Investigating changes in annual, monthly and seasonal rainfall trends in Sefidroud Valley

Academic Thesis for Master's Degree

Field: Natural Geography Major: Climate in Environmental Planning

Abstract

Atmospheric precipitation is one of the most important meteorological factors because all water resources in the region are provided through these precipitations. Precipitation studies are of great importance in terms of natural and human aspects because the effects of precipitation in different economic sectors and. It is different and can cause irreparable damage in different parts. In this research, the author investigated the rainfall changes in Sefidroud Valley by using regression line equation method and using 19 stations in order to investigate the climatic sensitivities of the rainfall in the study area, which happened in relation to the year, month and season. The results of the research show that the Sefidroud Valley has different conditions in the north and south based on the rainfall index method of 30 years of the studied statistical period. Based on this, two types of climate with different amounts of precipitation are observed in it. The amount of annual rainfall in these two climate types has had a different trend. In the north of the region, the rainfall is relatively high and in the south, the rainfall is low. The time trend of precipitation is also different in these two climate types, the most precipitation is in the north in October and in the south in the winter months. In terms of the seasons, autumn has the most rainfall in the north of Sefidroud valley and winter has the most rainfall in the south of Sefidroud valley.

Key words: precipitation, annual, Sefidroud valley, monthly, seasonal

Introduction

Weather comes from the Greek word kilima (kilima) which means desire. Weather is the result of the combined effect of meteorological phenomena and gives the average state of the air at a desired point. Therefore, when we discuss the climate of a region, we do not mention the Zama moment. Of course, climate has a broader meaning and is not limited to meteorological parameters, but includes a set of physical, chemical and environmental factors (Alizadeh, 2017).

Undoubtedly, one of the most effective factors in the natural structure of the earth is weather conditions or climate, and the living environment of all living things, including humans, animals and plants, is affected by climate variables. Wide, it shows a lot of connection and correlation with the distribution of various climatic forms. This influence is to such an extent that some animals and plants can survive, grow and develop only in certain climatic conditions, and for this reason, the climate of each region is considered a very important phenomenon in the division and classification of geographical and ecological areas.

The intelligent man, in the face of the merciless attack and invasion of the destructive phenomena of nature, through studying and knowing the conditions of these factors, rose to repel and eliminate them and by taking advantage of his scientific and technological achievements. These problems have been overcome.

According to what has been said, it can be seen that the knowledge of climate and weather is of special importance and validity in many human activities and is considered one of the effective factors in the development and evolution of environmental processes. And any construction and agricultural planning in order to exploit the potentials in nature as best as possible, regardless of climatic factors, will be insufficient and even doomed to failure. It is with the understanding and recognition of this fact that branches of climatology (climate and meteorology) such as applied climatology are emerging in the fields of science.

In every important issue of nature, in order to get the most economic benefit from any climate regime, it is necessary to carefully study the climate balance before any planning, so that finally by applying a correct management, the optimal use of nature can be achieved. It is a climatic discontinuity that has created two completely distinct climates in the north and south. The northern part of the highlands is called the Caspian climate and the southern part is called the Bari climate.

In terms of climate, the northern parts of the province belong to the Caspian climate. A part of the south of the province in the area around Manjil and Lushan has a bari climate. The areas between Sadd Tarik and Rudbar are located in the transition zone of the Caspian and Bari climates..

Sefidroud valley is considered the only communication route between the humid air of Caspian and Bari. The existence of the Manjil mountain pass and the pressure difference in Pishkoh and Pescoh Alborz creates a wind regime that is known by the same name (Pishkoh - Pescoh). The maximum speed of this wind is in Harzeville, which continues to the Qazvin plain and Tehran.

The difference in climatic conditions of the above-mentioned areas has caused major changes in the climate, vegetation, soil thickness, and rock weathering depth. The areas with Caspian climate, which includes the main part of the province in the south-west of the Caspian Sea, have dense vegetation, while the vegetation in the southern part of the province is insignificant. The last two climates have arisen due to the increase in altitude and as a result of the decrease in temperature, and their territory is the heights and slopes of the northern Alborz. It is obvious that the climate of the upper altitudes is also present in the southern Alborz highlands.

The main source of rainfall in the studied part is the suitable geographical and climatic system "sea-mountain-air flow". That is, on the one hand, the masses entering the region and on the other hand, the orographic precipitation caused by the region's physiography and the presence of two factors, the Alborz Mountains and the Caspian Sea, are in the vicinity. According to the above factors, there is a rainy core around Rudkhan Castle, and the area with low rainfall is around Sefidroud Dam. The rainiest months of the year in the stations located in the coastal area of ??the Caspian Sea are the months of Shahrivar and Mehr, and the driest months of the year in this area are the months of June and July. In the non-coastal area of ??the Caspian Sea, the rainiest months of the year are March, April and May, and the least rainy months in this area are the summer months. In the coastal areas of the study area, autumn is the rainiest season and spring is the least rainy season of the year, and in the non-coastal part of the study area, winter is the rainiest season and summer is the driest season.

The climate of the area was determined using the statistics of the stations in the area and in different ways. Stations Considering that the objective is to investigate the situation of annual, monthly and seasonal rainfall, two issues are carefully considered, the closest distance to the range and height of the stations in question, therefore, after preparing and collecting the available data and extracting information and checking the statistical deficiencies, we will investigate the climate of the region.

Regarding the above, this research intends to investigate the changes in precipitation in the Sefidroud Valley by using the existing methods, for this purpose, the current research is divided into seven chapters.

In this chapter, first, an abstract of the main climatic factors of the region is presented based on the available statistics, and the relationship between them is analyzed so that the general results obtained in general estimates and investigations can be exploited. Rainfall is considered one of the main climatic elements of any region. In many countries of the world, macro-planning is done based on annual, monthly and seasonal rainfall changes, because the changes in rainfall trends in different climates can cause minor problems to very big problems. Thus, the emergence of the effects of this trend in dry climates is faster and more mysterious and can be predicted with a high percentage, but in humid climates these changes are associated with smaller fluctuations but with more continuity, which the harmful effects of these fluctuations have always been studied by researchers. In 1961-1990, more than two-thirds of the country has an average annual rainfall of less than 300 mm, but there are cores with more than 1000 mm of rainfall in the Zagros region and the northern slopes of Alborz.