In this paper, we compared the concept of agricultural drought and its relationship with other types of droughts and reviewed the progress of research on agricultural drought monitoring indices on the basis of station...In this paper, we compared the concept of agricultural drought and its relationship with other types of droughts and reviewed the progress of research on agricultural drought monitoring indices on the basis of station data and remote sensing. Applicability and limitations of different drought monitoring indices were also compared. Meanwhile, development history and the latest progress in agricultural drought monitoring were evaluated through statistics and document comparison, suggesting a transformation in agricultural drought monitoring from traditional single meteorological monitoring indices to meteorology and remote sensing-integrated monitoring indices. Finally, an analysis of current challenges in ag- ricultural drought monitoring revealed future research prospects for agricultural drought monitoring, such as investigating the mechanism underlying agricultural drought, identifying factors that influence agricultural drought, developing multi-spatiotemporal scales models for agricultural drought monitoring, coupling qualitative and quantitative agricultural drought evaluation models, and improving the application levels of remote sensing data in agricultural drought monitoring.展开更多
The normalized difference vegetation index(NDVI) is one of the key input variables for developing drought indices.However,the NDVI quickly saturates in high vegetation surfaces,and thus,the generalization of a drought...The normalized difference vegetation index(NDVI) is one of the key input variables for developing drought indices.However,the NDVI quickly saturates in high vegetation surfaces,and thus,the generalization of a drought index over different ecosystems becomes a challenge.This paper presents a novel,dynamic stretching algorithm to overcome the saturation effect in NDVI.A scaling transformation function to eliminate saturation effects when the vegetation fraction(VF) is large is proposed.Dynamic range adjustment is conducted using three coefficients,namely,the normalization factor(a),the stretching range controlling factor(m),and the stretching size controlling factor(e).The results show that the stretched NDVI(S-NDVI) is more sensitive to vegetation fraction than NDVI when the VF is large,ranging from 0.75 to 1.00.Moreover,the saturation effect in NDVI is effectively removed by using the S-NDVI.Further analysis suggests that there is a good linear correlation between the S-NDVI and the leaf area index(LAI).At the same time,the proposed S-NDVI significantly reduces or even eliminates the saturation effect over high biomass.A comparative analysis is performed between drought indices derived from NDVI and S-NDVI,respectively.In the experiment,reflectance data from the moderate resolution imaging spectroradiometer(MODIS) products and in-situ observation data from the meteorological sites at a regional scale are used.In this study,the coefficient of determination(R2) of the stretched drought index(S-DI) is above 0.5,indicating the reliability of the proposed algorithm with surface soil moisture content.Thus,the S-DI is suggested to be used as a drought index in extended regions,thus regional heterogeneity should be taken into account when applying stretching method.展开更多
It is accepted that climate change has a great impact on water cycle and regional water balance,and thus it would change the formation and evolution conditions of drought in some degree. By using data at 42 meteorolog...It is accepted that climate change has a great impact on water cycle and regional water balance,and thus it would change the formation and evolution conditions of drought in some degree. By using data at 42 meteorological stations of the Pearl River Basin,the Standardized Precipitation Evapotranspiration Index（ SPEI） at different time scales was calculated. Based on the SPEIs of 1- 12 months,a newly proposed index for drought--Joint Drought Index（ JDI） was established under the multi-scale perspective through the copula function. Since short-term SPEIs are essential for the identification of emerging droughts and long-term SPEIs are useful for prolonged droughts,the JDI,which integrates all the usefull informations of drought and can thus form an overall judgement,is superior than the single SPEI in drought monitoring. By the forcast evaluation system and comparison to the actual drought,the accuracy and effectiveness of JDI in drought monitoring were verified. In general,JDI can be used as a new ideal index for future drought monitoring and assessment. Additionly,we analyzed the spatio-temperal characteristics of drought across the Pearl River Basin using the JDI. The results indicate that mild drought was the most frequent drought occurred in the Pearl River Basin over the past half century,and moderate drought followed. Severe drought and extreme drought would appear occasionally while exceptional drought could hardly be found. A dry-wet-dry interdecadal variation pattern had been found from the 1960 s to the 2000 s. Since the 21 stcentury,an obvious trend toward drought can be observed in the whole basin,especially in the Xijiang subbasin,which,consequently,poses an increasing challenge for the water resource planning and management.展开更多
