Author(s): Sandra Garcia Galiano; Claritza Tavarez Polonia; Fulgencio Canovas Garcia; Manuel Erena Arrabal

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Keywords: Extreme flash floods; Semiarid basins; Mediterranean basins; Climate change impacts on extreme events

Abstract: Due to climate change, the frequency and intensity of extreme events have increased in South East of Spain. Mediterranean semiarid basins are prone to flash floods. More frequently, convective storms are producing sudden extreme runoff, and high flow velocities with transport of sediment. In consequence, catastrophic impacts on natural environment, properties and even losses of human life, have been registered. The Rambla of Albujón basin, located in the Segura River Basin (South East of Spain), corresponds to a semiarid coastal basin that spills its waters to the Mar Menor water body. The Mar Menor coastal lagoon, is a fragile ecosystem that is suffering several human pressures such as nutrient and sediment inputs from agriculture and other activities and decreases in salinity. Therefore, on the one side, it is relevant to know the runoff input from coastal basins that contribute to Mar Menor lagoon. On the other side, an early warning of flash floods occurrence is required to protect the population. In the present work, the hydrological response of Rambla of Albujon wadi to various extreme events has been modelled with satisfactory results. Rambla of Albujon wadi is mainly controlled by the spatio-temporal characteristics of precipitation and the physical properties of the land surface. Innovative methodologies that allow a better knowledge of the dynamics of this coastal basin, have been considered. SWAT model (Soil & Water Assessment Tool) has been used at hourly scale, to simulate the physical processes. The hydrometeorological time series (rainfall and observed runoff) has been provided by automatic networks. While detailed information of relief (by a Digital Elevation Model), and digital thematic cartography (land use and soil types spatial distributions), were considered. Actual extreme events (registered in 2019 and 2020), producing flash floods in the study basin, have been selected for modelling purposes. Considering stream gauges with high reliability, Nash-Sutcliffe coefficients reached satisfactory values. The hydrograph and contribution volume of the Rambla del Albujón to the Mar Menor, for the selected extreme events, were estimated with adequate precision. In conclusion, Mar Menor coastal lagoon is suffering the negative impacts of different pressures. The main drivers are climate change and human activities (such as agriculture and urbanization). For monitoring the trophic state of the coastal lagoon, is relevant to know the runoff input from the semiarid basins that contribute to the coastal lagoon. However, some of these catchments are ungauged basins. In the present work, is presented a methodology to model extreme flash floods in a semiarid basin, that could be extrapolated to ungauged basins.

DOI: https://doi.org/10.3850/IAHR-39WC2521711920221097

Year: 2022