Role of blowing snow in snow processes in Qilian Mountainous region

Blowing snow is an important part of snow hydrologic processes in mountainous region, however the related researches were rare for the Qilian mountainous region where blowing snow is frequent. Using the observation dataset in 2008 snow season in Binggou wa- tershed in Qilian mountainous region, we systematically studied the energy and mass processes of blowing snow by field observation and model simulation. The results include the analysis of snow observation, the occurrence probability of blowing snow, blowing snow transport and blowing snow sublimation. It was found that blowing snow was obvious in high altitude region （4,146 m）, the snow redislribution phenomena was remarkable. In Yakou station in the study region, blowing snow was easily occurred in midwinter and early spring when no snowmelt, the blowing snow transport was dominated in this period; when snowmelt beginning, the occur- rence probability of blowing snow decreased heavily because of the increasing air temperature, melt, and refrozen phenomena. The blowing snow sublimation accounted for 41.5% of total snow sublimation at Yakou station in 2008 snow season.

Simulation of Snow Processes Beneath a Boreal Scots Pine Canopy

A physically-based multi-layer snow model Snow-Atmosphere-Soil-Transfer scheme （SAST） and a land surface model Biosphere-Atmosphere Transfer Scheme （BATS） were employed to investigate how boreal forests influence snow accumulation and ablation under the canopy. Mass balance and energetics of snow beneath a Scots pine canopy in Finland at different stages of the 2003-2004 and 2004-2005 snow seasons are analyzed. For the fairly dense Scots pine forest, drop-off of the canopy-intercepted snow contributes, in some cases, twice as much to the underlying snowpack as the direct throughfall of snow. During early winter snow melting, downward turbulent sensible and condensation heat fluxes play a dominant role together with downward net longwave radiation. In the final stage of snow ablation in middle spring, downward net all- wave radiation dominates the snow melting. Although the downward sensible heat flux is comparable to the net solar radiation during this period, evaporative cooling of the melting snow surface makes the turbulent heat flux weaker than net radiation. Sensitivities of snow processes to leaf area index （LAI） indicate that a denser canopy speeds up early winter snowmelt, but also suppresses melting later in the snow season. Higher LAI increases the interception of snowfall, therefore reduces snow accumulation under the canopy during the snow season; this effect and the enhancement of downward longwave radiation by denser foliage outweighs the increased attenuation of solar radiation, resulting in earlier snow ablation under a denser canopy. The difference in sensitivities to LAI in two snow seasons implies that the impact of canopy density on the underlying snowpack is modulated by interannual variations of climate regimes.

Snow depth simulated by BATS-SAST model and its improvement

A BATS-SAST model was employed to simulate the snow processes in four snow cases of Sk_OJP 2001/2002, 2002/2003, 2003/2004 and Sk_HarvestJP 2003/2004 of Canada. At Sk_OJP site we modified the long-wave radiation and precipitation schemes. Considering the different interceptions between rain and snow and the effect of wind and canopy temperature on snow download, we improved the canopy interception model. At Sk_HarvestJP site we modified the snow cover fraction scheme. Results show that the model reasonably simulates the basic processes of snow cover. The modified model, which considers the part of the long-wave radiation and precipitation transmitted through the canopy at Sk_OJP site, can increase the simulation of snow depth which is closer to the observations. The improved canopy interception model, which influences the variation of snow depth under the canopy by changing canopy interception, is a great improvement on simulation of snow depth, especially on the ablation of snow cover. At Sk_HarvestJP site, there are obvious improvements on simulation of snow depth on the ablation of snow cover.

A GIS-based modeling of snow accumulation and melt processes in the Votkinsk reservoir basin

Coupled hydrological and atmospheric modeling is an efficient method for snowmelt runoff forecast in large basins. We use short-range precipitation forecasts of mesoscale at- mospheric Weather Research and Forecasting （WRF） model combining them with ground-based and satellite observations for modeling snow accumulation and snowmelt processes in the Votkinsk reservoir basin （184,319 km2）. The method is tested during three winter seasons （2012-2015）. The MODIS-based vegetation map and leaf area index data are used to calculate the snowmelt intensity and snow evaporation in the studied basin. The GIS-based snow accumulation and snowmelt modeling provides a reliable and highly detailed spatial distribution for snow water equivalent （SWE） and snow-covered areas （SCA）. The modelling results are validated by comparing actual and estimated SWE and SCA data. The actual SCA results are derived from MODIS satellite data. The algorithm for assessing the SCA by MODIS data （ATBD-MOD 10） has been adapted to a forest zone. In general, the proposed method provides satisfactory results for maximum SWE calculations. The calculation accuracy is slightly degraded during snowmelt periods. The SCA data is simulated with a higher reliability than the SWE data. The differences between the simulated and actual SWE may be explained by the overestimation of the WRF-simulated total precipitation and the unrepresentativeness of the SWE measurements （snow survey）.

An Assessment and Identification of Avalanche Hazard Sites in Uri Sector and its Surroundings on Himalayan Mountain

Avalanches are one of the most natural hazard in the mountain areas and therefore, identification of avalanche hazard is necessary for planning future development activities. The study area falls under the international boundary region which generally covered by the snow(38%) on high altitude regions of the western part of Himalayas. Avalanches are triggered in study area during snowfall resulting in loss of human life, property and moreover the transportation and communication affected by the debris which ultimately delays the relief measures. Therefore in this study three major causative parameters i.e terrain, ground cover and meteorological have been incorporated for the identification of avalanche hazard zones(AHZ) by integrating Analytical Hierarchical Process(AHP) method in Geographical Information System(GIS). In the first part of study, avalanche sites have been identified by the criteria related to terrain(slope, aspect and curvature) and ground cover. Weights and ratings to these causative factors and their cumulative effects have been assigned on the basis of experience and knowledge of field. In the second part of the study, single point interpolation and Inverse Distance Weighted(IDW) method has been employed as only one weather station falls in study area. Accordingly, it has been performed to generate the meteorological parameter maps(viz. air temperature and relative humidity) from the field observatories and Automatic Weather Stations(AWS) located at Baaj OP in Uri sector. Finally, the meteorological parameter maps were superimposed on the terrain-based avalanche hazard thematic layers to identify the dynamic avalanche hazard sites. Conventional weighted approach and Analytical Hierarchical Process(AHP) method have been implemented for the identification of AHZ that shows approximately 55% area under maximum hazard zone. Further, the results were validated by overlapping the existing registered avalanche sites. The sites were identified through field survey and avalanche data card followed by its delineation from the toposheet(1:50,000 scale). Interestingly study found that 28% area under moderate and maximum AHZ correlated well with registered avalanche sites when they were overlapped. The accuracy for such works can be increased by field survey under favorable weather condition and by adding data from more number of AWS for predicting avalanche hazards in mountainous regions.

THE MICROPHYSICAL STRUCTURE OF SNOW CLOUDS AND THE GROWTH PROCESS OF SNOW PARTICLES IN WINTER IN XINJIANG

The microphysical structure of snow clouds and the growth process of snow crystals were observed by means of instrumented aircraft, weather radar, snow crystal observations etc. in Urumqi region during the winter of 1982. The analysis of three cases show that about 70% of snow mass growth is produced in the lower layer below 2000 m under the cold front, and that the concentration of ice crystals is as high as 60 L^(-1) and the supercooled water is absent in lower clouds. We may infer that the deposition of ice crystals and the aggregation of snow crystals are important processes for the snow development. The microphysical structure of the snow band near the front aloft and its characteristics as a seeder cloud are also described in this paper.