**Abstract**

Recently, the Kingdom of Saudi Arabia (KSA) has been facing significant changes in rainstorm patterns (rainstorm intensities, frequencies, distributions) causing many flash flood events. The city of Jeddah is located in a coastal plain area, in the middle of the western side of the KSA, which represents a clear case of changing rainstorm patterns. Jeddah has been hit by many rainstorm events, which increased dramatically since 2009 (e.g., one in 2009, one in 2011, one in 2015, and another one happened in 2017). However, in 2018 about six rainstorms occurred. Two major flash flood events occurred in the city in November 2009 and in January 2011. There were significant impacts of these two events causing severe flooding. During these events, 113 persons were announced dead (in the 2009 event), and infrastructures and properties were damaged (roads and highways, more than 10,000 homes and 17,000 vehicles). In addition to that, dam failure occurred in the 2011 event. This situation gives clear evidence in changing the climate system that could cause more storms in the future across the KSA. Generally, Jeddah city has a lack of short-duration data in rainfall stations. In addition to that, there are a limited number of studies that have been done in determining rainstorm patterns. Consequently, the approach of the current study will focus on understanding and determining rainstorm patterns in the period between 2011 and 2017 depending on some digital rainfall stations that have been installed recently in Jeddah city. Rainstorm pattern and the method of distribution are the most crucial factors affecting peak flow and volume calculations. Our findings showed that there are two pattern types for the rainstorms in Jeddah city. Finally, a comparison with SCS-type II distribution was carried out.

**Keywords:** rainfall patterns, floods, impacts, Jeddah, KSA, statistical analysis

## **1. Introduction**

Climate change is a debatable subject these days. Dealing with this topic is considered an enormous challenge of the coming years [1]. There are many definitions of climate; however, the common term of climate is the long-term pattern of meteorological conditions in a specific area [2]. It is measured by evaluating variations in temperature, humidity, atmospheric pressure, wind, precipitation, atmospheric particle, and other meteorological variables. Climate change can have significant impacts on weather conditions around the world, such as storms and heavy rainfall. Climate changes can occur due to different processes internal to the earth, external forces (e.g., variations in sunlight intensity), and human activities that have been increasing recently. Many shreds of strong evidence in many regions regarding the climate changes and variability that is impacted by anthropogenic activities, industries and natural specifications of climate systems are recently available. Among these factors that caused climate change due to changing of the composition of the atmosphere are the greenhouse gas emissions, CO2, CH4, and N2O [3–5].

Many studies related to climate change have emphasized that there is an increase in the rainfall events recently regarding frequency and intensity [6–14]. Rainfall patterns and rate over a region are reliant on the ambient and global water evaporation and to a significant extent on altitude, latitude, and level of humidity [15]. Warmer conditions brought out from increased emissions of greenhouse gases through industrialization cause evaporation and precipitation with varying degree of intensity on individual regions [16].

Various environmental impacts have been witnessed according to climate change including change in the hydrological cycles, availability of water resources, unprecedented rainfalls and floods, unexpected drought frequencies, and changes in natural ecosystems [5, 14, 17–20]. Rain is an essential natural phenomenon which can influence the human life and properties. There are many factors which affect rainfall, such as geographical position, monsoon, topographic, and other factors. Flash flood frequency and severity in the desert areas are generally unpredictable and vary from year to year due to variability in the rainfall values [21–23]. Rainfall in arid areas is spatially variable than that of humid regions and is often described as "spotty," and the impacted area is often limited by the radius of the clouds [24].

It is tough for hydrologists to use unreliable hydrological data (rainfall data) in the design of water-related structures. In most cases, the available rainfall data are limited (few records) and contain some gaps in the time series; rainfall stations are far from each other, with no intensity records; and records are not authentic values due to human errors. Previous studies used historical information to carry out the rainfall frequency analysis to understand the flooding behavior [25, 26]. These studies generally show that the use of historical information can be of great value in the reduction of the uncertainty in flood quantity estimators. A frequency analysis of the data is the most commonly applied method. Several studies were found dealing with the analysis of rainfall intensity in many areas [27–32].

