Abstract:Based on the Weighted Average Precipitation (WAP), an improvement study on drought index was carried out in two aspects. After determining the two parameters of the WAP index and removing regional and seasonal differences, an improved WAP drought index named IWAP index was developed. Then, comparison analysis between IWAP index and Ci index was done. The results show that: IWAP index has a good correlation with Ci index in most of China especially in mid eastern China with correlation coefficients above 0.7 in most of Central China, most of Guizhou, southern Yunnan and southern Xinjiang. In identifying regional meteorological drought events, IWAP index also shows good consistency with Ci index on beginning time, ending time, impacted area and drought center. Further comparison of IWAP index, Ci index and anomaly percentage Pa index on drought processes for individual station shows that IWAP index is consistent with Ci index on beginning time while Pa index generally shows a delayed beginning time. However, the three indices all show good consistency on ending time. In addition, IWAP index shows a stable ability during a drought process while Ci index and Pa index tend to show unreasonable instability due to their algorithms. IWAP index also has some limitations, unsuitable to be applied in most of the Tibet Plateau and the regions with annual average precipitation less than 300 mm. IWAP index can be calculated in simple way and has clear physical meanings. Considering the nature that the index is only based on precipitation, IWAP index is not only convenient for meteorological operation, but also has obvious potential advantages in drought simulation and prediction in the case of limited output elements from current available climate models.