Hydro-meteorological characteristics and occurrence probability of extreme flood events in Moroccan High Atlas

Abstract

Flood frequency analysis could be a tool to help decision-makers to size hydraulic structures. To this end, this article aims to compare two analysis methods to see how rare an extreme hydrometeorological event is, and what could be its return period. This event caused many deadly floods in southwestern Morocco. It was the result of unusual atmospheric conditions, characterized by a very low atmospheric pressure off the Moroccan coast and the passage of the jet stream further south. Assessment of frequency and return period of this extreme event is performed in a High Atlas watershed (the Ghdat Wadi) using historical floods. We took into account, on the one hand, flood peak flows and, on the other hand, flood water volumes. Statistically, both parameters are better adjusted respectively to Gamma and Log Normal distributions. However, the peak flow approach underestimates the return period of long-duration hydrographs that do not have a high peak flow, like the 2014 event. The latter is indeed better evaluated, as a rare event, by taking into account the flood water volumes. Therefore, this parameter should not be omitted in the calculation of flood probabilities for watershed management and the sizing of flood protection infrastructure.

Saharan Rainfall Climatology and its Relationship with Surface Cyclones

“…3c), but also because of its aftermath. It first produced massive rainfall and floods near the Atlantic coast, including tens of casualties in Morocco (Saidi et al, 2020;El Khalki et al, 2020) and then penetrated into the Sahara, with an exceptional rainfall amount (Fig. 3d) and floods in this arid region.…”

“…The African Monsoon and the Saharan heat low are often associated with Saharan precipitation, mainly at the desert's southern fringe, and during summer (e.g., Parker et al, 2005;Funk et al, 2016). However, a few case studies described HPEs occurring in winter or transition seasons, in the northern parts of the desert, usually in association with a surface cyclone (e.g., Fink and Knippertz, 2003;Saidi et al, 2020, and also the abovementioned Storm Daniel). Whereas case studies provide insight into the general processes, they are not necessarily representative of the entire population.…”

Flood Susceptibility Assessment through Statistical Models and HEC-RAS Analysis for Sustainable Management in Essaouira Province, Morocco

“…Morocco, a country situated in northwest Africa, is currently grappling with the impacts of climate change. One of the consequences is the occurrence of intense rainfall, which often leads to hazardous flooding situations [62][63][64]. Moreover, Morocco faces challenges in terms of unpredictable rainfall patterns [65][66][67].…”

Analysing frequent extreme flood incidences in Brahmaputra basin, South Asia

“…At higher temperatures, the air can hold more moisture content that tends to rise in the precipitation intensity, its duration, and frequency [5][6][7]. Therefore, floods are triggered by intense precipitation, anomalous longer duration, close repetition of precipitations, topographical characteristics or a combination of all these phenomenon [8][9][10][11]. For example, an extended period of very heavy precipitation leads to the development of a low-pressure system apart from extended monsoon depression during the Kerala flood in 2019 [12][13][14].…”