Snow Cover Depletion And Snowmelt Runoff Simulation In Manasi River Basin Of Xinjiang

The study was supported by National Science and Technology Major Project "snow and ice monitoring and its evaluation based on high-resolution remote sensing data in central Tianshan mountains in Xinjiang"(Grant No.E0405/1112/05).By using MODIS daily snow cover products to obtain satellite snow cover information,seasonal snowmelt runoff was simulated in Manasi river basin of Tianshan Mountains.Snowmelt runoff is an important part of water sources in arid-semiarid areas.It plays an essential role in daily water,agricultural and industrial water supply in the lower reaches.Seasonal snowmelt runoff is usually imperative for agricultural irrigation in arid-semiarid area of China.Manasi river basin,which is located in the arid region of the northwest of China,is not only the core region of economic zone of the northern slope of Tianshan Mountains,but also the typical irrigated agriculture area and ecologically fragile area in Xinjiang.As snowmelt is one of the major sources of runoff,it makes significant sense to obtain snow cover with remote sensing method,study the factors of snow depletion and stimulate seasonal snowmelt runoff.By using the MODIS daily snow cover products,digital elevation model(DEM),meteorological and hydrological data and other related materials,(a)the snow cover information of Manasi river basin was obtained and extracted,(b)the snow cover depletion curves was made,(c)the influences of topographical features and air temperature on the snow cover depletion process were investigated,and(d)seasonal snowmelt runoff of the study areas was stimulated with snowmelt runoff model(SRAM).The major contents and results were showed as below:(1)The satellite snow cover information was extracted.The snow cover information of all different time phases was extracted from MODIS daily snow cover products.Combining with DEM,characteristic of seasonal snow cover fraction(SCF)under different kinds of terrain were analyzed.The results showed that(a)average SCF increased along with the increasing elevation above 3200 m.SCF exceeded 80%above 4300 m and was less than 12%below 3200 m;(b)average SCF of different slope was between 23%and 35%.SCF in the area where the slope was below 100° was the highest,and it was the lowest in the area of slope between 30° and 40°;(c)average SCF varied significantly with aspects.The greatest SCF was in northern and northeast slope,and the lowest one was in western and southwest slope.(2)The influential factors of snow cover decline were analysed.The multi-temporal snow cover maps were overlaid with the map of elevation zone,slope and aspect,respectively,which was to analyse the processes of satellite snow cover depletion under different kinds of terrain.SCF was fitted with air temperature data so as to find out their relationship.The results showed that(a)the beginning and continuous time of snow cover depletion showed significant difference among different elevation zones.The snow in the low-lying area melted first and also ceased to melt earlier.Along with the increasing elevation,the beginning time and ceased time of snow cover depletion delayed,and the speed of depletion slowed down.(b)The greater slope was,the later snow began to melt.Different slopes had different effects on snow cover depletion.The speed of snow cover depletion in low-lying area slowed down along with the increasing slope.In middle and high altitude areas,the speed of snow cover depletion of different slopes showed no obvious difference.(c)The influential diversity of different aspects on snow cover depletion decreased as the elevation increased.The speed of snow cover depletion in northern,northeast and eastern was faster than other aspects.(d)The average SCF had significant negative correlation with daily average temperature.The higher temperature was,the lower SCF was.To some extent,the process of snow cover depletion in different kinds of terrain reflected the distribution of temperature.(3)Seasonal snowmelt runoff was simulated.By combining data of meteorology,seasonal characteristic of snow cover depletion and feature of river basin,seasonal snowmelt runoff was simulated with snowmelt runoff model(SRM).The results showed that SRM could simulate the snowmelt runoff of the study area well.On the whole,simulated daily runoff value reflected the changing trend of actual runoff value.The accuracy of simulated results was high.The deviation of simulation may come from lack of optimizing parameters,such as lag time.The shortage of meteorological data was another possible reason.