Impact evaluation of temperature increase on snowmelt and river runoff in hot months of the year in tandem with analysis of climate variables in Tamar basin, Iran

Document Type : Research Paper

Authors

1 Engineering Department of Water Resources, Department of Irrigation and Water Engineering, Faculty of Agricultural Engineering and Technology, University of Tehran

2 Irrigation and Reclamation Engineering Department, Faculty of Agricultural Engineering & Technology, College of Agriculture & Natural Resources, University of Tehran, Karaj, Iran

Abstract

Global warming has changed rainfall patterns and reduced snow sources. The main target of this research study was to evaluate the impact of temperature increase on snowmelt and river runoff in hot months of the year along with analysis of climate variables in Tamar basin, Iran, and its sensitivity analysis. To achieve this aim, the snow cover area was extracted from the daily images of Modis Satellite, based on height parameter. Then, the study area was divided to four districts, involving GIS software. Discharge flow measured data of Tamar hydrometric station, precipitation of Qarnaq and average temperature of Gidagh stations were used from 2013 to 2016, in calibration stage and from 2017 to 2019 for verification purposes, to simulate snowmelt runoff. Snow cover extent, in calibration stage, in January reached the highest values of 28% and 28.8% in the third and fourth districts, respectively. Furthermore, in the verification stage, the third and fourth districts in February had the highest percentages of 45.8 and 30.2, respectively. Comparison of predicted and measured runoff data revealed that the share of runoff due to snowmelt during the passage from February to April is significant. So that the highest increase in runoff amount related to the water year 2018-2019 from 1.8% to 39.1% estimated. The highest and lowest percentages of snowmelt in the water years 2014-2015 and 2017-2018 were 19 and 3.3 percent, respectively. The results of sensitivity analysis of model parameters including temperature decrease rate, critical temperature, delay time, degree-day factor, X and Y coefficients, precipitation runoff coefficient and snow runoff coefficient showed that rainfall coefficient and X parameters are the most effective parameters. The effect of temperature and rainfall on runoff trend was different in diverse months.

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