宁夏降水变化及其与ENSO事件的关系

分析1959~2001年的月降水数据发现:20世纪60~80年代宁夏降水有较明显的干旱趋势,但90年代降水较80年代有所增加。功率谱分析表明,ENSO和宁夏降水具有一致的变化周期,即14年、3.75年、准2年和1.5年。宁夏降水对EL Nino事件达到最显著响应需要滞后2~4个月,而对LA Nina事件的响应比对EL Nina迅速,只需滞后1~2个月便达到最显著响应。ENSO对宁夏不同季节降水的影响差异很大。EL Nino发生4个月后,春、夏、秋三个季节降水都偏少,但冬季降水却是增加了。LA Nina发生1个月后,夏、秋、冬三个季节降水都偏多,但春季降水减少了。EL Nino事件发生期间,宁夏年降水偏少28 mm,占常年降水量的10%,而LA Nina发生期间,年降水偏多24 mm,占年降水量9%。

Character of Precipitation in Ningxia and Its Response to ENSO

According to the monthly precipitation data during 1959-2001, we find the drought trend was obvious from the 1960s to the 1980s, and more precipitation was observed in the 1990s than in the 1980s. Power spectrum analysis shows that there exist three obviously simultaneous periods between precipitation in Ningxia and ENSO: 14 years, 3.75 years, approximately 2 years and 1.5 years. Precipitation in Ningxia responds quicker to La Nina than to El Nino, the lag time of the former is 1-2 months while the latter is 2-4 months. The impact that ENSO imposes on the seasonal precipitation varies tremendously. Four months later after the El Nino event, the precipitation decreases in spring, summer and autumn except a winter's increase. One month later after the La Nina event, the precipitation experienced a large increase in summer, autumn and winter except a spring's decrease. During the period of El Nino event the precipitation in Ningxia shows a 28mm decrement, whose proportion to the perennial year is 10?. However, during the period of El Nino event the precipitation in Ningxia has a 24-mm increment, which accounts for 9%.