Modification of the standardized precipitation evapotranspiration index based on actual evapotranspiration

In the report， to enhance the effectiveness of the SPEI in agricultural drought monitoring， a modified Standardized Precipitation Evapotranspiration Index （MSPEI） focused on water balance was proposed. The index was calculated by the difference between precipitation and actual evapotranspiration， and which were adaptive corrected based on the duration of the longest consecutive drought period. The visual inspection for probabilistic fitting curves and the Kolmogorov-Smirnov test were used to choose an appropriate distribution function. The drought index was obtained by a standardized transformation. The validity test for the aridity index demonstrated that the MSPEI accurately captures the distinctions under wet and dry conditions across seasons. During spring， when the wetness proportion was below 20%， the MSPEI registered below -0.5. For depicting drought trends， there are strong consistency between the MSPEI exhibited and the SPEI. The correlation between MSPEI and the vegetation index remain stable and high， ranging from 0.57 to 0.78. During the monitoring processes of typical drought， the MSPEI's depiction of the start， development， and the end of drought aligns was more realistic than that of SPEI. MSPEI adapts to various climatic backgrounds and can accurately depict the evolution of agricultural drought processes without requiring a specific time scale.