A comprehensive analysis of climate data(1958-2018)is carried out at the national scale in India to assess spatiotemporal variation in aridity.The aridity is analyzed using UNEP(United Nations Environment Programme)Ar...A comprehensive analysis of climate data(1958-2018)is carried out at the national scale in India to assess spatiotemporal variation in aridity.The aridity is analyzed using UNEP(United Nations Environment Programme)Aridity Index(AI),which is the ratio between Precipitation(P)and Potential Evapotranspiration(PET).Freely available Terra-Climate database,P and PET variables,offered an unprecedented opportunity for monitoring variations in AI and aridity index anomalies(AIA)at inter-seasonal and inter-decadal basis.The study also assesses longer term patterns of P and AI anomalies with vegetation anomalies.The results indicate that significant clustered areas with maximum dryness are located at west-central part of India,the state of Maharashtra.Overall,there is a gradual increase in the extent of arid zone during 60-year period and spatially maximum extent of percentage change in aridity area is observed.The change patterns of AI in India are largely driven by the changing patterns of precipitation.The maximum impact of decline in precipitation on AIA was observed during Kharif season frequently,for every 4-5 years during 1972-1992.The pattern repeated in the last few recent years(2013-2018),the decline in precipitation resulted increased aridity.The study also reveals that the availability and usage of irrigation sources have increased from 2014 to 2018.Thus,despite of less precipitation positive vegetation has been resulted in this period.The findings are important to understand the impacts of climate change on land use pattern,and land and water resource management.展开更多
Based on the data up to 1999 from hydroclimatological departments, this pape analyzes the climatic divide implications of the Qinling Mountains in regional response to the process of climate warming, due to which the ...Based on the data up to 1999 from hydroclimatological departments, this pape analyzes the climatic divide implications of the Qinling Mountains in regional response to the process of climate warming, due to which the grades of dryness/wetness (GDW) in 100 years show that the northern region has entered a drought period, while the southern is a humid period. In a course of ten years, the D-value of annual average air temperature over southern Shaanxi (the Hanjiang Valley) and the Central Shaanxi Plain (the Guanzhong Plain) has narrowed, i.e., the former with a slight change and the latter with rapid increase in temperature. Both regions were arid with the decrease in precipition D-value, namely the plain became warmer while the south was drier. The Qinling Mountains play a pronounced role in the climatic divide. The runoff coefficient (RC) of the Weihe River decreases synchronously with that of the Hanjiang due to climate warming. The RC of Weihe dropped from 0.2 in the 1950s to less than 0.1 in the 1990s. The Weihe Valley (the Guanzhong Plain) is practically an arid area due to shortage of water. The successive 0.5, 1.0°C temperature anomaly over China marks, perhaps, the improtant transition period in which the environment becomes more vulnerable than before. The study shows the obvious trend of environmental aridity, which is of help to the understanding of regional response to global climate change.展开更多
Detecting variation trend in dry-wet conditions can provide information for devel- oping strategic measures to mitigate the impacts of global warming, particularly in dry regions Taking the hilly region of northern Sh...Detecting variation trend in dry-wet conditions can provide information for devel- oping strategic measures to mitigate the impacts of global warming, particularly in dry regions Taking the hilly region of northern Shaanxi on the Loess Plateau as a case area, this study analyzed the trend of aridity variation during 1981-2012, and explored the effect of vegetation restoration promoted by the Grain-for-Green （GFG） program implemented in 1999. The re- sults indicated that the aridity in the region was non-significantly increased by 0.88% per year during 1981-2012, showing a drying trend. This drying trend and amplitude were changed by the influence of vegetation restoration promoted by the GFG program, based on two findings. The first one was that the aridity variation tended to increase during 1981-1999 while it turned to decrease during 2000-2012, with the regional mean relative change rate changed from 2.45% to -1.06%. This distinction was more remarkable in the loess gully region, where the vegetation was improved more obviously. The second one was that the mean vegetation coverage as indicated by EVI increased by 0.90% to 4.32% per year at county level, while the aridity decreased by 0.14% to 2.32% per year during 2000-2012. The regression analysis using the mean county data indicated that the change rate of aridity was negatively related to that of EVI with the coefficient of determination （R2） of 0.56, illustrating that around half of the aridity decline was explained by the EVI change. The mechanism of this effect was compli- cated, but it was found that the wind speed decline induced by the vegetation improvement could be an important contributor. It is concluded that the region became drier during 1981-2012, but the eco-restoration reduced the drying speed. However, this conclusion is involved in uncertainties, and further study based on experiments is needed to confirm the effect of the GFG-promoted vegetation restoration.展开更多
Aridity index reflects the exchanges of energy and water between the land surface and the atmosphere,and its variation can be used to forecast drought and flood patterns,which makes it of great significance for agricu...Aridity index reflects the exchanges of energy and water between the land surface and the atmosphere,and its variation can be used to forecast drought and flood patterns,which makes it of great significance for agricultural production.The ratio of potential evapotranspiration and precipitation is applied to analyse the spatial and temporal distributions of the aridity index in the Belt and Road region under the 1.5℃and 2.0℃global warming scenarios on the basis of outputs from four downscaled global climate models.The results show that:(1)Under the 1.5℃warming scenario,the area-averaged aridity index will be similar to that in 1986-2005(around 1.58),but the changes vary spatially.The aridity index will increase by more than 5%in Central-Eastern Europe,north of West Asia,the monsoon region of East Asia and northwest of Southeast Asia,while it is projected to decrease obviously in the southeast of West Asia.Regarding the seasonal scale,spring and winter will be more arid in South Asia,and the monsoon region of East Asia will be slightly drier in summer compared with the reference period.While,West Asia will be wetter in all seasons,except winter.(2)Relative to 1986-2005,both areal averaged annual potential evapotranspiration and precipitation are projected to increase,and the spatial variation of aridity index will become more obvious as well at the 2.0℃warming level.Although the aridity index over the entire region will be maintained at approximately 1.57 as that in 1.5℃,the index in Central-Eastern Europe,north of West Asia and Central Asia will grow rapidly at a rate of more than 20%,while that in West Siberia,northwest of China,the southern part of South Asia and West Asia will show a declining trend.At the seasonal scale,the increase of the aridity index in Central-Eastern Europe,Central Asia,West Asia,South Asia and the northern part of Siberia in winter will be obvious,and the monsoon region in East Asia will be drier in both summer and autumn.(3)Under the scenario of an additional 0.5℃increase in global temperature from 1.5℃to 2.0℃,the aridity index will increase significantly in Central Asia and north of West Asia but decrease in Southeast Asia and Central Siberia.Seasonally,the aridity index in the Belt and Road region will slightly increase in all other seasons except spring.Central Asia will become drier annually at a rate of more than 20%.The aridity index in South Asia will increase in spring and winter,and that in East Asia will increase in autumn and winter.(4)To changes of the aridity index,the attribution of precipitation and potential evapotranspiration will vary regionally.Precipitation will be the major influencing factor over southern West Asia,southern South Asia,Central-Eastern Siberia,the non-monsoon region of East Asia and the border between West Asia and Central Asia,while potential evapotranspiration will exert greater effects over Central-Eastern Europe,West Siberia,Central Asia and the monsoon region of East Asia.展开更多
