil）. The standard deviation of soil nutrient contents increased （except for TN in the paddy soil）. Agricultural production in the 20 years led to increases in SOC, TN, AP and AK by 74, 82, 89 and 65%, respectively, of the Taihu areas analyzed. From the 1980s to 2000s all the nugget/sill ratios of soil nutrients indices were between 25 and 75% （except for AK in the yellow brown soil in the 2000s）, indicating moderate spatial dependence. The ratio of AP in the yellow brown soil in the 2000s was 88.74%, showing weak spatial dependence. The spatial correlation range values for SOC, TN, AP and AK in the 2000s all decreased. The main areas showing declines in SOC, TN and AP were in the northwest. For AK, the main region with declining levels was in the east and middle of western areas. Apparently, the increase in soil nutrients in the Taihu region can be mainly attributed to the large increase in fertilizer inputs, change in crop systems and enhanced residues management since the 1980s. Future emphasis should be placed on avoiding excess fertilizer inputs and balancing the effects of the fertilizers in soils.
基金Major Project of National Natural Science Foundation of China, No.40490260
文摘The spatial and temporal variability of primary productivity in the China seas from 2003 to 2005 was estimated using a size-fractionated primary productivity model. Primary productivity estimated from satellite-derived data showed spatial and temporal variability. Annual averaged primary productivity levels were 564.39, 363.08, 536.47, 413.88, 195.77, and 100.09 gCm2a1 in the Bohai Sea, northern Yellow Sea （YS）, southern YS, northern East China Sea （ECS）, southern ECS, and South China Sea （SCS）, respectively. Peaks of primary productivity appeared in spring （April-June） and fall （October and November） in the northern YS, southern YS, and southern ECS, while a single peak （June） appeared in the Bohai Sea and northem ECS. The SCS had two peaks in primary productivity, but these peaks occurred in winter （January） and summer （August）, with the winter peak far higher than the summer peak. Monthly averaged primary productivity values from 2003 to 2005 in the Bohai Sea and southern YS were higher than those in the other four seas during most months, while those in the southem ECS and SCS were the lowest. Primary productivity in spring （March-June in the southern ECS and April-July in the other five areas） contributed approximately 41% on average to the annual primary productivity in all the study seas except the SCS. The largest interannual variability also occurred in spring （average standard deviation = 6.68）, according to the satellite-derived estimates. The contribution during fall （October-January in the southern ECS and August-November in the other five areas） was approximately 33% on average; the primary productivity during this period also showed interannual variability. However, in the SCS, the winter （December-March） contribution was the highest （about 42%）, while the spring （April-July） contribution was the lowest （28%）. The SCS did share a feature with the other five areas： the larger the contribution, the larger the interarmual variability. Spatial and temporal variability of satellite-derived ocean primary productivity may be influenced by physicochemical environmental conditions, such as the chlorophyll-a concentration, sea surface temperature, photosynthetically available radiation, the seasonally reversed monsoon, river discharge, upwelling, and the Kuroshio and coastal currents.
文摘It is essential to minimize soil quality degradation in sloping agricultural fields through stabilization and improvement of soil hydraulic properties using sustainable soil management.This study aimed to analyze the impact of different tillage practices,including conventional tillage(CT),minimum tillage(MT),and zero tillage(ZT),on soil hydraulic conductivity in a sloping agricultural field under maizeewheat rotation.The results showed that the highest runoff volume(257.40 m3),runoff coefficient(42.84%),and soil loss(11.3 t)were observed when the CT treatment was applied.In contrast,the lowest runoff volume(67.95 m3),runoff coefficient(11.35%),and soil loss(1.05 t)were observed when the ZT treatment was adopted.The soil organic carbon and aggregate mean weight diameter were found to be significantly greater(with mean values of 0.79%and 1.19 mm,respectively)with the ZT treatment than with the CT treatment.With the tilled treatments(CT and MT),substantial changes in the saturated soil hydraulic conductivity(ks),near-saturated soil hydraulic conductivity(k),and water-conducting porosity(ε)were observed between two crop seasons.These three soil parameters were significantly higher in the period after maize harvesting than in the wheat growing period.In contrast,no significant difference in these soil parameters was found when the untilled treatment(ZT)was carried out.With regard to the slope positions,ks,k,andεshowed different behaviors under different treatments.The toe slope position showed significantly lower ks andεvalues than the summit and middle slope positions.Of the evaluated tillage practices,ZT was found to be the most promising means to improve the soil hydro-physical properties and effectively reduce surface runoff and soil erosion.
