Drought Propagation Patterns And The Prediction Models Of Meteorological Drought,Hydrological Drought And Agricultural Drought

Droughts are one of the most damaging natural disasters in the world.The transition from one type of drought to another is known as drought propagation.At present,the spatial differentiation mechanism of the propagation relationship among meteorology,hydrology and agricultural drought is still unclear,which limits drought prevention and ecological restoration.The dry-hot valley in Southwest China is the most typical fragile ecosystem in China due to its frequent drought and complex terrain.The research on the spatio-temporal distribution characteristics of drought,the research on drought propagation relationship and the construction of drought prediction model in this region have important scientific and technological guiding significance for alleviating and preventing drought.In this study,the Longjiang River Basin(LRB)was taken as the study area.Based on the precipitation data of 31 meteorological stations,the runoff data of 4 hydrological stations and the Landsat remote sensing images,the meteorological,hydrological and agricultural drought indexes in the LRB were calculated to study the intensity,frequency and coverage of drought,and to clarify the spatio-temporal differentiation characteristics of three droughts in the Longchuan River Basin.Then,the time-lagged unbiased cross correlation coefficient between droughts was calculated by the time-lagged cross-correlation analysis method,the lagged time and occurrence order of three droughts in the basin were judged,and then the drought propagation patterns in the basin was summarized.Finally,based on Support Vector Machine(SVM),the drought level prediction training model was established and the accuracy was evaluated,and then the drought prediction model was optimized to obtain the drought level prediction model suitable for LRB.The main results were as follows:1.The spatio-temporal differentiation characteristics of different types of drought in Longchuan River Basin: in term of drought intensity,the meteorological drought and hydrological drought intensity showed an increasing trend while the agricultural drought intensity first increased and then decreased during 2000-2015.In term of drought frequency,overall frequency of hydrological drought was higher than that of meteorological drought.In term of drought coverage,the coverage of meteorological drought and hydrological drought was expanding,while that of agricultural drought was narrowing.Changing farming methods and planting low water consumption crops can reduce the risk of hydrological drought and agricultural drought in Longchuan River Basin.2.The drought propagation relationships among different types of drought in Longchuan River Basin: at higher altitudes with more forests,meteorological drought propagated to agricultural drought over 2 months,and then to hydrological drought over 2 more months.At lower altitudes with more arable lands,the meteorological and hydrological drought both propagated to agricultural drought over 1 months.Planting low water consumption plants in the basin can delay or prevent the propagation of meteorological drought to hydrological drought.Promoting efficient irrigation techniques can reduce hydrological drought.3.Prediction model of drought level for different types of drought in Longchuan River Basin: the prediction model of meteorological drought level is a SVM model based on C-classification classification method and Radial kernel function,with the same weight of each drought level.The prediction model of hydrological drought level is a SVM model based on C-classification classification method and Linear kernel function,with the same weight of each drought level.The prediction model of agricultural drought level is a SVM model based on C-classification classification method and Radial kernel function,and the weight of ‘normal' level is 1.1-1.2 times that of ‘partial drought' level.