Studies On Main Crops' Evapotranspiration In Hexi Corridor Based On The SIMETAW Model

Evapotranspiration is the uppermost water consumption in farmland, and accurate estimation of crop evapotranspiration is a primary base to improve the efficiency of agricultural water-use and plays an important role to the scientific management of water resources. In this study, we have measured the crop evapotranspiration and crop coefficient of three main crops (spring wheat,spring maize,potato) in farmland located at Zhangye county of Hexi corridor. The crop evapotranspiration model, SIMETAW or Simulation of Evapotranspiration of Applied Water developed by the University of California, was validated and calibrated by the measured data, and the historic analysis on evapotranspiration and irrigation for the main crops in Hexi corridor were analyzed based on the modified-model. The main research results listed as follows:(1) Field experimental results at Zhangye county showed that the crop evapotranspiration (ETc)of spring wheat, spring maize and potato were about 470 mm, 600 mm and 480 mm, with the average crop coefficient (Kc)of 0.71, 0.82 and 0.66, respectively, during the crop growth season.(2)The validation of the SIMETAW model showed that the model have good performances in simulating the changes in evapotranspiration of main crops in Zhangye county, especially for the total evapotranspiration at crop growth stage. The relative errors of ETc between simulated and measured value were 1.46% for spring wheat, 2.33% for spring maize, and 10.85% for potato, respectively.(3)The simulated reference crop evapotranspiration (ET0) by the SIMETAW model with the climate data from 1960 to 2006 showed that, the difference of ET0 between different subregions of Hexi corridor demonstrated significant discrepancy. The ET0 in western region showed highly significant downward trend, while significant upward trend in southern region due to the discrepancy of climate in different regions. The main influential factors on ET0 were the annual average wind speed for western region, and the annual radiation for the central and southern regions.(4)The evapotranspiration (ETc) and irrigation water demand (ETaw) of different crops (spring wheat, spring maize and potato) both showed a highly obvious downward trend in western of Hexi corridor, while there were no obvious changes for the central and southern regions during 1960 to 2006. The ETc and ETaw of the same crop were gradually decreased from the west to the south in Hexi corridor, there were great differences both in ETc and ETaw in different subregions.Monthly simulation of ETc and ETaw for many years indicated that, the water-sensitive period for spring wheat were on April and June, the averaged subtotal ETc was about 170 ~ 190 mm. The key period of water demand for spring maize was on July, averaged subtotal ETc ranged from 200 to 220 mm. The largest monthly evapotranspitation period was on July for potato, ranged from 180mm to 200mm. The irrigation supplement at the key period of water demand for crops were all more than 85% of the total ETc in different subregions.(5)The total sown areas of the three crops in the eleven countries in Hexi Corridor showed a significant decreasing trend in past 27 years from 1980 to 2006, but there were no obvious changes on the total water consumption and irrigation water requirement in this period of time. Because the wheat sown area decreased extremely, the total water consumption reduced 609 million m3, and the water demand for wheat irrigation reduced 535 million m3. However, the maize sown area showed highly increasing trend, so its water consumption and irrigation water demand increased by 345 and 277 million m3, respectively. The sown area of potato were kept stable, but its water consumption and irrigation water demand still have an increasing of 43 and 35 million m3, respectively.(6)The crop sown area, water consumption and irrigation water in Hexi corridor showed great discrepancy in different regions. Of which, Wuwei district had the largest amounts in crop sown area, water consumption and irrigation water demand, and the water consumption and irrigation were both increased significantly year by year. While the amounts were relatively smaller in Dunhuang, Anxi, Yumen, Jinta, Gaotai and Jinchang districts, and which had significant decreasing trends. No obvious changes were found in other regions.