我国长江中下游地区降水变化趋势分析

Trends of Precipitation Variations in the Mid-Lower Yangtze River Valley of China

利用1951-2001年10个代表站的逐日降水观测资料,运用线性趋势法分析了51年来长江中下游地区年和季的降水量、降水日数和降水强度的变化趋势,用Mann_Kendall法对降水日数和降水强度的突变进行了检验,并对日降水量分级别讨论了各等级对总降水量贡献的变化趋势.分析表明:(1)该区域年降水量变化趋势不明显,但春季和夏季降水量分别有显著减少和增加的趋势;(2)除夏季外,其余各季和年的降水日数均为显著减少,且年降水日数减少的突变发生在1977-1978年之间;(3)由于年降水量的微弱增加和年降水日数的显著减少,导致年降水强度的显著增加,且年降水强度的突变发生在20世纪80年代中期;(4)年降水强度增加主要是由于暴雨(日降水量≥50.0 mm)对降水总量贡献的增加,而暴雨对降水总量贡献的增加又是由于其对降水日数贡献的增加,因为暴雨本身强度的变化趋势不显著.

Based on the daily precipitation records of 10 selected stations over 1951 - 2001 period, the climatic variations, tendencies of yearly and seasonal precipitation amount, precipitation days and precipitation intensity in Mid- Lower Yangtze River valley during last 51 years are investigated with least square linear fitting method. The climate jumps of precipitation days and precipitation intensity are also examined by the non-parametric Mann-Kendall test. Furthermore, we calculate the trends of proportion of daily precipitation falling in six precipitation class intervals in each season and in a year compared with the corresponding total precipitation. The primary results are as follows. （1）The trend for precipitation amount in spring and summer is significantly negative and positive, respectively, while obvious trend for annual precipitation amount is not found. （2）It also provides evidence that in the studied area, the number of rainy days has a strong and significant negative trend both on a yearly basis and in all of the seasons except summer. And there is a climate jump of annual precipitation days between 1977 and 1978. （3）As a consequence, annual precipitation intensity has a very strong positive trend. However, abrupt change of annual precipitation intensity occurred in the middle of 1980s. （4）The increase in annual precipitation intensity is due to a positive trend in the proportion of total precipitationcontributed by heavy precipitation events （daily precipitation≥50.0 mm）, while this positive tendency of proportion is a result of increase in the proportion of precipitation days by heavy rainfall events by reason that trend in intensity of the heavy rainfall event itself is not evident.