The assessment of droughts in Northern China and Mongolian areas using PDSI and relevant large-scale environments

This study assessed drought conditions in northern China and Mongolian areas using the Palmer drought severity index (PDSI). Droughts in this area were intensified throughout all seasons. In particular, this intensifying trend was pronounced in the summer and autumn. In the summer, the PDSI showed an overall increase from the early 1990s to the late 1990s, and then, it rapidly decreased after the late 1990s. Therefore, this study focused on summer droughts and analysed mean differences before the late 1990s (9098) and after the late 1990s (9905). Regarding differences in 850 hPa stream flows between the two periods, anomalous anticyclonic circulations were strengthened in northern China andMongolia that showed strong negative anomalies in the PDSI. These anomalous anticyclones were formed as a positive North Atlantic Oscillation pattern formed in the European region spread eastward in the form of wave trains. The anomalous anticyclones formed in northern China and Mongolia led to reduced total cloud cover. As a result, this region exhibited high sensible heat net fluxes. Consequently, warm and dry anticyclones may have recently been strengthened in this region, thereby intensifying droughts. As this shows, recently strengthened warm and dry anticyclones in northern China andMongolia were associated with recently reduced snow depths in this region during the preceding spring. In recent years, the frequency of Asian dust has also increased due to warm and dry air conditions.