عنوان مقاله [English]
Analysis of precipitation intensity trend of Sudanese systems entering Iran
(Case study: Independent entry routes to Khuzestan, Bushehr and Hormozgan provinces)
Rainfall is the most important source of water supply in the south and southwest of Iran. The Sudanese system is the most important cause of rain in these areas, which occurs mainly in the short and severe. Optimal survival is directly and indirectly related to the quantity and quality of these precipitations. As mentioned earlier, one of the most important characteristics of Sudanese systems in the south and southwest of Iran is their intensity. In the study of rainfall regime in the south and southwest of Iran, The lack of study of the intensity of rainfall in Sudanese systems, especially in recent decades, is quite evident. Therefore, in the present study, the trend of rainfall intensity of Sudanese systems from three independent input routes of Khuzestan, Bushehr and Hormozgan, which corresponds to the three main routes (A, B and C) of Lashkari (2002) research, is investigated. To use its findings in the management of water resources and atmospheric events such as floods and droughts.
In the present study, in order to analyze the trend of rainfall intensity of Sudanese systems in the triple routes of Khuzestan, Bushehr and Hormozgan, first 43 study stations were separated in the form of three routes. In the entrance route of Khuzestan included: 23 stations from the provinces of Khuzestan, Ilam, Kohgiluyeh and Boyer-Ahmad, Chaharmahal and Bakhtiari and Lorestan, in the entrance route of Bushehr included; 15 stations from Bushehr, Fars, Kohgiluyeh and Boyer-Ahmad provinces and at the entrance of Hormozgan, including; 7 stations of the province itself. Then, based on the rainfall incidence index of 1 mm and more in 50% of the stations of each route, the frequency of annual, monthly and continuous rainfall periods of Sudanese systems were identified using daily rainfall data (1995-2017) and then their average rainfall was extracted. Finally, after validating the data, the trend of rainfall intensity in Sudanese systems (2017-1995), using the methods; line of best fit, Man-Kendall and Sen’s slop estimator and based on the annual average, monthly and rainfall continuity periods, at 95% confidence level, it was checked in Visual Basic Excel environment and SPSS software
Results and conclusion:
Sudanese systems operate in the cold period of the year in Iran (from the entrance routes of Khuzestan, Bushehr and Hormozgan). The rainfall of these systems in the triple routes is more 1 to 3 days, and rarely have rainfall of 5 days or more. The study of the trend of rainfall intensity of Sudanese systems (1995-2017) in the triple routes showed; the trend of rainfall intensity of these systems based on the annual average in the triple routes has a slope of decreasing changes of -0.04 to -0.1 mm during the period .However, these trends and the slope of changes are significant only in the rainfall of Bushehr route systems with a slope of very small decreasing changes (-0.1 mm during the period). The trend of rainfall intensity in Sudanese systems based on the monthly average of rainfall in the triple routes, is decreasing in some months and increasing in some. The slope of changes in these trends is in most cases zero and in some cases from 0.55 to -0.58 millimeters during the period, fluctuating. But in the meantime, only the increasing trend of November in Bushehr entrance route (0.55 one mm during the period) and the decreasing trend of February in Khuzestan entrance route (-0.21 mm during the period) is significant. The trend of rainfall intensity of Sudanese systems in the three routes is based on the average rainfall of different periods of continuity, in most cases decreasing and in some cases increasing. The slope of changes in these trends is in most cases zero and in some cases from 0.12 to -0.43 mm during the period. But in the meantime, only the decreasing trend of 2-day systems of Bushehr route with a slope of changes of -0.26 mm during the period is significant.
Despite the trend and slope of decreasing and increasing changes in the rainfall intensity of Sudanese systems, but due to the lack of significant trends and slope of changes (less than 0.6 ∓ one millimeter during the period), it can be concluded; The rainfall intensity of Sudanese systems in the entrance routes of Khuzestan, Bushehr and Hormozgan, lacks the trend and slope of significant changes at the 95% confidence level. But in general, Sudanese systems in most cases have short and heavy rainfall, and rarely light and long rainfall. As a result, the occurrence of heavy rains caused by Sudanese systems in the entrance routes of Khuzestan, Bushehr and Hormozgan should still be accepted as a principle. Therefore, floods are still one of the most important threats facing the study areas.
Keywords: Trend, precipitation intensity, Sudanese Systems, Man-Kendall, Sen,s Estimator, Iran.