Based on the National Centers for Environmental Prediction and National Center for Atmospheric Research （NCEP/NCAR） reanalysis data from 1950-1999, interdecadal variability of the East Asian Summer Monsoon （EASM） ...Based on the National Centers for Environmental Prediction and National Center for Atmospheric Research （NCEP/NCAR） reanalysis data from 1950-1999, interdecadal variability of the East Asian Summer Monsoon （EASM） and its associated atmospheric circulations are investigated. The EASM exhibits a distinct interdecadal variation, with stronger （weaker） summer monsoon maintained from 1950-1964 （1976-1997）. In the former case, there is an enhanced Walker cell in the eastern Pacific and an anti-Walker cell in the western Pacific. The associated ascending motion resides in the central Pacific, which flows eastward and westward in the upper troposphere, descending in the eastern and western ends of the Pacific basin. At the same time, an anomalous East Asian Hadley Cell （EAHC） is found to connect the low-latitude and mid-latitude systems in East Asia, which strengthens the EASM. The descending branch of the EAHC lies in the west part of the anti-Walker cell, flowing northward in the lower troposphere and then ascending at the south of Lake Baikal （40°-50°N, 95°- 115°E） before returning to low latitudes in the upper troposphere, thus strengthening the EASM. The relationship between the EASM and SST in the eastern tropical Pacific is also discussed. A possible mechanism is proposed to link interdecadal variation of the EASM with the eastern tropical Pacific SST. A warmer sea surface temperature anomaly （SSTA） therein induces anomalous ascending motion in the eastern Pacific, resulting in a weaker Walker cell, and at the same time inducing an anomalous Walker cell in the western Pacific and an enhanced EAHC, leading to a weaker EASM. Furthermore, the interdecadal variation of summer precipitation over North China is found to be the south of Lake Baikal through enhancing and reducing strongly regulated by the velocity potential over the regional vertical motions.展开更多
Mountains and plateaus in Southwest China contain many subalpine and alpine wetlands, with signifieant hydroecological functions. But ungauged or poorly gauged eonditions limit the study and understanding of hydrologi...Mountains and plateaus in Southwest China contain many subalpine and alpine wetlands, with signifieant hydroecological functions. But ungauged or poorly gauged eonditions limit the study and understanding of hydrological regimes of these wetland types. This study selects an ungauged subalpine wetland - Napahai in Northwest Yunnan, China - as a case for developing a practical approach to revealing its storage-area relationship of open water. A Trimble R8 GNSS （Global Navigation Satellites Systems） RTK （Real-time Kinematic system） and sonar fathometer were used to survey fine- resolution elevation data and generate a digital elevation model of the Napahai Wetland. Forty-four Landsat images from 1987 to 2Oll were collected, and the Normalized Difference Water Index was used to classify open water features in the area. The area of open water in Napahai was ealculated for each phase. With these data and a developed conceptual model, the storage of open water for each phase was estimated using ArcGIS tools. Both storage and area of open water showed significant intra-annual and inter-annual variations. In the rainy season, the monthly change of average storage of open water in Napahai showed about 1-2 months lag behind mean monthly rainfall. The storage-area relationship of open water was well fit by a power function equation （R2=0.91, n=44）. This study indicates that if detailedelevations are available for similarly ungauged subalpine wetlands in Southwest China, researchers can use this practical approach to estimate multi- temporal areas and storages and reveal the storage- area relationship of open water in the wetlands. The study provided valuable information of this ease wetland for optimizing its hydro-ecological managements and a new method to wetland researchers and managers for the hydrological study of similarly ungauged wetland complex.展开更多
