Flash floods are among the most devastating and lethal natural hazards. In 2018, three flash-flood episodes re- sulted in 46 casualties in the deserts of Israel and Jordan alone. This paper presents the hydrometeorological analysis and forecasting of a substantial storm (25-27 April 2018) that hit an arid desert basin (Zin, ~ 1400km2, southern Is- rael) claiming 12 human lives. This paper aims to (a) spa- tially assess the severity of the storm, (b) quantify the timescale of the hydrological response, and (c) evaluate the available operational precipitation forecasting. Return peri- ods of the storm's maximal rain intensities were derived lo- cally at 1 km2 resolution using weather radar data and a novel statistical methodology. A high-resolution grid-based hydro- logical model was used to study the intra-basin flash-flood magnitudes which were consistent with direct information from witnesses. The model was further used to examine the hydrological response to different forecast scenarios. A small portion of the basin (1 %-20 %) experienced extreme precip- itation intensities (75- to 100-year return period), resulting in a local hydrological response of a high magnitude (10- to 50-year return period). Hillslope runoff, initiated minutes after the intense rainfall occurred, reached the streams and resulted in peak discharge within tens of minutes. Available deterministic operational precipitation forecasts poorly pre- dicted the hydrological response in the studied basins (tens to hundreds of square kilometers) mostly due to location in- accuracy. There was no gain from assimilating radar esti- mates in the numerical weather prediction model. Therefore, we suggest using deterministic forecasts with caution as itmight lead to fatal decision making. To cope with such er- rors, a novel cost-effective methodology is applied by spa- tially shifting the forecasted precipitation fields. In this way, flash-flood occurrences were captured in most of the sub- basins, resulting in few false alarms.

Hydrometeorological analysis and forecasting of a 3-day flash-flood-triggering desert rainstorm

F Marra;
2021

Abstract

Flash floods are among the most devastating and lethal natural hazards. In 2018, three flash-flood episodes re- sulted in 46 casualties in the deserts of Israel and Jordan alone. This paper presents the hydrometeorological analysis and forecasting of a substantial storm (25-27 April 2018) that hit an arid desert basin (Zin, ~ 1400km2, southern Is- rael) claiming 12 human lives. This paper aims to (a) spa- tially assess the severity of the storm, (b) quantify the timescale of the hydrological response, and (c) evaluate the available operational precipitation forecasting. Return peri- ods of the storm's maximal rain intensities were derived lo- cally at 1 km2 resolution using weather radar data and a novel statistical methodology. A high-resolution grid-based hydro- logical model was used to study the intra-basin flash-flood magnitudes which were consistent with direct information from witnesses. The model was further used to examine the hydrological response to different forecast scenarios. A small portion of the basin (1 %-20 %) experienced extreme precip- itation intensities (75- to 100-year return period), resulting in a local hydrological response of a high magnitude (10- to 50-year return period). Hillslope runoff, initiated minutes after the intense rainfall occurred, reached the streams and resulted in peak discharge within tens of minutes. Available deterministic operational precipitation forecasts poorly pre- dicted the hydrological response in the studied basins (tens to hundreds of square kilometers) mostly due to location in- accuracy. There was no gain from assimilating radar esti- mates in the numerical weather prediction model. Therefore, we suggest using deterministic forecasts with caution as itmight lead to fatal decision making. To cope with such er- rors, a novel cost-effective methodology is applied by spa- tially shifting the forecasted precipitation fields. In this way, flash-flood occurrences were captured in most of the sub- basins, resulting in few false alarms.
2021
Istituto di Scienze dell'Atmosfera e del Clima - ISAC
extreme storm
desert
weather radar
SMEV
flash flood
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/20.500.14243/416324
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