Mid-western China is one of the most sensitive and fragile areas on the Earth.Evapotranspiration(ET)is a key part of hydrological cycle in these areas and is affected by both global climate change and human activities...Mid-western China is one of the most sensitive and fragile areas on the Earth.Evapotranspiration(ET)is a key part of hydrological cycle in these areas and is affected by both global climate change and human activities.The dynamic changes in ET and potential evapotranspiration(PET),which can reflect water consumption and demand,are still unclear,and there is a lack of predictive capacity on drought severity.In this study,we used global MODIS(moderate-resolution imaging spectroradiometer)terrestrial ET(MOD16)products,Morlet wavelet analysis,and simple linear regression to investigate the spatiotemporal variations of ET,PET,reference ET(ET0),and aridity index(AI)in mid-western pastoral regions of China(including Gansu Province,Qinghai Province,Ningxia Hui Autonomous Region,and part of Inner Mongolia Autonomous Region)from 2001 to 2016.The results showed that the overall ET gradually increased from east to southwest in the study area.Actual ET showed an increasing trend,whereas PET tended to decrease from 2001 to 2016.The change in ET was affected by vegetation types.During the study period,the average annual ET0 and AI tended to decrease.At the monthly scale within a year,AI value decreased from January to July and then increased.The interannual variations of ET0 and AI showed periodicity with a main period of 14 a,and two other periodicities of 11 and 5 a.This study showed that in recent years,drought in these pastoral regions of mid-western China has been alleviated.Therefore,it is foreseeable that the demand for irrigation water for agricultural production in these regions will decrease.展开更多
The olive species(Olea europaea L.)is an ancient traditional crop grown under rainfed conditions in the Mediterranean Basin.In response to the growing national and international demand for olive oil,the olive cultivar...The olive species(Olea europaea L.)is an ancient traditional crop grown under rainfed conditions in the Mediterranean Basin.In response to the growing national and international demand for olive oil,the olive cultivars are introduced into highly arid new bioclimatic areas.Subsequently,the morpho-physiology and phytochemistry of olive trees are potentially changing among cultivar types and geographical conditions.In the present work,we have undertaken an assessment on the impacts of geographical location and cultivar types on the leaf morpho-physiology and phytochemistry of olive trees.Thus,leaves of the two most cultivated olive tree varieties,Chemlal and Sigoise,were collected from three geographical regions(Setif,Batna,and Eloued)with increasing aridity in Algeria.Leaf samples from the geographical regions were analyzed using the standard physiological experiment,colorimetric method,and a chromatography assay.Leaves of both cultivars exhibited a significant variance in terms of the leaf shape index but not for the leaf tissue density,specific leaf weight,and specific leaf area.Photosynthetic pigment contents were affected by both cultivar type and geographical location,with the lowest pigment content recorded in the Sigoise cultivar from the Setif region.Compared with the Setif and Batna regions,dried leaves of both cultivars from the Eloued region showed the higher levels of the total polyphenol,total flavonoid,and total tannin,as well as a better antioxidant capacity.Liquid chromatography-mass spectrometry analysis of all leaf extracts identified the following phenolic acids as major compounds:oleuropein,naringin,apigenin-7-O-glucoside,kaempferol,quercetin,quercitrin,luteolin-7-O-naringenin,and quinic acid.Lower contents were found for p-Coumaric acid,trans-Ferulic acid,hyperoside,rutin,apigenin,caffeic acid,protocatechuic acid,o-Coumaric acid,and gallic acid.Also,epicatechin and catechin+were not found in the leaf extracts of the Sigoise cultivar.The leaf organic extracts in both cultivars displayed promising anti-cancer activity that was affected by geographical location and organic solvent polarity.Briefly,although increasing aridity and soil organic and mineral deficiency affected the leaf morpho-physiological parameters,both cultivars sustained a chemical richness,a good antioxidant,and an anti-tumoral capacity in leaves.Furthermore,the findings revealed that regardless the olive tree genotype,there was a significant impact of geographical location on the leaf morpho-physiology,bioactivity,and chemical composition,which may consequently modulate the growth and oil production of olive trees.展开更多
A distinct aridity trend in China in last 100 years is presented by applying a linear fitting to both the climate records and the hydrological records, which is supported by evidence of environmental changes and seems...A distinct aridity trend in China in last 100 years is presented by applying a linear fitting to both the climate records and the hydrological records, which is supported by evidence of environmental changes and seems to be associated with a global warming trend during this period.The Mann Kendall Rank statistic test reveals a very interesting feature that the climate of China entered into a dry regime abruptly in about 1920's, which synchronized with the rapid warming of the global temperature at almost the same time.According to an analysis of the meridional profile of observed global zonal mean precipitation anomalies during the peak period of global wanning (1930-1940), the drought occurred in whole middle latitude zone (25°N-55°N) of the Northern Hemisphere, where the most part of China is located in. Although this pattern is in good agreement with the latitude distribution of the difference of zonal mean rates of precipitation between 4 × CO2 and 1 × CO2 simulated by climate model (Manabe and Wetherald, 1983), more studies are required to understand the linkage between the aridity trend in China and the greenhouse effect.The EOF analysis of the Northern Hemisphere sea level pressure for the season of June to August shows an abrupt change of the time coefficient of its first eigenvector from positive to negative in mid-1920's, indicating an enhancement of the subtropical high over Southeast Asia and the western Pacific after that time. This is an atmospheric circulation pattern that is favorable to the development of dry climate in China.展开更多
Rainfall and evapotranspiration are two vital elements for food production under rainfed agriculture. This study aims at investigating the combined changes in these variables in the form of aridly index in the souther...Rainfall and evapotranspiration are two vital elements for food production under rainfed agriculture. This study aims at investigating the combined changes in these variables in the form of aridly index in the southern Senegal. The temporal trends in annual and monthly (from May to October) aridity index, rainfall and evapotranspiration are examined and adaptation strategies to the vulnerability of rainfed rice cultivation to the changes are developed. The results show a significant decreasing trend in annual rainfall at all study locations for the period 1922-2015. When analyzing the trends in sub-periods, there are two clear patterns in the annual rainfall series: a decreasing trend for the period 1922-1979 and a reversal increasing trend for the period 1980-2015. An increasing trend is also observed in annual reference evapotranspiration. The results reveal that the region will be drier with a significant increase in aridity at the annual and most monthly series. Appropriate adaptation strategies should be implemented to diminish the adverse influence of the increasing aridity on rice productivity for a sustainable agriculture.展开更多
Asian aridity can be traced back to the early Cenozoic(e.g.,Guo et al.,2008;Licht et al.,2016;Li et al.,2018a).Previous modelling studies focus mainly on the monsoon climate during the early Cenozoic,and studies for t...Asian aridity can be traced back to the early Cenozoic(e.g.,Guo et al.,2008;Licht et al.,2016;Li et al.,2018a).Previous modelling studies focus mainly on the monsoon climate during the early Cenozoic,and studies for the Asian aridity are still limited(e.g.,Huber and Goldner,2012;Zhang et al.,2012;Li et al.,2018b).Here Asian aridity during the early Cenozoic is investigated through climate modelling by changing atmospheric CO2 concentration,orbital parameters,and topography.展开更多
