A desert climate
Almost the entire Arabian Peninsula is subject to a desert climate. This means that temperatures are very high during the day, with a wide day/night temperature range. On average, temperatures in Riyadh exceed 40°C from June to September. In winter, from November to March, temperatures average below 30°C, the coldest month being January, with an average daytime temperature of 19°C and 11°C at night. The shoulder seasons are very short. In April and May, temperatures rise gradually to stabilize at around 35°C, as they do in October, when the phenomenon is reversed and temperatures fall more sharply. The day/night temperature range varies between 8 and 20°C, with the lowest ranges recorded in winter.
The desert climate is dry, but the coastal areas bordering the Red Sea and the Arabian Gulf are very humid, due to evaporation from the sea. The cities of Jeddah, Mecca, Medina and Dammam are stiflingly hot. Mecca is the hottest city in the country, but the heat record is held by Jeddah, with 52°C recorded on June 22, 2010. On the whole, Jeddah is a few degrees warmer than Riyadh, whatever the season, and has a smaller day/night temperature range.
There can be significant temperature variations within the country at any given time. This is due to the size of the country - over 2,000 kilometers separate the north from the south - but above all to significant differences in elevation. For example, in Tabouk, a northern city built at an altitude of 750 meters, it is advisable to cover up with a down jacket, hat, scarf and gloves in winter, whereas a light sweater is sufficient in Jeddah.
The climatic exception of the Southwest
The province of Asir, crossed by a mountain range, has a semi-arid climate, with limited rainfall, albeit higher than in the rest of the country. Situated in the south-west of the country, between the provinces of Mecca to the north and Jazan to the south, it is in this region that Saudi Arabia's highest peak, Jabal Sawda, rises to 3,133 meters. The temperature range here is one of the widest in the world. While temperatures flirt with 30°C during the day in all seasons, it's not uncommon to wake up to frost on the windows and fog so thick that visibility is close to zero. It can even snow in winter. For these reasons, the Asir region is the greenest in Saudi Arabia, but it also requires appropriate clothing.
Waiting for the rain
Saudi Arabia has very limited rainfall. In Riyadh, the capital in the center of the country, average annual rainfall is 110 mm. Winters are characterized by low rainfall, with a peak in March and April. The average rainfall for this period is 270 mm. The province of Asir, the country's wettest, records an annual average of 500 mm, with a higher rainfall period in March and April. There is no rain in the country during the 4 months of summer, from June to September. Annual rainfall in Saudi Arabia is below the potential evapotranspiration threshold. Evapotranspiration is a biophysical phenomenon that involves the evaporation of water from plants and soils into the atmosphere. As a result, the rare rains that do fall in Saudi Arabia are immediately absorbed by soils and plants, and do not return to the atmosphere to generate new rainfall, unlike in tropical countries.
