1- university of MAZANDARAN
Abstract: (37 Views)
Introduction and Objective: The purpose of this research is to investigate the synergistic and dynamic causes of heavy rainfall in the Babolroud river basin in Mazandaran province. To achieve the outcomes, the knowledge of the climate of the region and the frequency of floods in this area is essential. The other effective variable is precipitation which its type, amount and intensity is different and it would be changed by changing the place and the time. The occurrence of heavy Precipitation is a manifestation of these changes, which is a dangerous factor in the occurrence of natural disasters such as floods. Floods are one of the most important risks in the world, which cause a lot of damage to agriculture, fisheries, houses and infrastructures and severely affect economic and social activities. So, the floods include about 41% of the deaths caused by natural disasters and only in the last decade of the 20th century, the death of about 100 thousand people and the lives of about 1.4 billion people were affected. With the increase in the intensity and frequency of flood events, global concerns about the increase in deaths and the resulting economic losses have increased. In addition to environmental factors, the first factor in causing floods is the intensity of Precipitation, and the biggest floods are related to heavy Precipitations with the maximum momentary peak that occurs at a certain point in time. Knowing the regime and pattern of these rains will help a lot in identifying and predicting these floods.
Materials and methods: Babolsar, Quran Talar and Alasht stations were studied in order to investigate the cause of heavy rains in Babolroud river basin. Precipitation over the 90th percentile in at least 1 station and the occurrence of precipitation in other stations are the main conditions for the selected days. After determining the selected days, the average and anomaly of the height of 500 mb level and the sea level pressure and the omega index for the levels of 850 and 500 mb were obtained from the website (NCEP/NCAR). Divergence, relative humidity, temperature, zonal and meridional wind, relative humidity, vertical velocity and geopotential height parameters for levels 1000 to 500 mb in 20 days selected from ERA5 reanalysis model and then using GIS software numerical data for the coordinates of 3 stations were extracted.
Results: The obtained results of the Pearson's correlation coefficient indicated no significant relation between the selected three stations. Moreover, the out-puts indicated that there is a divers relation between the highest and lowest zone of the river basin. Investigations show that the event of heavy rainfall occurs simultaneously in the entire Babolrud basin, and the heaviest widespread rainfalls in the Babolrud basin follow the synoptic to private pattern; Therefore, revealing this pattern and the conditions of simultaneous occurrence of heavy rainfall in this area increases the importance of this research. The selected days as the 90th percentile of Babolsar station are 10 days, Quran Talar station: 7 days, Alasht station: 1 day, among which 2 days are common days of Babolsar and Qur'an Talar stations. After analyzing the data, 2 systems date 17th-22th July 2015 and 17th-23th March 2019 were selected under the title of the systems related to the heaviest rainfall occurred simultaneously in the entire Babolrud area, and both was the same in the selected legal conditions. In the system from 17th-22th July 2015, the highest rainfall of this system among these 3 stations was from Babolsar station at the rate of 107.2 mm and the lowest was at Quran Talar station at the rate of 68 mm. On average, a trough from northern latitudes penetrates the region in a meridian and direct manner, and its waves are located in the vicinity of the high-altitude or Bandali system, and also high-pressure tongues penetrated from the west on the surface of the earth. In the system of 17th-23th March 2019, the highest rainfall was 120 mm from Quran Talar station and the lowest was 97.5 mm from Babolsar station. They crossed the surface of the region, and on the surface of the earth, there were high-pressure tongues in the west, and in the center, low pressure in the east of Turkmenistan.
