عنوان مقاله [English]
نویسندگان [English]چکیده [English]
The use of models in snowy basins, due to the effect of snow’s properties, requires quantitative and qualitative knowledge of the factors on the melting and runoff resulting from it. Temperature is one of the factors. The impact of its variation on the performance of model based on the degree-day approach should be explained. For this purpose, in the Samsami catchment, the Longitude of ??, ??, ?.? seconds to ??, ??, ??.? seconds East and Latitude ??, ?, ??.? seconds to ??, ??, ? seconds North the area of ??? square kilometers evaluated the performance of the SRM model in different melting season in years ???? to ???? using a product of maximum eight-day snow cover (MOD??A?) and criteria for assessing EI efficiency and Volume Ratio. Then it was processed using ENVI software and ArcGIS software was provided with digital model, composition and snow cover curves. Determination of snow melting season was carried out using snow cover curves. To determine the beginning of the melting season, changes in snow cover levels between ???? and ???? were investigated in the Doab Samsami’ basin. This basin is one of the northern Karun sub basins in Chahar Mahal and Bakhtiari province with an average rainfall of ?,??? millimeters per year. ?? percent of the precipitation is snow and ?? percent is rain. Due to the significant drop of snow at the surface of the basin, there are large permanent and seasonal springs. The most important of these are the Dezdaran and Koufi springs. These springs have a relatively large reservoir and the origin of the formation of two rivers are named for these two. The two rivers joined in the geographical position of ?? degrees, ?? minutes and ?? seconds east longitude and ?? degrees, ?? minutes and ??.? second northern latitudes in the vicinity of Samsami village at altitudes of altitude of ???? meters from the sea level, the water of two waters of Samsami is formed. The study basin has the Doab Samsami meteorological station and Safa Abad hydrometric station at the outlet point of the basin. The basin lacked a snowstorm station, which is why the synoptic Kouhrang station, the nearest Synoptic station to the Doab Samsami basin, was assisted.
The use and interpretation of model simulation results is subject to the study of temperature’s variations in different altitudes. The performance of the model in different months of melting is different due to the variable state of the structure of snow accumulated due to temperature. The temperature difference in the melting months, with the effect of stacking on the snowpack, causes the snow to ripe. On the other hand, the ripening of snow causes delays in runoff due to melting and, as a result, the difference between observational and simulated discharge. Because the ripening phenomenon is directly related to the temperature, it can be said that the performance of the RMS model decreases with increasing temperature, in proportion to the melting season. Accuracy of model SRM decrease with increasing temperature. For February to May, the Volume Ratio rises from ?? to ?? percent for an increase of ?? ° C.
The observed difference between simulated and observational values in May, the end of the melting season, was such that the value of the volume difference increased to ??% and reduced the efficiency by minus ?.??. These results were obtained in March, the second month of melting, with a mean temperature of ? ° C, the volume difference decreased by ?.?% and the efficiency index increased to ?.??. Hence, due to the very good results of the SRM model in March, its simulation results can be used with acceptable capability to estimate snow flood from the studied basin. However, the use of the model in months with a mean high temperature and the end of the melting season, due to snow structure transformation, has a significant error in the simulation results. In order to estimate the snowflake outflow, more attention should be paid to the role of the springs and the necessary modifications are made in simulation results. Statistical simulations include Volumetric Difference (%) and Efficiency Index (Dimensionless) in each months of February, March, April, May are ??.?, ?.?, ??, ?? and ?.??, ?.??, ?.??, -?.?? respectively. It is therefore seen that, gradually, with the melting months, the accuracy of model estimation decreases. So, the use of model outcomes in the end months of melting requires temperature correction. In March, the best fit and in May, the lowest compliance is observed.