中国西北夏季干旱指数研究

Drought Index in Summer Season of Northwest China

根据中国西北5省（区）1960年～2004年125个台站夏季（6月～8月）无雨日数同降水量呈显著负相关的特点,定义了比较合适的干旱指数,并通过该干旱指数分析了中国西北夏季干旱的时空分布特征,结果表明：新疆西南部和青海西南部同其它地方呈反向变化及高原东部同其它地方呈反向变化特征是中国西北夏季干旱指数场的2个最主要的空间模态;中国西北夏季干旱指数场可分为以下5个次区域空间模态：高原东部型、河西走廊型、北疆型、南疆型及西北东部型;在中国西北夏季干旱指数的5个次区域空间模态中,高原东部型近45年来干旱指数表现为一致的增大趋势,南疆型45年来干旱指数表现为一致的减小趋势,而北疆型、西北东部型和河西走廊型干旱指数变化趋势以1982年为转折点,其前后呈相反变化趋势;在中国西北夏季干旱指数场的5个次区域空间模态中,近45年来主要以13年～15年和8年～11年的周期振荡为主,另外部分模态还存在4年～5年的高频振荡周期.

Based on the data from 125 stations during the periods of 1960-2004 in the Northwestern China, the number of rainless day and the total precipitation in summer season from June to August were calculated and found that there is a significantly negative correlation between the number of rainless day and the Precipitation. On the basis of the fact mentioned above, the drought index was defined and the spatial and temporal distribution of drought occurrence was analyzed through the drought index. The results show that the changing trend of drought index in Southern Part of Xinjiang and Southwest Part of Qinghain are reverse compared with other areas, which are two major features of spatial distribution of summer drought index in Northwestern China. According to summer drought index Northwestern China can be classified into five sub-regions： the Eastern Qinghai Plateau, the Hexi corridor, the North Area of Xinjiang, the South Area of Xinjiang and the East Area of Northwest China. Of which, spatial distribution of summer drought index in Eastern Qinghai Plateau over the last 45 years presents continuous increasing tendency and in the South Area of Xinjiang summer drought index during past 45 years presents constant declining tendency; while in the North Area of Xinjiang and the East Area of Northwest China as well the Hexi corridor the changing tendency of summer drought index are reverse with time series before and after 1982. In all five sub-regions, spatial distribution of summer drought index over the past 45 years presents remarkable vibrating change and high frequency vibrating change.