Analysis of the Difference between Climate Aridity Index and Meteorological Drought Index in the Summer Monsoon Transition Zone

The summer monsoon transition zone (SMTZ) in China represents an unusual land type with agro-pasture ecotone, and it is a climate-sensitive region. Changes climate aridity changes meteorological drought are mutually related yet fundamentally different. In this study, potential evapotranspiration (ETO) calculated using Penman–Monteith, based on China’s national stations data from 1961 to 2013. An ETO-based index (IAI) standardized precipitation (SPEI) used as the metrics for drought, respectively. result shows significant difference between SMTZ, compared non-monsoon zone. This varies different time scales (1–48 months), greatest differences IAI SPEI seasonal monthly (1–12 but lower at longer (>12 months). first reason desynchronicity of background climate. After becomes relatively arid state (such 0.96 < 1) semi-arid (0.50 0.80), continued weak fluctuations eventually results increasingly severe droughts, or recurrence equally droughts drastic reduction. Consequently, onset most two seven months (mostly three four months) ahead events, until returns state. Second, average over long period gently, while stochastic events change drastically. These findings indicate that can serve predictor especially fails characterize progression well. Therefore, great significance prediction early warning.