Over the last decades and centuries,European mountain landscapes have experienced substantial transformations.Natural and anthropogenic LULC changes(land use and land cover changes), especially agro-pastoral activitie...Over the last decades and centuries,European mountain landscapes have experienced substantial transformations.Natural and anthropogenic LULC changes(land use and land cover changes), especially agro-pastoral activities,have directly influenced the spatial organization and composition of European mountain landscapes.For the past sixty years, natural reforestation has been occurring due to a decline in both agricultural production activities and rural population.Stakeholders, to better anticipate future changes,need spatially and temporally explicit models to identify areas at risk of land change and possible abandonment.This paper presents an integrated approach combining forecasting scenarios and a LULC changes simulation model to assess where LULC changes may occur in the Pyrenees Mountains,based on historical LULC trends and a range of future socio-economic drivers.The proposed methodologyconsiders local specificities of the Pyrenean valleys,sub-regional climate and topographical properties,and regional economic policies.Results indicate that some regions are projected to face strong abandonment, regardless of the scenario conditions.Overall, high rates of change are associated with administrative regions where land productivity is highly dependent on socio-economic drivers and climatic and environmental conditions limit intensive(agricultural and/or pastoral) production and profitability.The combination of the results for the four scenarios allows assessments of where encroachment(e.g.colonization by shrublands) and reforestation are the most probable.This assessment intends to provide insight into the potential future development of the Pyrenees to help identify areas that are the most sensitive to change and to guide decision makers to help their management decisions.展开更多
A coupling model between the canopy layer(CL) and atmospheric boundary layer (ABL) for the study of dry deposition velocity is developed. The model consists of six parts: chemical species conservation equation includi...A coupling model between the canopy layer(CL) and atmospheric boundary layer (ABL) for the study of dry deposition velocity is developed. The model consists of six parts: chemical species conservation equation including absorptive factor; the species uptake action including detailed vertical variation of absorptive element in CL; momentum exchange in CL which is represented by a first-order closure momentum equation with an additional larger-scale diffusive term; momentum exchange in ABL which is described by a complete set of the ABL turbulent statistic parameters; absorptivity (or solubility or reflection) at the surface including effects of the physical and chemical characters of the species, land type, seasonal and diurnal variations of the meteorological variables; and deposition velocity derived by distributions of the species with height in CL. Variational rules of the concentration and deposition velocity with both height and time are simulated with the model for both corn and forest canopies. Results predicted with the bulk deposition velocity derived in the paper consist well with experimental data.展开更多
Delayed γ-ray spectroscopy of^(185)Au was studied at the Argonne Gas-Filled Analyzer.A new isomer at an excitation energy of 1504.2(4) keV with a half-life of 630(80) ns was identified via γ-γ coincidence analysis,...Delayed γ-ray spectroscopy of^(185)Au was studied at the Argonne Gas-Filled Analyzer.A new isomer at an excitation energy of 1504.2(4) keV with a half-life of 630(80) ns was identified via γ-γ coincidence analysis,decaying via a 294.8(3) keV transition.Based on Weisskopf estimates,the multipolarity of the 295 keV transition is assigned to be E1,M1,E2,or M2.Possible configurations for this new isomer are discussed based on configurationconstrained potential energy surface calculations.展开更多
As a critical index for monitoring the response of terrestrial ecosystems to climate change, net primary productivity （NPP） is widely used to reflect the vegetation productivity under natural conditions. However, li...As a critical index for monitoring the response of terrestrial ecosystems to climate change, net primary productivity （NPP） is widely used to reflect the vegetation productivity under natural conditions. However, little is known about vegetation NPP in Buryatiya Republic, Russia. To fully understand temporal and spatial variations in vegetation NPP and its response to climate change, satellite images of Moderate-resolution Imaging Spectroradiometer （MODIS） Normalized Difference Vegetation Index （NDVI） products in conjunction with ground-based observations of climatology were used to estimate vegetation NPP in Buryatiya Republic from 2000 to 2008. Observed values of vegetation