Introduction
The water entering wetlands located in arid and semi-arid geographical areas is caused by the atmospheric precipitation of rain and snow in the upper elevations of the watersheds leading to them. In order to investigate the factors affecting their changes, it is very important to monitor the atmospheric precipitation in the upstream, especially the snow. Due to the harsh physical conditions of mountainous environments, there is no possibility of permanent ground measurement to estimate snow resources. For this reason, using remote sensing data to monitor snow level changes can be a great help. Temporal-spatial changes in the snow cover of the Hamoon Hirmand basin in the northeast snow-bearing areas of the basin in Afghanistan can play a role in the changes in the water area of the wetlands. The reduction of snowfall and the area covered by snow is a global phenomenon and is affected by the phenomenon of global warming and climate change, which has affected different regions with severity and weakness, and the country of Afghanistan, is located in a region that is more vulnerable. Is. Temperature changes in the upstream of the basin affect the area covered by snow and affect the amount and distribution of water entering the Hamoons. Knowledge of the changes in the snow cover upstream of the basin and its relation to the water changes in the Hamoons can help the management of the water resources of the plain. Sistan help.
Materials and methods
According to the progress made in the last few decades, various sensors and satellites have been designed and sent into space by different countries, one of the most important of which is the modis sensor, which is installed on the TERRA and AQUA satellites. The mentioned satellites, according to their technical and optical capabilities, provide various images in different electromagnetic bands. Modis satellite images are suitable for preparing maps of the snow-covered surface due to its one-day return period and better ground resolution than similar satellites. However, in the use of modis images, due to the low spatial resolution, those snow covers that are inside the mountain valleys cannot be extracted. It is important to distinguish clouds from snow in satellite images. In order to prepare and convert the raw data of modis sensor raw images received from Terra and Aqua satellites. Three operations of format conversion, ground matching and calibration were performed on the data. At this stage, the corrections are general and it is necessary to correct the geometric, radiometric and atmospheric images in a more precise manner, and these steps were also carried out. It is necessary to reference the modis sensor satellite data with the resolution of 500 meters and considering that each pixel of the images covers an area equal to 500*500 meters. ENVI software has been used to georeference the figure. In order to investigate the temporal-spatial changes of the snow cover of the upstream Hamoon basin and its role in the changes of the water area of the wetlands, the images of the Madis sensor and the NDSI index were used.
Results and discussion
The long-term time distribution of monthly snow cover showed that the largest snow area is in February, March and January, respectively. Examining the trend of monthly changes in the snow-covered surface showed that the snow area decreases with a steep slope, so that almost in the month of June, the snow cover reaches zero in most years, and in some years, the number of months without snow reaches It reaches more than 6 months, the largest area covered by snow was in February of 2008, 2009 and 2014, while the largest area covered by water was in the years when the flood rains from the upstream of the basin towards the Hamoons with a delay of one It has been two months. The highest water area is related to the months of April 2005 and May 2007 and the lowest water area is related to April 2018, when the Hamoons are completely dry and only the semi-wells have water. The change trend of snow cover area and water cover area is decreasing. The slope of the decreasing change trend in the time series of data related to water area is faster than that of snow. The monthly temporal distribution of snowfall in the upstream of the Hamoons catchment area of Sistan showed that February and then March are the peaks of the snow-covered area. The monthly time distribution of the water area also showed that the peak of the water surface coverage area is in the months of April and May with a delay of two months. In the months of November and December, when the water area is reduced to a minimum, the snowfall starts to rise.
Conclusion
Hamoon wetlands are located in arid and semi-arid geographical areas, and the water entering them is caused by precipitation in the upper reaches of the watersheds. Any natural changes and human management in the upstream can lead to changes in the water cover of Hirmand hamoons. The monthly time distribution of snowfall showed that February and March have the peak area of snow cover. There is no snow on the ground for 5 to 6 months of the year, and the supply of water resources through snow storage is cut off for several months in a row. The monthly time distribution of the water area showed that the peak of the water surface coverage area is in the months of April and May with a delay of two months. There is no significant relationship between the area of snow cover in the upstream of the basin and the water area of Hamoons on a monthly scale; However, on an annual scale, there is a relatively significant relationship, so that the coefficient of explanation of water and snow area is close to 0.5, so the amount of snowfall in the upstream heights is effective in the water area of Hamoons, but due to the entry of water from melting snow from the inlets Many of the wetlands and its management in the upstream do not have a good explanatory coefficient with monthly changes and have a relatively acceptable explanatory coefficient with annual area changes The monthly time distribution of snowfall showed that February and March have the peak area of snow cover. There is no snow on the ground for 5 to 6 months of the year, and the supply of water resources through snow storage is cut off for several months in a row. The monthly time distribution of the water area showed that the peak of the water surface coverage area is in the months of April and May with a delay of two months. There is no significant relationship between the area of snow cover in the upstream of the basin and the water area of Hamoons on a monthly scale; However, on an annual scale, there is a relatively significant relationship, so that the coefficient of explanation of water and snow area is close to 0.5, so the amount of snowfall in the upstream heights is effective in the water area of Hamoons, but due to the entry of water from melting snow from the inlets Many of the wetlands and its management in the upstream do not have a good explanatory coefficient with monthly changes and have a relatively acceptable explanatory coefficient with annual area changes. |