Aim to linking the variability of drought in northwest China to the oceanic influence of North Atlantic SSTs at the background of global warming and at the regional climate change shifting stages, year aridity index v...Aim to linking the variability of drought in northwest China to the oceanic influence of North Atlantic SSTs at the background of global warming and at the regional climate change shifting stages, year aridity index variations in northwest China and summer North Atlantic sea surface temperature （SST） variations are examined for the 44 a period of 1961-2004 using singular value decomposition （SVD） analysis. Results show that the SST anomalies （SSTA）in the North Atlantic in summer reflected three basic models. The first SVD mode of SST pattern shows a dipole - like variation with the positive center located at southwest and negative center at northeast of extratropical North Atlantic. And it strongly relates to the positive trend in AI variation in northwest China. The second coupled modes display the coherent positive anomalies in extratropical North Atlantic SST and the marked opposite trend of AI variability between north and south of Xinjiang. In addition, the lag correlation analysis of the first mode of SSTA and geopotential heights at 500 hPa variations also shows that the indication of the former influencing the latter configuration, which result in higher air temperature and less precipitation when the SSTA in the North Atlantic Ocean in summer motivated Eurasian circulation of EA pattern, further to influence the wet - dry variations in northwest China by the ocean-to - atmosphere forcing.展开更多
Based on the data of monthly precipitation and other monthly meteorological elements of 661 meteorological stations over China from 1961 to 2013, the temporal evolution characteristics of aridity in Hetao area of Nort...Based on the data of monthly precipitation and other monthly meteorological elements of 661 meteorological stations over China from 1961 to 2013, the temporal evolution characteristics of aridity in Hetao area of North China which is drying significantly were studied by using REOF, and the effects of summer monsoon and meteorological factors on the aridity index were discussed. The results showed that climatic aridity in Hetac area of North China tended to increase with time during 1961 -2013. The annual variation and overall trend of climatic aridity in Hetao area of North China was mainly influenced by /SASM1 before the 1990s, and the degree of the influence weakened with global warming. There were certain differ- ences between annual and decadal variations in the effects of the meteorological elements on climatic aridity. The impact of the thermal factors on aridity index was more significant than the dynamic factor after the 1990s, revealing that climate warming aggravated climatic aridity in Hetao area of North China.展开更多
The impact of global warming on the aridity in South America (SA) is investigated. For this purpose, the methodology for generating surrogate climate-change scenarios with a RCM is employed. For the present climate (C...The impact of global warming on the aridity in South America (SA) is investigated. For this purpose, the methodology for generating surrogate climate-change scenarios with a RCM is employed. For the present climate (CTRL) the RCM is initialized with and driven by ECMWF/ERA-Interim reanalysis data. Two aridity indices are used: the Budyko and the UNEP indices. The results for the CTR are in agreement with other model studies which indicate future warming;rainfall increases in southeastern South America, Ecuador and Peru and decreases in the central and eastern Amazon. In general the model reproduces the aridity in the continent compared with the observed data for both indices. The distribution of aridity over SA in surrogate climate-change scenario shows an increase of the dryness in the continent. Over Amazonia the aridity increases 23.9% (for the UNEP index) and 3.1% (for the Budyko index), suggesting that portions of the Amazonia forest are replaced by dry land area. The semi-arid zone over northeast Brazil expands westward, attaining the interior of north Brazil. In this region the aridity increases 20% (for the UNEP index) and 0.6% (for the Budyko index) indicating that areas of humid regime may be occupied by areas with dry land regime. The RCM was also integrated driven by the AOGCM ECHAM5/MPI-OM for the reference climate (CTRL2) and under A1B SRES scenario. The results for the present-day climate are similar in CTRL2 and CTRL, and are in agreement with CRU data. The distribution of the aridity for the present climate seems to be better represented in CTRL using both Budyko and UNEP indices. The changes in aridity (future climate minus control) are higher in the run forced by the A1B SRES scenario. Although the UNEP and Budyko indices show potentialities and limitations to represent the aridity distribution over SA, the changes in aridity due to a pseudo-scenario of global warming are higher using the UNEP index.展开更多
As the increases of climatic aridity and grazing intensity, shrubs play an increasingly important role in grassland ecosystem in arid and semi-arid regions, and its abundance also generally increases. However, the eff...As the increases of climatic aridity and grazing intensity, shrubs play an increasingly important role in grassland ecosystem in arid and semi-arid regions, and its abundance also generally increases. However, the effects of climatic aridity and grazing intensity on sexual reproduction of shrubs in grassland remain largely unclear. In order to understand the effects of grazing intensity and climatic drought stress, and their interaction on seed production of shrub species, we examined the seed number, seed weight and seed yield of Caragana stenophylla under three grazing intensities （fenced, mild grazing and severe grazing） across a climatic aridity gradient （semi-arid, arid, very arid and intensively arid zones） in the Inner Mongolia Steppe, northern China during 2012-2013. The seed number, seed weight and seed yield gradually increased from the semi-arid to the very arid zones, but decreased from the very arid to the intensively arid zones in fenced plots. The seed number and seed yield decreased from the semi-arid to the intensively arid zones in mild and severe grazing treatment plots, therefore, grazing enhanced the suppression effect of climatic aridity on seed production of C. stenophylla. The seed number and seed yield gradually decreased as grazing intensity increased. The seed weight was highest in severe grazing plots, followed by the mild grazing plots and then the fenced plots. Precipitation varied interannually during the study period. We observed that the seed number seed weight and seed yield were lower in the low precipitation year （2013） than in the high precipitation year （2012）. As climatic drought stress increased, the negative effects of grazing on seed production of C. stenophylla also gradually increased. Our results indicated that climatic drought stress may contribute to the encroachment of C. stenophylla shrub in arid zones by promoting its seed production. However, grazing had negative effects on sexual reproduction of C. stenophylla, and the combined effects of drought stress and grazing seriously suppressed sexual reproduction of C. stenophylla in the intensively arid zone.展开更多
Leaf functional traits play a pivotal role in understanding the adaptive strategy of plants in extreme environments, as well as in assessing their potential distribution range sizes and extinction risks under global c...Leaf functional traits play a pivotal role in understanding the adaptive strategy of plants in extreme environments, as well as in assessing their potential distribution range sizes and extinction risks under global climate change. However, the response of leaf functional traits to aridity in drylands remains unclear for plants with different range sizes. To fill this gap, we measured 10 leaf functional traits of 152 plant species across 172 dryland sites in China, and classified these species as either narrow-(NRS) or wide-ranging species(WRS) based on worldwide occurrence data. Our results showed that the NRS generally occurred in more severe arid areas, and had higher leaf water content(LWC) than WRS at high aridity levels(aridity>0.8). The scaling exponents between leaf volume(LV) and leaf dry weight(LDW) at high aridity levels were 1 for WRS and 1.56 for NRS, indicating that LV increased at a faster rate than LDW and therefore enabled NRS to store more water than WRS. Using moving window analysis, the above scaling exponents increased in NRS and decreased in WRS with increasing aridity at high aridity levels. Moreover, NRS with higher LWC tended to be more abundant at high aridity levels. Our results highlighted that NRS had higher LWC than WRS under high aridity, conferring them with a key advantage in adapting to extreme arid environments. These findings suggest that NRS and WRS use distinct adaptive strategies to cope with aridity. In the conservation of NRS in drylands, enhancing leaf water storage capacity is of particular importance.展开更多