NPP and MODIS NPP products were jointly utilized to verify simulations of vegetation NPP in this area. The Carnegie Ames Stanford Approach （CASA） model was improved by adjusting its parameters with bio-temperature instead of monthly average temperature in a sub-model of soil water content. Model reliability was tested with observed vegetation NPP. Variation in vegetation NPP, and its relationship with climatic factors, was analyzed in detail. Results showed that the modified CASA model can be used to estimate vegetation NPP in Buryatiya Republic, and that the accuracy of the model was generally high with a correlation coefficient of 0.91 （P0.01）. The vegetation average annual NPP was 542.45 g C m^-2 y^ -1 and the total NPP was estimated as 1.91E＋14 g C y^ -1 from 2000 to 2008. Monthly vegetation NPP increased significantly from April to July, decreased rapidly from August to November, and remained steady from December to March of the next year. Vegetation NPP increased with increasing longitude and decreased with increasing latitude. Different vegetation types differ in total NPP, with the highest NPP in forests, followed by forest-steppe, high mountain vegetation, steppe and meadow-swamp. Temperature and precipitation were the primary factors limiting vegetation NPP in this area.展开更多
Based on the regional acid deposition model(RADM),a high resolution model for species exchange in the troposphere(EM3)is designed.EM3 differs considerably in the following 5 aspects from RADM.First,the vertical grid l...Based on the regional acid deposition model(RADM),a high resolution model for species exchange in the troposphere(EM3)is designed.EM3 differs considerably in the following 5 aspects from RADM.First,the vertical grid levels in the planetary boundary layer(PBL)are increased.Second,layered vertical eddy diffusivity patterns in the troposphere(TL)are considered.Third,layered horizontal eddy diffusivity patterns within TL is used.Fourth,new dry deposition velocity pattern including the effect of plant canopy layer(CL)vertical structure is adopted.Fifth,advective scheme of second-order moment conservation with less numerical diffusion is used.OSCAR 4 case is comparatively simulated with both EM3 and RADM.The results show that 3-D distribution laws of chemical species in whole TL are forecasted by EM3 better than by RADM.Under the same conditions,all ratios of the central concentrations simulated with both models in lower PBL are more than 1.8,the maximum can be more than 3.展开更多
Understanding the relationships between snow and vegetation is important for interpretation of the responses of alpine ecosystems to climate changes.The Qinghai-Tibetan Plateau is regarded as an ideal area due to its ...Understanding the relationships between snow and vegetation is important for interpretation of the responses of alpine ecosystems to climate changes.The Qinghai-Tibetan Plateau is regarded as an ideal area due to its undisturbed features with low population and relatively high snow cover.We used 500 m Moderate Resolution Imaging Spectroradiometer(MODIS)datasets during 2001–2010 to examine the snow–vegetation relationships,specifically,(1)the influence of snow melting date on vegetation green-up date and(2)the effects of snow cover duration on vegetation greenness.The results showed that the alpine vegetation responded strongly to snow phenology(i.e.,snow melting date and snow cover duration)over large areas of the Qinghai-Tibetan Plateau.Snow melting date and vegetation green-up date were significantly correlated(p<0.1)in 39.9% of meadow areas(accounting for 26.2% of vegetated areas)and 36.7% of steppe areas(28.1% of vegetated areas).Vegetation growth was influenced by different seasonal snow cover durations(SCDs)in different regions.Generally,the December–February and March–May SCDs played a significantly role in vegetation growth,both positively and negatively,depending on different water source regions.Snow’s positive impact on vegetation was larger than the negative impact.展开更多