The high resolution satellite precipitation products bear great potential for large-scale drought monitoring, especially for those regions with sparsely or even without gauge coverage. This study focuses on utilizing ...The high resolution satellite precipitation products bear great potential for large-scale drought monitoring, especially for those regions with sparsely or even without gauge coverage. This study focuses on utilizing the latest Version-7 TRMM Multi-satellite Precipitation Analysis （TMPA 3B42V7） data for drought condition monitoring in the Weihe River Basin （0.135×10^6 km2）. The accuracy of the monthly TMPA 3B42V7 satellite precipitation data was firstly evaluated against the ground rain gauge observations. The statistical characteristics between a short period data series （1998-2013） and a long period data series （1961-2013） were then compared. The TMPA 3B42V7-based SPI （Standardized Precipitation Index） sequences were finally validated and analyzed at various temporal scales for assessing the drought conditions. The results indicate that the monthly TMPA 3B42V7 precipitation is in a high agreement with the rain gauge observations and can accurately capture the temporal and spatial characteristics of rainfall within the Weihe River Basin. The short period data can present the characteristics of long period record, and it is thus acceptable to use the short period data series to estimate the cumulative probability function in the SPI calculation. The TMPA 3B42V7-based SPI matches well with that based on the rain gauge observations at multiple time scales （i.e., 1-, 3-, 6-, 9-, and 12-month） and can give an acceptable temporal distribution of drought conditions. It suggests that the TMPA 3B42V7 precipitation data can be used for monitoring the occurrence of drought in the Weihe River Basin.展开更多
Using Moderate Resolution Imaging Spectroradiometer(MODIS) data from the dry season during 2010–2012 over the whole Yunnan Province, an improved temperature vegetation dryness index(iTVDI), in which a parabolic dry-e...Using Moderate Resolution Imaging Spectroradiometer(MODIS) data from the dry season during 2010–2012 over the whole Yunnan Province, an improved temperature vegetation dryness index(iTVDI), in which a parabolic dry-edge equation replaces the traditional linear dry-edge equation, was developed, to reveal the regional drought regime in the dry season. After calculating the correlation coefficient, root-mean-square error, and standard deviation between the iTVDI and observed topsoil moisture at 10 and 20 cm for seven sites, the effectiveness of the new index in depicting topsoil moisture conditions was verified. The drought area indicated by iTVDI mapping was then compared with the drought-affected area reported by the local government. The results indicated that the iTVDI can monitor drought more accurately than the traditional TVDI during the dry season in Yunnan Province. Using iTVDI facilitates drought warning and irrigation scheduling, and the expectation is that this new index can be broadly applied in other areas.展开更多
The low spatial resolution of the Integrated Multi-satellitE Retrievals for Global Precipitation Measurement(IMERG),a mainstream Global Precipitation Measurement(GPM)product,limits its use in refined drought analysis ...The low spatial resolution of the Integrated Multi-satellitE Retrievals for Global Precipitation Measurement(IMERG),a mainstream Global Precipitation Measurement(GPM)product,limits its use in refined drought analysis over complex monsoon underlying surfaces.To resolve this issue,this study proposes an integrated meteorological drought monitoring framework(SPTI),which enhances accuracy by coupling 0.05°downscaled IMERG precipitation data with Moderate Resolution Imaging Spectroradiometer(MODIS)land surface temperature(LST)data.First,a Normalized Difference Vegetation Index(NDVI)-topography guided multivariate regression kriging downscaling scheme was built using monthly precipitation data from 23 Liaoning stations(2010–2018),geographic-topographic factors,and NDVI covariates,downscaling original 0.1°IMERG data to 0.05°(achieving R2>0.7 in ten months,except for June and July).Second,a high-performance multisource drought model was established via regression of Standardized Precipitation Evapotranspiration Index(SPEI)against downscaled IMERG-Z Index(derived from IMERG precipitation using the drought Z-index method)and Temperature Condition Index(TCI).Finally,SPTI was validated with four typical Liaoning drought events during 2014,2015,2017,and 2018.Results show that:(1)0.05°precipitation data captures fine spatial details,clearly depicting Liaoning’s southeast-tonorthwest precipitation gradient and central plain rainfall zones;(2)SPTI outperforms standalone IMERG-Z—it accurately identifies severe/extreme droughts,mitigates IMERG-Z’s underestimation bias,and reasonably characterizes drought alleviation after heavy rains by integrating TCI,avoiding IMERG-Z’s“abrupt drought-to-waterlogging”misjudgment;(3)SPTI results align well with the Liaoning Meteorological Disaster Bulletin,confirming its suitability for refined monsoon drought monitoring.展开更多
It has long been recognized that an effective drought monitoring and early warning system,which provides functions for real-time condition monitoring and prediction,risk assessment,information dissemination and respon...It has long been recognized that an effective drought monitoring and early warning system,which provides functions for real-time condition monitoring and prediction,risk assessment,information dissemination and response recommendation,is very important for the preparedness for and mitigation of drought impacts.In this article,we review the currently existing drought monitor and early warning systems,discuss applicable remote sensing datasets and drought indicators and present the development of a web-based quasi-real-time Global Drought Monitoring&Analysis Platform(Web-GDMAP).The Web-GDMAP is built upon a series of indicators derived from multi-source satellite remote sensing data and various other sources of data.From a technical perspective,the Web-GDMAP system includes a series of components from data storage,model implementation and distribution,to client-side visualization and user intuitive interaction.From a theoretical perspective,the Web-GDMAP system integrates multi-indicators on different aspects of drought,including anomalies in precipitation,anomalies in land surface thermal and vegetation conditions,water deficit of soil and plants,etc.Several case studies on applying the developed Web-GDMAP in the Asian region are demonstrated.Further improvements and perspectives are discussed.展开更多
