Dissertation for Master Degree (M.A)
Department of Geography and Climatology in Environmental Planning
Abstract
Due to the significant role of snow cover in the hydrological cycle, it seems necessary to investigate the characteristics of snow cover (snow cover level) with a high spatial and temporal resolution. The measurement of this parameter is generally done using field observations in meteorological stations. However, since the snow measurement stations do not have a proper spatial distribution and generally in the heights of the basin where the density of snow and days with snow are higher, the number of these stations is very limited, so the use of traditional methods of ground measurement do not have the necessary efficiency for intermittent monitoring of the physical characteristics of snow. Therefore, the determination of these parameters must rely on methods that are not in direct contact with the snow and indirectly provide us with an acceptable estimate of these parameters. Topographic maps, 8-day MODIS satellite images, and climate data of temperature and daily and monthly precipitation of meteorological stations are the tools and data used in this research. Also, Arc GIS and ERDAS IMAGINE software and other software were used for data analysis. In this regard, using this information in a 13-year statistical period from the water year of 1379-1379 to 1391-1992 and in the months of November to April, using daily snowfall statistics, monthly temperatures (maximum, minimum and average), the line of advance and retreat of snow in different months of the year and the potential of the surfaces under its fall were determined and by comparing with the images of the snow cover, the snow line of the border at the province level was determined and investigated. The results show the high correspondence of this line in the satellite images of the snow cover in the months of December, January, February, and March with the height of zero degrees corresponding to the average monthly temperature, which indicates the average lines of snow melting and falling on the ground, in these months.
Key words: border snow line, Arc GIS and ERDAS IMAGINE software, MODIS satellite images.
Chapter 1
Overview of the research
1-1. Statement of the problem and the necessity of research
Since determining the climatic limits in mountainous areas in the form of altitude levels is of interest, therefore, the researchers' attention is focused on obtaining altitude figures that indicate the specific boundary and dominance of different erosion factors. In other words, the effort is to determine a limit beyond which the effects of erosion factors have appeared in a different way in the environment.
Controlling and restraining the limited fresh water resources is one of the main priorities of planning for the country's water resources. One of these sources is precipitation in high altitudes, of which snow is a major part. Snow is an important source for the flow of rivers during all seasons of the year in Gilan province.
The occurrence of recent droughts and the severe reduction of water resources on the one hand, and the role and importance of snowfall in feeding underground water sources in mountainous areas, suggest that the maximum use of the available resources is made possible by applying the necessary and appropriate measures. Preservation of surface water and efforts to allow more water from melting snow into the soil can be effective and useful in this connection. Considering that most of the rainfall falls in the form of snow in mountainous areas, the management of snow resources in mountainous areas is very important.
In cold, mountainous and high areas, most of the rainfall falls in the form of snow. The water resources available in such areas are affected by the amount of snowfall and are often fed through the waters resulting from snow melting, and the state of the water balance and the watering regime of the water resources in such areas depends on the amount and speed of snow melting or its persistence on the ground and water catchment surfaces and their nourishment. (day length) depends. On the other hand, the temperature of the environment depends on the slope and height of the area and the temperature of the ground also depends on its material and color. Dark and murky objects usually absorb more heat from the sun's radiation and naturally become warmer than light surfaces under the same conditions. The density and accumulated depth of snow are also not unaffected in this process and due to the low speed of heat transfer, dense and accumulated snow will have a lower melting speed.
Snow and water equivalent reserves provide about one-third of the water needed for agricultural and irrigation activities around the globe. In our country, these deposits in the highlands can be considered as a rich source of fresh water. Snow is an important source of river flow during the spring and summer seasons. Until now, it has not been possible to accurately identify this sweet and important source of water due to the lack of sufficient information and statistics. The lack of weather stations in high altitude areas, the inaccessibility of mountainous areas, the lack of suitable equipment and facilities for statistics in these areas, especially in the cold and snowy months, the low accuracy of information collected from stations in mountainous areas, and so on. It has caused the lack of accurate knowledge of this important water resource.
Gilan province with an area of ??14047 square kilometers is one of the northern provinces of Iran, which is located in the geographical range of 11° 32° 48° to 44° 36° 50° east longitude and 21° 33° 36° to 38° 27° north latitude and is located between the Caspian Sea and the provinces Ardabil, Mazandaran, Zanjan and Qazvin are surrounded.
The geographical features of Gilan province and the presence of the Alborz mountain range and its proximity to the Caspian Sea have made this province the rainiest province in the country, so that its annual rainfall in some areas exceeds 2000 mm.
Suitable climatic conditions, fertile alluvial soils, rivers Abundant and full of water, thick and vast forests and natural pastures of this province have provided a favorable ground for agricultural activities and transformation industries, so that some of the productions and products of this area, such as rice, tobacco, tea, silk cocoons, peanuts, olives, citrus fruits, hazelnuts, oilseeds, flowers and ornamental plants, etc., have a special reputation not only in the country, but also in the world. Gilan speaks of the favorable conditions of the region's water potential, so that the amount of precipitation and runoff in this province is about six times the average of the country and almost twice the world average. However, due to the fact that most of the rains in the region occur in autumn and winter and due to the lack of water infrastructure, even 50% of the province's water potential cannot be used at the moment. For this reason, every year there is a concern of water scarcity in the irrigation season of agricultural crops, especially the strategic crop of rice, which most of the water needed is provided by rain.
Guilan province has a humid and moderate climate in the plains and a cold and semi-arid climate in the mountainous areas [1] and its heights are always covered with snow in the cold months of the year. These falls generally start from the beginning of November and continue until the end of April and have a very important effect on feeding the base discharges of the rivers in the spring and summer seasons.
In this research, an attempt is made to obtain a relatively accurate estimate of the snow limit in the high areas of the province in different months of the year, by combining the data of meteorological stations in the province and the data of satellite images of the snow surface coverage of the MODIS sensor from the TERRA satellite. Determining the snow cover levels in these areas can be of great help to water resource planners for the optimal use of this important water source in the province and especially in the highlands that face water shortages in the hot months of the year.
1-2. Research question
Does the combined use of data from meteorological stations along with data from satellite images of MODIS snow cover level to determine the border snow line in the mountainous areas of the province increase the accuracy of the results?
1-3. Research objectives
- The use of weather station data along with MODIS snow cover satellite images to increase the accuracy of estimates in determining the snow boundary line in mountainous areas
- Knowing the capabilities of Arc GIS and ERDAS IMAGINE software in determining the snow boundary line
- Using daily snowfall statistics, monthly temperatures (maximum, minimum and average) to determine the advance and retreat line of snow in the cold months of the year (November to Farvardin) and determine the potential of the surfaces under its fall.
1-4. Research Hypotheses
According to the objectives and the main question of the research, the following hypotheses are discussed, and in this research, an effort is made to discuss the hypotheses.
The 8-day snow cover satellite image data of the MODIS sensor increases the accuracy in determining the snow line of the border of the mountainous areas of the province.