**5. Research findings and discussion**

### **5.1 Variable and torrential rainfall**

It can be seen from **Figures 7** and **8** that the rainfall pattern of the Jeddah area is characterized by a great interannual variability marked by the alternation between wet years (as in 1996, when 284 mm was recorded) and completely dry years, as in 1986 (where no raindrop was reported according to the data processed). As for the seasonality of the rains, it is observed that the precipitation is winter (they begin in October and end in April, **Figure 8**) [8]. These are the typical characteristics of the temperate and Mediterranean climate. This is not the monsoon regime that is generally active in July and September. We can also say that it is the month of November which records the maximum of precipitations and for which the services of civil protection must be more vigilant to envisage periods of water levels in *wadis* and floods. Analysis of daily rainfall (even if the latter do not cover the whole period) is revealing. It shows that the daily rainfall during the 2009 flood (70 mm) "Flash flood or crue eclair" are the largest in 24 hours since 1979. This extreme event combined with the urban growth experienced in the city in this period explains the severity and magnitude of the disasters recorded. The 1970s did not experience major floods, despite large amounts of precipitation falling (1972, 1973, 1978, and 1979); this is due to the absence of urban expansion in this period in risk areas (*wadi* beds). The year 1996 had an exceptional year-to-date, but did not do any damage because the rains fell over several days [9, 10].

**73**

**Figure 9.**

*Flood Risk and Vulnerability of Jeddah City, Saudi Arabia*

It has become clear that Saudi Arabia is located in new climatic trends, represented mainly by torrential rains. This was obviously marked by events of frequent natural disasters and especially intense rainfall in different parts of the territory [4]. Disasters recorded in 2009 and 2011 are caused by problems of urbanization combined with the frequency of precipitation that was recorded in less than 2 hours. The city of Jeddah does not have a truly effective system of sanitation and drainage, especially the southern part of the city where the houses are located in *wadi* beds and poorly built because they do not conform to technical standards. Significant rainfall events recorded in recent years and widely reported in the media are those of January 2011 "75.9 mm"; December, 2010 "65.6 mm"; and November,

We put emphasis on the fact that anthropogenic pressure has aggravated the extent and scope of flooding, in particular the phenomenon of urban extension along the rivers in their lower reaches, as is the case, for example, in "*wadi* Assir, *wadi* Al Asla" (**Figure 10**) where homes were recently built without taking into account any assessment of natural disaster risks. A recommendation is made to apply similar studies for flood risk assessment in Saudi Arabia using the same

Constructions in littoral zones result in a destruction of the environment. The sea is a space that is subject to planning and development for leisure activities. The population has no sense of the littoral environment; thus, it takes an education policy, aiming to enhance the image of the environment and to demonstrate the factors that could effectively contribute to stopping the destruction of nature [6]. The impact of urbanization and the delimitation of its extension is one of the

*DOI: http://dx.doi.org/10.5772/intechopen.82073*

*Average monthly rainfall in Jeddah 1970–2014.*

2009 "70 mm" (**Figure 9**).

**Figure 8.**

method applied in this research.

*Total daily maximum rainfall in Jeddah (1970–2010).*

**Figure 7.** *Annual total rainfall in Jeddah 1970–2017.*

*Flood Risk and Vulnerability of Jeddah City, Saudi Arabia DOI: http://dx.doi.org/10.5772/intechopen.82073*

**Figure 8.**

*Recent Advances in Flood Risk Management*

**5. Research findings and discussion**

because the rains fell over several days [9, 10].

**5.1 Variable and torrential rainfall**

It should be noted, however, that the data used do not allow for immediate monitoring of the catastrophic floods that occurred in 2009 and 2011. The lack of information on the intensity and duration of rainfall data that caused the floods does not allow for a detailed analysis of rainfall conditions. For this reason, we will limit ourselves to a general descriptive analysis of the 1970-2017 rainfall data sets for the Jeddah station. At the level of remote sensing data, we did not find SPOT or Landsat images within 3 days after the floods, whereas beyond this period the traces of flood are no longer visible on the satellite imagery, as shown in **Figure 6**. We note that phenomena are as violent as ephemeral. The only image in our possession that is close to the January 27 flood is a Landsat ETM+ acquired on February 1, 2011 (**Figure 6**). The data at our disposal nevertheless allow the monitoring and mapping of the most vulnerable areas.

It can be seen from **Figures 7** and **8** that the rainfall pattern of the Jeddah area is characterized by a great interannual variability marked by the alternation between wet years (as in 1996, when 284 mm was recorded) and completely dry years, as in 1986 (where no raindrop was reported according to the data processed). As for the seasonality of the rains, it is observed that the precipitation is winter (they begin in October and end in April, **Figure 8**) [8]. These are the typical characteristics of the temperate and Mediterranean climate. This is not the monsoon regime that is generally active in July and September. We can also say that it is the month of November which records the maximum of precipitations and for which the services of civil protection must be more vigilant to envisage periods of water levels in *wadis* and floods. Analysis of daily rainfall (even if the latter do not cover the whole period) is revealing. It shows that the daily rainfall during the 2009 flood (70 mm) "Flash flood or crue eclair" are the largest in 24 hours since 1979. This extreme event combined with the urban growth experienced in the city in this period explains the severity and magnitude of the disasters recorded. The 1970s did not experience major floods, despite large amounts of precipitation falling (1972, 1973, 1978, and 1979); this is due to the absence of urban expansion in this period in risk areas (*wadi* beds). The year 1996 had an exceptional year-to-date, but did not do any damage

**72**

**Figure 7.**

*Annual total rainfall in Jeddah 1970–2017.*

*Average monthly rainfall in Jeddah 1970–2014.*

It has become clear that Saudi Arabia is located in new climatic trends, represented mainly by torrential rains. This was obviously marked by events of frequent natural disasters and especially intense rainfall in different parts of the territory [4]. Disasters recorded in 2009 and 2011 are caused by problems of urbanization combined with the frequency of precipitation that was recorded in less than 2 hours. The city of Jeddah does not have a truly effective system of sanitation and drainage, especially the southern part of the city where the houses are located in *wadi* beds and poorly built because they do not conform to technical standards. Significant rainfall events recorded in recent years and widely reported in the media are those of January 2011 "75.9 mm"; December, 2010 "65.6 mm"; and November, 2009 "70 mm" (**Figure 9**).