The normalized difference vegetation index （NDVI） has proven to be typically employed to assess terrestrial vegetation conditions. However, one limitation of NDVI for drought monitoring is the apparent time lag betw...The normalized difference vegetation index （NDVI） has proven to be typically employed to assess terrestrial vegetation conditions. However, one limitation of NDVI for drought monitoring is the apparent time lag between rainfall deficit and NDVI response. To better understand this relationship, time series NDVI （2000-2010） during the growing season in Sichuan Province and Chongqing City were analyzed. The vegetation condition index （VCI） was used to construct a new drought index, time-integrated vegetation condition index （TIVCI）, and was then compared with meteorological drought indices-standardized precipitation index （SPI）, a multiple-time scale meteorological-drought index based on precipitation, to examine the sensitivity on droughts. Our research findings indicate the followings： （1） farmland NDVI sensitivity to precipitation in study area has a time lag of 16-24 d, and it maximally responds to the temperature with a lag of about 16 d. （2） We applied the approach to Sichuan Province and Chongqing City for extreme drought monitoring in 2006 and 2003, and the results show that the monitoring results from TIVCI are closer to the published China agricultural statistical data than VCI. Compared to VCI, the best results from TIVCI3 were found with the relative errors of -4.5 and 6.36% in 2006 for drought affected area and drought disaster area respectively, and 5.11 and -5.95% in 2003. （3） Compared to VCI, TIVCI has better correlation with the SPI, which indicates the lag and cumulative effects of precipitation on vegetation. Our finding proved that TIVCI is an effective indicator of drought detection when the time lag effects between NDVI and climate factors are taken into consideration.展开更多
Meteorological drought is a natural hazard that can occur under all climatic regimes. Monitoring the drought is a vital and important part of predicting and analyzing drought impacts. Because no single index can repre...Meteorological drought is a natural hazard that can occur under all climatic regimes. Monitoring the drought is a vital and important part of predicting and analyzing drought impacts. Because no single index can represent all facets of meteorological drought, we took a multi-index approach for drought monitoring in this study. We assessed the ability of eight precipitation-based drought indices（SPI（Standardized Precipitation Index）, PNI（Percent of Normal Index）, DI（Deciles index）, EDI（Effective drought index）, CZI（China-Z index）, MCZI（Modified CZI）, RAI（Rainfall Anomaly Index）, and ZSI（Z-score Index）） calculated from the station-observed precipitation data and the Ag MERRA gridded precipitation data to assess historical drought events during the period 1987–2010 for the Kashafrood Basin of Iran. We also presented the Degree of Dryness Index（DDI） for comparing the intensities of different drought categories in each year of the study period（1987–2010）. In general, the correlations among drought indices calculated from the Ag MERRA precipitation data were higher than those derived from the station-observed precipitation data. All indices indicated the most severe droughts for the study period occurred in 2001 and 2008. Regardless of data input source, SPI, PNI, and DI were highly inter-correlated（R^2=0.99）. Furthermore, the higher correlations（R^2=0.99） were also found between CZI and MCZI, and between ZSI and RAI. All indices were able to track drought intensity, but EDI and RAI showed higher DDI values compared with the other indices. Based on the strong correlation among drought indices derived from the Ag MERRA precipitation data and from the station-observed precipitation data, we suggest that the Ag MERRA precipitation data can be accepted to fill the gaps existed in the station-observed precipitation data in future studies in Iran. In addition, if tested by station-observed precipitation data, the Ag MERRA precipitation data may be used for the data-lacking areas.展开更多
Satellite hydrology has reached a new era where a variety of earth observing systems,in conjunction with the development of data integrations,can provide a consistent monitoring of groundwater change,wetland dynamics,...Satellite hydrology has reached a new era where a variety of earth observing systems,in conjunction with the development of data integrations,can provide a consistent monitoring of groundwater change,wetland dynamics,and drought evolution in regions where observations on the ground remain sparse or patchy.This synthesis review highlights the physical observables that are most useful to terrestrial hydrology:variable time-dependent gravity,passive and active microwave signals,optical reflectance,thermal infrared measurements,and altimetry,and this has been translated into hydrologic states and water fluxes:terrestrial water storage,ground water storage anomalies,inundation extent and hydroperiod,evapotranspiration,and multi-timescale drought indicators.We call attention to the role of satellite gravimetry in the transformation of basin-scale groundwater evaluation,synthetic aperture radar(SAR),and optical time series in transforming wetland science,however,to the characterization of hydroperiod and connectivity.In the case of drought,we recommend the use of both fast-responsive(soil moisture,evapotranspiration,thermal stress,and vegetation condition)in conjunction with slowly integrating storage anomalies to detect onset,intensification,and recovery,as well as rely on to diagnose the spread of deficits through the hydrologic system.In all these themes,we recognize the central action of enabling approaches that include multi-sensor fusion,data assimilation,and hybrid machine learning schemes in reducing ambiguity,scale gaps,and producing products of decision interest,and also highlighting ongoing issues in the quantification of uncertainty,consistency across long periods of time,and the separation of climate influence on human management of water.Research and operational priorities come as our final deduction to develop satellite hydrology to more trustworthy,explanation-seeking,and operationalizing monitoring designs of water security and ecosystem resilience.展开更多
