基于包气带水分运移数值模型的黄河三角洲蒸发量研究

Evapotranspiration from modeling of soil water flow in the Yellow River Delta

蒸发是重要的水循环过程，在野外试验和室内分析的基础上，建立了黄河三角洲地下水浅埋区观测试验场土壤水分运移数值模拟模型，模型中对上边界条件处理采用了考虑气象因素、地表覆盖条件和表层土壤含水量的Penman-Wilson公式。利用模型对试验点1999年、2000年、2002年的蒸发量进行了数值模拟计算，计算并分析了裸地、棉花地、芦苇地不同地表植被条件下，地表蒸发量(包括棵间裸地蒸发量和植物蒸腾量)的变化规律。从时间上看，黄河三角洲7、8月是蒸发量较高的时期，1、2月是蒸发量最低时期，一般日蒸发量在0～8mm／d。影响地面蒸发的主要因素除气象因素外，还有植被类型和覆盖程度、地下水位埋深等因素。植被覆盖程度越高、地下水位埋深越浅，则蒸发量越大，从而导致裸地蒸发量相对较小，农田年蒸发量稍大，而芦苇地蒸发量最大。研究表明，土壤水分运移模型是估算各种复杂条件下蒸发量的有效工具。

Evapotranspiration (EPT) is one of the most important water cycle processes. On the basis of field tests in the Yellow River Delta where the groundwater is shallow, and laboratory experiments, a numerical modelling of soil water flow has been carried out. The influence of weather, land cover and soil moisture are integrated in the model. For three land cover conditions, including bare land with no vegetation, cotton growing land and reedy land, the numerical model was used for EPT simulation for 1999, 2000 and 2002. The results indicate that for these years the EPT is maximal in July and August and minimal in January and February. In general, the quantity of EPT is between 0 mm and 8 mm per day. Besides meteorological conditions, the main factors of affecting the EPT are the vegetation type and cover rate, and the groundwater depth. Higher rates of vegetation cover and the shallower the groundwater, the larger EPT. Therefore, the quantity of EPT is relatively low in bare land, relatively high in farmland and highest in reedy land. This study shows that the model of soil water flow is an effective tool to estimate EPT in complex conditions.