Rangeland systems play an important role in ecological stabilization and the terrestrial carbon cycle in arid and semiarid regions. However, little is known about the vegetative carbon dynamics and climatic and topog-...Rangeland systems play an important role in ecological stabilization and the terrestrial carbon cycle in arid and semiarid regions. However, little is known about the vegetative carbon dynamics and climatic and topog- raphical factors that affect vegetative carbon stock in these rangelands. Our goal was to assess vegetative carbon stock by examining meteorological data in conjunction with NDVI （normalized difference vegetation index） time se- ries datasets from 2001-2012. An improved CASA （Carnegie Ames Stanford Approach） model was then applied to simulate the spatiotemporal dynamic variation of vegetative carbon stock, and analyze its response to climatic and topographical factors. We estimated the vegetative carbon stock of rangeland in Gansu province, China to be 4.4×10^14 gC, increasing linearly at an annual rate of 9.8×10^11 gC. The mean vegetative carbon density of the whole rangeland was 136.5 gC m-2. Vegetative carbon density and total carbon varied temporally and spatially and were highly associated with temperature, precipitation and solar radiation. Vegetative carbon density reached the maximal value on elevation at 2500-3500 m, a slope of 〉30°and easterly aspect. The effect of precipitation, tem- perature and solar radiation on the vegetative carbon density of five rangeland types （desert and salinized meadow, steppe, alpine meadow, shrub and tussock, and marginal grassland in the forest） depends on the acquired quantity of water and heat for rangeland plants at all spatial scales. The results of this study provide new evidence for ex- plaining spatiotemporal heterogeneity in vegetative carbon dynamics and responses to global change for rangeland vegetative carbon stock, and offer a theoretical and practical basis for grassland agriculture management in arid and semiarid regions.展开更多
Floods have become increasingly prominent in recent decades causing devastating effects on lives and livelihoods worldwide.Efficient tools to assess the drivers of floods,such as increasing urbanization,could help to ...Floods have become increasingly prominent in recent decades causing devastating effects on lives and livelihoods worldwide.Efficient tools to assess the drivers of floods,such as increasing urbanization,could help to minimize flood hazards.Urbanization increases the design peak flow(maximum potential surface water flow from a precipitation event with an average probability of occurring once in a specific recurrence interval),which is a key information needed for designing stormwater management infrastructures such as culverts and storm sewers.A web-based application was developed to explore the potential changes(1985 to 2020)in design peak flow of urban areas across the conterminous United States driven by land cover change.The results indicate a potential increase in design peak flow in urban areas up to 126.6% in 2020 compared to 1985.Of the total 3,535 study urban areas,about 80%(2,840)urban areas increased design peak flow,and about 19%(654)decreased design peak flow.A general pattern of increasing design peak flow was observed during 1985 to 2010,and decreasing pattern was observed during 2010 to 2020,primarily driven by respective increasing(decreasing)and decreasing(increasing)developed areas(croplands).The application provides crucial information by visualizing both spatial and temporal data that could be useful for decision-makers in developing and improving urban stormwater management plans and policies for efficient resource allocations and reducing flood risks.展开更多
The National Land Cover Database(NLCD)2016 products show that,between 2001 and 2016,nearly half of the land cover change in the conterminous United States(CONUS)involved forested areas.To ensure the quality of NLCD la...The National Land Cover Database(NLCD)2016 products show that,between 2001 and 2016,nearly half of the land cover change in the conterminous United States(CONUS)involved forested areas.To ensure the quality of NLCD land cover and land cover change products,it is important to accurately detect the location and time of forest disturbance.We designed a comprehensive strategy to integrate a continuous time series forest change detection method and a discrete 2-date forest change detection method to produce the NLCD 1986-2019 forest disturbance product,which shows the most recent forest disturbance date between the years 1986 and 2019 for every 2-to 3-year interval.This method,the Time-Series method Using Normalized Spectral Distance(NSD)index(TSUN),uses NSD to detect multi-date forest land cover changes and was shown to be easily extended to a new date even when new images were processed in a different way than previous date images.The discrete 2-date method uses the Multi-Index Integrated Change Analysis(MIICA)method to detect changes between 2-date images.A method based on confidence and object grouping was designed to combine the multiple MIICA outputs to improve change detection accuracy.Finally,an aggregation scheme was implemented to combine the TSUN output,the integrated MIICA results,and ancillary data to produce the NLCD 2019 forest disturbance 1986–2019 product.The initial accuracy assessments from 1,600 samples over 4 Landsat path/rows show that the producer’s and user’s accuracies of the 2001-2019 forest disturbance map are 76% and 74%,respectively.The final CONUS-wide forest disturbance product is provided at https://www.mrlc.gov/nlcd-2019-scienceresearch-products.展开更多
