Abstract
The present study aims to evaluate the effect of heat waves on the early melting of snow cover in the Karkheh catchment of Iran. After collecting daily data on the maximum temperature of meteorological stations in the catchment during the statistical period (2000–2019), three indices of WSDI, Baldi, and ocular method were used to determine the threshold of days with heat wave. By extracting the hot waves and applying programming, the snow cover maps were drawn in the Google Earth Engine system and the area of snow cover zones was calculated in the Model Builder. Finally, the atmospheric data were received from the NCEP/NCAR site and their generating patterns were examined after drawing in Grads software environment after determining the atmospheric synoptic patterns. The results indicated that the slope trend of hot waves is increasing at the catchment level. The average annual frequency of heat waves extracted for the snow cover growth period (November–May) was equal to 24 days of hot waves during the year. Regarding the ground pressure conditions and synoptic conditions of high atmospheric levels, two dominant synoptic patterns of heat waves were identified in the region as follows: (1) The Siberian high-pressure synoptic pattern at the ground level and the Saudi-African high-pressure ridge at high atmospheric levels. This synoptic pattern reduces snow cover area by an average of 40% in the Karkheh catchment and the highest frequency of the occurrence of this synoptic pattern is in February and March. (2) Pakistan-Africa low-pressure synoptic pattern at ground level and Saudi-African high-pressure ridge at high atmospheric levels, the frequency of the occurrence of which is higher in April and May months and reduces the snow cover area in the Karkheh catchment by an average of more than 55%.
Highlights
The extent and variability of snow covers are important parameters in hydrological and meteorological systems (Udnaes et al, 2007; Brown and Armstrong, 2010)
The average annual frequency of heat waves extracted in the studied statistical period (2019 − 2000) in Karkheh catchment is equal to 24 days of heat wave during the year for cold seasons of the year (November, December, January, February, March, April, May) based on the Baldi index
The present study aimed to investigate the frequency of heat waves and identify the synoptic patterns of heat waves on the Karkheh catchment
Summary
The extent and variability of snow covers are important parameters in hydrological and meteorological systems (Udnaes et al, 2007; Brown and Armstrong, 2010). In terms of longitudinal and transverse expansion, massive heights of the Zagros Mountains are located at the upstream of the catchment, where most of the rainfall falls in the form of snow and accumulates during the cold period of the year This massive snow is the source of the springs that supply the water of the Karkheh River and the water needed by the extensive agricultural fields, towns, and villages downstream of the catchment during the spring and summer seasons. By using nonparametric tests, Changchun et al,(2008)investigated the annual temperature and precipitation of 19 meteorological stations over a period between 1958 and 2002, and examined the effects of climate change on the snow cover of the Tarom River catchment. By monitoringthe atmospheric synoptic conditions, the necessary warnings to the inhabitants of the river and its tributaries are given by the relevant organizations in case of the occurrence of patterns similar to heat waves
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