A rain gauge is an instrument that measures how much rain falls in a given set time. Automatic rain gauges are rain gauges that electronically start working once it feels rain on the gauge. They automatically record the data, from measuring to removing the rainfall afterward [33]. Automatic rain gauge systems are required to collect rainfall data at remote locations, especially oceanic sites where logistics prevent regular visits [34]. It is usually based on tipping-bucket rainfall sensor and data logger for measuring the rainfall quantity and intensity during a given period and transmits the data through the GSM/GPRS modem to the desired e-mails and server at user-defined time intervals, and records obtained are of high reliability.

The Kingdom of Saudi Arabia (KSA) is one of the other countries that is impacted by severe events of rainfall in the last decade due to climate change. The intensity and frequency of the rainfalls are unprecedented and cause devastating floods in many KSA regions. Due to the lack of short-duration data in the Kingdom in general and in Jeddah in particular, and the limited number of studies that have determined the pattern of rainstorms, the current research will be a cornerstone in establishing rainfall pattern and behaviors. Determination of rainstorm pattern and method of distribution is one of the most critical factors affecting peak flow calculations. In this work, the Jeddah area was chosen as a unique example of unprecedented rainfall events in the last decade. The rainfall rate and patterns of the Jeddah area will be discussed in detail to extract

**19**

**Figure 1.**

*masses, and (3) maritime polar air masses [39].*

*Statistical Analysis of Rainfall Patterns in Jeddah City, KSA: Future Impacts*

**2. Rainfall distribution in the KSA and recent problems**

been discussed and mapped by several investigators [35–38].

the adequate rainfall intensity patterns that could be used for future predictions. In the current study, the short duration rainfall data recorded by climate stations of the Saudi Geological Survey during the period from 2011 to 2017, as well as the data available at station J134 of the Ministry of Environment, Water and Agriculture, And the conclusion of the general pattern prevailing in these storms, as well as their comparison with the distribution of SCS-Type II, and the conclusion of the intensity curves based on available data. Many rainfall storms were analyzed in this study. It includes the following events (intensity records) 2011, 2014, 2015, 2016 and 2017. However, in the devastating floods that occur in 2009, we do not have intensity records for that event.

The KSA climate is mainly arid and semiarid, except in the northern and southern areas. The arid and semiarid regions have an extreme continental climate with warm and dry summer and very cold winter especially in the central regions of the KSA. To assess rainfall pattern over the study area, it is necessary to define the dominant climatic patterns that have an influence on rainfall distribution over the western province of the KSA. The climatic pattern can best be described by considering the various air masses that affect the rainfall distribution over the KSA area. The influence of the different air masses and the rainfall patterns over the KSA has

Different air masses, which influence the Kingdom's climate, are illustrated in **Figure 1**. These air masses include (1) the monsoon front during the late autumn (maritime tropical air mass) reaches the area from the south, southwest, and southeast. This front that originates in the Indian Ocean and the Arabian Sea during the autumn brings warm and moist air. Outbreaks of westerly air become more frequent, characterized by medium to high intensity over the western and northwesterly regions of the country. This front often picks up further moisture while moving through the Red Sea Trough. (2) The continental tropical air masses are warm and moist coming from the Atlantic Ocean through the Central and North African continent. (3) The maritime polar air masses are derived from the Eastern Mediterranean

*Air masses affecting the climate of the KSA: (1) maritime tropical air masses, (2) continental tropical air* 

*DOI: http://dx.doi.org/10.5772/intechopen.86774*

*Statistical Analysis of Rainfall Patterns in Jeddah City, KSA: Future Impacts DOI: http://dx.doi.org/10.5772/intechopen.86774*

*Rainfall - Extremes, Distribution and Properties*

of intensity on individual regions [16].

