Abstract
Today, climate change imposes enormous challenges on a global scale. The interactions of the balances between the need for development, population growth, massive urbanization generate a negative impact on the presence of these climate changes. One of the direct consequences of these changes is the phenomenon of flash floods, a phenomenon that hit the city of Jeddah (city located in west of Saudi Arabia) twice, one in 2009 and the other in 2011, causing significant human and material damage. Floods are considered as a direct result of the combination of extreme weather and hydrological phenomena; in most cases, the magnitude of these floods is magnified by anthropogenic factors, which increases the risk. According to the risk triangle, risk is defined as a probabilistic function that depends on three essential elements: exposure, vulnerability and hazard. If any of these three elements undergo growth the risk also does so and vice versa. Exposure and vulnerability will depend on the presence of human activities in the study area. This study is conducted on the Wadi Goss watershed as it was one of the most violent basins during the 2009 and 2011 floods. Indeed, we present in this study the extent of the urban extension in the Wadi Goss watershed, since 1984 to days and this by the using Landsat images. Given the nature of the study area, we present a method based on the calculation of various indices followed by a classification operation in order to define the urbanized zones inside the Wadi Goss watershed and then estimate the urban sprawl inside the watershed. We also present in this paper, the characteristics of the watershed as well as the evolution of the urbanized areas exposed to the phenomenon of floods and their contribution to the changes of the hydrological behavior of the basin, and to increase the evolution of the risk of the floods. We have shown through this study that the urban footprint has increased from 90 hectares in 1985 to 850 hectares in 2015. This urban footprint represents 12% of the total area of the watershed. Most of the urban evolution was operated on the wadi area with a concentration in the western part of the basin and especially at its outlet.
Highlights
Jeddah is the second largest city in Saudi Arabia with a population of around 3.5 million, containing about 14% of the total population of Saudi Arabia
One of the direct consequences of these changes is the phenomenon of flash floods, a phenomenon that hit the city of Jeddah twice, one in 2009 and the other in 2011, causing significant human and material damage
Given the nature of the study area, we present a method based on the calculation of various indices followed by a classification operation in order to define the urbanized zones inside the Wadi Goss watershed and estimate the urban sprawl inside the watershed
Summary
Jeddah is the second largest city in Saudi Arabia with a population of around 3.5 million, containing about 14% of the total population of Saudi Arabia It is located in the west coast of Saudi Arabia at latitude 29.21 ̊ North and longitude 39.7 ̊ East (Figure 1). The climate of Jeddah is characterized by high temperatures (Figure 2) and humidity during the summer months with temperatures reaching 40 degrees Celsius This is because of warm air masses with the highest levels of moisture in summer because rising sea temperatures go down in the winter. Most of the rain are light accompanied by thunderstorms usually during the winter months i.e., mainly in November, December and January, and in the spring and autumn resulting from the passage of air depressions from west to east.
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