文摘Based on the National Centers for Environmental Prediction and National Center for Atmospheric Research （NCEP/NCAR） reanalysis data from 1950-1999, interdecadal variability of the East Asian Summer Monsoon （EASM） and its associated atmospheric circulations are investigated. The EASM exhibits a distinct interdecadal variation, with stronger （weaker） summer monsoon maintained from 1950-1964 （1976-1997）. In the former case, there is an enhanced Walker cell in the eastern Pacific and an anti-Walker cell in the western Pacific. The associated ascending motion resides in the central Pacific, which flows eastward and westward in the upper troposphere, descending in the eastern and western ends of the Pacific basin. At the same time, an anomalous East Asian Hadley Cell （EAHC） is found to connect the low-latitude and mid-latitude systems in East Asia, which strengthens the EASM. The descending branch of the EAHC lies in the west part of the anti-Walker cell, flowing northward in the lower troposphere and then ascending at the south of Lake Baikal （40°-50°N, 95°- 115°E） before returning to low latitudes in the upper troposphere, thus strengthening the EASM. The relationship between the EASM and SST in the eastern tropical Pacific is also discussed. A possible mechanism is proposed to link interdecadal variation of the EASM with the eastern tropical Pacific SST. A warmer sea surface temperature anomaly （SSTA） therein induces anomalous ascending motion in the eastern Pacific, resulting in a weaker Walker cell, and at the same time inducing an anomalous Walker cell in the western Pacific and an enhanced EAHC, leading to a weaker EASM. Furthermore, the interdecadal variation of summer precipitation over North China is found to be the south of Lake Baikal through enhancing and reducing strongly regulated by the velocity potential over the regional vertical motions.
基金supported by the National Special Basic Research Fund(Grant No.2008FY110300)National Science and Technology Support Program(Grant No.2011BAC09B07)+1 种基金National Natural Science Foundation of China(Grant No.40961003)Scientific Research Fund Project of Yunnan Education Department(Grant No.2011J018)
文摘Mountains and plateaus in Southwest China contain many subalpine and alpine wetlands, with signifieant hydroecological functions. But ungauged or poorly gauged eonditions limit the study and understanding of hydrological regimes of these wetland types. This study selects an ungauged subalpine wetland - Napahai in Northwest Yunnan, China - as a case for developing a practical approach to revealing its storage-area relationship of open water. A Trimble R8 GNSS （Global Navigation Satellites Systems） RTK （Real-time Kinematic system） and sonar fathometer were used to survey fine- resolution elevation data and generate a digital elevation model of the Napahai Wetland. Forty-four Landsat images from 1987 to 2Oll were collected, and the Normalized Difference Water Index was used to classify open water features in the area. The area of open water in Napahai was ealculated for each phase. With these data and a developed conceptual model, the storage of open water for each phase was estimated using ArcGIS tools. Both storage and area of open water showed significant intra-annual and inter-annual variations. In the rainy season, the monthly change of average storage of open water in Napahai showed about 1-2 months lag behind mean monthly rainfall. The storage-area relationship of open water was well fit by a power function equation （R2=0.91, n=44）. This study indicates that if detailedelevations are available for similarly ungauged subalpine wetlands in Southwest China, researchers can use this practical approach to estimate multi- temporal areas and storages and reveal the storage- area relationship of open water in the wetlands. The study provided valuable information of this ease wetland for optimizing its hydro-ecological managements and a new method to wetland researchers and managers for the hydrological study of similarly ungauged wetland complex.
