白银市作物生长期降水变化的稳定性分析

利用甘肃白银市4站1957年-2005年49a的降水资料，通过计算方差、变差系数、皮尔森Ⅲ型分布拟合降水保证率、小波分析等方法分析了4～10月降水的空间分布特征和时间变化规律．结果表明：（1）白银市4～10月降水量从北向南增加．南部降水量是北部各县的2倍左右．（2）4～10月降水量的平均年际变化在50～100mm之间，全市大多数地方年际变化在50～60mm之间；（3）4～10月降水量的相对变化在30％以内，靖远、会宁两县比景泰、白银两县降水量稳定；（4）在75％的概率保证下，北部各县的降水在150～180mm之间，南部至少为315mm，除几个较大的干旱年，大多数年份各县的降水偏少量不低于20％，即在正常年景以上；（5）南部降水量显著减少，市北部则变化不大．全市5a左右的年际周期比较明显．

An Analysis of the Stability of Precipitations in the Period of Plant Growth in Baiyin Area

By using the precipitation data of 4 observational stations in the period from 1957 to 2005 in Baiyin area, the spatial features and time evolution rule of precipitation for 49 years were analyzed. By calculating the variance, the coefficient of variation, Pearson Ⅲ distribution and wavelet analytic method, the spatial distribution and the time variation of precipitation from April to October were analyzed. The results indicated. （1） Baiyin＇s precipitation from April to October was increasing from north to south. The precipitation of the south was about two times as much as that of the north. （2）The average annual change of precipitation during the period varied between 50 and 100 mm , and most of the area changed in 50-60 mm; （3）The relative change rate of Baiyin＇s precipitation during this time was less than 30% ,and the precipitation of Jingyuan and Huining was stabler than that of Jingtai and Baiyin; （4） With a probabilits of 75%, the precipitation of every county in the north was in 150-180 mm ,and that of the south was more than 315 mm. For most of the year, every eounties＇s precipitation was scarce but it was not less than 20%, namely enough for the normal year＇s harvest. （5） The precipitation in the south of the city reduced remarkably, while in the north it did not change obviously. About five year＇s interannual cycle of the whole city was obvious.