A Downscaling Method For Snow Water Equivalent Using Passive Microwave Remote Data And MODIS Products In The Tianshan Mountains

Object: Snow water equivalent is a key parameter in hydrologic simulation, and could reflect snow water resources. The study improve the spatial resolution of snow water equivalent by passive microwave sensors.Methods: Downscaling method of mathematical statistics was put forward based on eight-day synthetic MODIS(500 m×500 m) data and five-day AMSR-E(25 km×25 km) snow water equivalent. Observed SWE was also used for parameter revision and optimization. Finally, snowing days and the spatial distribution of downscaling SWE were analyzed.Results:(1)The annual maximum of snowing days is 193 days. The snowing days of 83.92% of Tianshan Mountain area changed little during study period. About 48% is no more than 30 days. The snowing days increase with elevation, but the difference in space is very significant. The high values of(>30 d) are gathered at the north, northeast, east, west and northwest aspect. This study could provide a reference for the estimation of water resources in arid area.(2)SWE could be overestimated by common downscaling method. Therefore, parameter optimization and revision were used to reduce error according to the woodland, grassland, bare land and cultivated land in the study area, the spatial SWE could be more accurate by the fitting linear equations of different underlying surface.(3)The accumulation of snow starts form October through May in Tianshan mountains. SWE changes obviously with seasonal: higher in winter, lower in summer. There is a same trend between monthly average maximum of SWE and the monthly-average value. The SWE increases from August to February. There are two-month persistence in spring and fall.(4)The changes of SWE typical months is very small in the Tianshan Mountains during 2002-2014 with a increasing trend. There is a eparate change system in each zone in the Tianshan Mountains, but still existed regional uniformity. The SWE variety of the Tianshan Mountains in January was equal to the sum of South Tianshan, Central Tianshan and North Tianshan. In April, the SWE variety was mainly affected by the South Tianshan and North Tianshan. In October, the role of the Central Tianshan is most obvious for SWE, the second one is the North Tianshan, and the minimum is the South Tianshan.Conclusion: A downscale model based on AMSR-E SWE under different underlying surface and SWE data(500 m×500 m) from June 2002 to December 2014 were obtained. The results had reference significance for estimating and forecast water resource.