Preliminary Examination Tests Of The Reference Crops Evapotranspiration Quantity (ET₀) And The Pesponse Analysis Research Of The Input Factor

Abstract*2 The reference crops evapotranspiration quantity (ET0) is the international general foundation of appraising water resource and calculating crop water requirement, and also the basis of formulating water law and allocating international river water resource. The calculation of ET0 value and research at present has entered the stage of standardization and universality. Since in Chian lacks ET0 experimental research, the calculation of ET0 in China at present only purely pauses in using modified Penman(MP) and Penman-Motheith(PM) method which are recommended by Food and Agricultural Organization of the United Nations(FAO) as the ways of calculation or comparability which caused a lot of uncertainties on the worth of ET0. As a result, the basic research of ET0 in China became the weak link during introduction. this article analyzes on the basis of overseas ET0 the newest research processes, with Chinese semi-arid area-Yangling(humid) and reference crop(alfalfa) implementing ET0 experimental calibration and its related application of basically experimental research in 2005 as well as Chinese semi-arid area—Huhhot(arid), in 1961-2003,43 years long-term meteorological data as the foundation of ET0 input factor response analysis research. Some conclusions have been drawn bellow:This paper systematically transferred advanced accomplishment abroad; analyzed the adaptability of the ET0 calculation on Yangling semi-arid district according to artificial weight-measure lysimeter experiment, and quoted newest ET0 for the first time in the experimental rating which American engineer the association - environment and the water resources organization(ASCE—EWRI)(2005) recommended formula - standard ASCE-PM and other formulas, confirmed in Yangling semi-arid climate condition : With day as steps, ASCE-PM standardized method is better than PM; PM method is better than other representative methods; discussed the application condition with hour as steps; made better digestion and filled the research blank in China in this aspect.Reference crop (alfalfa) surface resistance was deeply rating researched for the first time according to the set condition of PM and ASCE-PM standardized method, promulgated the change value of the reference crops surface resistance in the entire period of duration. Pointing out that the experiment condition and result during mid-term growth period are more near reference crop ET0 value set condition abroad(70/m);rc value of growth has greater discrepancy with sets value during early stage and later stage. The major factor that affects surface resistance is ET0 value and aerodynamic resistance ra. This result also confirms the calculation result using new RC approaches actual measured value.The paper made briefly demonstration on MP, PM and ASCE-PM standardized method; pointed out that the theoretical foundations of the three methods were based on the identical kind of principle: Energy balance and steam proliferation principle, only strictly using conditions and the consideration factor have difference. The main set parameters of...