Determining the degree-days factor and snow melt in Central ‎Zagross, case study: Chery region

Various models have been used for snow melt computation. From which degree-day model is one of the most common one that estimates snow melt based on one of temperature’s parameters. In this model, in addition to temperature, degree-day factor is used by calibration in each region and derivation of model factor based on gained data with correlation. This investigation was executed in Chari region in Chaharmahal va Bakhtiari province as "Snow gauge representative area” in Central Zagross. Seven sites were determined for snow operations and three indexes were installed with rectangular triangle arrangement with 20 m length in the sides in each site. Scale-density methods were used to determine the amount of snowmelt. The average daily temperature in each site was calculated based on information of weather stations around the region and thermal gradient relations. From November 2005 to May 2011, snow depth and density were recorded weekly and its water equivalent was measured simultaneously. The amount of snow melt was calculated due to the depth of equivalent snow water of two consequent records (with no rain periods). Data from four different temperature index including 1) sum of the average temperature of the period, 2) sum of the positive mean temperature of the period, 3) mean of the average temperature of the period, and 4) mean of the average positive temperature of the period, were analyzed and degree–day factor (K) was calculated. The results showed that the highest correlation coefficient (r2=0.63) was related to correlation between the sum of positive temperatures of the period (2nd index) and snow melt. The K value was 4.2 mm per degree–day for the study area which shows the rate of four mm per day of snow melt for each degree of positive temperature. This result is similar to the previous studies and it is proposed for application in central Zagross zone.