基金supported by the MODE RESPYR project(ANR 2010 JCJC 1804-01)founded by the French National Science Agency(ANR)
文摘Over the last decades and centuries,European mountain landscapes have experienced substantial transformations.Natural and anthropogenic LULC changes(land use and land cover changes), especially agro-pastoral activities,have directly influenced the spatial organization and composition of European mountain landscapes.For the past sixty years, natural reforestation has been occurring due to a decline in both agricultural production activities and rural population.Stakeholders, to better anticipate future changes,need spatially and temporally explicit models to identify areas at risk of land change and possible abandonment.This paper presents an integrated approach combining forecasting scenarios and a LULC changes simulation model to assess where LULC changes may occur in the Pyrenees Mountains,based on historical LULC trends and a range of future socio-economic drivers.The proposed methodologyconsiders local specificities of the Pyrenean valleys,sub-regional climate and topographical properties,and regional economic policies.Results indicate that some regions are projected to face strong abandonment, regardless of the scenario conditions.Overall, high rates of change are associated with administrative regions where land productivity is highly dependent on socio-economic drivers and climatic and environmental conditions limit intensive(agricultural and/or pastoral) production and profitability.The combination of the results for the four scenarios allows assessments of where encroachment(e.g.colonization by shrublands) and reforestation are the most probable.This assessment intends to provide insight into the potential future development of the Pyrenees to help identify areas that are the most sensitive to change and to guide decision makers to help their management decisions.
文摘A coupling model between the canopy layer(CL) and atmospheric boundary layer (ABL) for the study of dry deposition velocity is developed. The model consists of six parts: chemical species conservation equation including absorptive factor; the species uptake action including detailed vertical variation of absorptive element in CL; momentum exchange in CL which is represented by a first-order closure momentum equation with an additional larger-scale diffusive term; momentum exchange in ABL which is described by a complete set of the ABL turbulent statistic parameters; absorptivity (or solubility or reflection) at the surface including effects of the physical and chemical characters of the species, land type, seasonal and diurnal variations of the meteorological variables; and deposition velocity derived by distributions of the species with height in CL. Variational rules of the concentration and deposition velocity with both height and time are simulated with the model for both corn and forest canopies. Results predicted with the bulk deposition velocity derived in the paper consist well with experimental data.
基金Supported by the National Natural Science Foundation of China (12405140, 12135004, 11961141004, U2032138, 12275369)the Natural Science Foundation of Gansu Province, China (24JRRA033)+4 种基金financial support from the STFCfunded by the Chinese Academy of Sciences President's International Fellowship Initiative (2020VMA0017)Supported by the U.S. Department of Energy, Office of Nuclear Physics, (DE-AC02-06CH11357, DE-FG02-94ER41041 (UNC), DE-FG02-97ER41033 (TUNL))supported by the Slovak Research and Development Agency (APVV-22-0282)Slovak Grant Agency VEGA (1/0019/25)。
文摘Delayed γ-ray spectroscopy of^(185)Au was studied at the Argonne Gas-Filled Analyzer.A new isomer at an excitation energy of 1504.2(4) keV with a half-life of 630(80) ns was identified via γ-γ coincidence analysis,decaying via a 294.8(3) keV transition.Based on Weisskopf estimates,the multipolarity of the 295 keV transition is assigned to be E1,M1,E2,or M2.Possible configurations for this new isomer are discussed based on configurationconstrained potential energy surface calculations.
基金National Natural Science Foundation of China(No.30960264 and 40771146)Basic Research Project of the Ministry of Science and Technology(No.2007FY110300-1)
文摘As a critical index for monitoring the response of terrestrial ecosystems to climate change, net primary productivity （NPP） is widely used to reflect the vegetation productivity under natural conditions. However, little is known about vegetation NPP in Buryatiya Republic, Russia. To fully understand temporal and spatial variations in vegetation NPP and its response to climate change, satellite images of Moderate-resolution Imaging Spectroradiometer （MODIS） Normalized Difference Vegetation Index （NDVI） products in conjunction with ground-based observations of climatology were used to estimate vegetation NPP in Buryatiya Republic from 2000 to 2008. Observed values of vegetation NPP and MODIS NPP products were jointly utilized to verify simulations of vegetation NPP in this area. The Carnegie Ames Stanford Approach （CASA） model was improved by adjusting its parameters with bio-temperature instead of monthly average temperature in a sub-model of soil water content. Model reliability was tested with observed vegetation NPP. Variation in vegetation NPP, and its relationship with climatic factors, was analyzed in detail. Results showed that the modified CASA model can be used to estimate vegetation NPP in Buryatiya Republic, and that the accuracy of the model was generally high with a correlation coefficient of 0.91 （P0.01）. The vegetation average annual NPP was 542.45 g C m^-2 y^ -1 and the total NPP was estimated as 1.91E＋14 g C y^ -1 from 2000 to 2008. Monthly vegetation NPP increased significantly from April to July, decreased rapidly from August to November, and remained steady from December to March of the next year. Vegetation NPP increased with increasing longitude and decreased with increasing latitude. Different vegetation types differ in total NPP, with the highest NPP in forests, followed by forest-steppe, high mountain vegetation, steppe and meadow-swamp. Temperature and precipitation were the primary factors limiting vegetation NPP in this area.
