Propagation characteristics from meteorological drought to agricultural drought over the Heihe River Basin, Northwest China

In the context of global warming,drought events occur frequently.In order to better understanding the process and mechanism of drought occurrence and evolution,scholars have dedicated much attention on drought propagation,mainly focusing on drought propagation time and propagation probability.However,there are relatively few studies on the sensitivities of drought propagation to seasons and drought levels.Therefore,we took the Heihe River Basin(HRB)of Northwest China as the case study area to quantify the propagation time and propagation probability from meteorological drought to agricultural drought during the period of 1981–2020,and subsequently explore their sensitivities to seasons(irrigation and non-irrigation seasons)and drought levels.The correlation coefficient method and Copula-based interval conditional probability model were employed to determine the drought propagation time and propagation probability.The results determined the average drought propagation time as 8 months in the whole basin,which was reduced by 2 months(i.e.,6 months)on average during the irrigation season and prolonged by 2 months(i.e.,10 months)during the non-irrigation season.Propagation probability was sensitive to both seasons and drought levels,and the sensitivities had noticeable spatial differences in the whole basin.The propagation probability of agricultural drought at different levels generally increased with the meteorological drought levels for the upstream,midstream,and southern downstream regions of the HRB.Lesser agricultural droughts were more likely to be triggered during the irrigation season,while severer agricultural droughts were occurred mostly during the non-irrigation season.The research results are helpful to understand the characteristics of drought propagation and provide a scientific basis for the prevention and control of droughts.This study is of great significance for the rational planning of local water resources and maintaining good ecological environment in the HRB.

Comprehensive evaluation of hydrological drought characteristics and their relationship to meteorological droughts in the upper Tarim River Basin,central Asia

Comprehensive evaluation of the characteristics and mechanisms of droughts is of great significance to drought risk prediction and prevention.The 3-monthly scale Standardized Runoff Index(SRI-3)and 3-monthly scale Standardized Precipitation Evapotranspiration Index(SPEI-3)were employed herein to characterize hydrological and meteorological droughts,respectively,within the four upper subbasins of the Tarim River Basin(TRB)during 1961-2015.The propagation of droughts was also evaluated.The hydrological drought duration(Dd)and drought severity(Ds)were determined by Run theory,and Copula functions were adopted to investigate the hydrological drought probabilities and return periods.The propagation relationships of hydrological and meteorological droughts were assessed.The results indicated that:1)hydrological drought index(SRI-3)significantly increased in the TRB from 1961 to 2015;the increase was most significant in winter.Meteorological drought index(SPEI-3)exhibited a weak upward trend through time;2)the characteristics of hydrological droughts varied between the subbasins;increases in the SRI were most significant in the Yarkand and Hotan Rivers,whereas the Dd and Ds of hydrological droughts were higher in the Kaidu and Yarkand Rivers;3)Frank Copula was the most closely fitted Copula function in the four subbasins of the TRB and yielded average drought return periods of 4.86,4.78,3.72,and 5.57 years for the Kaidu,Aksu,Yarkand,and Hotan River Basins,respectively.The return periods in the four subbasins were generally less than 10 years from 1961 to 2015;4)a cross wavelet transform(XWT)exhibited a significant positive correlation between hydrological and meteorological droughts,except for the Yarkand River Basin,which exhibited a significant negative correlation.Besides,the propagation relationship of meteorological droughts to hydrological droughts showed remarkable seasonal variations.