| From 2000 to 2020,the lower reaches of the Tarim River experienced 21 times of ecological water conveyance.The groundwater level increased significantly,the growth of natural vegetation improved significantly,and the ecological water conveyance effect was remarkable.However,with the increase in the number of ecological water conveyance,restricted by the solidification of existing water conveyance methods,a series of new problems have emerged,such as unbalanced spatial distribution of ecological water,increased invalid dissipation,and decreased conversion ratio of river water to groundwater,which are the key problems to be solved at present.The main conclusions of this paper are as follows:(1)Based on the calculation method of vegetation water consumption recommended by the World Food and Agriculture Organization(FAO),the water consumption of natural vegetation under incomplete cover and water stress in the lower reaches of the Tarim River was calculated on a 30 m spatial grid scale.It is determined that the vegetation coefficient(K_c)of forest land is 0.85,grassland is 0.44,desert vegetation is0.21,and the soil moisture limit coefficient(K_s)of forest land is 0.65,grassland is 0.46,desert vegetation is0.35,which is a basic result of vegetation restoration research and ecological water conveyance effect evaluation in the downstream Tarim River.(2)By 2020,the area of each land use type in the lower reaches of the Tarim River has changed significantly after 21 times of ecological water conveyance.The desert area decreased at the rate of 75.73km~2/5a for many years,and the forest and grassland increased at the rates of 13.18 km~2/5a and 81.63 km~2/5a,respectively.The coverage of natural vegetation showed an overall upward trend.The coverage of forest land,grassland and desert vegetation increased by 4.18%/5a,2.67%/5a and 0.19%/5a,respectively.The double growth of natural vegetation area and vegetation coverage led to the increase of water consumption at a rate of 0.26×10~8 m~3/5a;by 2020,the cumulative water consumption of vegetation is 43.56×10~8 m~3,accounting for 58.68%of the total downstream consumption,which has become the main conversion term of river consumption.(3)Early stage of ecological water conveyance,the growth rate of natural vegetation area was 64.12km~2/5a.The groundwater level recovered obviously along the main river.The growth rate of natural vegetation area increased to 125.51 km~2/5a in 2010 and after,the center of gravity of vegetation water consumption moved along the main river,and the groundwater level began to rise in a wide range of natural overflow areas.The change trend of vegetation restoration rate,water consumption characteristics and groundwater level rise range had a good response to the ecological water conveyance and water conveyance mode in the early and late stages,and the ecological water conveyance effect was remarkable.(4)GLDAS grid meteorological data in the study area the period from 2000 to 2010 show that the average temperature and specific humidity in the study area show an indigenous upward trend.The change trend of temperature and specific humidity in the study area is the result of the combined effect of global warming trend and ecological water conveyance.Ecological water conveyance has a certain regulatory effect on the local temperature and humidity changes in the downstream Tarim River.21 Years of Ecological Water Transportation Practice:the natural vegetation in the lower reaches of the Tarim River was significantly improved,the groundwater level was significantly increased,and the ecological water conveyance effect was obvious.At the same time,in order to solve a series of problems caused by the solidification of existing water conveyance methods,such as the unbalanced spatial distribution of ecological water,the decrease of groundwater conversion ratio,and the increase of ineffective dissipation,Under the premise of ensuring 3.50×10~8 m~3 ecological discharge of the Daxihaizi Reservoir,30 km~2 lake area of Taitema Lake and 1050 km~2 oasis scale in the lower reaches of the Tarim River,based on natural terrain,considering the distribution of existing natural vegetation,water consumption characteristics,ecological corridor desertification prevention and control,railway and highway protection and other objectives,the artificial control method is adopted to divide the water conveyance mode of the overflow area,and the ecological water is rationally allocated in space to reduce the ineffective consumption,so as to realize the maximization of ecological restoration goals. |