Climate change is expected to introduce more water demand in the face of diminishing water supplies,intensifying the degree of aridity observed in terrestrial ecosystems in the 21st century.This study investigated spa...Climate change is expected to introduce more water demand in the face of diminishing water supplies,intensifying the degree of aridity observed in terrestrial ecosystems in the 21st century.This study investigated spatiotemporal variability within global aridity index(AI)values from 1970-2018.The results revealed an overall drying trend(0.0016 yr-1,p<0.01),with humid and semi-humid regions experiencing more significant drying than other regions,including those classified as arid or semi-arid.In addition,the Qinghai-Tibet Plateau has gotten wetter,largely due to the increases in precipitation(PPT)observed in that region.Global drying is driven primarily by decreasing and increasing PPT and potential evapotranspiration(PET),respectively.Decreases in PPT alone or increases in PET also drive global aridification,though to a lesser extent.PPT and increasing potential evapotranspiration(PET),with increasing PET alone or decreasing PPT alone.Slightly less than half of the world’s land area has exhibited a wetting trend,largely owing to increases in regional PPT.In some parts of the world,the combined effects of increased PPT and decreased PET drives wetting,with decreases in PET alone explaining wetting in others.These results indicate that,without consideration of other factors(e.g.,CO_(2)fertilization),aridity may continue to intensify,especially in humid regions.展开更多
The rainfall of China is scanty when compared with the northeas ern partof the United States of Ameriea,almost identical in location and in latitude,The aridity of north China was found to be due to the following four...The rainfall of China is scanty when compared with the northeas ern partof the United States of Ameriea,almost identical in location and in latitude,The aridity of north China was found to be due to the following four causes:(1)the decrease of number of cyclones from south China to north China,(2)the deflecting of Kurosiwo farther and farther away from the Chinese coast as we go northward from the Yangtze estuary,(3)the presence of mountain barrier of Tsingling,and(4)the sinister influence of Siberian anticyclone in the winter half year.展开更多
The global warming slowdown or warming hiatus, began around the year 2000 and has persisted for nearly 15 years. Most studies have focused on the interpretation of the hiatus in temperature. In this study, changes in ...The global warming slowdown or warming hiatus, began around the year 2000 and has persisted for nearly 15 years. Most studies have focused on the interpretation of the hiatus in temperature. In this study, changes in a global aridity index （AI） were analyzed by using a newly developed dynamical adjustment method that can successfully identify and separate dynamically induced and radiatively forced aridity changes in the raw data. The AI and Palmer Drought Severity Index produced a wetting zone over the mid-to-high latitudes of the Northern Hemisphere in recent decades. The dynamical adjustment analysis suggested that this wetting zone occurred in response to the global warming hiatus. The dynamically induced AI （DAI） played a major role in the AI changes during the hiatus period, and its relationships with the North Atlantic Oscillation （NAO）, Pacific Decadal Oscillation （PDO）, and Atlantic Multi-decadal Oscillation （AMO） also indicated that different phases of the NAO, PDO, and AMO contributed to dif- ferent performances of the DAI over the Northern Hemisphere. Although the aridity wetting over the mid-to-high lat- itudes may relieve long-term drying in certain regions, the hiatus is temporary, and so is the relief. Accelerated glob- al warming will return when the NAO, PDO, and AMO revert to their opposite phases in the future, and the wetting zone is likely to disappear.展开更多
Northern China is a prominent “hotspot” for land–atmosphere interactions, with substantial gradients in both moisture and thermal conditions. Previous studies have identified a link between land–atmosphere couplin...Northern China is a prominent “hotspot” for land–atmosphere interactions, with substantial gradients in both moisture and thermal conditions. Previous studies have identified a link between land–atmosphere coupling and the individual roles of each factor, but the synergistic effect of the two factors remains unclear. This study considers the covariation of evapotranspiration and precipitation to assess evapotranspiration–precipitation(ET–P) coupling across northern China,exploring its spatial variations and their linkage to water and heat factors. Our findings reveal a transition from strongly positive coupling in the northwest to weakly negative coupling in the southeast, peaking in spring. These spatial variations are attributable to water(soil moisture) and heat(air temperature), which explain 39% and 25% of the variability,respectively. The aridity index(AI), a water–heat synergy factor, is the dominant factor, explaining 66% of the spatial variation in ET–P coupling. As the AI increases, ET–P coupling shifts from strongly positive to weakly negative, with an AI around 0.7. This shift is determined by a shift in the evapotranspiration–lifting condensation level(LCL) coupling under an AI change. Regions with an AI below 0.7 experience water-limited evapotranspiration, where increased soil moisture enhances evapotranspiration, reduces sensible heat(H), and lowers the LCL, resulting in a negative ET–LCL coupling.Conversely, regions with an AI above 0.7 experience energy-limited evapotranspiration, where the positive ET–LCL coupling reflects a positive H–LCL coupling or a positive impact of the LCL on evapotranspiration. This analysis advances our understanding of the intricate influences of multifactor surface interactions on the spatial variations of land–atmosphere coupling.展开更多
Drought is a natural disaster that significantly impacts the Earth's ecological environment,especially in arid and semi-arid areas.However,drought at a large watershed scale,which plays an important role in sustai...Drought is a natural disaster that significantly impacts the Earth's ecological environment,especially in arid and semi-arid areas.However,drought at a large watershed scale,which plays an important role in sustainable environmental development,has received limited attention.In this study,we analyzed the spatial and temporal variations in drought in the Yellow River Basin,China from 2002 to 2022 and its driving factors using a vegetation health index(VHI).Results showed that average VHI in the Yellow River Basin from 2002 to 2022 was 0.581,with the most severe drought occurring in summer and autumn.The basin showed a slow decreasing trend in drought during the study period.Regarding spatial distribution of monthly drought frequency and trend of VHI,the mean of the frequency was 13.00%,and 78.00%had a drought frequency of 10.00%–20.00%,with moderate drought generally prevailing.Regarding land use types,forest land,grassland,agricultural land,construction land,water body,and wasteland showed a descending order for the annual average VHI.VHI of each land use type was the lowest in summer and autumn,with pronounced seasonal characteristics.The uneven distribution of drought in the Yellow River Basin was primarily influenced by annual precipitation,solar-induced chlorophyll fluorescence,and relative humidity.VHI effectively quantified drought conditions at a regional scale and proved to be highly applicable in the Yellow River Basin.The results clarify the effectiveness of VHI for drought monitoring in the Yellow River Basin and can provide a reference for drought monitoring across the basin.展开更多
文摘A comprehensive analysis of climate data(1958-2018)is carried out at the national scale in India to assess spatiotemporal variation in aridity.The aridity is analyzed using UNEP(United Nations Environment Programme)Aridity Index(AI),which is the ratio between Precipitation(P)and Potential Evapotranspiration(PET).Freely available Terra-Climate database,P and PET variables,offered an unprecedented opportunity for monitoring variations in AI and aridity index anomalies(AIA)at inter-seasonal and inter-decadal basis.The study also assesses longer term patterns of P and AI anomalies with vegetation anomalies.The results indicate that significant clustered areas with maximum dryness are located at west-central part of India,the state of Maharashtra.Overall,there is a gradual increase in the extent of arid zone during 60-year period and spatially maximum extent of percentage change in aridity area is observed.The change patterns of AI in India are largely driven by the changing patterns of precipitation.The maximum impact of decline in precipitation on AIA was observed during Kharif season frequently,for every 4-5 years during 1972-1992.The pattern repeated in the last few recent years(2013-2018),the decline in precipitation resulted increased aridity.The study also reveals that the availability and usage of irrigation sources have increased from 2014 to 2018.Thus,despite of less precipitation positive vegetation has been resulted in this period.The findings are important to understand the impacts of climate change on land use pattern,and land and water resource management.
