Modification of Palmer Drought Severity Model Based on Improving Water Loss Pattern and Increasing Sample Stations

After the modification of Palmer Drought Severity Model in 2003, it is found that the soil water loss pattern needs to be improved according to the actual soil water loss process. Also, in order to apply the Palmer Drought Severity Model more practical and more suitable in most arid and semi arid regions in north parts of China, Palmer Drought Severity Model is once again modified from the aspect of optimizing the soil water loss pattern and increasing the sample numbers of modeling stations.From the aspect of soil water loss pattern, in consideration that in most arid and semi arid regions in north parts of China, evapotranspiration will stop when soil water content in 0—20 cm layer is about 5% of available water consumption (C_aw). Thus in the soil water loss pattern in modeling Palmer Drought Severity, it is supposed that the soil water loss in upper soil layer will be no less than 5% of C_aw.Besides Jinan, Zhengzhou, and Taiyuan stations, Qiqihaer station in Heilongjiang Province and Haiyuan station in Ningxia Province are selected and added to the modeling process. Totally 25 stations in north parts of China are used to modify the weight factors (4 new selected stations, in addition to 21 stations in modeling in 2003). The drought index calculated by latest modified Palmer Drought Severity Model is compared with that modified in 2003 and the actual drought and wetting records in history. The result indicates that the latest modified Palmer Drought Severity Model can better evaluate the drought and wetting situations, especially in de scribing the extreme drought and extreme wet development processes, and can be better applied in most arid and semi arid regions in north parts of China.