Drought Characterizations In The Mekong River Basin And Adjacent Regions

The Mekong River Basin and adjacent regions have been seriously affected by drought disasters and will continue to face the threat in the future.However,existing studies are lacking in revealing the characteristics and changes of drought in the region over a long time series,monitoring agricultural drought,and quantifying the mitigation effects of human activities on drought.This dissertation reveals the spatial and temporal distribution characteristics and future development trends of meteorological drought and hydrological drought in the Mekong River basin and adjacent regions using ISIMIP data and the distributed hydrological model GBHM.And an agricultural drought monitoring indicator based on satellite-based soil moisture products was developed and used to analyze the mitigation effect of irrigation on agricultural drought.Finally,the mitigation of downstream hydrological drought by upstream reservoir release was quantified.Based on the analysis of historical and future simulation data provided by ISIMIP,this study finds that the trend of meteorological drought in the future period is aggravated and then alleviated.However,the future meteorological drought intensity,severity,and duration will rise by 30% in China's “Yunnan-Guizhou-Sichuan” and Mekong Delta regions.The discharge simulations based on GBHM also indicate that the hydrological drought will tend to intensify and then alleviate in the future period,and the hydrological drought at all discharge gauges will be reduced by more than 50% after the middle future,yet the future hydrological drought will be concentrated in the dry season,with an increasing drought frequency of 80%.This dissertation developed the Soil Moisture Drought Index SMDI based on remote sensing soil moisture product and Beta distribution fitted,which is capable of monitoring agricultural drought in the study area at the 8-day scale and can quickly respond to changes in agricultural drought under different land characteristics.Based on SMDI,this study quantitatively investigates the mitigation effect of irrigation on agricultural drought and finds that irrigation can effectively mitigate agricultural drought,when the irrigation ratio > 50%,irrigation can provide about 30% mitigation effect on agricultural drought above the moderate level.Based on a distributed hydrological model driven by satellite precipitation products,this study simulates the natural discharge in the Mekong River in 2016,an extremely dry year,and extracts the discharge increment curves by upstream reservoir release in the 2016 dry season.Then quantifies the mitigation effect of this reservoir release on the downstream hydrological drought,and finds that the release process was able to completely mitigate the monthly or seasonal hydrological drought and reduce about 10% Standardized Streamflow Index SSI on the yearly hydrological drought.After combining with the future simulated discharge,it is found that the upstream reservoir release can effectively alleviate the hydrological drought under different scenarios and scales,the closer the station is to the upstream,the greater the mitigation effect is.The mitigation effect can decrease more than 95% SSI of monthly and seasonal scale hydrological drought,while the mitigation effect can decrease more than10% SSI of annual scale hydrological drought.This dissertation suggests that the drought in the Mekong River basin and adjacent regions mainly shows a trend of aggravation followed by mitigation in the future period;human activities such as irrigation and upstream reservoirs release can effectively mitigate drought disasters.The results of this dissertation are important for drought mitigation and sustainable development in the study area,and can also provide scientific and technological support for China's water diplomacy in Southeast Asia.