The researchers analyzed long-term precipitation trends in the Beijing region from 1961 to 2004. They found that overall, annual precipitation is decreasing at a rate of 1.72 mm per year, mainly due to less rain in summer and winter. However, spring and autumn are getting slightly wetter. The rainy season from June to August accounts for 72.5% of yearly rainfall. Precipitation is highest in the piedmont windward slopes, decreasing towards the northwest and southeast. Urban areas, like Haidian District, are experiencing a significant decrease in precipitation.