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Volume 21, issue 10 | Copyright

Special issue: Environmental changes and hazards in the Dead Sea region (NHESS/ACP/HESS/SE...

Hydrol. Earth Syst. Sci., 21, 5165-5180, 2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 12 Oct 2017

Research article | 12 Oct 2017

Convective rainfall in a dry climate: relations with synoptic systems and flash-flood generation in the Dead Sea region

Idit Belachsen1,2, Francesco Marra2, Nadav Peleg3, and Efrat Morin2 Idit Belachsen et al.
  • 1Hydrology and Water Resources Program, Hebrew University of Jerusalem, 91904, Israel
  • 2Institute of Earth Sciences, Hebrew University of Jerusalem, 91904, Israel
  • 3Institute of Environmental Engineering, Hydrology and Water Resources Management, ETH Zurich, Switzerland

Abstract. Spatiotemporal patterns of rainfall are important characteristics that influence runoff generation and flash-flood magnitude and require high-resolution measurements to be adequately represented. This need is further emphasized in arid climates, where rainfall is scarce and highly variable. In this study, 24 years of corrected and gauge-adjusted radar rainfall estimates are used to (i) identify the spatial structure and dynamics of convective rain cells in a dry climate region in the Eastern Mediterranean, (ii) to determine their climatology, and (iii) to understand their relation with the governing synoptic systems and with flash-flood generation. Rain cells are extracted using a segmentation method and a tracking algorithm, and are clustered into three synoptic patterns according to atmospheric variables from the ERA-Interim reanalysis. On average, the cells are about 90km2 in size, move 13ms−1 from west to east, and live for 18min. The Cyprus low accounts for 30% of the events, the low to the east of the study region for 44%, and the Active Red Sea Trough for 26%. The Active Red Sea Trough produces shorter rain events composed of rain cells with higher rain intensities, longer lifetime, smaller area, and lower velocities. The area of rain cells is positively correlated with topographic height. The number of cells is negatively correlated with the distance from the shoreline. Rain-cell intensity is negatively correlated with mean annual precipitation. Flash-flood-related events are dominated by rain cells of large size, low velocity, and long lifetime that move downstream with the main axis of the catchments. These results can be further used for stochastic simulations of convective rain storms and serve as input for hydrological models and for flash-flood nowcasting systems.

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Spatiotemporal rainfall patterns in arid environments are not well-known. We derived properties of convective rain cells over the arid Dead Sea region from a long-term radar archive. We found differences in cell properties between synoptic systems and between flash-flood and non-flash-flood events. Large flash floods are associated with slow rain cells, directed downstream with the main catchment axis. Results from this work can be used for hydrological models and stochastic storm simulations.
Spatiotemporal rainfall patterns in arid environments are not well-known. We derived properties...