To develop a suitable method for monitoring wheat yield loss caused by drought for dry farming areas in northwestern China, daily ET0 and ETC were calculated using KC and FAO- PM from 1961 to 2000, and wheat evapotr...To develop a suitable method for monitoring wheat yield loss caused by drought for dry farming areas in northwestern China, daily ET0 and ETC were calculated using KC and FAO- PM from 1961 to 2000, and wheat evapotranspiration with an interval of 10 days was estimated with soil water balance equation for the mountainous areas in southern Ningxia, China. Actual water consumption and water requirements of wheat during growing season was calculated using soil water balance equation by correcting leakage of soil water and run-off of precipitation every year. A model for estimation of yield loss by drought was established based on crop growth-water consumption function and yield potential. The results show that it is an effective method for monitoring drought and estimating yield loss. This method is suitable for monitoring drought and estimating yield loss of wheat in dry farming areas in northwestern China.展开更多
Togo’s economy is heavily dependent on rainfed agriculture. Therefore, anomalies in precipitation can have a significant impact on crop yields, affecting food production and security. Thus, monitoring anomalous clima...Togo’s economy is heavily dependent on rainfed agriculture. Therefore, anomalies in precipitation can have a significant impact on crop yields, affecting food production and security. Thus, monitoring anomalous climate conditions in Togo through the combination of precipitation satellite-based data and Standard Precipitation Index (SPI) help anticipate the development of drought scenarios or excessive rainfall, allowing farmers to adjust their strategies and minimize losses. Continuous and adequate spatial monitoring of these climate anomalies provided by satellite-based products can be central to an effective early warning system (EWS) implementation in Togo. Precipitation satellite-based products have been presented invaluable tools for assessing droughts and , offering timely and comprehensive data that supports a wide range of applications. In this study, we applied the Integrated Multi-satellite Retrievals for GPM (IMERG) rainfall product, a unified satellite global precipitation product developed by NASA, to identify and characterize the severity of dry and wet climate events in Togo during the period from 2001 to 2019. The Standard Precipitation Index (SPI), as the main index recommended by the World Meteorological Organization to monitor drought wide world, was selected as the reference index to monitor dry and wet climate events across Togo regions. The results show two distinct major climate periods in Togo in the timeframe analyzed (2001-2019), one dominated by wet events from 2008 to 2010, and a second marked by severe and extreme dry events from 2013 to 2015;MERG rainfall and SPI combination were able to capture these events consistently.展开更多
随着气候变化加剧干旱风险,精准监测干旱对水资源管理和生态保护至关重要。标准化蒸散发亏缺指数(SEDI)与标准化降水蒸散指数(SPEI)作为新一代干旱监测指标,其适用性研究具有显著的理论与应用价值。文中基于CiteSpace软件对2010—2025年...随着气候变化加剧干旱风险,精准监测干旱对水资源管理和生态保护至关重要。标准化蒸散发亏缺指数(SEDI)与标准化降水蒸散指数(SPEI)作为新一代干旱监测指标,其适用性研究具有显著的理论与应用价值。文中基于CiteSpace软件对2010—2025年间CNKI与Web of Science核心数据库的652篇中英文文献进行可视化分析,系统梳理了SEDI与SPEI的研究趋势、热点及区域适用性。核心发现与突破在于:1)机理互补与精度提升:SEDI基于实际蒸散发亏缺(P-AET),对植被水分胁迫高度敏感,在干旱半干旱区(PET/P>1.5)监测误差较传统指数降低62%;SPEI基于降水与潜在蒸散差值(P-PET),在多时间尺度气象干旱表征中误差降低35%,突破SPI忽视温度影响、PDSI参数复杂的局限。2)动态阈值模型的突破:基于Budyko水热耦合理论,创新性建立了以PET/P比值为核心的动态阈值模型(阈值1.5),明确了干旱半干旱区优先适用SEDI、湿润区优选SPEI、过渡区需双指数交叉验证的区域适用原则,显著提升了不同气候区干旱监测的针对性和准确性。3)实际应用成果:研究表明,SEDI在季风区雨季可提前2—3周识别干旱信号,为农业灌溉决策提供关键时间窗口;融合高分卫星数据的SEDI/SPEI协同应用在国内已实现30m/日级高精度监测,为黄河流域等脆弱生态区干旱风险管理提供了有力支撑。由此可见,SEDI与SPEI通过其互补机理与区域适配性,在提升干旱监测精度、时效性及生态响应表征方面取得了实质性突破,但仍需在复杂下垫面适应性、数据融合模型等方面深化研究。展开更多
基金Major Project of High-resolution Earth Observation System
文摘In this paper, we compared the concept of agricultural drought and its relationship with other types of droughts and reviewed the progress of research on agricultural drought monitoring indices on the basis of station data and remote sensing. Applicability and limitations of different drought monitoring indices were also compared. Meanwhile, development history and the latest progress in agricultural drought monitoring were evaluated through statistics and document comparison, suggesting a transformation in agricultural drought monitoring from traditional single meteorological monitoring indices to meteorology and remote sensing-integrated monitoring indices. Finally, an analysis of current challenges in ag- ricultural drought monitoring revealed future research prospects for agricultural drought monitoring, such as investigating the mechanism underlying agricultural drought, identifying factors that influence agricultural drought, developing multi-spatiotemporal scales models for agricultural drought monitoring, coupling qualitative and quantitative agricultural drought evaluation models, and improving the application levels of remote sensing data in agricultural drought monitoring.
