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William Amponsah, Lorenzo Marchi, Davide Zoccatelli, Giorgio Boni, Marco Cavalli, Francesco Comiti, Stefano Crema, Ana Lucía, Francesco Marra, and Marco Borga


Postflood indirect peak flow estimates provide key information to advance understanding of flash flood hydrometeorological processes, particularly when peak observations are combined with flood simulations from a hydrological model. However, indirect peak flow estimates are affected by significant uncertainties, which are magnified when floods are associated with important geomorphic processes. The main objective of this work is to advance the integrated use of indirect peak flood estimates and hydrological model simulations by developing and testing a procedure for the assessment of the geomorphic impacts–related uncertainties. The methodology is applied to the analysis of an extreme flash flood that occurred on the Magra River system in Italy on 25 October 2011. The event produced major geomorphic effects and peak discharges close to the maxima observed for high-magnitude rainstorm events in Europe at basin scales ranging from 30 to 1000 km2. Results show that the intensity of geomorphic impacts has a significant effect on the accuracy of postflood peak discharge estimation and model-based flood response analysis. It is shown that the comparison between rainfall–runoff model simulations and indirect peak flow estimates, accounting for uncertainties, may be used to identify erroneous field-derived estimates and isolate consistent hydrological simulations. Comparison with peak discharges obtained for other Mediterranean flash floods allows the scale-dependent flood response of the Magra River system to be placed within a broader hydroclimatological context. Model analyses of the hydrologic response illustrate the role of storm structure and evolution for scale-dependent flood response.

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Nadav Peleg, Francesco Marra, Simone Fatichi, Peter Molnar, Efrat Morin, Ashish Sharma, and Paolo Burlando


This study contributes to the understanding of the relationship between air temperature and convection by analyzing the characteristics of rainfall at the storm and convective rain cell scales. High spatial–temporal resolution (1 km, 5 min) estimates from a uniquely long weather radar record (24 years) were coupled with near-surface air temperature over Mediterranean and semiarid regions in the eastern Mediterranean. In the examined temperature range (5°–25°C), the peak intensity of individual convective rain cells was found to increase with temperature, but at a lower rate than the 7%°C−1 scaling expected from the Clausius–Clapeyron relation, while the area of the individual convective rain cells slightly decreases or, at most, remains unchanged. At the storm scale, the areal convective rainfall was found to increase with warmer temperatures, whereas the areal nonconvective rainfall and the stormwide area decrease. This suggests an enhanced moisture convergence from the stormwide extent toward the convective rain cells. Results indicate a reduction in the total rainfall amounts and an increased heterogeneity of the spatial structure of the storm rainfall for temperatures increasing up to 25°C. Thermodynamic conditions, analyzed using convective available potential energy, were determined to be similar between Mediterranean and semiarid regions. Limitations in the atmospheric moisture availability when shifting from Mediterranean to semiarid climates were detected and explain the suppression of the intensity of the convective rain cells when moving toward drier regions. The relationships obtained in this study are relevant for nearby regions characterized by Mediterranean and semiarid climates.

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