白银市近48 a地表干湿状况及变干趋势

利用1958~2005年48 a白银市4个站的月降水量、月平均气温和相对湿度资料,计算了各站历年的湿润度指数,并利用湿润度指数对地表干湿状况进行分析。结果表明,白银市地表状况整体上反映出明显的干旱特征。在此背景下,不仅呈现“北干南湿”地域分布上的差异性,而且在干湿交替中出现了景泰、白银、靖远偏北地方有8~10 a的年代际准周期变化,偏南地方有3~5 a的年际准周期变化,并在年际变化中呈缓慢变干趋势,这种状况可能是由于降水量减少和气温升高直接造成的。

Surface Dryness/Wetness State and Its Tendency in Baiyin City for Recent 48 Years

Based on monthly precipitation,monthly mean temperature and relative humidity of four meteorological stations in Baiyin city from 1958 to 2005,the yearly surface wetness index was calculated.The results show that the surface condition of Baiyin presented visible arid characteristic on the whole,under this background,there was not only difference in local distribution of "dry in the north and wet in the south" but also presented a quasi-periodical variation of 8-10 years in some northern localities such as Jingtai,Baiyin and Jingyuan,and 3 to 5 years quasi-periodical variation in some southern localities.The trend of turning drier slowly in interannual variation was presented,and it might result directly from precipitation decrease and temperature increase these years.