干旱是陕北农业生产的主要灾害。据历史资料记载,自明代洪武元年至今(1368年至1975年)共607年,陕北地区共发生旱年247个,其中大旱年,即一个旱期的最高峰,共发生56次。旱期和大旱年的出现,往往是连续二年以上范围比较广的干旱,对农业生产的危害性最大。本区多年平均降雨量是500—600毫米,年际降雨不均。以延安为例,自1952年至 Drought is the major disaster of agricultural production in northern Shaanxi. According to historical records, a total of 247 dry years occurred in northern Shaanxi since the first year of Hongwu from the first year of the Ming Dynasty (1368-1975). In the great dry year, the highest peak in a dry season, a total of 56 times occurred. The emergence of dry seasons and drought years are often the more extensive droughts over two consecutive years, with the greatest danger to agricultural production. The average annual rainfall in this area is 500-600 mm with uneven rainfall on an annual basis. Take Yanan for example, since 1952