محیط زیست و توسعه فرابخشی (Jul 2024)
Analyzing the Temporal and Spatial Variability of Decade Droughts in Iran
Abstract
Introduction: Drought can occur in all climatic regions, that's why its characteristics are different in different regions. The concept of drought is a temporary disturbance and is different from with dry, because dry spells is limited to areas with little precepitation and is a permanent state of the climate of a region. Drought also occurs in dry and wet areas and is a natural state of climate. So far, not presentation exact and universal definition of the phenomenon of drought that is accepted by everyone. This phenomenon can occur in all climate and diffrent regions, that's why its characteristics are different in different regions. Researchers consider drought to be the result of a lack of rainfall over an extended period of time. In most definitions, a drought refers to a continuous and sustained period when the amount of water available in an area decreases significantly.Materials and Methods: To conduct this research, several methods were used in several stages. in First step, daily precipitation data for the synoptic station (411-precipitation), rain gauge (3303-precipitation) and climatology (546-precipitation) have been extracted during a long-term period of 51 years, from 1970 to 2020. for interpolation we used Kriging method in time period of data. Also, 4260×18628 grid or matrix was selected for each daily precipitation map. In this way, 18,628 daily maps were formed with 30,459 cells. After forming a database, SPEI has been used to calculate the drought index. Finally, by calculating the SPEI index, a matrix with dimensions of 51*30459 was formed. After extracting this index, Mann-Kendall's method was used to investigate the trend of drought severity, and spectrum analysis was used to investigate fluctuations of drought. for analysis trend period we use Mann-Kendall model.Results: According to the findings of this research during the first period, the drought areas of Iran are scattered in different parts of the country. During this period (1970-1990), there has been moderate and severe drought in the country. In the often of area in country has faced drought. During this period, 39% of the country experienced moderate and severe drought. In this period (1991-2010), moderate and severe drought and moderate and severe drought have prevailed in different regions of the country. The level of areas with drought in this period has increased by about 7% compared to the first period. In this period a large part of the country experienced drought and drought areas are seen scattered in the northwest, northeast, central and western regions. In the fourth period (2000-2010), against the third period, the drought has advanced to large parts of the country. The central parts of the country such as Isfahan, Yazd and Semnan occur wet condition. In Third period (2001-2020), a large part of the country is suffering from drought. against the previous period, in this period severe drought is also seen in many parts of the country.Discussion: Drought and its degree of occurrence are not related to a specific area of the country and every part of the country will be exposed to this random phenomenon. Therefore, droughts have been increasing all over the country. The lowest increasing trend can be seen in part of center and desert areas, part of the southern coast, west, northwest and also small areas in the northeast. The highest increasing trend of droughts is also seen in the southwest of the country in Khuzestan province.
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