基金Knowledge Innovation Project of Chinese Academy of Sciences, KZCX2-310-05 National Natural Science Foundation of China, No.4007
文摘Based on the data up to 1999 from hydroclimatological departments, this pape analyzes the climatic divide implications of the Qinling Mountains in regional response to the process of climate warming, due to which the grades of dryness/wetness (GDW) in 100 years show that the northern region has entered a drought period, while the southern is a humid period. In a course of ten years, the D-value of annual average air temperature over southern Shaanxi (the Hanjiang Valley) and the Central Shaanxi Plain (the Guanzhong Plain) has narrowed, i.e., the former with a slight change and the latter with rapid increase in temperature. Both regions were arid with the decrease in precipition D-value, namely the plain became warmer while the south was drier. The Qinling Mountains play a pronounced role in the climatic divide. The runoff coefficient (RC) of the Weihe River decreases synchronously with that of the Hanjiang due to climate warming. The RC of Weihe dropped from 0.2 in the 1950s to less than 0.1 in the 1990s. The Weihe Valley (the Guanzhong Plain) is practically an arid area due to shortage of water. The successive 0.5, 1.0°C temperature anomaly over China marks, perhaps, the improtant transition period in which the environment becomes more vulnerable than before. The study shows the obvious trend of environmental aridity, which is of help to the understanding of regional response to global climate change.
基金National Basic Research Program of China,No.2012CB955304
文摘Detecting variation trend in dry-wet conditions can provide information for devel- oping strategic measures to mitigate the impacts of global warming, particularly in dry regions Taking the hilly region of northern Shaanxi on the Loess Plateau as a case area, this study analyzed the trend of aridity variation during 1981-2012, and explored the effect of vegetation restoration promoted by the Grain-for-Green （GFG） program implemented in 1999. The re- sults indicated that the aridity in the region was non-significantly increased by 0.88% per year during 1981-2012, showing a drying trend. This drying trend and amplitude were changed by the influence of vegetation restoration promoted by the GFG program, based on two findings. The first one was that the aridity variation tended to increase during 1981-1999 while it turned to decrease during 2000-2012, with the regional mean relative change rate changed from 2.45% to -1.06%. This distinction was more remarkable in the loess gully region, where the vegetation was improved more obviously. The second one was that the mean vegetation coverage as indicated by EVI increased by 0.90% to 4.32% per year at county level, while the aridity decreased by 0.14% to 2.32% per year during 2000-2012. The regression analysis using the mean county data indicated that the change rate of aridity was negatively related to that of EVI with the coefficient of determination （R2） of 0.56, illustrating that around half of the aridity decline was explained by the EVI change. The mechanism of this effect was compli- cated, but it was found that the wind speed decline induced by the vegetation improvement could be an important contributor. It is concluded that the region became drier during 1981-2012, but the eco-restoration reduced the drying speed. However, this conclusion is involved in uncertainties, and further study based on experiments is needed to confirm the effect of the GFG-promoted vegetation restoration.
文摘Aridity index reflects the exchanges of energy and water between the land surface and the atmosphere,and its variation can be used to forecast drought and flood patterns,which makes it of great significance for agricultural production.The ratio of potential evapotranspiration and precipitation is applied to analyse the spatial and temporal distributions of the aridity index in the Belt and Road region under the 1.5℃and 2.0℃global warming scenarios on the basis of outputs from four downscaled global climate models.The results show that:(1)Under the 1.5℃warming scenario,the area-averaged aridity index will be similar to that in 1986-2005(around 1.58),but the changes vary spatially.The aridity index will increase by more than 5%in Central-Eastern Europe,north of West Asia,the monsoon region of East Asia and northwest of Southeast Asia,while it is projected to decrease obviously in the southeast of West Asia.Regarding the seasonal scale,spring and winter will be more arid in South Asia,and the monsoon region of East Asia will be slightly drier in summer compared with the reference period.While,West Asia will be wetter in all seasons,except winter.(2)Relative to 1986-2005,both areal averaged annual potential evapotranspiration and precipitation are projected to increase,and the spatial variation of aridity index will become more obvious as well at the 2.0℃warming level.Although the aridity index over the entire region will be maintained at approximately 1.57 as that in 1.5℃,the index in Central-Eastern Europe,north of West Asia and Central Asia will grow rapidly at a rate of more than 20%,while that in West Siberia,northwest of China,the southern part of South Asia and West Asia will show a declining trend.At the seasonal scale,the increase of the aridity index in Central-Eastern Europe,Central Asia,West Asia,South Asia and the northern part of Siberia in winter will be obvious,and the monsoon region in East Asia will be drier in both summer and autumn.(3)Under the scenario of an additional 0.5℃increase in global temperature from 1.5℃to 2.0℃,the aridity index will increase significantly in Central Asia and north of West Asia but decrease in Southeast Asia and Central Siberia.Seasonally,the aridity index in the Belt and Road region will slightly increase in all other seasons except spring.Central Asia will become drier annually at a rate of more than 20%.The aridity index in South Asia will increase in spring and winter,and that in East Asia will increase in autumn and winter.(4)To changes of the aridity index,the attribution of precipitation and potential evapotranspiration will vary regionally.Precipitation will be the major influencing factor over southern West Asia,southern South Asia,Central-Eastern Siberia,the non-monsoon region of East Asia and the border between West Asia and Central Asia,while potential evapotranspiration will exert greater effects over Central-Eastern Europe,West Siberia,Central Asia and the monsoon region of East Asia.
