Simulation of Flash-Flood-Producing Storm Events in Saudi Arabia Using the Weather Research and Forecasting Model*

Abstract

The challenges of monitoring and forecasting flash-flood-producing storm events in data-sparse and arid regions are explored using the Weather Research and Forecasting (WRF) Model (version 3.5) in conjunction with a range of available satellite, in situ, and reanalysis data. Here, we focus on characterizing the initial synoptic features and examining the impact of model parameterization and resolution on the reproduction of a number of floodproducing rainfall events that occurred over the western Saudi Arabian city of Jeddah. Analysis from the European Centre for Medium-Range Weather Forecasts (ECMWF) interim reanalysis (ERA-Interim) data suggests that mesoscale convective systems associated with strong moisture convergence ahead of a trough were the major initial features for the occurrence of these intense rain events. The WRF Model was able to simulate the heavy rainfall, with driving convective processes well characterized by a high-resolution cloud-resolving model. The use of higher (1 km vs 5 km) resolution along the Jeddah coastline favors the simulation of local convective systems and adds value to the simulation of heavy rainfall, especially for deep-convection-related extreme values. At the 5-km resolution, corresponding to an intermediate study domain, simulation without a cumulus scheme led to the formation of deeper convective systems and enhanced rainfall around Jeddah, illustrating the need for careful model scheme selection in this transition resolution. In analysis of multiple nested WRF simulations (25, 5, and 1 km), localized volume and intensity of heavy rainfall together with the duration of rainstorms within the Jeddah catchment area were captured reasonably well, although there was evidence of some displacements of rainstorm events.

Exploring Jeddah Floods by Tropical Rainfall Measuring Mission Analysis

“…This is in line with the topography where high mountains on the east cause large amounts of rainfall that flow It is seen that 3B42RT intensities increase towards to the east of Jeddah (Figure 4). This is in line with the topography where high mountains on the east cause large amounts of rainfall that flow down quickly to Jeddah city [16,24]. Moreover, Haggag and El-Badry [10] also mentioned that eastern parts of the catchment receive 220mm/year more rainfall than other parts.…”

“…In addition, the seasonal variation of flood occurrences could be represented by 3B42RT data. Moreover, the rainfall timing and rates seemed to match the Weather Research Forecasting (WRF) Model simulations performed by [16]. The movements of storms from the northwest to southeast seen in 3B42RT images were in parallel with the model results of [16].…”

“…Moreover, the rainfall timing and rates seemed to match the Weather Research Forecasting (WRF) Model simulations performed by [16]. The movements of storms from the northwest to southeast seen in 3B42RT images were in parallel with the model results of [16]. Using 3B42RT data, three different indices, constant threshold (CT), cumulative distribution functions (CDFs) and Jeddah Flood Index (JFI), were developed and compared for Jeddah flood detection capability.…”

“…In addition Borga et al [5] indicated the inadequacy of ground-based rain gauges in showing the spatial variability of rainfall. Moreover, insufficiency in spatial and temporal coverage, particularly for rainfall observations over Jeddah, is mentioned in Deng et al [16].…”

Changes in the frequency and severity of hydrological droughts over Ethiopia from 1960 to 2013

“…As illustrated in Figure 1, the annual rainfall totals range from 100-150 mm in arid and semi-arid NE lowlands to more than 1700 mm in the southwest region (Griffiths, 1972;Korecha and Barnston, 2007). Rainfall in the region is largely impacted by the latitudinal migration of the Red Sea Trough (RST), which moves to the north of the equator during summer and to the northern hemisphere during spring (Deng et al, 2015). The study domain is also influenced by the tropical and extratropical atmospheric circulations (e.g., ENSO), as well as the Indian monsoon system that brings substantial moisture from the Indian Ocean into the region (Beltrando and Camberlin, 1993).…”