基金Under the auspices of National Natural Science Foundation of China(No.41071221)National Science Technology Support Program(No.2008BAC34B06)China Postdoctoral Science Foundation(No.20110490200)
文摘The normalized difference vegetation index(NDVI) is one of the key input variables for developing drought indices.However,the NDVI quickly saturates in high vegetation surfaces,and thus,the generalization of a drought index over different ecosystems becomes a challenge.This paper presents a novel,dynamic stretching algorithm to overcome the saturation effect in NDVI.A scaling transformation function to eliminate saturation effects when the vegetation fraction(VF) is large is proposed.Dynamic range adjustment is conducted using three coefficients,namely,the normalization factor(a),the stretching range controlling factor(m),and the stretching size controlling factor(e).The results show that the stretched NDVI(S-NDVI) is more sensitive to vegetation fraction than NDVI when the VF is large,ranging from 0.75 to 1.00.Moreover,the saturation effect in NDVI is effectively removed by using the S-NDVI.Further analysis suggests that there is a good linear correlation between the S-NDVI and the leaf area index(LAI).At the same time,the proposed S-NDVI significantly reduces or even eliminates the saturation effect over high biomass.A comparative analysis is performed between drought indices derived from NDVI and S-NDVI,respectively.In the experiment,reflectance data from the moderate resolution imaging spectroradiometer(MODIS) products and in-situ observation data from the meteorological sites at a regional scale are used.In this study,the coefficient of determination(R2) of the stretched drought index(S-DI) is above 0.5,indicating the reliability of the proposed algorithm with surface soil moisture content.Thus,the S-DI is suggested to be used as a drought index in extended regions,thus regional heterogeneity should be taken into account when applying stretching method.
基金Supported by National Natural Science Foundation,China(41371498)Comprehensive Process Observation and Test Platform Construction of Natural Geography in Marina Small Watershed,Sun Yat-sen University,China
文摘It is accepted that climate change has a great impact on water cycle and regional water balance,and thus it would change the formation and evolution conditions of drought in some degree. By using data at 42 meteorological stations of the Pearl River Basin,the Standardized Precipitation Evapotranspiration Index（ SPEI） at different time scales was calculated. Based on the SPEIs of 1- 12 months,a newly proposed index for drought--Joint Drought Index（ JDI） was established under the multi-scale perspective through the copula function. Since short-term SPEIs are essential for the identification of emerging droughts and long-term SPEIs are useful for prolonged droughts,the JDI,which integrates all the usefull informations of drought and can thus form an overall judgement,is superior than the single SPEI in drought monitoring. By the forcast evaluation system and comparison to the actual drought,the accuracy and effectiveness of JDI in drought monitoring were verified. In general,JDI can be used as a new ideal index for future drought monitoring and assessment. Additionly,we analyzed the spatio-temperal characteristics of drought across the Pearl River Basin using the JDI. The results indicate that mild drought was the most frequent drought occurred in the Pearl River Basin over the past half century,and moderate drought followed. Severe drought and extreme drought would appear occasionally while exceptional drought could hardly be found. A dry-wet-dry interdecadal variation pattern had been found from the 1960 s to the 2000 s. Since the 21 stcentury,an obvious trend toward drought can be observed in the whole basin,especially in the Xijiang subbasin,which,consequently,poses an increasing challenge for the water resource planning and management.