基金This work was supported by the earmarked fund for China Agriculture Research System of Ministry of Finance and Ministry of Agriculture and Rural Affairs(CARS-34)the National Key Research and Development Program of China(2016YFC0400302).
文摘Mid-western China is one of the most sensitive and fragile areas on the Earth.Evapotranspiration(ET)is a key part of hydrological cycle in these areas and is affected by both global climate change and human activities.The dynamic changes in ET and potential evapotranspiration(PET),which can reflect water consumption and demand,are still unclear,and there is a lack of predictive capacity on drought severity.In this study,we used global MODIS(moderate-resolution imaging spectroradiometer)terrestrial ET(MOD16)products,Morlet wavelet analysis,and simple linear regression to investigate the spatiotemporal variations of ET,PET,reference ET(ET0),and aridity index(AI)in mid-western pastoral regions of China(including Gansu Province,Qinghai Province,Ningxia Hui Autonomous Region,and part of Inner Mongolia Autonomous Region)from 2001 to 2016.The results showed that the overall ET gradually increased from east to southwest in the study area.Actual ET showed an increasing trend,whereas PET tended to decrease from 2001 to 2016.The change in ET was affected by vegetation types.During the study period,the average annual ET0 and AI tended to decrease.At the monthly scale within a year,AI value decreased from January to July and then increased.The interannual variations of ET0 and AI showed periodicity with a main period of 14 a,and two other periodicities of 11 and 5 a.This study showed that in recent years,drought in these pastoral regions of mid-western China has been alleviated.Therefore,it is foreseeable that the demand for irrigation water for agricultural production in these regions will decrease.
文摘The olive species(Olea europaea L.)is an ancient traditional crop grown under rainfed conditions in the Mediterranean Basin.In response to the growing national and international demand for olive oil,the olive cultivars are introduced into highly arid new bioclimatic areas.Subsequently,the morpho-physiology and phytochemistry of olive trees are potentially changing among cultivar types and geographical conditions.In the present work,we have undertaken an assessment on the impacts of geographical location and cultivar types on the leaf morpho-physiology and phytochemistry of olive trees.Thus,leaves of the two most cultivated olive tree varieties,Chemlal and Sigoise,were collected from three geographical regions(Setif,Batna,and Eloued)with increasing aridity in Algeria.Leaf samples from the geographical regions were analyzed using the standard physiological experiment,colorimetric method,and a chromatography assay.Leaves of both cultivars exhibited a significant variance in terms of the leaf shape index but not for the leaf tissue density,specific leaf weight,and specific leaf area.Photosynthetic pigment contents were affected by both cultivar type and geographical location,with the lowest pigment content recorded in the Sigoise cultivar from the Setif region.Compared with the Setif and Batna regions,dried leaves of both cultivars from the Eloued region showed the higher levels of the total polyphenol,total flavonoid,and total tannin,as well as a better antioxidant capacity.Liquid chromatography-mass spectrometry analysis of all leaf extracts identified the following phenolic acids as major compounds:oleuropein,naringin,apigenin-7-O-glucoside,kaempferol,quercetin,quercitrin,luteolin-7-O-naringenin,and quinic acid.Lower contents were found for p-Coumaric acid,trans-Ferulic acid,hyperoside,rutin,apigenin,caffeic acid,protocatechuic acid,o-Coumaric acid,and gallic acid.Also,epicatechin and catechin+were not found in the leaf extracts of the Sigoise cultivar.The leaf organic extracts in both cultivars displayed promising anti-cancer activity that was affected by geographical location and organic solvent polarity.Briefly,although increasing aridity and soil organic and mineral deficiency affected the leaf morpho-physiological parameters,both cultivars sustained a chemical richness,a good antioxidant,and an anti-tumoral capacity in leaves.Furthermore,the findings revealed that regardless the olive tree genotype,there was a significant impact of geographical location on the leaf morpho-physiology,bioactivity,and chemical composition,which may consequently modulate the growth and oil production of olive trees.
文摘A distinct aridity trend in China in last 100 years is presented by applying a linear fitting to both the climate records and the hydrological records, which is supported by evidence of environmental changes and seems to be associated with a global warming trend during this period.The Mann Kendall Rank statistic test reveals a very interesting feature that the climate of China entered into a dry regime abruptly in about 1920's, which synchronized with the rapid warming of the global temperature at almost the same time.According to an analysis of the meridional profile of observed global zonal mean precipitation anomalies during the peak period of global wanning (1930-1940), the drought occurred in whole middle latitude zone (25°N-55°N) of the Northern Hemisphere, where the most part of China is located in. Although this pattern is in good agreement with the latitude distribution of the difference of zonal mean rates of precipitation between 4 × CO2 and 1 × CO2 simulated by climate model (Manabe and Wetherald, 1983), more studies are required to understand the linkage between the aridity trend in China and the greenhouse effect.The EOF analysis of the Northern Hemisphere sea level pressure for the season of June to August shows an abrupt change of the time coefficient of its first eigenvector from positive to negative in mid-1920's, indicating an enhancement of the subtropical high over Southeast Asia and the western Pacific after that time. This is an atmospheric circulation pattern that is favorable to the development of dry climate in China.
文摘Rainfall and evapotranspiration are two vital elements for food production under rainfed agriculture. This study aims at investigating the combined changes in these variables in the form of aridly index in the southern Senegal. The temporal trends in annual and monthly (from May to October) aridity index, rainfall and evapotranspiration are examined and adaptation strategies to the vulnerability of rainfed rice cultivation to the changes are developed. The results show a significant decreasing trend in annual rainfall at all study locations for the period 1922-2015. When analyzing the trends in sub-periods, there are two clear patterns in the annual rainfall series: a decreasing trend for the period 1922-1979 and a reversal increasing trend for the period 1980-2015. An increasing trend is also observed in annual reference evapotranspiration. The results reveal that the region will be drier with a significant increase in aridity at the annual and most monthly series. Appropriate adaptation strategies should be implemented to diminish the adverse influence of the increasing aridity on rice productivity for a sustainable agriculture.
基金granted by the Strategic Priority Research Program of Chinese Academy of Sciences(Grant No.XDA20070103)the National Natural Science Foundation of China(Grant Nos.41775088 and 41625018).
文摘Asian aridity can be traced back to the early Cenozoic(e.g.,Guo et al.,2008;Licht et al.,2016;Li et al.,2018a).Previous modelling studies focus mainly on the monsoon climate during the early Cenozoic,and studies for the Asian aridity are still limited(e.g.,Huber and Goldner,2012;Zhang et al.,2012;Li et al.,2018b).Here Asian aridity during the early Cenozoic is investigated through climate modelling by changing atmospheric CO2 concentration,orbital parameters,and topography.
