Research Of Snow Temporal And Spatial Variation Characteristics In Qilian Mountains Based On Satellite RS

As a special kind of underlying surface, snow has profound impacts on the earth energy, radiation balance and hydrologic cycle with high reflectivity, low thermal conductivity and Snowmelt hydrological effects. Snow is abundant in the Qilian Mountains. Due to low-temperature and high-cold condition, a part of precipitation is stored in solid form, which became natural solid reservoir, is the cradle of inland rivers and streamflow forming region in the Hexi Corridor in Gansu Province. Snow in Qilian Mountains Provides with plentiful water for the industrial and agricultural production of the arid Oasis Irrigation District in the Hexi Corridor, it is called the life source of the Hexi Corridor. So it is especially important for Gansu Province which is located in northwest region to understand the distribution and variation characteristics of snow in Qianlian Mountains timely. This article studies the monthly variation of snow in Qilian Mountains with 2000.3-2003.3 three years's MODIS/MOD10A2 snow data which is 500m resolution, and studies the annual variation of snow in the winter half year in Qilian Mountain with the data between month 11 to 4 in year 1996-2005 of 5km resolution which get from the combination of 2000.3-2006.12's MODIS/MOD10C snow data and month 11-4 of year 1996-2002 snow data. We also established quantitative relation between snowline altitude and temperature & precipitation elements. The main conclusions are as follows:(1) As to the seasonal variation of snow in Qilian Mountains, the period of accumulation snow is between month 9 to month 4 in next year. The maximum peak of snow cover frequency appears during the period of month 11 to month 1 in next year, the second peak occurrs at month 5. This is basically identical to previous results.(2) The variation of the seasonal snow in Qilian Mountains is obvious. Snowline altitude is almost above 3700m, other month snowline altitude is around 4000m except summer. The snowline altitude of month 7 is the highest, month 12 is the lowest, this is related to characteristic temperature and snowfall. As to the snowline altitude of east-middle-west part of Qilian Mountains, the west part is the highest, the middle part is the second and the east part is the third.(3) The monthly variation of snowline altitude in three major inland river basin in Qilian Mountains has different characteristics, the peak appearing time is not the same, but the valley value almost occur at month 7. The monthly variation of snow in Shule River Basin presents obvious double peak type. The maximum peak appears at the end of month 11 to the beginning of month 12, the second peak occurs at the middle of month 5. The period of more-snow in Hei River Basin is from month 11 to month 2 in next year and month 5, the variation rate of this period is small. Snow in Shiyang river basin begin to increase from month 9, it reaches the maximum at the end of month 11, month 5 is the second peak..(4) The spatial distribution of 10-years averaged winter half year snow frequency in Qilian Mountains is that the west part is the most, the east takes the second place, the middle is third. The basic trend of the average snow distribution height of different frequency is that the higher of the snow frequency, the higher of the distribution height. The average height of the snow is 3500-4500m.(5) As to snow cover frequency of three parts in Qilian Mountains,. snow cover frequency in the east and middle part is the least at the winter half year of 1998, it presents a trend of increase after 1998. The snow cover frequency variation in the east and middle part is similar. The west part increased continuously from 1996, and average snow cover frequency in the west part is higher than the east and middle part obviously.(6) As to the annual change of snowline altitude in Qilian Mountains in recent ten winter half years, the snowline height of both the east and middle part shows a decreasing trend, the trend is more obvious in the east part than in the middle part. The middle part showed a little increasing trend. The snowline altitude of the three major inland basin --Shiyang, Hei, Shule River basin all have decreasing trend, the Shiyang River basin decrease the most, Hei River takes the second place, Shule River is third.(7) According to the correlation analysis, the snowline altitude has a close relationship with the average temperature and snow day. Based on these analyses, we established quantitative relations between the snowline altitude and the average temperature & the snow day.