基金supported jointly by the National Key Research and Development Program(Grant No.2016YFA0600603)the National Basic Research of China(Grant No.2013CB430201)the National Natural Science Foundation of China(Grant Nos.41605058,41375065,41461164005,41230527,and 41375082)
文摘This paper analyzes the differences in the characteristics and spatio–temporal variabilities of summertime rainfall and water vapor transport between the East Asian summer monsoon（EASM） and South Asian summer monsoon（SASM） systems. The results show obvious differences in summertime rainfall characteristics between these two monsoon systems. The summertime rainfall cloud systems of the EASM show a mixed stratiform and cumulus cloud system, while cumulus cloud dominates the SASM. These differences may be caused by differences in the vertical shear of zonal and meridional circulations and the convergence of water vapor transport fluxes. Moreover, the leading modes of the two systems＇ summertime rainfall anomalies also differ in terms of their spatiotemporal features on the interannual and interdecadal timescales. Nevertheless, several close links with respect to the spatiotemporal variabilities of summertime rainfall and water vapor transport exist between the two monsoon systems. The first modes of summertime rainfall in the SASM and EASM regions reveal a significant negative correlation on the interannual and the interdecadal timescales. This close relationship may be linked by a meridional teleconnection in the regressed summertime rainfall anomalies from India to North China through the southeastern part over the Tibetan Plateau, which we refer to as the South Asia/East Asia teleconnection pattern of Asian summer monsoon rainfall. The authors wish to dedicate this paper to Prof. Duzheng YE, and commemorate his 100 thanniversary and his great contributions to the development of atmospheric dynamics.
文摘Rivers are progressively being exposed to increased anthropogenic pollution stresses that are undermining their designated uses and affecting sensitive coastal areas. In this study, three adjacent eastern Mediterranean coastal rivers, Ibrahim, Kaleb and Beirut, were evaluated. Water quality samples were collected in dry and wet seasons from different sampling sites along the river from the source to the outlet which represent a gradient of increased urbanization. The spatiotemporal variability of the physio-chemical properties, heavy metals (Zn, Pb, Cu, Cr, and Cd) and organic matter (DOC) were statistically analyzed to better understand the contribution of point and nonpoint pollution sources. The three rivers (Beirut, Kaleb and Ibrahim) show a similar behavior in calcium and carbonate alkalinity due to the carbonate mineral weathering effect, so they are of calcium bicarbonate type due to their calcareous geological nature. The speciation of anions was affected by temporal variation. Moreover, it is obvious that the Beirut River has a different behavioral characteristic where the water is a sulfate type water with a preferable metal-OM complexation mainly with lead, zinc and copper, whereas Kaleb and Ibrahim are considered to be of a nitrate phosphate type with a preferable metal inorganic complexation, especially copper, that has a consistent behavior in both types of waters. This difference is attributed to the urbanization effect highly impacting the Beirut River.