基金jointly supported by the National Key Research and Development Program approved by Ministry of Science and Technology,China(2016YFA0601504)the Program of Introducing Talents of Discipline to Universities by the Ministry of Education and the State Administration of Foreign Experts Affairs,China(B08048)+1 种基金the National Natural Science Foundation of China(41501017,51579066)the Natural Science Foundation of Jiangsu Province(BK20150815)
文摘The high resolution satellite precipitation products bear great potential for large-scale drought monitoring, especially for those regions with sparsely or even without gauge coverage. This study focuses on utilizing the latest Version-7 TRMM Multi-satellite Precipitation Analysis （TMPA 3B42V7） data for drought condition monitoring in the Weihe River Basin （0.135×10^6 km2）. The accuracy of the monthly TMPA 3B42V7 satellite precipitation data was firstly evaluated against the ground rain gauge observations. The statistical characteristics between a short period data series （1998-2013） and a long period data series （1961-2013） were then compared. The TMPA 3B42V7-based SPI （Standardized Precipitation Index） sequences were finally validated and analyzed at various temporal scales for assessing the drought conditions. The results indicate that the monthly TMPA 3B42V7 precipitation is in a high agreement with the rain gauge observations and can accurately capture the temporal and spatial characteristics of rainfall within the Weihe River Basin. The short period data can present the characteristics of long period record, and it is thus acceptable to use the short period data series to estimate the cumulative probability function in the SPI calculation. The TMPA 3B42V7-based SPI matches well with that based on the rain gauge observations at multiple time scales （i.e., 1-, 3-, 6-, 9-, and 12-month） and can give an acceptable temporal distribution of drought conditions. It suggests that the TMPA 3B42V7 precipitation data can be used for monitoring the occurrence of drought in the Weihe River Basin.
基金supported by the National Key Research and Development Program of China (2016YFA0601601)National Natural Science Foundation of China (Grants Nos. U1502233,41405001)+1 种基金the Jiangsu Collaborative Innovation Center for Climate ChangePh.D. Programs Foundation of Ministry of Education of China (20135301120010)
文摘Using Moderate Resolution Imaging Spectroradiometer(MODIS) data from the dry season during 2010–2012 over the whole Yunnan Province, an improved temperature vegetation dryness index(iTVDI), in which a parabolic dry-edge equation replaces the traditional linear dry-edge equation, was developed, to reveal the regional drought regime in the dry season. After calculating the correlation coefficient, root-mean-square error, and standard deviation between the iTVDI and observed topsoil moisture at 10 and 20 cm for seven sites, the effectiveness of the new index in depicting topsoil moisture conditions was verified. The drought area indicated by iTVDI mapping was then compared with the drought-affected area reported by the local government. The results indicated that the iTVDI can monitor drought more accurately than the traditional TVDI during the dry season in Yunnan Province. Using iTVDI facilitates drought warning and irrigation scheduling, and the expectation is that this new index can be broadly applied in other areas.
基金Foundation： National Natural Science Foundation of China （No.41101314, 41101318） Institute of Arid Meteorology, CMA Open Fund （No.IAM201102） Major Projects of Southwest Regional Meteorological Center of CMA （2011）
基金supported by Liaoning Provincial Natural Science Foundation of China(General Project 2024-MS-094).
文摘The low spatial resolution of the Integrated Multi-satellitE Retrievals for Global Precipitation Measurement(IMERG),a mainstream Global Precipitation Measurement(GPM)product,limits its use in refined drought analysis over complex monsoon underlying surfaces.To resolve this issue,this study proposes an integrated meteorological drought monitoring framework(SPTI),which enhances accuracy by coupling 0.05°downscaled IMERG precipitation data with Moderate Resolution Imaging Spectroradiometer(MODIS)land surface temperature(LST)data.First,a Normalized Difference Vegetation Index(NDVI)-topography guided multivariate regression kriging downscaling scheme was built using monthly precipitation data from 23 Liaoning stations(2010–2018),geographic-topographic factors,and NDVI covariates,downscaling original 0.1°IMERG data to 0.05°(achieving R2>0.7 in ten months,except for June and July).Second,a high-performance multisource drought model was established via regression of Standardized Precipitation Evapotranspiration Index(SPEI)against downscaled IMERG-Z Index(derived from IMERG precipitation using the drought Z-index method)and Temperature Condition Index(TCI).Finally,SPTI was validated with four typical Liaoning drought events during 2014,2015,2017,and 2018.Results show that:(1)0.05°precipitation data captures fine spatial details,clearly depicting Liaoning’s southeast-tonorthwest precipitation gradient and central plain rainfall zones;(2)SPTI outperforms standalone IMERG-Z—it accurately identifies severe/extreme droughts,mitigates IMERG-Z’s underestimation bias,and reasonably characterizes drought alleviation after heavy rains by integrating TCI,avoiding IMERG-Z’s“abrupt drought-to-waterlogging”misjudgment;(3)SPTI results align well with the Liaoning Meteorological Disaster Bulletin,confirming its suitability for refined monsoon drought monitoring.
基金the Strategic Priority Research Program of the Chinese Academy of Sciences[grant number XDA19030203]the National Key Research and Development Program of China[grant number 2017YFB0504105].
