Study On Ecological Water Demand In Qaidam Basin

The Qaidam Basin is located in the arid region of northwest China.The annual precipitation is scarce,the climate is dry and the evaporation is strong.In the development of water resources,the focus is on the use of agricultural irrigation,followed by industrial and greening.Due to the backwardness of agricultural irrigation technology and low management level,water resources are seriously wasted,and agricultural irrigation water accounts for important water resources.The Qaidam Basin has extremely serious ecological and environmental problems.Mainly manifested by severe damage to natural shrub forests and fine pastures,as well as increased desertification.Studying the ecological water demand of the Qaidam Basin is of great significance to the management of water resources in the basin and the sustainable development of the ecological environment.Based on a large number of literatures,this study uses hydrological methods,Penman's formula method,and remote sensing method based on surface energy balance system to estimate the ecological water demand of the study area.Based on this,the applicable estimation methods of the study area are discussed.The main research results are as follows:(1)The ecological water demand of the river channel was calculated by the Tennant method,the minimum monthly runoff method,the monthly minimum flow method,and the90%guaranteed rate monthly average flow method.The calculation results of ecological water demand calculated by the four methods are 1.952 billion m~3/a,2.363 billion m~3/a,3.151billion m~3/a,and 3.635 billion m~3/a,respectively.(2)Using the Penman-Menteith formula to calculate the reference crop ET0,ET0reached the maximum in July,and the average value of ET0 of each weather station from May to September was 753.71 mm.Based on the MODIS13Q1 data,the vegetation types in the study area were divided according to the NDVI value,and the evapotranspiration of the vegetation was calculated according to the vegetation coefficient Kc and the soil moisture limit coefficient Ks.Finally,the ecological water demand of grassland,sparse forest land,forest land and shrub forest in the study area was 455 million m~3,229 million m~3,335 million m~3 and 338 million m~3 respectively.The ecological water requirement of vegetation is 1.357billion m~3.(3)Interpreting the remote sensing image based on the surface energy balance,inverting the instantaneous evapotranspiration of the satellite transit time,and then determining the daily evapotranspiration of the study area according to the integral relationship method.In June,the daily evapotranspiration was the largest,and the daily evapotranspiration reached3.9 mm/d.Finally,the vegetation ecological water demand is calculated according to the vegetation coverage area and vegetation coverage.The ecological water demand of grassland,sparse forest land,forest land and shrub forest are 528 million m~3,425 million m~3,479million m~3 and 402 million m~3 respectively.Vegetation ecological water demand is 1.84billion m~3.(4)Four methods for estimating ecological water demand were compared and studied.Based on the characteristics of hydrology,meteorology,vegetation and geography in the study area,the most reasonable method for estimating ecological water demand in the study area was determined,i.e.the monthly average flow method with 90%guarantee rate based on hydrological principles.The estimated ecological water demand is 3.635 billion m~3/a.