用Palmer湿润指数作西北地区东部冬小麦旱涝评估

根据Palmer气象干旱指数 (PDSI) 的中间量Palmer湿润指数原理, 计算了西北地区东部冬小麦农气观测站延安、咸阳等多个站点1961—2000年逐月Palmer湿润指数, 对各站点的冬小麦不同发育期的旱涝情况做了初步的验证和应用。Palmer湿润指数与Z指数对比结果表明:Palmer湿润指数对农作物旱情分析更具有客观性, 分析结果更符合实际情况, 因而可以作为我国西北地区东部农作物旱涝的评估工具。

Evaluating Aridity and Wetness of the Wheat with Palmer Moisture Anomaly Index in the East of Northwest China

Considering the lack of agriculture drought index in China, Palmer moisture anomaly index is introduced. Taking example for Yan'an, theoretical formula and physical meaning of Palmer moisture anomaly index is described. Using the method, the monthly Palmer moisture anomaly indexes of twenty wheat observation stations, such as Yan'an, Wuwei, Jingtai, Xining, Guide, Lanzhou etc, from 1961 to 2000 are calculated in the east of Northwest China, and the aridity and wetness of different period of growth for wheat are evaluated. The calculation of Palmer moisture anomaly index values is based on a supply and demand model of the soil moisture at a location. In addition to the current precipitation, air temperature, available water holding capacity (C_WA), some factors derived from water balance equation are considered such as potential evapotranspiration, potential recharge, potential runoff, potential loss, surface soil moisture content, and underlying soil moisture content. Factors of several previous months are based on to establish each Palmer moisture anomaly index value. It shows that the method of Palmer moisture anomaly index is more reasonable to study the flood or drought of different period of wheat growth in the east of Northwest China. The extent of drought and flood event of different periods of wheat growth can't be objectively assessed by Z-index. The difference of years with same precipitation and different temperature and C_WA can't be distinguished. Palmer moisture anomaly index in comparison with others is a good indication of the severity and extent of flood/drought event and of more objective classification of them, which is therefore quite applicable to an extended area. All these show that Palmer moisture anomaly index is more objective than Z-index for analysis on aridity and wetness in different period of wheat growth, and more accords with the results of analysis on aridity and wetness of the wheat in different period of growth. Analysis shows that Palmer moisture anomaly index can be the analysis tool of agriculture aridity and wetness in semiarid and semi-wetness regions in the east of Northwest China.