The 9th International Conference on Water Resource and Environment (WRE 2023)

Abstract: In the arid regions, some heavy rainstorms and weather states may be happened annually and continued for few to many days resulting in large, or extreme flood events. The western and southwestern regions in the Kingdom of Saudi Arabia (KSA); Al Madinah, Makkah, Al Bahah, Asir, Jazan, and Najran, as well as some parts of the neighboring countries such as Oman, United Arab Emirates, and Yemen have been exposed to a summer weather state which is locally named by Saudi Committee of Nomenclature of Distinguished Weather States as “Rahw”. This weather state lasted for 18 d started from 24 July 2020 to 10 August 2020 and resulted in moderate to heavy daily rains. The present study deals with the hydrometeorological impacts of the weather state “Rahw” depending upon the statistical analyses and ARC GIS spatial distribution of 193 rainfall and weather stations, as well as daily records of water levels in 165 constructed and under construction dams’ reservoirs. The total geographic areas of Al Madinah, Makkah, Al Bahah, Asir, Jazan, and Najran Regions attain 522,000 km², representing 26.6% of the total area of KSA. According to the present study, the total geographic areas that have received rainfall precipitation in these regions during “Rahw” are estimated as 212,672 km² and the average total rainfall depth over these regions only is estimated as 69.59 mm, representing 45.8% of the total annual average rainfall depth over these regions. Also, the average total rainfall depth over all KSA during “Rahw” is estimated as 32.56 mm, representing 30.1% of the total annual average rainfall depth over all KSA regions. On the other hand, the calculated average precipitation depth in July 2020 only, attains 32.9 mm and 9.4 rainy days, compared to 20 mm and 5 rainy days of the same month during the interval from 2010 to 2019. Also, the present study concluded that the average precipitation depth in August 2020 is estimated as 27.5 mm and 9.2 rainy days, compared to 27 mm rainfall depth and 7 d rainy during August in interval from 2010–2019. The total rainfall volume received during “Rahw” weather state estimated as 10,894 million m³ representing 20.2% of the total annual average rainfall volume in these regions, and 7.2% of the total annual average rainfall volume over all KSA regions. Also, the total rainfall volume received during “Rahw” weather state resulted to 1,308 million m³ direct surface runoff, among of these 352 million m³ were retained behind 147 constructed dams, and 18 million m³ behind 8 under construction dams, and the remaining 938 million m³ is recharged in wadi deposits aquifers in those areas. Also, 201.6 million m³ of water was released from dams’ gates to meet the demands of farmers on the down-stream of dams during the rainy state, in addition 8.3 million m³ was supplied for drinking waters and treatment plants. The net increase in the water volume behind the dams as a result of “Rahw” weather stations estimated as 142 million m³. The present study recommends developing and update the operational plans of dams in western and southwestern regions to maximize the benefits from the surface runoff and enhance the water resources during the occurrence of such weather states.