Climate changes can occur due to different processes internal to the earth, external forces (e.g., variations in sunlight intensity), and human activities that have been increasing recently. Many shreds of strong evidence in many regions regarding the climate changes and variability that is impacted by anthropogenic activities, industries and natural specifications of climate systems are recently available. Among these factors that caused climate change due to changing of the composition of the

Many studies related to climate change have emphasized that there is an increase in the rainfall events recently regarding frequency and intensity [6–14]. Rainfall patterns and rate over a region are reliant on the ambient and global water evaporation and to a significant extent on altitude, latitude, and level of humidity [15]. Warmer conditions brought out from increased emissions of greenhouse gases through industrialization cause evaporation and precipitation with varying degree

Various environmental impacts have been witnessed according to climate change including change in the hydrological cycles, availability of water resources, unprecedented rainfalls and floods, unexpected drought frequencies, and changes in natural ecosystems [5, 14, 17–20]. Rain is an essential natural phenomenon which can influence the human life and properties. There are many factors which affect rainfall, such as geographical position, monsoon, topographic, and other factors. Flash flood frequency and severity in the desert areas are generally unpredictable and vary from year to year due to variability in the rainfall values [21–23]. Rainfall in arid areas is spatially variable than that of humid regions and is often described as "spotty," and the impacted area is often limited by the radius of the clouds [24]. It is tough for hydrologists to use unreliable hydrological data (rainfall data) in the design of water-related structures. In most cases, the available rainfall data are limited (few records) and contain some gaps in the time series; rainfall stations are far from each other, with no intensity records; and records are not authentic values due to human errors. Previous studies used historical information to carry out the rainfall frequency analysis to understand the flooding behavior [25, 26]. These studies generally show that the use of historical information can be of great value in the reduction of the uncertainty in flood quantity estimators. A frequency analysis of the data is the most commonly applied method. Several studies were found deal-

ing with the analysis of rainfall intensity in many areas [27–32].

A rain gauge is an instrument that measures how much rain falls in a given set time. Automatic rain gauges are rain gauges that electronically start working once it feels rain on the gauge. They automatically record the data, from measuring to removing the rainfall afterward [33]. Automatic rain gauge systems are required to collect rainfall data at remote locations, especially oceanic sites where logistics prevent regular visits [34]. It is usually based on tipping-bucket rainfall sensor and data logger for measuring the rainfall quantity and intensity during a given period and transmits the data through the GSM/GPRS modem to the desired e-mails and server at user-defined time intervals, and records obtained are of high reliability. The Kingdom of Saudi Arabia (KSA) is one of the other countries that is impacted by severe events of rainfall in the last decade due to climate change. The intensity and frequency of the rainfalls are unprecedented and cause devastating floods in many KSA regions. Due to the lack of short-duration data in the Kingdom in general and in Jeddah in particular, and the limited number of studies that have determined the pattern of rainstorms, the current research will be a cornerstone in establishing rainfall pattern and behaviors. Determination of rainstorm pattern and method of distribution is one of the most critical factors affecting peak flow calculations. In this work, the Jeddah area was chosen as a unique example of unprecedented rainfall events in the last decade. The rainfall rate and patterns of the Jeddah area will be discussed in detail to extract

atmosphere are the greenhouse gas emissions, CO2, CH4, and N2O [3–5].

**18**

the adequate rainfall intensity patterns that could be used for future predictions. In the current study, the short duration rainfall data recorded by climate stations of the Saudi Geological Survey during the period from 2011 to 2017, as well as the data available at station J134 of the Ministry of Environment, Water and Agriculture, And the conclusion of the general pattern prevailing in these storms, as well as their comparison with the distribution of SCS-Type II, and the conclusion of the intensity curves based on available data. Many rainfall storms were analyzed in this study. It includes the following events (intensity records) 2011, 2014, 2015, 2016 and 2017. However, in the devastating floods that occur in 2009, we do not have intensity records for that event.
