Extreme Rainfall and Flash Flooding in Jeddah City
In 2009 and 2011, Jeddah City in the middle of the western region of Saudi Arabia experienced short, but intense rainfall events with rainfall precipitation values of 70 mml and 110 mml that led to flash floods. The World Bank climate adaptation expert, Balgis Osman-Elasha, defines an extreme rainfall event as one with “an intense rainfall and high quantities of rain (more than 90 millimeters) over a short span of time (four hours) over an area that normally receives 45 millimeters per year.” These flash floods had catastrophic consequences resulting in the death of 113 people in 2009 and damage to 10,000 houses and to 17,000 vehicles.
When analyzing the factors that led to the flash floods, rainfall and climate change factors played a major role contributing to the worsening of the flood disaster. Youssef et al.’s study in 2015 indicates a direct correlation between the magnitude and frequency of intense rainfall events and climate change. This result was reached by conducting a frequency analysis in which the maximum daily rainfall amount corresponding to a set of return periods of 25, 50, 100, and 200 years were calculated for the Jeddah city to determine the temporal effect of climate change on rainfall characteristics. These effects can include an increase or decrease in precipitation. A study using time-series data and descriptive statistics were used to determine the temporal trend in rainfall data and found a trend slope of 0.35, with a Pearson’s correlation coefficient (r) of 0.16, with a p-value of 0.36. These results indicate a moderate positive correlation of the annual maximum rainfall with increasing time. Based on this result, the precipitation was increased by about 27.8%. Thus, the study showed that the rainfall values changes and the increasing number of rainfall events are consequences of climatic changes. Many of the policy changes are in the form of recommendations such as conducting a detailed hydrological study of the recently-constructed human settlements that are along watercourses and at outlets downstream of wadis (valleys), and establishing a flash flood warning system for all areas that are subjected to flash floods.
Climate Change to hit Saudi’s Agriculture, Water
Ahmed M. Youssef, Saleh A. Sefry, Biswajeet Pradhan & Emad Abu Alfadail (2016) Analysis on causes of flash flood in Jeddah city (Kingdom of Saudi Arabia) of 2009 and 2011 using multi-sensor remote sensing data and GIS, Geomatics, Natural Hazards and Risk, 7:3, 1018-1042, DOI: