华北农牧交错带夏季降水有很大的变率 ,频繁的干旱对农牧业生产有严重影响。论文分析了1880年以来的夏季降水变化特征 ,近百年来农牧交错带夏季降水有明显的阶段性。功率谱分析显示有35年左右的周期。年代际尺度的波动是干湿变化的重要背景。以250mm等雨量线表示的农牧交错带南北位置也有明显的年际和年代际的变化 ,在1978年以前和以后的两段时期 ,平均位置有显著的差别 ,前后平均有大约1.5个纬度的变化。农牧交错带夏季降水与前期春季亚欧地区大范围的温度异常有较好的关系。印度和巴基斯坦及相邻印度洋地区是显著的正相关区 ;亚洲西部的内陆地区是显著的负相关区。这两个地区春季的温度能解释农牧交错带夏季降水方差的15 %左右。

The high variability of summer rainfall over northern China has great impacts on environmental and socio economic system.In this manuscript,the decadal variability is analyzed.Power spectral analysis indicates a 35 yr period dominated by low frequent variations exists.The locations of 250 mm isohyet also show great annual variations and dramatic decadal changes.The averaged latitudinal location before and after 1978 changed about 1.5 degrees.The relationship between summer rainfall over northern China and spring surface temperature over vast expanse is investigated.There are two regions found connecting to summer rainfall significantly,one is India,Pakistan and their adjacent ocean sectors where positive correlation occurs,and the other is over inner continent in central and West Asia where negative relationships exist.The spring temperature of these two regions can explain 15% of the difference in summer rainfall in northern China.