Desert Climate

Desert climate is a type of climate characterized by extremely low precipitation throughout the year, where evaporation exceeds rainfall and arid conditions dominate. It is commonly found around the 30th parallels, within the tropics. Due to descending air movements in this zone, cloud formation is inhibited and rainfall becomes exceedingly rare. Desert climates can occur in both hot and cold regions.

In the Köppen climate classification, desert climate is denoted by the letters “BW.” Hot desert climate is classified as BWh, while cold desert climate is designated as BWk. This classification is determined based on the relationship between precipitation and temperature, as well as vegetation cover. In hot desert climates, temperatures remain high throughout the year, whereas winters in cold desert climates can be severely harsh.

Climate Characteristics

• Precipitation: Annual precipitation in desert regions is generally below 250 mm, and in some areas it can drop as low as 50 mm.
• Temperature: The temperature difference between day and night is very large. Daytime temperatures can exceed 45°C, while nighttime temperatures may fall below 0°C.
• Humidity: Humidity levels are very low, which enhances evaporation.
• Evaporation: Evaporation rates far exceed precipitation. This is one of the most important factors accelerating desertification.
• Vegetation Cover: Water-resistant (xerophytic) plants are found only in limited numbers. In some areas, no vegetation grows at all.

Causes of Formation

Several key factors contribute to the formation of desert climate:

• Atmospheric circulation: High-pressure zones at 30° latitude cause descending air movements that prevent cloud formation and precipitation.
• Continentality: In inland areas far from the sea, moist air masses cannot reach, leading to desertification (e.g., the deserts of Central Asia).
• Orographic barriers: When warm, moist air masses are blocked by mountains, precipitation occurs on the windward slopes, while the leeward side experiences aridity (rain shadow effect).

Global Distribution

The hot desert climate is found in regions such as the Sahara Desert in North Africa, the Arabian Peninsula in the Middle East, the interior of Australia, and the Atacama Desert in South America.

The cold desert climate predominates in the interior regions of Central Asia and certain high-altitude areas, such as the Gobi Desert.

Situation in Türkiye

Türkiye does not have a classic hot desert climate. However, certain regions, particularly the Central Fırat section of Southeastern Anatolia, may experience conditions similar to desert climate during summer months. According to the Aydeniz classification method, desert climate conditions have been observed in some months at stations such as Gaziantep, Adıyaman, and Şanlıurfa. In particular, the Şanlıurfa station has been identified as the region experiencing the highest annual frequency of desert climate conditions. Analyses indicate that desert climate conditions prevail in this area for approximately 47% of the year.

Drought and Its Effects

Desert climate is synonymous with persistent drought. Low rainfall renders agricultural production nearly impossible, and limited water resources restrict human settlement. Soil fertility declines due to high temperatures, dryness, and wind erosion, leading to degradation. The persistence of drought brings about socioeconomic challenges.

Evaluation According to Climate Classifications

• Köppen: A distinction is made between hot desert (BWh) and cold desert (BWk), classified based on annual average temperature and precipitation distribution.
• Trewartha: Similar to Köppen, desert climate is denoted by the BW symbol, but the desert threshold is determined by a different formula:

BW is defined by Y<10×(T−10)+3P

Where T is the annual average temperature and P is the summer precipitation ratio.

• Aydeniz Method: Months with a humidity coefficient (Nks) below 0.40 are classified as desert.
• De Martonne: Areas with a very low aridity index (Ia) are defined as desert.
• Erinç and Thornthwaite: Aridity levels are determined based on the evaporation-precipitation relationship; desert regions are those with the most severe water deficits.