基金supported by the Special Funds of the State Environmental Protection Public Welfare Industry (Nos. 201509001, 201509002)the National Key Research and Development Program of China (No. 2016YFC0201800)the National Major Scientific Instruments and Equipment Development Projects of China (No. 2011YQ120024)
文摘Owing to the vast territory of China and strong regional characteristic of ozone pollution,it＇s desirable for policy makers to have a targeted and prioritized regulation and ozone pollution control strategy in China based on scientific evidences. It＇s important to assess its current pollution status as well as spatial and temporal variation patterns across China.Recent advances of national monitoring networks provide an opportunity to insight the actions of ozone pollution. Here, we present rotated empirical orthogonal function（REOF）analysis that was used on studying the spatiotemporal characteristics of daily ozone concentrations. Based on results of REOF analysis in pollution seasons for 3 years＇ observations, twelve regions with clear patterns were identified in China. The patterns of temporal variation of ozone in each region were separated well and different from each other, reflecting local meteorological, photochemical or pollution features. A rising trend in annual averaged Eight-hour Average Ozone Concentrations（O3-8 hr） from 2014 to 2016 was observed for all regions, except for the Tibetan Plateau. The mean values of annual and 90 percentile concentrations for all 338 cities were 82.6 ± 14.6 and 133.9 ± 25.8 μg/m3,respectively, in 2015. The regionalization results of ozone were found to be influenced greatly by terrain features, indicating significant terrain and landform effects on ozone spatial correlations. Among 12 regions, North China Plain, Huanghuai Plain, Central Yangtze River Plain, Pearl River Delta and Sichuan Basin were realized as priority regions for mitigation strategies, due to their higher ozone concentrations and dense population.
基金supported by the National Natural Science Foundation of China (Grant No. U20A2094).
文摘The hydrogen isotope composition of leaf wax n-alkanes (δ2Halk) has been used to reconstruct hydroclimate conditions, yet the factors that influence it are not fully understood, particularly the control of soil pore water δ2H. This study monitored the temporal and vertical variations of peat pore water δ2H (δ2H_(pw)) from 2015 to 2019 in the Dajiuhu peatland, central China. Results showed that δ2H_(pw) was highly variable in the surface layers (0−10 cm;avg. −47‰, 1σ = 11‰) and remained almost constant in deeper depths (below 50 cm;avg. −56‰, 1σ = 2‰). The δ2H_(pw) of the 0−10 cm layer was strongly correlated with the preceding month’s precipitation δ2H (δ2Hp) in the adjacent area (r = 0.7, p < 0.01), indicating that δ2Hp is the main factor affecting the temporal variations of δ2H_(pw) in the upper layers. Moreover, the surface (0−10 cm) peat pore water slightly deviated from the local meteoric water line, suggesting that evaporation may also have an effect on the δ2H_(pw). These findings emphasize the importance of precipitation isotope composition in interpreting the δ2Halk in peat deposits under subtropical climates.
基金Under the auspices of National Natural Science Foundation of China(No.42271125)Jilin Province Foreign Expert Project(No.L202322)Doctoral Research Initiation Project of Jilin Normal University(No.0420237)。
文摘The Songhua River Basin(SRB),ranking third largest in China in terms of both runoff volume and basin area,has experi-enced frequent disasters and drastic changes in runoff since the early 20th century.Many studies have analyzed the causes of runoff re-duction;however,the spatiotemporal differences in runoff contributions and their underlying mechanisms remain poorly understood,which are crucial for regional water resources management and effective utilization.This study used the Mann-Kendall rank correlation trend test,continuous wavelet analysis,cumulative anomaly,and the slope change ratio of cumulative quantities(SCRCQ)method to explore the runoff changes characteristics and spatiotemporal differences of the contributions of climate change and human activities to runoff changes across three sub-basins of the SRB.The results show that:1)runoff from 1955 to 2022 in all the three sub-basins exhibit a statistically significant decreasing trend at 0.05 significant level.2)Four abrupt change points in runoff were detected in Nenjiang River Basin(NRB)and the mainstream of the SRB(MSRB),whereas only two change points in the Second Songhua River(SSRB).3)Runoff and precipitation series of the NRB and MSRB exhibit similar multi-timescale cycle characteristics with the most dominated cycles of 45-58 yr.In contrast,it is 12-18 yr for SSRB.4)Anthropogenic activities are the primary factor leading to in the reduction of runoff in NRB(74.33%-91.67%)and MSRB(50.11%-102.12%),whereas it is only 5.38%-33.12%in SSRB.This is attributed to the uneven distribution of regional climate and human activities in the entire SRB.5)With the growing demand for water diversion for agri-cultural irrigation,anthropogenic activities in the NRB and MSRB have increased.However,the opposite is found in SSR,where the in-creased influence of precipitation on runoff and water conservation policies are identified.
