Predicting extreme rainfall events over Jeddah, Saudi Arabia: impact of data assimilation with conventional and satellite observations

Abstract

The impact of variational data assimilation for predicting two heavy rainfall events that caused devastating floods in Jeddah, Saudi Arabia is studied using the Weather Research and Forecasting (WRF) model. On 25 November 2009 and 26 January 2011, the city was deluged with more than double the annual rainfall amount caused by convective storms. We used a high resolution, two-way nested domain WRF model to simulate the two rainfall episodes.Simulations include control runs initialized with National Center for Environmental Prediction (NCEP) Global Forecasting System (GFS) data and 3-Dimensional Variational (3DVAR) data assimilation experiments conducted by assimilating NCEP prepbufr and radiance observations.Observations from Automated Weather Stations (AWS), synoptic charts, radar reflectivity and satellite pictures from the Presidency of Meteorology and Environment (PME), Jeddah, Saudi Arabia are used to assess the forecasting results. To evaluate the impact of the different assimilated observational datasets on the simulation of the major flooding event of 2009, we conducted 3DVAR experiments assimilating individual sources and a combination of all data sets. Results suggest that while the control run had a tendency to predict the storm earlier than observed, the assimilation of profile observations greatly improved the model's thermodynamic structure and lead to better representation of simulated rainfall both in timing and amount. The experiment with assimilation of all available observations compared best with observed rainfall in terms of timing of the storm and rainfall distribution, demonstrating the importance of assimilating different types of observations. Retrospective experiments with and without data assimilation, for three different model lead times (48, 72 and 96-h), were performed to examine the skill of WRF model to predict the heavy rainfall events. Quantitative rainfall analysis of these simulations suggests that 48-h lead time runs with assimilation of all observational data provide best statistical scores.

Impact of Urbanization on the Simulation of Extreme Rainfall in the City of Jeddah, Saudi Arabia

“…During the storm event, the Presidency of Meteorology and Environment (PME) surface observatory at King Abdulaziz International (KAI) Airport in Jeddah recorded accumulated rainfall of 140 mm between 0600 and 1200 UTC. The synoptic meteorological conditions of the event have been well described by (de Vries et al 2016;Yesubabu et al 2016) and are summarized below.…”

“…The large-scale features are important regional factors that produce extreme precipitation, which for a particular case, may exceed three times the average annual rainfall. During such events, a short quasi-stationary mesoscale convective system (MCS) often produces severe weather with heavy precipitation and flash flooding (de Vries et al 2016;Deng et al 2015;Yesubabu et al 2016). The impact of urbanization on thunderstorm development and evolution in the Jeddah area is yet to be revealed when these extreme events occur during the winter season.…”

“…Ten severe weather events were simulated in numerical weather prediction (NWP) mode with a convectionpermitting regional atmospheric model. The strategy for simulating and evaluating the results is as follows: We focused on and analyzed in details the event of the 2009 flood (Yesubabu et al 2016), which is one of the most severe and well-documented weather event that occurred in the Jeddah area. We retrospectively modeled it following a short-term, numerical weather forecasttype mode, based on two simulations accounting for desert and urban land use/land cover: one being desert with no urban scheme and one being city with urban scheme.…”

Analysis of a severe weather event over Mecca, Kingdom of Saudi Arabia, using observations and high-resolution modelling

“…The model has been used to simulate and predict extreme weather events on several scales (e.g. Smith and Barstad, ; Caroletti and Barstad, ; Andrade et al ., ; Ball, ; Fragoso et al ., ; Mukhopadhyay et al ., ; Vicente‐Serrano et al ., ; Couto et al ., ; Hari Prasad and Salgado, ; Raju et al ., ; Yesubabu et al ., ). Most of these studies have focused on the sensitivity of the model to resolve different physical processes contributing to convective systems.…”

“…Previous studies (e.g. Kahana et al, 2004;Krichak et al, 2012;De Vries et al, 2013;Yesubabu et al, 2016) investigated extreme winter rainfall events in the region, showing that these are highly dependent on southeastward propagation of a synoptic scale system from the Mediterranean, the Red Sea Trough. In the present study, a 1 km resolved WRF model was used to investigate the mechanisms that triggered the extreme winds and rainfall on 11 September 2015 over the Mecca region.…”