文摘It has long been recognized that an effective drought monitoring and early warning system,which provides functions for real-time condition monitoring and prediction,risk assessment,information dissemination and response recommendation,is very important for the preparedness for and mitigation of drought impacts.In this article,we review the currently existing drought monitor and early warning systems,discuss applicable remote sensing datasets and drought indicators and present the development of a web-based quasi-real-time Global Drought Monitoring&Analysis Platform(Web-GDMAP).The Web-GDMAP is built upon a series of indicators derived from multi-source satellite remote sensing data and various other sources of data.From a technical perspective,the Web-GDMAP system includes a series of components from data storage,model implementation and distribution,to client-side visualization and user intuitive interaction.From a theoretical perspective,the Web-GDMAP system integrates multi-indicators on different aspects of drought,including anomalies in precipitation,anomalies in land surface thermal and vegetation conditions,water deficit of soil and plants,etc.Several case studies on applying the developed Web-GDMAP in the Asian region are demonstrated.Further improvements and perspectives are discussed.
基金supported by the National Key Technologies R&D Program of China (2011BAD32B01)the Ph D Programs Foundation of Ministry of Education of China (20100101110035)
文摘The normalized difference vegetation index （NDVI） has proven to be typically employed to assess terrestrial vegetation conditions. However, one limitation of NDVI for drought monitoring is the apparent time lag between rainfall deficit and NDVI response. To better understand this relationship, time series NDVI （2000-2010） during the growing season in Sichuan Province and Chongqing City were analyzed. The vegetation condition index （VCI） was used to construct a new drought index, time-integrated vegetation condition index （TIVCI）, and was then compared with meteorological drought indices-standardized precipitation index （SPI）, a multiple-time scale meteorological-drought index based on precipitation, to examine the sensitivity on droughts. Our research findings indicate the followings： （1） farmland NDVI sensitivity to precipitation in study area has a time lag of 16-24 d, and it maximally responds to the temperature with a lag of about 16 d. （2） We applied the approach to Sichuan Province and Chongqing City for extreme drought monitoring in 2006 and 2003, and the results show that the monitoring results from TIVCI are closer to the published China agricultural statistical data than VCI. Compared to VCI, the best results from TIVCI3 were found with the relative errors of -4.5 and 6.36% in 2006 for drought affected area and drought disaster area respectively, and 5.11 and -5.95% in 2003. （3） Compared to VCI, TIVCI has better correlation with the SPI, which indicates the lag and cumulative effects of precipitation on vegetation. Our finding proved that TIVCI is an effective indicator of drought detection when the time lag effects between NDVI and climate factors are taken into consideration.
文摘Meteorological drought is a natural hazard that can occur under all climatic regimes. Monitoring the drought is a vital and important part of predicting and analyzing drought impacts. Because no single index can represent all facets of meteorological drought, we took a multi-index approach for drought monitoring in this study. We assessed the ability of eight precipitation-based drought indices（SPI（Standardized Precipitation Index）, PNI（Percent of Normal Index）, DI（Deciles index）, EDI（Effective drought index）, CZI（China-Z index）, MCZI（Modified CZI）, RAI（Rainfall Anomaly Index）, and ZSI（Z-score Index）） calculated from the station-observed precipitation data and the Ag MERRA gridded precipitation data to assess historical drought events during the period 1987–2010 for the Kashafrood Basin of Iran. We also presented the Degree of Dryness Index（DDI） for comparing the intensities of different drought categories in each year of the study period（1987–2010）. In general, the correlations among drought indices calculated from the Ag MERRA precipitation data were higher than those derived from the station-observed precipitation data. All indices indicated the most severe droughts for the study period occurred in 2001 and 2008. Regardless of data input source, SPI, PNI, and DI were highly inter-correlated（R^2=0.99）. Furthermore, the higher correlations（R^2=0.99） were also found between CZI and MCZI, and between ZSI and RAI. All indices were able to track drought intensity, but EDI and RAI showed higher DDI values compared with the other indices. Based on the strong correlation among drought indices derived from the Ag MERRA precipitation data and from the station-observed precipitation data, we suggest that the Ag MERRA precipitation data can be accepted to fill the gaps existed in the station-observed precipitation data in future studies in Iran. In addition, if tested by station-observed precipitation data, the Ag MERRA precipitation data may be used for the data-lacking areas.