文摘Based on the regional acid deposition model(RADM),a high resolution model for species exchange in the troposphere(EM3)is designed.EM3 differs considerably in the following 5 aspects from RADM.First,the vertical grid levels in the planetary boundary layer(PBL)are increased.Second,layered vertical eddy diffusivity patterns in the troposphere(TL)are considered.Third,layered horizontal eddy diffusivity patterns within TL is used.Fourth,new dry deposition velocity pattern including the effect of plant canopy layer(CL)vertical structure is adopted.Fifth,advective scheme of second-order moment conservation with less numerical diffusion is used.OSCAR 4 case is comparatively simulated with both EM3 and RADM.The results show that 3-D distribution laws of chemical species in whole TL are forecasted by EM3 better than by RADM.Under the same conditions,all ratios of the central concentrations simulated with both models in lower PBL are more than 1.8,the maximum can be more than 3.
基金This work was supported by the National Natural Science Foundation of China(Grant 41271372)the National Basic Research Program of China(973)(Grant No.2009CB723906)。
文摘Understanding the relationships between snow and vegetation is important for interpretation of the responses of alpine ecosystems to climate changes.The Qinghai-Tibetan Plateau is regarded as an ideal area due to its undisturbed features with low population and relatively high snow cover.We used 500 m Moderate Resolution Imaging Spectroradiometer(MODIS)datasets during 2001–2010 to examine the snow–vegetation relationships,specifically,(1)the influence of snow melting date on vegetation green-up date and(2)the effects of snow cover duration on vegetation greenness.The results showed that the alpine vegetation responded strongly to snow phenology(i.e.,snow melting date and snow cover duration)over large areas of the Qinghai-Tibetan Plateau.Snow melting date and vegetation green-up date were significantly correlated(p<0.1)in 39.9% of meadow areas(accounting for 26.2% of vegetated areas)and 36.7% of steppe areas(28.1% of vegetated areas).Vegetation growth was influenced by different seasonal snow cover durations(SCDs)in different regions.Generally,the December–February and March–May SCDs played a significantly role in vegetation growth,both positively and negatively,depending on different water source regions.Snow’s positive impact on vegetation was larger than the negative impact.
