Study On Water Saving Potential Of Hotan Oasis Based On Four-Water Conversion Model

According to the relevant plans of the Tarim River Basin,the total water consumption in the Tarim Basin slightly exceeds the "three red lines" of the total water consumption control index,of which irrigated agriculture in the oasis is the major user of water and the level of water consumption is relatively low.Therefore,it is important to study the water saving potential of irrigated agriculture for the sustainable development of water resources in the oasis.This paper collects information on hydro-meteorology,topography and geology,land use,water use and socio-economics of Hotan Oasis,and takes Hotan Oasis Irrigation District as the research object,with 2020 as the status quo year and 2025 and 2030 as the planning years.Based on the analysis of water consumption level in the current year,the model is used to simulate the annual water consumption of the oasis irrigation area under 100 scenarios,taking into account the runoff characteristics of the Hotan River basin and the runoff forecast in the planning year,the water balance of the oasis in the current year,the development indexes in the planning year,the identification of the upper and lower limit elements of water conservation and the formulation of different water conservation schemes,and on this basis,an in-depth analysis is made to meet the constraints of ecological water use,surface and groundwater red lines and the Hotan River.The main research results obtained from the thesis are as follows:(1)The runoff characteristics of the 64-year(1957-2020)runoff series in the Hotan River basin were analyzed,and the results showed that the interannual variation of runoff in the two upper tributaries of the Hotan River,the Khar River and the Yu River,was not significant,but the intra-annual distribution was very heterogeneous,and the annual runoff all showed a non-significant increasing trend with no obvious periodicity present.(2)A three-layer BP neural network time series prediction model was constructed,and the model was trained and tested to obtain a runoff prediction model with high accuracy.The monthly runoff values for the planning year 2025 and 2030 were thus obtained by recursive prediction,which were judged to be flat water years by back-checking the frequency curves.(3)For the characteristics of water resources in Hotan Oasis,the four-water transformation model was used,some parameters of the model were adjusted and debugged and tested,and the water balance elements of Hotan Oasis in the current year were simulated with high accuracy,and the overall water balance and water consumption of the oasis in the current year,the soil water balance and groundwater balance of the irrigated land were obtained.The average annual water consumption of irrigated land in the current year is 663 mm,and the average annual water consumption of non-irrigated forest and grassland is 280 mm.The results show that the water consumption level of irrigated land in Hotan Oasis is low and has certain water saving potential;the water consumption of non-irrigated land is moderate and can maintain the ecological water requirement.(4)On the premise of identifying the upper and lower limit elements of annual water saving in planning,a total of 100 scenarios were formed considering factors such as economic development index,incoming water of Hotan River and water utilization coefficient of canal system,etc.The water balance elements were simulated by using four water transformation models;the simulation results were plotted by interpolation method with annual water consumption of irrigated land as the parameter;based on this,the water saving potential under different water saving scenarios was analyzed by considering factors such as annual water consumption of non-irrigated forest and grassland,surface and groundwater red line and discharge threshold of Hotan River.The results show that under the upper limit of water saving,the water saving potential under the planned irrigation target is the largest in 2025 and 2030,which is 8.16 billion m3 and 8.18 billion m3 respectively,and the corresponding surface diversions are 1.244 billion m3 and 1.242 billion m3 respectively,and the canal water utilization coefficients are 0.600 and 0.601 respectively;under the lower limit of water saving,the water saving potential under the planned irrigation target is the largest in 2025 and 2030.Under the condition of lower limit of water saving,2025 and 2030 have the largest water saving potential under the planning irrigation index,which are 6.79 billion m3 and 7.22 billion m3 respectively,and the corresponding surface diversions are 1.381 billion m3 and 1.338 billion m3 respectively,and the canal water utilization coefficients are 0.616 and 0.612 respectively.