基金The National Natural Science Foundation of China under contract No.904110017
文摘Aim to linking the variability of drought in northwest China to the oceanic influence of North Atlantic SSTs at the background of global warming and at the regional climate change shifting stages, year aridity index variations in northwest China and summer North Atlantic sea surface temperature （SST） variations are examined for the 44 a period of 1961-2004 using singular value decomposition （SVD） analysis. Results show that the SST anomalies （SSTA）in the North Atlantic in summer reflected three basic models. The first SVD mode of SST pattern shows a dipole - like variation with the positive center located at southwest and negative center at northeast of extratropical North Atlantic. And it strongly relates to the positive trend in AI variation in northwest China. The second coupled modes display the coherent positive anomalies in extratropical North Atlantic SST and the marked opposite trend of AI variability between north and south of Xinjiang. In addition, the lag correlation analysis of the first mode of SSTA and geopotential heights at 500 hPa variations also shows that the indication of the former influencing the latter configuration, which result in higher air temperature and less precipitation when the SSTA in the North Atlantic Ocean in summer motivated Eurasian circulation of EA pattern, further to influence the wet - dry variations in northwest China by the ocean-to - atmosphere forcing.
基金Supported by the State Key Development Program for Basic Research of China(2013CB430200)
文摘Based on the data of monthly precipitation and other monthly meteorological elements of 661 meteorological stations over China from 1961 to 2013, the temporal evolution characteristics of aridity in Hetao area of North China which is drying significantly were studied by using REOF, and the effects of summer monsoon and meteorological factors on the aridity index were discussed. The results showed that climatic aridity in Hetac area of North China tended to increase with time during 1961 -2013. The annual variation and overall trend of climatic aridity in Hetao area of North China was mainly influenced by /SASM1 before the 1990s, and the degree of the influence weakened with global warming. There were certain differ- ences between annual and decadal variations in the effects of the meteorological elements on climatic aridity. The impact of the thermal factors on aridity index was more significant than the dynamic factor after the 1990s, revealing that climate warming aggravated climatic aridity in Hetao area of North China.
文摘The impact of global warming on the aridity in South America (SA) is investigated. For this purpose, the methodology for generating surrogate climate-change scenarios with a RCM is employed. For the present climate (CTRL) the RCM is initialized with and driven by ECMWF/ERA-Interim reanalysis data. Two aridity indices are used: the Budyko and the UNEP indices. The results for the CTR are in agreement with other model studies which indicate future warming;rainfall increases in southeastern South America, Ecuador and Peru and decreases in the central and eastern Amazon. In general the model reproduces the aridity in the continent compared with the observed data for both indices. The distribution of aridity over SA in surrogate climate-change scenario shows an increase of the dryness in the continent. Over Amazonia the aridity increases 23.9% (for the UNEP index) and 3.1% (for the Budyko index), suggesting that portions of the Amazonia forest are replaced by dry land area. The semi-arid zone over northeast Brazil expands westward, attaining the interior of north Brazil. In this region the aridity increases 20% (for the UNEP index) and 0.6% (for the Budyko index) indicating that areas of humid regime may be occupied by areas with dry land regime. The RCM was also integrated driven by the AOGCM ECHAM5/MPI-OM for the reference climate (CTRL2) and under A1B SRES scenario. The results for the present-day climate are similar in CTRL2 and CTRL, and are in agreement with CRU data. The distribution of the aridity for the present climate seems to be better represented in CTRL using both Budyko and UNEP indices. The changes in aridity (future climate minus control) are higher in the run forced by the A1B SRES scenario. Although the UNEP and Budyko indices show potentialities and limitations to represent the aridity distribution over SA, the changes in aridity due to a pseudo-scenario of global warming are higher using the UNEP index.
基金supported by the National Natural Science Foundation of China(31570453,31170381,31270502,31300386)the PhD Candidate Research Innovation Fund of Nankai Universitythe Doctoral Fund of Tianjin Normal University(52XB1208)
文摘As the increases of climatic aridity and grazing intensity, shrubs play an increasingly important role in grassland ecosystem in arid and semi-arid regions, and its abundance also generally increases. However, the effects of climatic aridity and grazing intensity on sexual reproduction of shrubs in grassland remain largely unclear. In order to understand the effects of grazing intensity and climatic drought stress, and their interaction on seed production of shrub species, we examined the seed number, seed weight and seed yield of Caragana stenophylla under three grazing intensities （fenced, mild grazing and severe grazing） across a climatic aridity gradient （semi-arid, arid, very arid and intensively arid zones） in the Inner Mongolia Steppe, northern China during 2012-2013. The seed number, seed weight and seed yield gradually increased from the semi-arid to the very arid zones, but decreased from the very arid to the intensively arid zones in fenced plots. The seed number and seed yield decreased from the semi-arid to the intensively arid zones in mild and severe grazing treatment plots, therefore, grazing enhanced the suppression effect of climatic aridity on seed production of C. stenophylla. The seed number and seed yield gradually decreased as grazing intensity increased. The seed weight was highest in severe grazing plots, followed by the mild grazing plots and then the fenced plots. Precipitation varied interannually during the study period. We observed that the seed number seed weight and seed yield were lower in the low precipitation year （2013） than in the high precipitation year （2012）. As climatic drought stress increased, the negative effects of grazing on seed production of C. stenophylla also gradually increased. Our results indicated that climatic drought stress may contribute to the encroachment of C. stenophylla shrub in arid zones by promoting its seed production. However, grazing had negative effects on sexual reproduction of C. stenophylla, and the combined effects of drought stress and grazing seriously suppressed sexual reproduction of C. stenophylla in the intensively arid zone.
基金supported by the National Key Research and Development Program of China (2023YFF0805600)the National Natural Science Foundation of China (32225032, 31901087, 32001192)+3 种基金the Innovation Base Project (2021YFF0703904)Major Science and Technology Special Projects (23ZDKA0010, 23ZDNA009) of Gansu ProvinceNatural Science Foundation of Gansu Province (21JR1RA138, 22JR5RA525, 23JRRA1157)supported by the Guazhou Desert Ecosystem Field Observation Research Station。
文摘Leaf functional traits play a pivotal role in understanding the adaptive strategy of plants in extreme environments, as well as in assessing their potential distribution range sizes and extinction risks under global climate change. However, the response of leaf functional traits to aridity in drylands remains unclear for plants with different range sizes. To fill this gap, we measured 10 leaf functional traits of 152 plant species across 172 dryland sites in China, and classified these species as either narrow-(NRS) or wide-ranging species(WRS) based on worldwide occurrence data. Our results showed that the NRS generally occurred in more severe arid areas, and had higher leaf water content(LWC) than WRS at high aridity levels(aridity>0.8). The scaling exponents between leaf volume(LV) and leaf dry weight(LDW) at high aridity levels were 1 for WRS and 1.56 for NRS, indicating that LV increased at a faster rate than LDW and therefore enabled NRS to store more water than WRS. Using moving window analysis, the above scaling exponents increased in NRS and decreased in WRS with increasing aridity at high aridity levels. Moreover, NRS with higher LWC tended to be more abundant at high aridity levels. Our results highlighted that NRS had higher LWC than WRS under high aridity, conferring them with a key advantage in adapting to extreme arid environments. These findings suggest that NRS and WRS use distinct adaptive strategies to cope with aridity. In the conservation of NRS in drylands, enhancing leaf water storage capacity is of particular importance.
