Climate

Saudi Arabia climate is mostly a desert with extreme temperature swings between hot days and cold nights with little rainfall. The exception is the region of Asir in the southwest that is humid and warm weather. Factors that control the climate in the Arabian Peninsula are altitude and location to a major water body that can be observed between coastal and inland areas.

Climate Stations

With 30 rain gauge stations that has low spatial and temporal correlation with nearby stations, Saudi Arabia has an insufficient number of rain gauges to analyze the spatial distribution of rainfall. Rainfall analysis is augmented with the use of satellite precipitation data such as Tropical Rainfall Measurement Mission (TRMM), Global Precipitation Measurement and other satellite rainfall products.

Temperature

Saudi Arabia is one of the hottest places in the world where the average annual temperature ranges from 27°C-43°C in the inland to 27°C-38°C in the coastal region. High temperatures and the high annual evaporation rate that from 2500-4500 mm/year would cause additional system losses to the environment. Additional impacts are to agriculture productivity since crops water requirements would be higher due to the higher evapotranspiration rates.

Trends: Temperature has increased over the previous decade. The average temperature has increased 0.60°C per decade over the period during 1979-2009 along with annual minimum and maximum temperature. This trend has also extended to extreme temperatures where the number of stations that has annual occurrence of warm days or warm nights was 92 and 89 percent respectively while there was a significant decrease in the number of cool days and nights at 96 and 93% respectively. Impact of higher temperatures would affect water quality with a decrease in dissolved oxygen and an increase in dissolved organic matter along with more water is required to meet agriculture productivity.

Precipitation

Saudi Arabia is one of the driest places on earth. Rainfall outside the mountains in the southwest is very sporadic within the year, between years and place to place. The average yearly rainfall is 103 mm/year with an annual volume of 166 billion cubic meters where five billion cubic meters is harvestable. The mountainous areas to the southwest receive precipitation in the range of 400-600 mm per year since rainfall frequently occurs throughout the year. For the rest of Saudi Arabia, the central and northern region rainfall is approximately 50-100 mm while the southern and the northwest areas receive 25 mm of annual precipitation. Annual rainfall occurs over one to two thunderstorm events.

Rainfall in the summer or dry season only occurs in the southwestern region due to mountains and strong winds. In autumn, winter, spring season, or the wet season, most of the country receives rainfall that is transported from the Red Sea and the Arabian Sea.

Trend: Rainfall in Saudi Arabia has been decreasing since 1994 for the wet and dry season.  During the wet season from 1979-1994, precipitation was increasing at 12.6 mm/decade, and since 1994 it has been decreasing at 35.1 mm per decade. During the dry season from 1979-1994, rainfall was increasing at 2.0 mm/decade, and from 1994-2009, the rate of decline was 5.5 mm/decade.

Natural Disasters

Saudi Arabia is subject to several different types of disasters from a GFDRR profile, which hydro-meteorological are more prevalent and described here: GFDRR Profile

Saudi Arabia is subject to flash floods in the mountains, and all wadis (ephemeral channels) are in the floodplain and structures are vulnerable after a significant rainfall event. Based on EM-DAT data, the number of floods per decade have been increasing with a varying degree of damages in terms of loss of life, structures and total number of people affected. Jeddah has been vulnerable to major flash floods. For example, the worst flood that occurred was in 2009 that killed 123 people and destroyed over 10,000 buildings and a video show car floating by. The flood observatory map displays flooding location from 2013.

Torrential rainfall is defined as rainfall above 20 mm/day. The total number of torrential rainfalls varies spatially and over time and shown in the table below. When comparing torrential rains based on seasonality between Jeddah and Sharourah, Jeddah did not have any torrential rainfall events from May to September and the average monthly rainfall is less than 0.5 mm. Torrential rainfall in Sharouah happens most months of the year.

As rainfall is a renewable resource that can potentially provide 5 BCM to annual recharge to the shallow aquifer, Saudi Arabia has 22 pools to harvest rainwater and 521 surface and underground dams to currently capture 2.3 BCM in 2019. There are plans to build an additional 1000 dams and 50 pools to capture an additional 1.82 BCM.