Impacts of high temperatures with varied hit timing on soil moisture drought

High temepratures can impose different effects on soil mositure drought development depending on their hit timing. Based on the reanalysis soil moisture data, we identified the duration of soil moisture drought onset (defined as the time period for moisture to transition from a normal state to below-average condition), and designed a random forest based experimental framework to measure how rapidly soil mositure drought develops under varied high temeprature conditions in China. Results show that the duration of soil mositure drought onset would be shorten by 10-50 days under high temperatures in relative to that of annual mean temperature scenarios. With regard to the timing of high temepratures, the associated impacts were the greatest for high temperatures  of 1 month prior to soil moisture drought occurrence. In densely vegetated areas, pre-drought high temperatures played positively in accelerating the formation of soil moisture drought. In sparse vegetated areas by contrast, post-drought high temperatures contributed to the ongoing development of soil drought. The findings show the asymmetrical impacts of pre-drought and post-drought high temperatures on soil drought development, which may provide some references for improving the understanding of soil moisture drought mechanism in a warming future.