We put emphasis on the fact that anthropogenic pressure has aggravated the extent and scope of flooding, in particular the phenomenon of urban extension along the rivers in their lower reaches, as is the case, for example, in "*wadi* Assir, *wadi* Al Asla" (**Figure 10**) where homes were recently built without taking into account any assessment of natural disaster risks. A recommendation is made to apply similar studies for flood risk assessment in Saudi Arabia using the same method applied in this research.

Constructions in littoral zones result in a destruction of the environment. The sea is a space that is subject to planning and development for leisure activities. The population has no sense of the littoral environment; thus, it takes an education policy, aiming to enhance the image of the environment and to demonstrate the factors that could effectively contribute to stopping the destruction of nature [6]. The impact of urbanization and the delimitation of its extension is one of the

**Figure 9.** *Total daily maximum rainfall in Jeddah (1970–2010).*

**Figure 10.** *Urban extension along the wadis beds, flood 2009 (IKONOS image, after [7]).*

fundamental concerns of the management and planning of space. The urban perimeter is an essential data in an analysis for the determination of the peripheral growth of large cities and to highlight the choice of the location of new constructions [11] in [12]. Beginning around 1980, an accelerated impact of construction of buildings, roads, port facilities, and recreational areas has affected the urban area of Jeddah. The area of the city increased from 6200 ha in 1966 to 9500 ha in 1972 and 68,500 ha in 1986; it reached 110,000 ha in 2018 (**Figure 11**).

The growth of the city is mainly toward the north along the plain of Tihamah. The urban expansion that started out in anarchy is nowadays planned. The first steps to be adopted were legislative, beginning with the regulation of the private and public uses of space and activities.

The demarcation of risk areas was established by spatial analysis. The map was made by combining the layers of urban extension zones and the hydrographic network (**Figure 12**). The approach to identifying flooded areas from satellite images was mainly applied using direct visual interpretation and field verification.

**Figure 11.** *Urban extension of Jeddah city between 1966 and 2018 and its topographic context (from remote sensed data).*

**75**

**Figure 12.**

priate management of natural risks [13].

*Natural flood and torrent risk map (after Al Saud M [14]).*

**5.2 Environmental impact assessment of floods**

*Flood Risk and Vulnerability of Jeddah City, Saudi Arabia*

As a result, a map showing risk areas with different levels of damage was produced. For this purpose, we have identified three flood risk zones: the first zone, representing the very high risk, refers to the direct contact strip between the *wadis* and the urban fabric. The second zone presents a high risk, which groups the zones next to the first, at the level of the third zone, which, with moderate risk, is located in the sectors bordering on the second zone. The proposed map is the result of a synthesis that should be completed and validated to adjust and take into account other risk factors. This research could therefore serve as a decision-making tool and constitute a discussion paper for a rigorous spatial planning of the city of Jeddah. Strengthening the legislative framework is necessary at the present time for appro-

The rainfall that fell over certain areas of the study area was concentrated, but many of the natural-like areas of the affected area are still at risk if the same

*DOI: http://dx.doi.org/10.5772/intechopen.82073*

*Recent Advances in Flood Risk Management*

fundamental concerns of the management and planning of space. The urban perimeter is an essential data in an analysis for the determination of the peripheral growth of large cities and to highlight the choice of the location of new constructions [11] in [12]. Beginning around 1980, an accelerated impact of construction of buildings, roads, port facilities, and recreational areas has affected the urban area of Jeddah. The area of the city increased from 6200 ha in 1966 to 9500 ha in 1972 and 68,500 ha

The growth of the city is mainly toward the north along the plain of Tihamah. The urban expansion that started out in anarchy is nowadays planned. The first steps to be adopted were legislative, beginning with the regulation of the private

The demarcation of risk areas was established by spatial analysis. The map was made by combining the layers of urban extension zones and the hydrographic network (**Figure 12**). The approach to identifying flooded areas from satellite images was mainly applied using direct visual interpretation and field verification.

*Urban extension of Jeddah city between 1966 and 2018 and its topographic context (from remote sensed data).*

in 1986; it reached 110,000 ha in 2018 (**Figure 11**).

*Urban extension along the wadis beds, flood 2009 (IKONOS image, after [7]).*

and public uses of space and activities.

**74**

**Figure 11.**

**Figure 10.**

**Figure 12.** *Natural flood and torrent risk map (after Al Saud M [14]).*

As a result, a map showing risk areas with different levels of damage was produced. For this purpose, we have identified three flood risk zones: the first zone, representing the very high risk, refers to the direct contact strip between the *wadis* and the urban fabric. The second zone presents a high risk, which groups the zones next to the first, at the level of the third zone, which, with moderate risk, is located in the sectors bordering on the second zone. The proposed map is the result of a synthesis that should be completed and validated to adjust and take into account other risk factors. This research could therefore serve as a decision-making tool and constitute a discussion paper for a rigorous spatial planning of the city of Jeddah. Strengthening the legislative framework is necessary at the present time for appropriate management of natural risks [13].
