Temporal And Spatial Variation Of Snow Cover And Its Response To Temperature And Precipitation In The Kashi River Basin In The Western Tianshan Mountains

Under the trend of global warming,snow is one of the important parts of the earth's surface cover,sensitive to the change of climate and environment,and it is the main source of fresh water for mountain runoff,especially in arid areas of northwest China.River runoff has a strong dependence on ice-snow melting water,so it has become a hot topic of many scholars.Snow cover is the most direct environmental factor in response to climate change in the region,and it is very important to the economic development and ecosystem in arid areas.With the development of remote sensing technology,because of its wide coverage,low cost,strong real-time and other advantages,it makes up for the shortcomings of traditional snow monitoring,and has been widely used in snow cover research..Located in the west Tianshan mountain area,the Kashi River is one of the three major sources of the Yili River.Glacier melting water and seasonal snow melting water are important water sources for the economic development of the Kashi Valley,and this basin is a sensitive area for responding to climate change.The change of snow cover directly reflects the climate change in the basin.Therefore,the temporal and spatial changes of snow cover and climate change characteristics in the Yili Kashi River basin are studied,and the spatial and temporal distribution characteristics and changing rules are understood,so as to provide reference for the strategic protection of water resources in this basin.It is of great significance to the utilization and ecological sustainable development of water resources in the Kashi River and its lower reaches,and to enrich the arid areas.The study of hydrological process also has some academic value.In this paper,the spatial and temporal characteristics of snow cover in the Kashi River Basin in the last 10 years are analyzed by using the MODIS snow cover products in 2008/03,combined with the air temperature.The characteristics of climate change and the correlation between meteorological factors and snow cover area were analyzed by precipitation data.The conclusions are as follows:(1)The spatial distribution of snow cover in the Kashi River basin is uneven and has obvious seasonal variation.The distribution pattern of snow cover in the basin is low in the west and high in the east,high in the north and low in the south.With the increase of the altitude,the snow cover frequency increases,but the snow cover frequency in the low altitude region in the west is small.The snow cover frequency is higher(80%)in the high altitude mountain area,accounting for 6.79%of the total watershed.The snow cover mainly comes from winter,and the snow cover is the least in summer,which is concentrated in high altitude mountain area,which is permanent all the year round,and the whole basin is basically covered with snow cover in winter,with a coverage rate of more than 98%.(2)The snow cover area in the watershed showed a single peak trend during the year,with the largest snow cover area in February and the smallest snow cover area of 9208.909 km~2;in July,only 860.259 km~2.in July.The average snow cover area of the basin increased slightly in the last 10 years,with an increase rate of 21.50km~2/10a,with a large inter-annual fluctuation.The maximum annual snow cover area occurred in 2010,and the smallest annual snow cover area occurred in 2008.The snow cover area has obvious seasonal variation.The average snow cover area is winter>spring>autumn>summer.The total area of permanent snow shows a downward trend,with a permanent snow cover area of near 10a in 2017,with the largest change in snow cover in 2016.(3)The interannual mean air temperature and the temperature of different seasons in the Kashi River Basin showed an upward trend.In the last 50 years,the average air temperature of many years was 6.58?,increasing at a rate of 0.50?/10a,and the lowest annual mean temperature was 4.53?in 1972.The highest annual mean temperature was 8.77?in 2008.In different time scales,the air temperature has the oscillation period of different time scale,and the alternation change is remarkable,and there exists the phenomenon of alternation of cold and warm.(4)The annual precipitation in the basin during the past 50 years is increasing at the speed of 24.57mm/10a,and the precipitation in the four seasons of the basin is not significantly increasing.The abrupt change point of inter-annual precipitation is1992,and the precipitation has increased from 363.28mm before the sudden change to430.17 mm.There is a strong periodic oscillation of precipitation in spring and autumn season,the oscillation is global and has remarkable change,but the oscillation of summer and winter is not significant.(5)The analysis of snow cover area,air temperature,precipitation and time series shows that there is significant negative correlation between the air temperature factor and snow cover area in different seasons.There was a negative correlation between the minimum mean air temperature and snow cover area(0.05),and other meteorological factors failed to pass the significance test.Snow cover area was negatively correlated with precipitation in spring,and there was a positive correlation between snow cover area and precipitation in summer and autumn.Air temperature is the main factor affecting snow cover area,and precipitation has little effect on snow cover area.(6)The distribution of the river runoff is not uniform in the year,mainly in May-August.The increase of air temperature affects the ablation of the snow,resulting in the difference of the runoff in the river,and the temperature has a significant effect on the runoff.