Conclusion: By finding a common feature, it was observed that for the occurrence of heavy rainfall in the entire Babolroud basin, according to the climate of each region, conditions such as the direct penetration of the trough to the central coast of the southern Caspian Sea, the penetration of high-pressure tongues from the west and north and west into the region must prevail. The convergence of north-northwest currents in the entire Babulrud area, the rising air in all layers, the vorticity of positive at the level of 500 mb and negative in the lower layers, and the dominance of relatively strong winds in the sea for the flow of moisture and the highest relative humidity in the lower layers are intact. The studies showed that during the penetration of high-pressure tongues from the west and northwest, on the surface of the earth and lower levels, as long as the anticyclonic currents prevail over the cyclonic currents, the peak of rainfall extends from the coasts to the slopes to the middle elevations. On the contrary, during the peak of rainfall on the coast, the anticyclonic currents are weakened and at the level of 500 mb, the divergence and ascent of the air is accompanied by strengthening. When the peak of rainfall moves from the highlands and slopes towards the coast, the low-altitude center becomes stronger and the depth of trough penetration to lower latitudes becomes less.
Materials and methods: Babolsar, Quran Talar and Alasht stations were studied in order to investigate the cause of heavy rains in Babolroud river basin. Precipitation over the 90th percentile in at least 1 station and the occurrence of precipitation in other stations are the main conditions for the selected days. After determining the selected days, the average and anomaly of the height of 500 mb level and the sea level pressure and the omega index for the levels of 850 and 500 mb were obtained from the website (NCEP/NCAR). Divergence, relative humidity, temperature, zonal and meridional wind, relative humidity, vertical velocity and geopotential height parameters for levels 1000 to 500 mb in 20 days selected from ERA5 reanalysis model and then using GIS software numerical data for the coordinates of 3 stations were extracted.
Results: The obtained results of the Pearson's correlation coefficient indicated no significant relation between the selected three stations. Moreover, the out-puts indicated that there is a divers relation between the highest and lowest zone of the river basin. Investigations show that the event of heavy rainfall occurs simultaneously in the entire Babolrud basin, and the heaviest widespread rainfalls in the Babolrud basin follow the synoptic to private pattern; Therefore, revealing this pattern and the conditions of simultaneous occurrence of heavy rainfall in this area increases the importance of this research. The selected days as the 90th percentile of Babolsar station are 10 days, Quran Talar station: 7 days, Alasht station: 1 day, among which 2 days are common days of Babolsar and Qur'an Talar stations. After analyzing the data, 2 systems date 17th-22th July 2015 and 17th-23th March 2019 were selected under the title of the systems related to the heaviest rainfall occurred simultaneously in the entire Babolrud area, and both was the same in the selected legal conditions. In the system from 17th-22th July 2015, the highest rainfall of this system among these 3 stations was from Babolsar station at the rate of 107.2 mm and the lowest was at Quran Talar station at the rate of 68 mm. On average, a trough from northern latitudes penetrates the region in a meridian and direct manner, and its waves are located in the vicinity of the high-altitude or Bandali system, and also high-pressure tongues penetrated from the west on the surface of the earth. In the system of 17th-23th March 2019, the highest rainfall was 120 mm from Quran Talar station and the lowest was 97.5 mm from Babolsar station. They crossed the surface of the region, and on the surface of the earth, there were high-pressure tongues in the west, and in the center, low pressure in the east of Turkmenistan.
Conclusion: By finding a common feature, it was observed that for the occurrence of heavy rainfall in the entire Babolroud basin, according to the climate of each region, conditions such as the direct penetration of the trough to the central coast of the southern Caspian Sea, the penetration of high-pressure tongues from the west and north and west into the region must prevail. The convergence of north-northwest currents in the entire Babulrud area, the rising air in all layers, the vorticity of positive at the level of 500 mb and negative in the lower layers, and the dominance of relatively strong winds in the sea for the flow of moisture and the highest relative humidity in the lower layers are intact. The studies showed that during the penetration of high-pressure tongues from the west and northwest, on the surface of the earth and lower levels, as long as the anticyclonic currents prevail over the cyclonic currents, the peak of rainfall extends from the coasts to the slopes to the middle elevations. On the contrary, during the peak of rainfall on the coast, the anticyclonic currents are weakened and at the level of 500 mb, the divergence and ascent of the air is accompanied by strengthening. When the peak of rainfall moves from the highlands and slopes towards the coast, the low-altitude center becomes stronger and the depth of trough penetration to lower latitudes becomes less.
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