文摘Background Understanding of mosquito spatiotemporal dynamics is central to characterize candidate field sites for the sterile insect technique(SIT)testing,and is critical to the effective implementation and evaluation of pilot sterile male release programs.Here,we present a detailed description of Aedes albopictus(Skuse)egg-laying activity over a 6-year period in urban areas identified as potential SIT testing sites on Reunion Island.Method Weekly entomological collections using ovitraps were carried out in residential and adjacent uninhabited habitats in two urban areas,Duparc and Bois Rouge,in the municipality of Sainte Marie,Reunion Island.Time-series data incorporating the frequency of positive ovitraps and the total number of eggs/ovitrap recorded each time at each locality during the study period from May 2013 to December 2018 were analyzed with multifaceted statistical approaches including descriptive statistics and spatiotemporal analyses incorporating the role of climatic factors on overall ovitrap productivity.Results During the ovitrap survey,the proportion of egg-positive ovitraps differed among study sites(χ2=50.21,df=2,P<0.001),being relatively lower in Duparc(89.5%)than in Bois-Rouges(95.3%)and the adjacent buffer zone(91.2%).Within each neighborhood,Ae.albopictus egg abundance varied by month in a roughly seasonal pattern marked by a single peak occurring more regularly February each year,a decline at the onset of the austral winter in July,followed by a period of lower ovitrap productivity in August and September.Fluctuation in both positivity rate and eggs densities per ovitraps were related to annual and seasonal variations in local temperature and rainfall(P<0.001 in all cases).The spatial analysis also captured substantial between-and within-habitats heterogeneity,whereby the overall ovitrap productivity was higher in residential areas than in the buffer zone.Conclusions Collectively,these results reveal that the distribution of Ae.albopictus oviposition activity is shaped by local habitat heterogeneity and seasonal climatic factors.Overall,this study provides baseline insights into the reproductive dynamics of Ae.albopictus,which would assist in planning locally tailored SIT interventions,while addressing concerns related to focal areas of high egg-laying intensity and potential immigration of females from natural areas.
文摘In this study,we employ advanced data-driven techniques to investigate the complex relationships between the yields of five major crops and various geographical and spatiotemporal features in Senegal.We analyze how these features influence crop yields by utilizing remotely sensed data.Our methodology incorporates clustering algorithms and correlation matrix analysis to identify significant patterns and dependencies,offering a comprehensive understanding of the factors affecting agricultural productivity in Senegal.To optimize the model's performance and identify the optimal hyperparameters,we implemented a comprehensive grid search across four distinct machine learning regressors:Random Forest,Extreme Gradient Boosting(XGBoost),Categorical Boosting(CatBoost),and Light Gradient-Boosting Machine(LightGBM).Each regressor offers unique functionalities,enhancing our exploration of potential model configurations.The top-performing models were selected based on evaluating multiple performance metrics,ensuring robust and accurate predictive capabilities.The results demonstrated that XGBoost and CatBoost perform better than the other two.We introduce synthetic crop data generated using a Variational Auto Encoder to address the challenges posed by limited agricultural datasets.By achieving high similarity scores with real-world data,our synthetic samples enhance model robustness,mitigate overfitting,and provide a viable solution for small dataset issues in agriculture.Our approach distinguishes itself by creating a flexible model applicable to various crops together.By integrating five crop datasets and generating high-quality synthetic data,we improve model performance,reduce overfitting,and enhance realism.Our findings provide crucial insights for productivity drivers in key cropping systems,enabling robust recommendations and strengthening the decision-making capabilities of policymakers and farmers in datascarce regions.