基金National Natural Science Foundation of China(30960264 and 31160475)Science and technology program of Gansu province(1107RJYA058)+1 种基金open project of Key Laboratory of Grassland Ecosystem(Gansu Agricultural University),Ministry of Education(CYZS–2011014)Fund of technology innovation commemorated Sheng Tongsheng in Gansu Agricultural University(GSAU-STS-1304 and GSAU-STS-1505)
文摘Rangeland systems play an important role in ecological stabilization and the terrestrial carbon cycle in arid and semiarid regions. However, little is known about the vegetative carbon dynamics and climatic and topog- raphical factors that affect vegetative carbon stock in these rangelands. Our goal was to assess vegetative carbon stock by examining meteorological data in conjunction with NDVI （normalized difference vegetation index） time se- ries datasets from 2001-2012. An improved CASA （Carnegie Ames Stanford Approach） model was then applied to simulate the spatiotemporal dynamic variation of vegetative carbon stock, and analyze its response to climatic and topographical factors. We estimated the vegetative carbon stock of rangeland in Gansu province, China to be 4.4×10^14 gC, increasing linearly at an annual rate of 9.8×10^11 gC. The mean vegetative carbon density of the whole rangeland was 136.5 gC m-2. Vegetative carbon density and total carbon varied temporally and spatially and were highly associated with temperature, precipitation and solar radiation. Vegetative carbon density reached the maximal value on elevation at 2500-3500 m, a slope of 〉30°and easterly aspect. The effect of precipitation, tem- perature and solar radiation on the vegetative carbon density of five rangeland types （desert and salinized meadow, steppe, alpine meadow, shrub and tussock, and marginal grassland in the forest） depends on the acquired quantity of water and heat for rangeland plants at all spatial scales. The results of this study provide new evidence for ex- plaining spatiotemporal heterogeneity in vegetative carbon dynamics and responses to global change for rangeland vegetative carbon stock, and offer a theoretical and practical basis for grassland agriculture management in arid and semiarid regions.
基金funded by the US Geological Survey Land Change Science program(contract number:140G0119C0001).
文摘Floods have become increasingly prominent in recent decades causing devastating effects on lives and livelihoods worldwide.Efficient tools to assess the drivers of floods,such as increasing urbanization,could help to minimize flood hazards.Urbanization increases the design peak flow(maximum potential surface water flow from a precipitation event with an average probability of occurring once in a specific recurrence interval),which is a key information needed for designing stormwater management infrastructures such as culverts and storm sewers.A web-based application was developed to explore the potential changes(1985 to 2020)in design peak flow of urban areas across the conterminous United States driven by land cover change.The results indicate a potential increase in design peak flow in urban areas up to 126.6% in 2020 compared to 1985.Of the total 3,535 study urban areas,about 80%(2,840)urban areas increased design peak flow,and about 19%(654)decreased design peak flow.A general pattern of increasing design peak flow was observed during 1985 to 2010,and decreasing pattern was observed during 2010 to 2020,primarily driven by respective increasing(decreasing)and decreasing(increasing)developed areas(croplands).The application provides crucial information by visualizing both spatial and temporal data that could be useful for decision-makers in developing and improving urban stormwater management plans and policies for efficient resource allocations and reducing flood risks.
基金supported by the USGS-NASA Landsat Science Team Program for Toward Near Real-time Monitoring and Characterization of Land Surface Change for the Conterminous US(140G0119C0008).
文摘The National Land Cover Database(NLCD)2016 products show that,between 2001 and 2016,nearly half of the land cover change in the conterminous United States(CONUS)involved forested areas.To ensure the quality of NLCD land cover and land cover change products,it is important to accurately detect the location and time of forest disturbance.We designed a comprehensive strategy to integrate a continuous time series forest change detection method and a discrete 2-date forest change detection method to produce the NLCD 1986-2019 forest disturbance product,which shows the most recent forest disturbance date between the years 1986 and 2019 for every 2-to 3-year interval.This method,the Time-Series method Using Normalized Spectral Distance(NSD)index(TSUN),uses NSD to detect multi-date forest land cover changes and was shown to be easily extended to a new date even when new images were processed in a different way than previous date images.The discrete 2-date method uses the Multi-Index Integrated Change Analysis(MIICA)method to detect changes between 2-date images.A method based on confidence and object grouping was designed to combine the multiple MIICA outputs to improve change detection accuracy.Finally,an aggregation scheme was implemented to combine the TSUN output,the integrated MIICA results,and ancillary data to produce the NLCD 2019 forest disturbance 1986–2019 product.The initial accuracy assessments from 1,600 samples over 4 Landsat path/rows show that the producer’s and user’s accuracies of the 2001-2019 forest disturbance map are 76% and 74%,respectively.The final CONUS-wide forest disturbance product is provided at https://www.mrlc.gov/nlcd-2019-scienceresearch-products.
