Fig. 4: Percentage contribution of AED and precipitation to trends in 6-month SPEI.

a,b, The percentage contribution of AED (a) and the percentage contribution of precipitation (b) to the observed changes in 6-month HRSPEI during 1981–2022. The contributions are computed by calculating the difference between the observed trend and the trend based on the climatological values of AED (AEDclm) and precipitation (Prclm). The contribution of AED is determined by the difference between the trend using observed AED and precipitation and the trend using observed precipitation and AEDclm. Similarly, the contribution of precipitation is calculated as the difference between the trend using observed precipitation and AED and the trend using observed AED and Prclm. The percentage contribution of each factor is then calculated as the absolute value of the difference divided by the total absolute difference, providing a relative measure of each factor’s influence on the observed trend. c, The regional and global average contribution of precipitation and AED to the changes in SPEI.