利用最近50年气象站观测的降水量以及根据史料和树轮重建的近400年来的降水量,根据回归分析和合成分析研究了黄河流域降水与全球气温变化的关系及其可能成因。结果表明,全球平均气温偏高(低)与黄河中游地区年降水量偏少(多)存在一定的对应关系。夏末秋初的8～9月是决定全年降水变化的关键时期,全球气候变暖会引起8～9月西太平洋副热带高压增强、扩大,从而有利于东亚夏季风锋面位置北移,进而使东亚夏季风北界南侧黄河中游一带的降水减少。

Using the recent 50-year precipitation data observed at weather stations and nearly-400-year precipitation data reconstructed with historical documents and tree rings in the Yellow River valley, the relationship between variations of the precipitation and global average temperature was examined by regression and composite analyses. The results show that the higher (lower) global average temperature corresponds to the less(more)-than-normal precipitation in the middle reaches of the Yellow River to a certain degree on different time scales. When the global mean air temperature increases by 1℃, the annual precipitation is found to decrease more than 20% over the middle reaches of the Yellow River from Shaanxi to Shanxi provinces. The difference between the annual precipitation averaged for the warmest three years and that for the coldest three years can reach 40% in the study area in last 50 years. However, the annual precipitation near the area of China-Mongolia boundary is decreased with the global warming. Our result from the observational study is consistent with that obtained from climate models under conditions of the atmospheric CO₂ doubling and the global climate warming. The present result also shows that August-September, late summer-early autumn, is a key period which determines inter-annual variations of annual precipitation in the middle reaches of the Yellow River. The variation of August-September precipitation contributes more than 50% variance of inter-annual variability of annual precipitation in this area. Moreover, it is found that there is a close relationship between the rainfall anomaly and activity of the subtropical West Pacific High in August and September. A warmer global climate may intensify and enlarge the subtropical West Pacific High, thus induce the front of East Asian summer monsoon to move northwards and to act frequently there, and eventually bring about the decreased rainfall in the south side of north boundary of the East Asian summer monsoon. The situation will be opposite when the global climate becomes colder. This study suggests that we should pay great attention to the dryness induced by the global warming over the Yellow River valley.