A Daily Drought Index-based Dry and Wet Variation Analyses over the Qinghai-Xizang Plateau from 1979 to 2020

Abstract

The Qinghai-Xizang Plateau is one of the most sensitive areas to global climate change and plays an important role in regional water cycle.Many studies have been conducted on the dry and wet variations over the Qinghai-Xizang Plateau in recent decades.However， the previous studies were based on monthly drought indices， the daily day and wet variations over the Qinghai-Xizang Plateau in the last decades are still unclear.In this study， a daily drought index named Daily Evapotranspiration Deficit Index （DEDI） calculated using the ERA5 reanalysis data was utilized to analyze the daily dry and wet variations over the Qinghai-Xizang Plateau from 1979 to 2020， especially the seasonal differences in the number of occurrence days for dry and wet categories with different intensities （i.e.， extreme， severe， moderate， and abnormal conditions）.The main results are as follows： （1） The dry-wet variations over the Qinghai-Xizang Plateau experienced remarkable interdecadal transition from 1979 to 2020， and basically characterized as dry-humid-dry-humid in the last 40 decades.（2） In the past 40 years， daily droughts with four intensities （i.e.， extreme， severe， moderate， and abnormal droughts） over the Qinghai-Xizang Plateau showed increasing tendencies in spring and winter， and showed decreasing tendencies in summer.In autumn， extreme， severe， and moderate droughts showed increasing trends， and abnormal drought had a decreased trend.In contrast to the tendencies of drought occurrence days， extreme wetness in spring， autumn， and winter showed increasing trends， while severe， moderate， and abnormal wetness had decreased trends.Wetness in all the four intensities over the Qinghai-Xizang Plateau in summer showed increasing trends.Compared with other seasons， the number of wet/drought days with four intensities had the most significantly increasing trend in summer/winter， i.e.， summer/winter had the strongest wetting/drying tendency.In addition， the occurrence days of extreme drought/wetness were much smaller than drought/wetness in other intensities in each season.Drought/wetness in moderate and abnormal intensities occurred most frequently and had close numbers of occurrence days.

Keywords

• daily drought index
• actual evapotranspiration
• potential evapotranspiration
• dry and wet variations
• seasonal differences
• qinghai-xizang plateau