Zoning of 24-hour rainfall in Anzali lagoon basin

Dissertation for M.A

Field: Natural Geography

Treatment: Climatology in Environmental Planning

Abstract

Climate is one of the most important basic factors for identifying the natural regions of the earth, and precipitation is very important among the climatic elements. By examining the rainfall areas, the potential of the country's water resources can be identified, as well as the natural characteristics of each region (especially the climate), and climate zoning (that is, identifying areas with the same climate) is necessary to achieve comprehensive development, in different temporal and spatial dimensions.

In this regard, monthly, daily, and seasonal climate zoning is done using the data of rain gauge stations (with a 5-year average). Anzali Wetland basin has been analyzed using GIS software. Investigations showed that in wetland zoning, the number of annual rainfall days at Qalae Rudkhan station was accompanied by rainfall with 152 days in a year, and the lowest number of annual rainfall days was at Kiashahr station with 93 days of rainfall. Among the stations adjacent to the Anzali lagoon basin, the highest rainfall is in autumn and winter at Sanger Dam station and the lowest rainfall is in autumn, winter, spring and summer at Gilvan station.

Key words: climate zoning, daily rainfall, annual rainfall, seasonal rainfall, Anzali lagoon, GIS

Introduction

The average annual rainfall of Iran is 250 mm, which is less than a third of the average rainfall. It is universal. According to the results of many climate classifications, this land has arid and semi-arid climates. The low amount of atmospheric precipitation, high variability, strong fluctuations of rainfall from year to year, are among the characteristic features of Iran's climate. In addition to the above features, the spatial distribution of rainfall in this land is also not uniform and its amount decreases from west to east and from north to south. (Zulfaqari, 1379: 23).

The main feature of rainfall in Iran is that the annual rainfall in the country shows huge differences both in terms of location and time. While the amount of rainfall in the Caspian, Zagros and Alborz coasts is about 1560 mm respectively. meter is 930 mm, 530 mm, it reaches 62 mm in the central areas, where, in addition to spatially heterogeneous distribution, strong temporal fluctuations are also seen in it; In such a way that the coefficient of rainfall changes in a large number of stations reaches more than 40%. Examining the ratio of maximum daily rainfall to annual rainfall in Iran 169 The temporal and spatial distribution of rainfall in Iran is affected by the distribution of global circulation systems, the least change in its pattern leads to extreme weather anomalies. Therefore, spatial and temporal anomalies of rainfall and extreme changes in the intensity of rainfall and differences in the type of rainfall are the main features of rainfall in Iran (Babaei and Farajzadeh, 2010: 14)

Iran is a vast country and Pahnawar is a vast area with a lot of climatic diversity, and due to the relatively large latitude difference between the north and the south of the country, conflicting and heterogeneous topography, as well as numerous atmospheric systems that affect Iran's climate, the ratio of maximum daily rainfall to annual rainfall is different in Iran. By comparing this ratio, the temporal and spatial distribution of rainfall in different regions of the country can be determined and the ruling regimes of different regions can be determined. Considering the practical results of using daily rainfall data in different fields, this study tried to It is that first by using the rain gauge statistics, the most daily rainfall was calculated and according to it, the rainfall was zoned by GIS software. Chapter 1: Research Plan 1-1: Statement of the problem Climatologists believe that with the increase in global temperature, rainfall will also change and adverse effects such as resource depletion, sea level rise, frequency and intensification of drought, forest destruction and health threats. It will follow people. Also, the increase in the intensity of rains increases the risk of floods caused by melting snow, which has disastrous results. Fluctuations in rainfall are one of the most important climatic issues in Iran, which have harmful effects in all economic and social fields. Investigating the ratio of maximum daily rainfall to annual rainfall in Iran 169 The temporal and spatial distribution of rainfall in Iran is affected by the distribution of global circulation systems, the smallest change in its pattern leads to extreme weather anomalies.Therefore, the spatial and temporal anomalies of precipitation and extreme changes in the intensity of precipitation and the difference in the type of precipitation are the main characteristics of precipitation in Iran (Babaei and Farajzadeh, 1380: 40). The high ratio indicates that all or most of the annual rainfall is likely to occur in just a few days; In other words, the high ratio shows that most of the rains are mostly heavy and torrential, and on the contrary, the low ratio indicates the occurrence of light rains and the frequency of rainy days. In water resources planning, the length of the return period for the occurrence of a possible maximum rainfall is important. Because the occurrence of floods and acute hydrological conditions due to maximum rainfall are different according to the return period, and these floods are mostly caused by the fall of maximum atmospheric rainfall. Temporal-spatial changes of precipitation have various effects on the management and planning of water resources along a water basin at the national level. Changes in climatic elements are one of the factors affecting the change of water sources. Precipitation as a highly variable element and as a fundamental factor in the water balance has always been of interest to climatologists and hydrologists (Asakreh, 2016: 164).

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1-4: hypothesis

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1-5: research records

1-5-1: background of studies in the world

- Huo [1] and his colleagues (1966), by studying rainfalls above 63.5 mm per day, concluded that the number of repetitions of such rainfalls in the period 29 years between 1911 and 1940, is less than the number of their repetitions in the 25-year period between 1940 and 1964.

- Drosdusky [2] (1993), in a research paper entitled Seasonal Rainfall Anomalies in Australia, using the seasonal time scale during the period 1950-1987, describes the variability patterns of Australian rainfall. (1995), studied the daily rainfall in Botswana during a 9-year statistical period from 1980 to 1988 using the method of decomposition into principal components and discussed the temporal and spatial changes of the atmospheric systems affecting the region. Gregory[3] (1956), during his research on the rainfall in England by dividing England into 4 regions, believes that although the annual rainfall undergoes changes, these changes are everywhere. It is not the same and at the same time as the rainfall decreases in one place, the rainfall increases in another place.

- In addition to the method of decomposition into main components, the cluster analysis method is also one of the advanced statistical methods that have been used for zoning and analyzing the spatial patterns of rainfall. Gong and Richman (1995), in a study entitled: Application of cluster analysis for growing season rainfall data in the eastern Rocky Mountains in North America, showed that different methods of cluster analysis are remarkably effective in zoning rainfall in the region. Drought analyzed the statistics of 9 meteorological stations and concluded that the rainfall in the region is decreasing from north to south, and also considers the decrease in the length of crop plants in the first six months of the year as a result of the temperature decrease and believes that the region is witnessing a mild change in climate.

- Zulfaghari (1377), in an article entitled: An analysis of spring rainfall in western Iran during a 30-year statistical period (1967-1996) by dividing the monthly rainfall in the spring season into 3 independent periods of 10 years that most of the rainfall in the west of Iran as well as Ardabil station was in the spring season and he considers the reason for this to be the late exit of the western rain-bearing currents from the region.

- Samani (2012), in another article under the titles: Revealing the changes in temperature and precipitation compared to the average in Chahar Mahal and Bakhtiari province, it concludes that the maximum temperatures are decreasing and the minimum have been increasing and this problem shows the lack of change in the average, which itself has caused the moderation of the air in the region.