Impacts Of Environment Change On Agricultural Water Consumption In Shiyang River Basin In Arid Region Of Northwest China

The Shiyang River Basin is one of the three largest inland river basins in the Hexi Corridor of Northwest China, with the rapid development of local industry and agriculture, water demand increases dramatically, and contradiction of water supply and demand becomes more and more severe. This research analyzed the complex impacts of environment (climate, topography, vegetation and irrigation agriculture development) change on the regional agricultural water consumption, and explored the variation of temporal and spatial distribution of agricultural water consumption on the basin scale, which is conducive to establish water resources development planning of the basin, and determine reasonable scale of agriculture and faming system in oasis. Through the present research, the following main results were obtained:(1) The linear regression analysis of reference crop evapotranspiration (ET0) showed that, significant decreasing trend was found at Liangzhou in recent 50 years, while significant and highly significant increasing trend was found respectively at Gulang and Tianzhu, and the trend was not significant at other stations. The Mann-Kendall test obtained the similar results with the liner regression analysis. The non-parameter Pettitt test for change-point of annual mean ET0 showed that, the change-point of the ET0 happened in 1962 at Liangzhou, in 1989 and 1996 at Tianzhu, while no change-point happened at other stations. The correlation analysis of ET0 and meteorological parameters showed that, the leading influential factors on ET0 were the annual average relative humidity (RH) at Minqin, Yongchang, Gulang and Menyuan, the annual sunshine duration (n) at Shandan, the annual average wind speed (u2) at Liangzhou, and the annual average maximum temperature (Tmax) at Tianzhu respectively.(2) The evapotranspiration of different crops (ETc) showed a highly significant decreasing trend at Liangzhou in recent 50 years, while a significant increasing trend at Tianzhu. The ETc of spring wheat and sesame showed a significant decreasing trend at Shandan, while no significant trend was found at other stations.(3) Using the scale-transfer function which is set up from elevation (H), aspect (A) and latitude (V) which derived from digital elevation model (DEM), the spatial distribution model of ETc and net irrigation water requirement (I) of different crops in the basin were obtained through GIS softwares, based on the DEM and land use map. The spatial distribution of ETc and I showed an increasing trend from southwest to northeast, from mountainous area to oasis. The ETc and I of spring wheat is largest at Minqin, while that of cotton is least at Tianzhu.(4) The total agricultural water consumption and total net irrigation water requirement of the basin showed a highly significant increasing trend in recent 50 years, of which, 0.576 billion m3 up for the total agricultural water consumption, and 0.297 billion m3 up for the total net irrigation water requirement. In 2003, the total agricultural water consumption is 1.761 billion m3, and total net irrigation water requirement is 1.303 billion m3. The percentage of total net irrigation water requirement over the total agricultural water consumption showed a highly significant decreasing trend, at present 74% of the total agricultural water consumption need to be supplied through irrigation.The percentage of agricultural water consumption at Liangzhou and Jinchang over the total agricultural water consumption in the whole basin was in a highly significant increasing trend, while in a very significant decreasing trend at Minqin, and no significant trend at Tianzhu and Gulang. For the percentage of net irrigation water requirement over the total irrigation water requirement in the whole basin, it was in a significant increasing trend at Liangzhou, highly significant increasing trend at Jinchang, while in a highly significant decreasing trend at Minqin, and showed no significant trend at Tianzhu and Gulang. For the percentage of net irrigation water requirement for a county over the total net irrigation water requirement for the whole basin, and the percentage of crops sown area for that county over the total crops sown area for the whole basin, the former was larger than the latter in the middle and lower reaches'Liangzhou and Minqin while that relation was opposite in the upper reaches'Gulang and Tianzhu, which showed uneven spatial distribution of water consumption.(5) The temperature (T) and annual sunshine duration (n) had much significant impacts on total agricultural water consumption, among which, the leading influential factor was mean temperature (Tmean) at Liangzhou and Gulang, n at Minqin and Tianzhu, and Tmax at Jinchang respectively. The temperature and annual precipitation (P) had much significant impacts on total net irrigation water requirement, among which, the leading influential factor was Tmax at Liangzhou and Jinchang, P at Minqin and Tianzhu, and Tmean at Gulang respectively.(6) With the adjustment of crop composition (reducing the sown area percentage of high water-consumption cereal crop such as spring wheat, and increasing that of low water-consumption cash crop such as cotton), the agricultural water consumption and net irrigation water requirement per unit area in the basin showed a highly significant decreasing trend. The agricultural water consumption per unit area decreased from 506.9 mm in the 1950s to present 449.1 mm, and net irrigation water requirement per unit area decreased from 455.7 mm in the 1950s to present 331.9 mm. On the condition of total sown area being fixed, reducing the percentage of cereal crop and increasing cash and other crops both can significantly reduce agricultural water consumption and net irrigation water requirement per unit area. But after the area percentage of the cash and other crops raised to a given extent, the water consumption per unit area may not be effectively reduced by further adjusting crop composition.Compare the correlation coefficients between different environment factors and agricultural water consumption, and the change of agricultural water consumption with the change of these factors, the conclusion can be obtained that, the human activities had much more impacts than climate on agricultural water consumption. The human activities had larger impacts on total agricultural water consumption than on total net irrigation water requirement.(7) According to the harnessing planning of the Shiyang River Basin on key aspects in the near future, under the condition of reducing the irrigated area (i.e., the total irrigated area will be decreased from 30.30×104hm2 in 2003 to 21.03×104hm2 in the planning), agricultural water consumption and net irrigation water requirement can be decreased respectively by 0.513-0.558 billion m3 and 0.399-0.499 billion m3; while through further adjusting the crop composition (i.e., the area percentage of cereal crop: cash crop: other crops will change from 61.8: 14.5: 23.7 in 2003 to 51.2: 29: 19.8 in the planning), the agricultural water consumption and net irrigation water requirement can be decreased respectively by 0.541-0.590 billion m3 and 0.435-0.535 billion m3, which is conducive to solve the ecological problem in the basin. Applying the Agricultural Water Consumption Driving Force Model (AWCDF Model) which set up in the dissertation and equation 5-1 & equation 5-2 to predict the agricultural water consumption in the whole basin, the results showed that the relative error was less than 8%.