An improvement of the dual - source model based on penman - monteith formula 公式的双源模型的改进
2.
Acceding to the theory of crop water requirement , maximum potential evapotranspirations are calculated by applying fao penman - monteith method , and then we obtain the water requirement , water balance and water correction factors ect . of main crops ( spring maize , summer maize , spring wheat , winter wheat , cotton ) and different type grasslands , and the space - time distribution regularities of water requirement of cropland and natural grassland are analysed , the result show : the water requirements of same kind crop in different areas are different , water satified degrees are different to different crops in the same area , and water requirement of same crop are different between years for climatic variation ; the water requirements of main crops are increasing from east to west and from south to north , water satified degrees are decreasing from east to west and from south to north . in growing season , there are deficits in crops water supply in most area , so the irrigation is needed to meet the requirement for crop growing normally 根据作物需水的理论和方法，采用计算精度较高的faopenman - monteith方法( 1998 )计算了半干旱区最大可能蒸散，并基于此计算五种主要旱地作物(春玉米、夏玉米、春小麦、冬小麦、棉花)和不同类型的天然草地的需水量、水分盈亏、水分订正系数等，分析了农田和天然草地水分供需的时空分布规律，结果表明：不同地区同一种作物的需水量是不同的，同一地区对不同作物的水分满足程度是不同的，而且同一种作物在同一地区随着气候的变化需水量也会有一个年际变化；主要作物需水量由东向西，由南向北递增，正常生长发育的水分保证程度由东向西，由南向北递减。
3.
On the base of the palmer drought severity model of america and the modificated palmer drought severity model ( 1986 ) , we further modificate the palmer drought severity model in the following aspects ; ? 4 stations were chosen to develope the model and adjust the weighting factor ; ? he potential evapotranspiration for an each month was computed by the penman - monteith equation commended by fao ; ( 3 ) the getting of available water capacity of the soil ( awc ) in each station was based on the data of awc that we can find and the characteristic of soil in each station 在美国帕默尔旱度模式和我国1985年修正的帕默尔旱度模式的基础上，针对其中存在的问题，从建模选用较多站点、可能蒸散计算采用彭曼?蒙特斯公式和土壤田间有效持水量进一步准确划分等三个方面进一步修正了帕默尔旱度模式。
4.
In the fourth part , the field irrigated water requirement were gotten based on the recommended irrigation schedules and irrigated areas often crops . in this paper , the reference evapotranspition et0 in three counties in bid was computed by penman - monteith method and the crop coefficients , kc of ten crops by kcisa model and the crop water requirements , etc , were computed simply by kc et0 . meanwhile , four representative years by frequency analysis are gotten according to net irrigation requirements and planted areas of different crops in bojili irrigation district 本文首先采用fao最新推荐的penman - monteith方法计算灌区的参照腾发量et _ 0 ，用kcisa按照fao的计算方法推求十种作物的作物系数k _ c ；由此基础上计算出作物需水量et _ c ，根据结果分析了不同作物的需水规律；同时用作物缺水量nir (净灌溉需水量)进行频率计算，求出了灌区的四个代表年，并分析了代表年年内自然水分状况和作物缺水规律。
