Document Type : Original Article
Authors
1 PhD in irrigation and drainage,, Bu Ali Sina University, Hamedan.
2 Assistant Professor; Agricultural Engineering Research Institute (AERI); Agricultural Research, Education and Extension Organization (AREEO); Karaj; Iran
Abstract
Extended Abstract
Introduction
Snow is an important source for water supply in the agricultural sector, electricity production, groundwater reserves, and rivers. This natural resource is important since it stores water in winter with low demand and releases it in hot seasons with high demand. Melted snow flow can be very useful in low-water seasons. In arid and semi-arid regions, snow is considered a basic source of fresh water. Significant spatiotemporal changes in distribution of snow on the scale of a basin can be important in determining the time and amount of snow melting in spring. These changes can increase the probability of drought and runoff. Therefore, snow cover plays an important role in the study of hydrological processes and climate changes. Snow cover is sensitive to temperature and environmental changes and can be a good indicator for local and global climate changes. The lack of sufficient and correct information about snow reserves can lead to inappropriate use of water resulting from snow melting and, as a result, irreparable damages. Therefore, measuring the surface covered by snow and its water equivalent, along with other information such as snow density, especially in areas where snow accounts for a large share of precipitation, is essential for resource planning and management. However, it is not possible to measure it in many areas due to harsh environmental conditions. Also, the data measured at one point cannot be generalized to a wide area of a basin. Thus, the use of satellite images can be considered as one of the methods of investigating spatial and temporal changes in distribution of snow in a region. The use of these images is much more economical and efficient, compared to the point data of ground stations, due to the high coverage and the ability to take pictures of an area at different times with high accuracy.
Hamadan is one of the provinces with a lot of snowfall in Iran, whose economy is largely dependent on agriculture, and snowfall plays a significant role in supplying the water needed for agriculture and drinking. However, there is no research on the temporal changes of snow cover in this province and its relation with changes in important climatic parameters such as temperature and precipitation. Considering the effect of climate change on changes in snowfall over time, the aim of this study was to investigate the temporal distribution of snow cover in the province of Hamedan during 1982-2023. For this purpose, the data of snow cover, snow depth and snow water equivalent in different months of the year were estimated using satellite images obtained from the FLDAS product. Then, the increasing or decreasing trend of these data was determined. Finally, their correlation with meteorological parameters of temperature and precipitation was obtained.
Materials and methods
To obtain the monthly values of snow cover (SC), snow water equivalent (SWE) and snow depth (SDepth) from January 1982 to December 2023, the FLDAS (Famine Early Warning Systems Network—FEWS NET—Land Data Assimilation System) product from the Noah 3.6.1 Land Surface model was used. This product is at latitude 90° to -60° and longitude 180° to -180° with a spatial resolution of 0.1°×0.1° in netCDF format and its images are available monthly from January 1982 until now.
The non-parametric Mann-Kendall test was used to investigate the increasing, decreasing or constant trend of the data during specific time intervals in the period. The Theil-Sen slope was used to calculate the slope of the trends. The correlation of the temporal distribution of snow cover with the two meteorological parameters of temperature and precipitation was determined using the Pearson's method.
Results and discussion
The results showed that the year 1982 with a total of 41043.04 km2 had the highest and the year 2021 with a total of 4048.12 km2 had the lowest SC. These data indicated a 90.13 percent decrease in SC in 42 years, which is understandable considering the 35.08 percent increase in the mean temperature (from 9.49 to 12.82 ºC) in this period. The monthly average of SC in this period showed that there was no snow cover from May to October, and in April and November it was very insignificant and negligible compared to in January, February, March and December. Among these four months, January had the highest average SC.
According to the Mann-Kendall test, the trends of SC, SWE and SDepth was decreasing in all the four months of January, February, March and December. Temperature and precipitation values had increasing and decreasing trends, respectively.
According to the Theil-Sen slope test, SC had the steepest and gentlest decreasing slope in January and December, respectively. In the case of SWE and SDepth, the steepest decreasing slope was related to February, and the gentlest decreasing slope occurred in December. The increase in temperature had the gentlest slope in the two consecutive months of December and January, and the steepest slope in the two consecutive months of February and March. The steepest and gentlest slope of decrease in precipitation occurred in March and February, respectively.
The Pearson's correlation coefficient values indicated that SC, SWE and SDepth had inverse correlation with temperature and direct correlation with precipitation. Overall, SC, SWE, and SDepth were more correlated with temperature than with precipitation, especially in February and March when temperature was higher than in December and January.
Conclusion
In this study, using the satellite images obtained from the FLDAS product, the data of snow cover, snow water equivalent and snow depth were obtained in the province of Hamedan for the 42-year period of 1982-2023. The results showed a significant decrease in the snow cover during this period, which was expected due to the climate change and temperature increase. The snow cover, snow water equivalent and snow depth had decreasing trends. The trends of the two climatic parameters, temperature and precipitation, were increasing and decreasing, respectively. The steepest and gentlest slope of the decrease in snow cover occurred in January and December, respectively. There was an inverse correlation of snow cover, snow water equivalent and snow depth with temperature, and a direct correlation with precipitation. In general, the correlation of snowfall parameters with temperature, especially in warmer months, was more than their correlation with precipitation.
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