基金supported by the Special Funds of the State Environmental Protection Public Welfare Industry(201509001,201309016)the Transformation Project of China National Environmental Monitoring Center(2011ZX-010-001)
文摘In order to provide scientific support to policy makers in the regulation of PM2.5 pollution in China, it is important to accurately assess the current status, spatiotemporal characteristics and regionalization data for this air pollutant. An analysis of the pollution status of PM2.5 was conducted using daily averaged mass concentration data recorded in 74 cities in 2013 and 161 cities in 2014. The rotated empirical orthogonal function(REOF) method was applied to analyze this data. Results showed that the average annual PM2.5 concentration in urban areas of China is 62.2±21.5 ?g/m3, and that the distribution is spatially heterogeneous. The North China Plain, middle and lower Yangtze River Plain, Sichuan Basin and Guanzhong Plain had relatively high annual PM2.5 concentrations compared with the southeast coastal region, the Tibetan Plateau and the Yungui Plateau. PM2.5 mass concentrations tended to be higher in winter than in summer, however, the data for many cities showed a small peak in concentrations from May to July. An analysis of the spatial correlation of PM2.5 indicated a significant influence of topographic conditions. A lower correlation was observed where terrain features varied greatly. Based on the results of the REOF analysis and topographic characteristics, ten regions were identified in mid-eastern China, which could be considered as basic pollution prevention divisions for PM2.5; these include the North China Plain region, Pearl River Delta region, Jianghuai Plain region, middle Yangtze River Plain region, Northeast Plain region, Jiangnan coastal region, Sichuan Basin region, Qiantao Plain region, Guanzhong-Central Plain region and Yungui Plateau region. Seasonal variations in the regionalization data were observed, especially for the North China Plain and Pearl River Delta regions. Among the ten regions identified in this study, the North China Plain, Guanzhong-Central Plain, middle Yangtze River Plain and Jianghuai Plain had relatively high PM2.5 mass concentrations in comparison with the others. Therefore, these regions should be considered as the key regions to target in developing PM2.5 pollution prevention strategies. This study improves the present understanding of the spatial distribution, seasonal changes and regional status of PM2.5 pollution in China and helps establish possible control strategies for the reduction of this air pollutant.
基金supported by the National Key Research and Development Program of China (Grant No. 2018YFA0605400)the Frontier Science Project of Chinese Academy of Sciences (Grant No. QYZDY-SSW-DQC011-03)+1 种基金the National Natural Science Foundation of China (Grant No. 91537210)the 13th Five-year Informatization Plan of Chinese Academy of Sciences (Grant No. XXH13505-06)。
文摘Soil moisture is an essential climate variable(ECV) concerned widely. Due to its high spatial variability, it is costly to measure soil moisture at tens of kilometers scale. In this study, a ten-year(2002–2011) daily soil moisture dataset at 0.25° spatial resolution for Chinese mainland was produced through assimilating the Advanced Microwave Scanning Radiometer for Earth Observing System(AMSR-E) brightness temperature(TB) data into a land surface model(LSM). The obtained soil moisture data was evaluated against soil moisture-measuring networks deployed in two wet areas and one dry area of the Tibetan Plateau.The results show that for the wet areas the accuracy of the soil moisture product obtained from the assimilation is considerably higher than that of both AMSR-E official soil moisture products and land surface simulation results, and for the dry area their accuracy is comparable to each other. The spatial pattern of the soil moisture from the new product is consistent with that of soil porosity from an independent survey-based dataset, further confirming the credibility of the new product. According to this product, the transition regions in China show stronger seasonal variation of soil moisture than dry and wet regions, and drier regions have stronger inter-annual variability of soil moisture than wetter regions, particularly during transitional seasons(spring and autumn). The soil moisture product is accessible at the National Tibetan Plateau Data Center.
