| Drought is a widespread and severe natural disaster that affects social and economic sustainability.It is classified by the World Meteorological Organization into four types: meteorological,hydrological,agricultural,and socio-economic.Agriculture is the most impacted sector,with agricultural drought causing the most severe damage.Southwest China is a main karst landscape region with delicate ecosystems that are vulnerable to drought.Recently,the frequency and intensity of droughts in this area have risen,impacting economic growth,food security,and drinking water.This has caused vegetation death and worsened rock desertification.Monitoring agricultural droughts in Southwest China is essential to understand their characteristics and causes.In this study,we use the Community Land Model version 4.5(CLM)combined with remote sensing and reanalysis data to study the agricultural drought in Southwest China from 2005 to 2020 in the context of global climate change.The focus of this research is to analyze the spatial and temporal characteristics of agricultural droughts in Southwest China from 2005 to 2020 and to investigate the driving factors of agricultural droughts in Southwest China from the perspective of water and energy balance.The main findings of this study are as follows:(1)CLM model combined with the standardized soil moisture index SSMI can provide accurate monitoring of the occurrence and development process of agricultural drought in Southwest China.By comparing the CLM simulation outcomes with the commonly used reanalysis and remote sensing data at the present stage,it can be concluded that the CLM simulation outcomes have good accuracy and can be applied to the research of regional water cycle and other aspects.The time series analysis of CLM simulation outcomes reveals that there are remarkably dry and wet seasons in southwest China: precipitation in southwest China is scarce in spring and winter and abundant in summer and autumn.In addition,there are highly significant differences in the seasonal variations of hydrological elements such as soil evaporation and soil moisture in Yunnan,Sichuan and Chongqing.Between 2005 and2020,the droughts in the Southwest region were monitored using CLM simulated soil moisture to calculate SSMI.The results indicated the presence of four drought-prone regions in southwest China.Yunnan and Sichuan-Chongqing border areas had the highest frequency of drought,at around 10%,followed by Guizhou and Guangxi,with a frequency of approximately 8%.The northwestern part of southwest China had the lowest frequency of drought.Overall,the frequency of drought in Southwest China shows a spatial distribution that decreases from southwest to northeast along a line.(2)Between 2005 and 2020,the severity,coverage and duration of agricultural droughts in Southwest China have apparent spatial and temporal characteristics.Analyzing the trend changes of drought MK in Southwest China reveals a notable rise in drought frequency from 2005 to 2014,followed by a significant decrease in both frequency and duration of drought in the region from 2015 to 2020.The four high agricultural drought-prone regions in Southwest China exhibit distinct seasonal characteristics of drought.The Yunnan region experiences droughts primarily in the spring and winter seasons,with severe and extreme droughts occurring at a frequency of about 10%.The Sichuan and Chongqing border areas,Guizhou,and Guangxi are prone to moderate droughts in the spring and winter seasons,while severe and extreme droughts occur during the summer and autumn seasons.The frequency of extreme droughts in the summer and autumn seasons in the Sichuan-Chongqing border area is about 6%,while the frequency of extreme droughts in the summer season in Guangxi and Guizhou is about 4%.Furthermore,the duration of a single agricultural drought in Southwest China is typically concentrated in 2-4 months,with an average duration of about 4 months.(3)There are significant differences in the characteristics of water and energy balances in different agricultural drought zones in Southwest China.Combined with the results of the Budyko model,seasonal agricultural drought in Southwest China is found to be impacted by different driving factors.The Budyko model is a widely accepted theoretical framework for studying the hydrological and climatic dependencies of watersheds worldwide.According to the results of the Budyko model,the Budyko points in the Yunnan and Sichuan-Chongqing regions tend to be in the water-limited region,whereas those in Guizhou and Guangxi are closer to the water-energy partitioning region.As the severity of drought in southwest China increases,the proportion of evapotranspiration in the regional land surface water cycle also increases,while the availability of water resources decreases.Comparing the changes in drivers during drought years with those during normal years,it is evident that low rainfall and high temperatures are closely linked to drought in southwest China.Additionally,in the spring and winter,vigorous vegetation evaporation contributes to drought,whereas in the summer and autumn,vigorous vegetation transpiration and soil evaporation are primary factors.In the months with high occurrences of agricultural drought in southwest China,there are significant reductions in rainfall and soil moisture,and an increase in temperature,vegetation evaporation,and soil evaporation.By combining relevant studies and experimental results,it is evident that meteorological factors play a primary role in causing agricultural drought,whereas human factors can both exacerbate and alleviate the problem. |
