Using integrated hydrological-hydraulic modelling and global data sources to analyse the February 2023 floods in the Umbeluzi catchment (Mozambique)

Abstract

Abstract. On 9–13 February 2023 an intense flood event took place in the province of Maputo (Mozambique), resulting in severe damage to agricultural lands and transport infrastructure, and with serious consequences for the population. In the district of Boane, located a few kilometres downstream of the Pequenos Libombos dam, the flood destroyed many food crops as well as two bridges linking the district to Maputo, thus affecting the food security of the population. These events are quite frequent in this region, making necessary the delineation of improved flood hazard maps and the development of new flood risk management plans. We reproduce this flood event with a high resolution integrated hydrologic-hydraulic model fed with freely available global data sources, using a methodology that can be easily reproduced in other data-scarce regions. The model results are validated with observed estimations of the inflow to the Pequenos Libombos reservoir, with water marks left by the flood in the district of Boane, and with a Sentinel-1 image taken during the recession of the flood. We analyse the effect of the Pequenos Libombos reservoir on the flood hazard, which was subject to debate amongst the affected population and in the media. The results obtained show that integrated hydrologic-hydraulic models based on the two-dimensional shallow water equations, combined with global databases, are currently able to reliably reproduce extreme flood events in data-scarce basins, and are therefore very useful tools for the development of flood management plans in these regions.

A Runoff‐On‐Grid Approach to Embed Hydrological Processes in Shallow Water Models

“…To test the advancements of the hydrological‐hydrodynamic approach presented here, we conducted a comparison with other commonly used FHA approaches. In particular, we applied the widely accepted Soil Conservation Service—Curve Number (SCS‐CN) method for net rainfall evaluation, which was used in other event‐based hydrological simulations of floods within the Iber software (Cea et al., 2022, 2024).…”

“…This has undergone testing and validation in various research encompassing multiple objectives (Fiorentino et al., 2007; Gigante et al., 2009; Iacobellis et al., 2013; Manfreda et al., 2011; Milella et al., 2012). The shallow water model used is Iber, which has already been validated for OF applications in several studies (Cea & Bladé, 2015; Cea et al., 2014, 2022, 2024; Cea, Garrido, & Puertas, 2010). The roles of the two models are complementary, but conceptually different.…”

“…The calibration was achieved progressively by selecting the set of parameters that maximize the KGE coefficient (Gupta et al., 2009), exploiting an iterative approach that prioritized first the two lumped hydrological parameters and then the distributed Manning coefficient. In scenarios where extensive data sets are available, this type of simulator favors the actuation of multiple sources of validation, such as operational testing with space‐time hydrological measurements (Dal Molin et al., 2020; Fenicia et al., 2022), but emerging satellite techniques can also be used as a reference of flood extent for the validation of hydrodynamic outcomes (Albertini et al., 2022; Cea et al., 2024; Di Baldassarre et al., 2009; Masafu & Williams, 2024; Schumann & Moller, 2015).…”

“…The widespread success of this approach in flood hazard assessment can be credited to recent advances in High Performance Computing (HPC) techniques using Graphics Processing Units (GPU), and to the availability of high‐resolution topographic data. In recent years, the FHA has been tested for urban drainage modeling (Buttinger‐Kreuzhuber et al., 2022; Cea, Garrido, Puertas, et al., 2010; Montalvo et al., 2024; Sañudo et al., 2024), flood hazard modeling at regional and continental scale (Bates et al., 2021; Cea et al., 2022, 2024; Fraga et al., 2019; Lacasta et al., 2015; Xia et al., 2019), real‐time flood forecasting (Ming et al., 2020), soil erosion modeling at the catchment scale (Costabile et al., 2024; Uber et al., 2021), rainwater harvesting techniques (Tamagnone, Cea, et al., 2020; Tamagnone, Comino, & Rosso, 2020), and hydro‐morphological characterization of basins and streams (Barbero et al., 2022; Costabile & Costanzo, 2021; Costabile et al., 2019).…”