Standardized Precipitation Evapotranspiration Index is highly correlated with total water storage over China under future climate scenarios

A Standardized Precipitation Evapotranspiration Index (SPEI) model, which uses the FAO-56 Penman-Monteith equation to calculate potential evapotranspiration, has been developed and is considered appropriate for drought monitoring and assessment. However, the correlation of SPEI to total water storage (TWS) across multiple timescales, derived from future climate scenarios, is still unclear for China. In this study, the correlation of SPEI on different timescales (1-, 3-, 6-, 12-, 24- and 48-month) to TWS projected by a global climate model [the Community Climate System Model, version 4 (CCSM4)] under two representative concentration pathway scenarios (RCP2.6 and RCP8.5) for the period 2021-2100 in China is analyzed. The results show that, in general, SPEI is highly correlated with CCSM TWS in most of China (especially in eastern China) at the 12-month timescale, and is therefore regarded as an adequate indicator for representing situations of water resources and evaluating hydrological droughts. At the 12-month timescale, the correlations of SPEI to CCSM TWS vary across different river basins; and the variations in the pattern of correlations are greater due to faster warming and greater precipitation under RCP8.5. It is hoped that this article will provide guidance on the use of SPEI for detecting the impacts of future climate change on drought severity in China.