Hydrometeorological ensemble simulations of flood events over a small basin of Majorca Island, Spain

Abstract

[eng] A hydrometeorological modelling study is designed in order to assess the feasibility of high-resolution mesoscale-model-driven runoff simulations for a small basin of Majorca in the Balearic Islands. Four intense precipitatio events, which caused flood events of different magnitudes over the Albufera basin (with a drainage area of 610 km2), are analysed. The Hydrologic Engineering Center’s Hydrologic Modeling System (HEC-HMS) runoff model is used to generate the hydrological simulations. The lack of flow measurements in the basin poses great difficulties in the evaluation of the rain-gauge-driven runoff simulations. Therefore the runoff model is run under the assumption that a best estimation of the hydrological model parameters, mainly related to the infiltration properties of the watershed, can be obtained from the high-resolution observational campaign developed by the Coordination of Information on the Environment (CORINE) Land Cover project. The non-hydrostatic fifth-generation Pennsylvania State University / NCAR Mesoscale Numerical Model (MM5) is used to provide quantitative precipitation forecasts for the events. The MM5-driven runoff simulations are compared against stream-flow simulations driven by the rainfall observations, thus employing the hydrological model as a validation tool. In addition to the control MM5 simulations, a multi-physics ensemble is carried out: various combinations of the physical parametrizations of the MM5 model (cloud microphysics, moist convection and boundary-layer schemes) are adopted, in order to better encompass the atmospheric processes leading to the high precipitation amounts. Results show that high-resolution numerical weather experiments in this area of complex orography accurately reproduce most of the extreme precipitation events under study, enabling potentially valuable discharge simulations, despite the small size of the basin. The value of the multi-physical model ensemble in conveying the uncertainty of precipitation, and therefore the discharge experiments, is also discussed.