A drought index: The standardized precipitation evapotranspiration runoff index

Based on the principles underlying the calculation of the standardized precipitation index (SPI) and standardized precipitation evapotranspiration index (SPEI), this study selects precipitation, temperature, relative humidity, sunshine hours, wind speed and runoff data to develop a multi-scalar drought index, the standardized precipitation evapotranspiration runoff index (SPERI), using methods such as Penman-Monteith and Copula. This index is applied along with the SPI and SPEI to Yunnan Province of China. The results show that the changes in the SPERI are close to those in the SPI and SPEI. They are well correlated and can all reflect drought conditions. In addition, comparisons among these three drought indexes and the actual extreme drought during September 2009-August 2010 showed that the SPERI was superior to the SPI and SPEI and that the 3-month SPERI assessment was the most accurate. Therefore, the SPERI can be used to analyze, assess and forecast drought conditions in different areas as well as to assess the impacts of climate change on drought.