基金National Natural Science Foundation of China,No.31922053The Second Tibetan Plateau Scientific Expedition and Research Program,No.2019QZKK0405+1 种基金The Hainan University Start-up Fund,No.KYQD(ZR)21096The Key R&D Program of Hainan,No.ZDYF2022SHFZ042。
文摘Climate change is expected to introduce more water demand in the face of diminishing water supplies,intensifying the degree of aridity observed in terrestrial ecosystems in the 21st century.This study investigated spatiotemporal variability within global aridity index(AI)values from 1970-2018.The results revealed an overall drying trend(0.0016 yr-1,p<0.01),with humid and semi-humid regions experiencing more significant drying than other regions,including those classified as arid or semi-arid.In addition,the Qinghai-Tibet Plateau has gotten wetter,largely due to the increases in precipitation(PPT)observed in that region.Global drying is driven primarily by decreasing and increasing PPT and potential evapotranspiration(PET),respectively.Decreases in PPT alone or increases in PET also drive global aridification,though to a lesser extent.PPT and increasing potential evapotranspiration(PET),with increasing PET alone or decreasing PPT alone.Slightly less than half of the world’s land area has exhibited a wetting trend,largely owing to increases in regional PPT.In some parts of the world,the combined effects of increased PPT and decreased PET drives wetting,with decreases in PET alone explaining wetting in others.These results indicate that,without consideration of other factors(e.g.,CO_(2)fertilization),aridity may continue to intensify,especially in humid regions.
文摘The rainfall of China is scanty when compared with the northeas ern partof the United States of Ameriea,almost identical in location and in latitude,The aridity of north China was found to be due to the following four causes:(1)the decrease of number of cyclones from south China to north China,(2)the deflecting of Kurosiwo farther and farther away from the Chinese coast as we go northward from the Yangtze estuary,(3)the presence of mountain barrier of Tsingling,and(4)the sinister influence of Siberian anticyclone in the winter half year.
基金Supported by the National Natural Science Foundation of China(41575006,41521004,and 91637312)China 111 Project(B13045)
文摘The global warming slowdown or warming hiatus, began around the year 2000 and has persisted for nearly 15 years. Most studies have focused on the interpretation of the hiatus in temperature. In this study, changes in a global aridity index （AI） were analyzed by using a newly developed dynamical adjustment method that can successfully identify and separate dynamically induced and radiatively forced aridity changes in the raw data. The AI and Palmer Drought Severity Index produced a wetting zone over the mid-to-high latitudes of the Northern Hemisphere in recent decades. The dynamical adjustment analysis suggested that this wetting zone occurred in response to the global warming hiatus. The dynamically induced AI （DAI） played a major role in the AI changes during the hiatus period, and its relationships with the North Atlantic Oscillation （NAO）, Pacific Decadal Oscillation （PDO）, and Atlantic Multi-decadal Oscillation （AMO） also indicated that different phases of the NAO, PDO, and AMO contributed to dif- ferent performances of the DAI over the Northern Hemisphere. Although the aridity wetting over the mid-to-high lat- itudes may relieve long-term drying in certain regions, the hiatus is temporary, and so is the relief. Accelerated glob- al warming will return when the NAO, PDO, and AMO revert to their opposite phases in the future, and the wetting zone is likely to disappear.
基金jointly supported by the National Science Foundation of China (Grant No.42230611)the Meteorological Joint Fund (Grant No.U2142208)+2 种基金the Second Tibetan Plateau Scientific Expedition and Research (STEP) program (grant no.2019QZKK0102)the National Science Foundation of China (Grant No.42005071)the Gansu Province Key Talent Project (Grant No.2023RCXM37)。
文摘Northern China is a prominent “hotspot” for land–atmosphere interactions, with substantial gradients in both moisture and thermal conditions. Previous studies have identified a link between land–atmosphere coupling and the individual roles of each factor, but the synergistic effect of the two factors remains unclear. This study considers the covariation of evapotranspiration and precipitation to assess evapotranspiration–precipitation(ET–P) coupling across northern China,exploring its spatial variations and their linkage to water and heat factors. Our findings reveal a transition from strongly positive coupling in the northwest to weakly negative coupling in the southeast, peaking in spring. These spatial variations are attributable to water(soil moisture) and heat(air temperature), which explain 39% and 25% of the variability,respectively. The aridity index(AI), a water–heat synergy factor, is the dominant factor, explaining 66% of the spatial variation in ET–P coupling. As the AI increases, ET–P coupling shifts from strongly positive to weakly negative, with an AI around 0.7. This shift is determined by a shift in the evapotranspiration–lifting condensation level(LCL) coupling under an AI change. Regions with an AI below 0.7 experience water-limited evapotranspiration, where increased soil moisture enhances evapotranspiration, reduces sensible heat(H), and lowers the LCL, resulting in a negative ET–LCL coupling.Conversely, regions with an AI above 0.7 experience energy-limited evapotranspiration, where the positive ET–LCL coupling reflects a positive H–LCL coupling or a positive impact of the LCL on evapotranspiration. This analysis advances our understanding of the intricate influences of multifactor surface interactions on the spatial variations of land–atmosphere coupling.
基金funded by the Natural Science Foundation Project of Inner Mongolia Autonomous Region(2023LHMS04013)the Research Program for Higher Education Institutions in Inner Mongolia Autonomous Region(STAQZX202319).
文摘Drought is a natural disaster that significantly impacts the Earth's ecological environment,especially in arid and semi-arid areas.However,drought at a large watershed scale,which plays an important role in sustainable environmental development,has received limited attention.In this study,we analyzed the spatial and temporal variations in drought in the Yellow River Basin,China from 2002 to 2022 and its driving factors using a vegetation health index(VHI).Results showed that average VHI in the Yellow River Basin from 2002 to 2022 was 0.581,with the most severe drought occurring in summer and autumn.The basin showed a slow decreasing trend in drought during the study period.Regarding spatial distribution of monthly drought frequency and trend of VHI,the mean of the frequency was 13.00%,and 78.00%had a drought frequency of 10.00%–20.00%,with moderate drought generally prevailing.Regarding land use types,forest land,grassland,agricultural land,construction land,water body,and wasteland showed a descending order for the annual average VHI.VHI of each land use type was the lowest in summer and autumn,with pronounced seasonal characteristics.The uneven distribution of drought in the Yellow River Basin was primarily influenced by annual precipitation,solar-induced chlorophyll fluorescence,and relative humidity.VHI effectively quantified drought conditions at a regional scale and proved to be highly applicable in the Yellow River Basin.The results clarify the effectiveness of VHI for drought monitoring in the Yellow River Basin and can provide a reference for drought monitoring across the basin.
