Saeed Jahanbakhsh asl; Behroz Sari Sarraf; Tayeb Raziei; Akram Parandeh khouzani
Abstract
In order to monitor spatiotemporal variability of snow in mountainous areas such as Zagros in Iran, long-term records of snow observations with high spatial resolution are required. However, no such data are either observed or available for the stations of the Zagros region. Therefore, in this study, ...
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In order to monitor spatiotemporal variability of snow in mountainous areas such as Zagros in Iran, long-term records of snow observations with high spatial resolution are required. However, no such data are either observed or available for the stations of the Zagros region. Therefore, in this study, the Era-Interim/Land snow depth data for the period 1979-2010 were used in order to investigate the spatiotemporal variability of snow season length and the associated starting and ending dates in the Zagros region. To do so, for each hydrological year starting from October and ending in September, the first and last snow dates with snow depth equal to or greater than one centimeter were defined as the first and last day of observed snow on the ground and the time period between these two dates was considered as the snow season length. For each grid points over the study area, the time series of snow start and end dates, as well as the length of the snow season, were extracted and the rate of their temporal changes was estimated using the Sen Slope estimator and were examined using the Mann-Kendal trend test to test if they are statistically significant. Moreover, the considered time period was divided into three different sub-periods and the mean values of these parameters (i.e., first and last snow dates and snow season length) in the three sub-periods were also compared. The links between these parameters and the latitude, longitude, and altitude of the grid points were also examined. Results indicated that the spatial pattern of the first and last snow dates and snow season length fairly follow the geographical features of the study area and thus have a statistically significant relationship with the latitude, longitude, and altitude. Time variability of the considered parameters over all the studied grid points revealed that the date of the first snow in the most proportion of the study area retreated towards the late autumn and January and the date of the last snow also retreated towards March and February, thus, resulting in the shorter winter season in recent years. The observed statistically significant decreasing trend in the time series of the last snow dates towards March and February has the most contribution in shortening the length of the snow season.