文摘Satellite hydrology has reached a new era where a variety of earth observing systems,in conjunction with the development of data integrations,can provide a consistent monitoring of groundwater change,wetland dynamics,and drought evolution in regions where observations on the ground remain sparse or patchy.This synthesis review highlights the physical observables that are most useful to terrestrial hydrology:variable time-dependent gravity,passive and active microwave signals,optical reflectance,thermal infrared measurements,and altimetry,and this has been translated into hydrologic states and water fluxes:terrestrial water storage,ground water storage anomalies,inundation extent and hydroperiod,evapotranspiration,and multi-timescale drought indicators.We call attention to the role of satellite gravimetry in the transformation of basin-scale groundwater evaluation,synthetic aperture radar(SAR),and optical time series in transforming wetland science,however,to the characterization of hydroperiod and connectivity.In the case of drought,we recommend the use of both fast-responsive(soil moisture,evapotranspiration,thermal stress,and vegetation condition)in conjunction with slowly integrating storage anomalies to detect onset,intensification,and recovery,as well as rely on to diagnose the spread of deficits through the hydrologic system.In all these themes,we recognize the central action of enabling approaches that include multi-sensor fusion,data assimilation,and hybrid machine learning schemes in reducing ambiguity,scale gaps,and producing products of decision interest,and also highlighting ongoing issues in the quantification of uncertainty,consistency across long periods of time,and the separation of climate influence on human management of water.Research and operational priorities come as our final deduction to develop satellite hydrology to more trustworthy,explanation-seeking,and operationalizing monitoring designs of water security and ecosystem resilience.
文摘To develop a suitable method for monitoring wheat yield loss caused by drought for dry farming areas in northwestern China, daily ET0 and ETC were calculated using KC and FAO- PM from 1961 to 2000, and wheat evapotranspiration with an interval of 10 days was estimated with soil water balance equation for the mountainous areas in southern Ningxia, China. Actual water consumption and water requirements of wheat during growing season was calculated using soil water balance equation by correcting leakage of soil water and run-off of precipitation every year. A model for estimation of yield loss by drought was established based on crop growth-water consumption function and yield potential. The results show that it is an effective method for monitoring drought and estimating yield loss. This method is suitable for monitoring drought and estimating yield loss of wheat in dry farming areas in northwestern China.
文摘Togo’s economy is heavily dependent on rainfed agriculture. Therefore, anomalies in precipitation can have a significant impact on crop yields, affecting food production and security. Thus, monitoring anomalous climate conditions in Togo through the combination of precipitation satellite-based data and Standard Precipitation Index (SPI) help anticipate the development of drought scenarios or excessive rainfall, allowing farmers to adjust their strategies and minimize losses. Continuous and adequate spatial monitoring of these climate anomalies provided by satellite-based products can be central to an effective early warning system (EWS) implementation in Togo. Precipitation satellite-based products have been presented invaluable tools for assessing droughts and , offering timely and comprehensive data that supports a wide range of applications. In this study, we applied the Integrated Multi-satellite Retrievals for GPM (IMERG) rainfall product, a unified satellite global precipitation product developed by NASA, to identify and characterize the severity of dry and wet climate events in Togo during the period from 2001 to 2019. The Standard Precipitation Index (SPI), as the main index recommended by the World Meteorological Organization to monitor drought wide world, was selected as the reference index to monitor dry and wet climate events across Togo regions. The results show two distinct major climate periods in Togo in the timeframe analyzed (2001-2019), one dominated by wet events from 2008 to 2010, and a second marked by severe and extreme dry events from 2013 to 2015;MERG rainfall and SPI combination were able to capture these events consistently.
文摘随着气候变化加剧干旱风险,精准监测干旱对水资源管理和生态保护至关重要。标准化蒸散发亏缺指数(SEDI)与标准化降水蒸散指数(SPEI)作为新一代干旱监测指标,其适用性研究具有显著的理论与应用价值。文中基于CiteSpace软件对2010—2025年间CNKI与Web of Science核心数据库的652篇中英文文献进行可视化分析,系统梳理了SEDI与SPEI的研究趋势、热点及区域适用性。核心发现与突破在于:1)机理互补与精度提升:SEDI基于实际蒸散发亏缺(P-AET),对植被水分胁迫高度敏感,在干旱半干旱区(PET/P>1.5)监测误差较传统指数降低62%;SPEI基于降水与潜在蒸散差值(P-PET),在多时间尺度气象干旱表征中误差降低35%,突破SPI忽视温度影响、PDSI参数复杂的局限。2)动态阈值模型的突破:基于Budyko水热耦合理论,创新性建立了以PET/P比值为核心的动态阈值模型(阈值1.5),明确了干旱半干旱区优先适用SEDI、湿润区优选SPEI、过渡区需双指数交叉验证的区域适用原则,显著提升了不同气候区干旱监测的针对性和准确性。3)实际应用成果:研究表明,SEDI在季风区雨季可提前2—3周识别干旱信号,为农业灌溉决策提供关键时间窗口;融合高分卫星数据的SEDI/SPEI协同应用在国内已实现30m/日级高精度监测,为黄河流域等脆弱生态区干旱风险管理提供了有力支撑。由此可见,SEDI与SPEI通过其互补机理与区域适配性,在提升干旱监测精度、时效性及生态响应表征方面取得了实质性突破,但仍需在复杂下垫面适应性、数据融合模型等方面深化研究。
