北京市是我国以地下水为主要供水水源的大城市之一。本区属于干旱、半干旱气候区,多年平均降雨量为635毫米,丰水年份雨量最大可达1000毫米以上,枯水年份小于400毫米,多集中在七、八月份。雨量差异很大,分配极不均匀。雨量的多寡直接控制着北京地下水的丰富程度,遇到干旱年份城市供水就很紧张。从长远看,必须采取积极措施。我们分析了国内 Beijing is one of the big cities where groundwater is the main water supply source in China. This area belongs to the arid and semi-arid climatic zone. The average annual rainfall is 635 millimeters. The maximum rainfall in wet years is more than 1000 millimeters and the dry years is less than 400 millimeters, mostly concentrated in July and August. The amount of rainfall varies widely and the distribution is extremely uneven. The amount of rainfall directly controls the abundance of groundwater in Beijing and is very tense in urban water supply in drought years. In the long run, we must take positive measures. We analyzed the domestic