两种判断月干旱过程的方法在黄河流域的对比研究

利用黄河流域160个气象站1961-2010年逐日综合气象干旱指数(CI)指数, 对比分析两种用逐日CI指数判断月干旱过程的方法. 结果表明: 对重大干旱事件个例来说, 两种方法都能大体描述事件的月干旱过程, 但干旱的强度和范围有所不同. 从干旱发生的范围来看, 两种结果的差别较小, 方法I的识别结果范围更大、更连续, 特别是对青海旱情的判断常常比实际范围大;而方法II的识别结果范围稍小, 大体上能反应干旱的整体范围, 但有时也偶尔会遗漏小部分旱区;从干旱发生的强度来看, 方法I对干旱事实的描述偏轻, 而方法II以重-特旱为主, 与实际情况更相符. 从对黄河流域近50 a月干旱频率的分析结果来看, 两种方法一致表明黄河流域分界线以西的地区常年不容易发生干旱, 而对于分界线以东地区, 两种方法的统计结果有较大差异. 方法I的结果表明, 分界线以东地区干旱的月发生频率较大, 其中, 轻旱的月发生频率最大, 其次为中旱, 而重旱和特旱的发生频率很小;方法II的结果表明, 分界线以东地区干旱的月发生频率在60%~80%左右, 其中重旱的月发生频率最大, 其次为中旱, 轻旱和特旱的发生频率很小. 总体来说, 方法II对黄河流域月干旱情况的评估结果与干旱实际情况更一致.

Comparative Study of the Two Methods for Identifying Monthly Drought Process in the Yellow River Basin

Two methods for identifying monthly drought process are contrastively analyzed by using daily CI index of 160 stations in the Yellow River basin during 1961-2008. The results show that generally speaking, both methods can identify severe drought events in the basin in monthly time scale, but the identified intensity and range are not the same. Spatially, the first method can identify the severe drought events in a large scale;the whole identified drought area includes or even sometimes exceeds the real drought area. While, the second method can roughly identify the drought area, and usually miss some small part;As regards the drought intensity, the first method may identify the severe drought under weight, while the second way may identify the drought more consistent with the actual situation. In the middle-west part of in the Yellow River, we can draft a line of southwest-northeast direction for the boundary, the Yellow River basin is divided into two parts, the west of the boundary is including the regions of the northwestern Qinghai, middle-western Gansu, western Inner Mongolia, the east of the boundary is including the regions of the southeastern Qinghai, southeastern Gansu, eastern Inner Mongolia, Ningxia, Shaanxi, Shanxi, Henan and Shandong provinces. According to monthly drought frequency analysis, for the west regions of boundary of the Yellow River basin, there are less drought events, while for the east regions of boundary of the Yellow River basin, there are different results. According to the first method identifying, monthly drought frequency is larger in the west regions of boundary of the Yellow River basin, with frequent light drought and low frequency of extreme severe drought. According to the second method identifying, monthly drought frequency is not so large in the east regions of boundary of the Yellow River basin, about 60%~80%.The second method is recommended to use. By this method, severe drought frequency is the first, followed by medium drought.