نوع مقاله : مقاله پژوهشی
نویسندگان
1 گروه اموزشی جغرافیا دانشکده ادبیات لرستان خرم آباد
2 دانشیار گروه جغرافیا، دانشکده ادبیات و علوم انسانی، دانشگاه لرستان ، خرم آباد، ایران
3 استادپژوهشگاه هواشناسی و علوم جو تهران ، ایران
4 دانشیار گروه جغرافیا دانشکده ادبیات و علوم انسانی دانشگاه لرستان خرم آباد ایران
5 دانشیار و عضو هئیت علمی پژوهشگاه هواشناسی تهران ایران
چکیده
کلیدواژه‌ها
عنوان مقاله [English]
نویسندگان [English]
Investigation of Winter Floods Lasting More Than Four Days (October-March) From 1989-2021 in Iran
Extended Abstract
Introduction
The phenomenon of precipitation is the final product of several complex atmospheric processes that are different in terms of time and place, and it can be considered one of the climatic characteristics of each region. The diversity of origin, temporal-spatial changes of rainfall systems, ground conditions such as altitude and topography, and distance and proximity to moisture sources cause precipitation behaviors, including continuity, to have temporal-spatial changes. Heavy and continuous rains are significantly effective in supplying water, feeding the underground water table, and storing it in the soil. It can also cause landslides, destruction of vegetation of forests and pastures, severe soil erosion, destruction of water structures, and waste of high volume of surface water resources in arid and semi-arid areas; therefore, it has always interested climate and meteorology researchers. In Iran, heavy and moderate rainfalls have been investigated from different perspectives. Some researchers have investigated heavy rains leading to floods in different regions of the country, and others have zoned rains lasting several days using the clustering method. Despite the various analyses conducted by the researchers, due to the difference in the selection of rainfall amounts and the different behavior of synoptic systems, the factors affecting rainfall lasting several days remain in the veil of ambiguity. This research aims to identify the synoptic patterns of rainfall lasting more than 4 days and to investigate the horizontal flux of specific moisture so that by identifying the behavior of this variable and its related fluctuations, accurate and comprehensive planning can be carried out in the direction of managing the country's water resources. What distinguishes this research from other studies is the method of estimating the limited rainfall of the study stations and the selection of the statistical period leading to 2022.
Methodology (Materials and Methods)
This research used two series of data; the first series was the daily rainfall data of 120 synoptic stations of the country from its establishment until 2022, which was taken from the National Meteorological Organization. First, the total four-day rainfall of weather stations from October to March was calculated. Then, based on the Andersen-Darling index, the best probability distribution function was fitted to the obtained data, and precipitation values above 99% of the fitted curve were obtained, among which the heaviest precipitation was selected. Five distinct clusters were identified using the hierarchical clustering technique based on the height of the middle level of the atmosphere. From each cluster, a precipitation system was chosen for synoptic analysis based on three criteria - intensity, continuity, and comprehensiveness of precipitation.
The second series of data used in this research, which was used for the case study of synoptic systems, was taken from the NCEP/NCAR archive. These data in a regular grid are limited to 0 to 80 degrees east longitude and 10 to 60 degrees north latitude with a grid step of two and a half degrees, including an area where synoptic waves can be detected. From this series of data, we can refer to the average sea level pressure, altitude, temperature, and relative humidity of the pressure level of 850 hPa, the wind field and specific humidity of the pressure levels of 925 and 700 hPa, the height and the vertical component of the wind level of 500 hPa and the wind field of the level of 200 hPa.
Results and discussion
Five specific patterns were obtained in the hierarchical clustering of the middle level's height. In the four obtained patterns, mid-level troughs with different depths are located in different geographical positions, and in the other pattern, a cut low pressure with a cold core was revealed in the north of the Black Sea. From examining the uncovered troughs, it was seen that in two cases, in the eastern part of the trough, there was a strong pile of height, which prevented the eastward movement of the trough and made it last. In these cases, the stack becomes more profound as the ship's depth increases and the ship's movement becomes slower. In two cases, short and low-amplitude waves caused by the rotating movement of the ship periodically passed through the study area and caused the instability of the atmosphere. In the case of a low-pressure cut, a deep ridge has caused the system to last and continue to rain. Since the water vapor is more in the lower levels above the water sources, the upward movement caused by the eastern circulation of pressure systems has caused the water vapor to be transferred into it and increased the amount of precipitation. Therefore, the persistence and transfer of water vapor have caused the continuation of precipitation in the study area.
Conclusion
Investigations showed that the synoptic systems of mid-latitudes, when passing over the warm waters of the Mediterranean Sea, caused an upward movement due to the gyre circulation and transferred a large amount of moisture on the sea to higher altitudes. In addition, the eastern winds of the high-pressure southern part over the Oman Sea have transferred a large amount of special moisture to the south of the Red Sea, which has been transferred to the south, southwest, and western regions of Iran with the southern winds of the eastern part of the Red Sea pressure trough. As a result of the upward movement, these values have participated in the precipitation process and increased the amount of precipitation and the continuity of rain in the western half of Iran.
Key words: Clustering, Synoptic Systems, Andersen-Darling Index, Horizontal Flux of Specific Moisture.
کلیدواژه‌ها [English]
)