基于MODIS叶面积指数的大渡河流域作物生态需水研究

利用大渡河流域30年的气象资料，采用FAO最新修订的Penman Monteith方程计算流域参考作物腾发量。同时获取大渡河流域2007年内45期MODIS LAI数据，根据叶面积指数与作物系数的经验关系得到作物系数2007年年内的变化情况，利用GIS中的Zonalmean函数对大渡河流域平均作物生态需水量年内变化进行估算。在根据年干燥度进行干湿区划的基础上，对作物生态需水来源进行分析。结果表明：大渡河流域2007年内生态需水总量为6188 mm，月平均值为516 mm。其中作物生态需水量年内变化过程为夏季最高，占全年总需水量的357%，春季、秋季、冬季生态需水量逐渐减少分别占全年总量的304%、201%和138%。在雨季，降水完全可以满足流域生态需水量，降水是这一时期生态需水的主要来源。在旱季，半干旱区的生态需水来源受区域干燥度的影响较大，越干燥的地区降水占作物生态需水百分比就越高；半湿润区作物生态需水来源仍以降水为主，但降水占作物生态需水百分比除了受区域干燥度影响之外，可能还受到其它因素如：陡坡耕地占耕地总面积的比例的影响。

ECOLOGICAL CROP WATER REQUIREMENT IN DADU RIVER WATERSHED BASED ON MODIS LAI

The meteorological data of Dadu River Watershed of 30 years were used to calculate the reference evapotranspiration based on the newly revised FAO Penman Monteith equation.Forty five scenes of MODIS LAI in 2007 were acquired at the same time.Based on the empirical relation between LAI and crop coefficient，the variation of crop coefficient in 2007 was obtained.The GIS Zonal analysis was conducted to estimate the annual variation of watershed mean crop water requirement.The analysis of the variation in source of crop water requirement was conducted based on the climate division by annual aridity index.Results show that the annual watershed mean crop water requirement in 2007 was 618.8 mm with monthly average of 51.6 mm.The crop water requirement is monomodally distributed in 2007 with a peak in summer (from June to August) of 221.2 mm that accounted for 35.7% of the annual amount.The crop water requirement in spring (March to May)，autumn (September to November) and winter (December to February) accounted for 30.4%、20.1% and 13.8% of the annual amount respectively.In rainy season (May to October)，the precipitation completely meets crop water requirement in both semi humid and semi arid areas.In arid season，while crop water requirement was mainly supplied by precipitation in semi humid region，irrigation was the main source of crop water requirement in semi arid region.While only aridity index imposed great influence on the precipitation percentage in the total amount of crop water requirement in semi arid region，other factors such as topography may also plays important role in precipitation percentage of crop water requirement in semi humid region.