Spatio-temporal Distribution Characteristics Of Oasis And Evapotranspiration In Ningxia Yellow River Economic Zone

In the arid inland,oasis is a place for local residents to live and develop,and evapotranspiration(ET)is the main way of discharge of groundwater and surface water.Ningxia Yellow River Economic Zone is an important economic development belt in northwest China.Study on oasis and evapotranspiration in this area is of great significance in the rational allocation of water resources,ecological environment protection and economic development.Based on MODIS remote sensing data,the temporal and spatial variation of oasis in Ningxia Yellow River Economic Zone from 2001 to 2014 was studied.The changes of farmland and planting structure in 2000,2003,2007,2010 and 2014 were analyzed using TM satellite data.And the relationship between oasis vegetation and meteorology,groundwater table depth was also discussed.Using Surface Energy Balance System(SEBS),the regional ET of Ningxia Yellow River economic zone during the period of 2001-2014 was researched by means of quantitative remote sensing,and the spatio-temporal distribution characteristics and the main influencing factors of ET were considered in the meantime.The ET of the cultivated land of the Yellow River Economic Zone was extracted,and the ET coefficient was determined.Besides,the reliability of the ET results was validated using the principle of water budget.On the basis of the estimation of regional ET,taking into account the precipitation,under the current situation(in 2014)the ecological water demand in Ningxia Yellow River Economic Zone and the minimum value of the diverted water volume of the Yellow River were estimated.The results indicated that:(1)The vegetation coverage of Ningxia Yellow River Economic Zone is well,mainly in the eastern part of the Weining plain and the south-central areas of the Yinchuan plain.Furthermore the normalized difference vegetation index(NDVI)showed an increasing trend.(2)There is a great quantity of farmland in the study area and the area of farmland increased in the period of 2001 to 2014.(3)The appropriate groundwater depth for vegetation growth in this region is 0-8 meters.(4)In terms ofevapotranspiration,the annual actual ET of Ningxia Yellow River economic zone gradually increased from 2001 to 2014 with the value varying from 434.27 mm 2001 to 517.82 mm in 2014.(5)The farmland ET is the major part of the total ET.And the agricultural water consumption accounted for nearly 2/3 of the regional water consumption,and the proportion of that is increasing with time.(6)According to the statistical results of 6 meteorological stations along the Yellow River Economic Zone,the ET coefficient was determined to be 0.468.(7)The SEBS ET is consistent with the value by water budget method,which is validated the reliability of SEBS model in regional ET estimation.(8)The variation of ET was positively correlated with air temperature and precipitation,and increased with the increase of NDVI,vegetation area and wetland area in the study area.(9)Under the current situation(in 2014),the ecological water demand is 48.36×108 m~3 in Ningxia Yellow River Economic Zone.In view of average annual precipitation(12.04×108 m~3),in order to maintain the current ecological environment conditions unchanged,the minimum value of the diverted water volume of the Yellow River were 36.32×108m~3.