甘肃河东旱作区不同强度日降水特征

利用1971~2007年甘肃河东旱作区分布较为均匀的13个气象站(兼有农业气象试验观测)共37年的逐日降水量资料,按照Bonsal边缘分布函数方法将日降水量划分为弱、较弱、中等、较强和强5个不同强度等级,从而分析了各强度等级的降水量和降水日数在旱作区的时空分布特征及变化趋势。结果表明:旱作区平均降水日数与降水量的分布不一致,平均年降水日数最多(少)的地方并不对应年降水量最大(小)的地方。各站不同强度等级的降水日数均表现为弱降水日数最多,强降水日数最少。弱降水日数的分布决定了平均总的降水日数的分布;而强降水日数的变化,对降水量的变化起到了决定性的作用。降水量的变化趋势较之降水日数的变化趋势要复杂得多,旱作区中各站降水日数变化趋势的一致性强,而降水量变化的区域性特征却比较明显。较之其它等级的降水,旱作区强降水的年际变化剧烈,各年强降水的日数和降水量都有很大的不确定性变化。

Characteristics of daily precipitation with different intensity in the rain-fed area east of the Yellow River of Gansu province

According to the Bonsal marginal distribution function, daily precipitation data from 1971~2007 are used and divided into five grades of intensity, i.e., weak, relatively weak, medium, relatively heavy and heavy. These data are from 13 meteorological stations (with agricultural weather experiment observation also) over the rain-fed area east of the Yellow River in Gansu province. The temporal-spatial distribution and tendency characteristics of various gTades of precipitation are analyzed. The results show that the distnbution of average precipitation days and amount of precipitation are different . The area with the most (least) precipitation days is not the corresponding area along with the highest (low-est) amount of precipitation. The precipitation days of diverse grades of intensity have the most days in weak grade and the least days in heavy grade . The precipitation days of weak grade detemine the average precipitation days . The precip-itation days of heavy grade has the main contribution to the amount of precipitation . The tendency of amount of precipita-tion is more complicated than that of precipitation days. The tendency of precipitation days has the same characteristics in different regions in the study area, but the tendency of amount of precipitation has obvious regional features. The heavy grade precipitation has more intense inter- annual change and greater uncertainty characteristics than those of other intensi-ty grades.