Climate: Dry

Although the scarcity of water resources in dry climates makes them inimical in modern times for habitation and settlement, dry climates were more favorable for early civilizations. Dry climatic conditions provided a suitable niche for the establishment of Neolithic and Chalcolithic settlements as debilitating waterborne diseases such as malaria and schistosomiasis, which inflict the more humid areas, were less common in arid and semiarid zones.

Flaming mountain, Xinjiang, in northwestern China. Cut off from marine climatic influences and surrounded by high mountains, the region has a dry climate and is extremely hot in summer.

Source: Xiaoping Liang/iStockphoto.

Dry climates have unique qualities, both majestic and fearsome, that have intrigued travelers and investigators alike (see photo). Some hyperarid climates have almost Martian-like landscapes with distinct aeolian features. These climates pose a potential danger for those attempting to travel there because of harsh and extreme weather elements such as high temperature, solar radiation, and lack of humidity. People living in this climate regime were forced to adapt to the very meager, sporadic, and uncertain land productivity and had developed a nomadic lifestyle where grazing was, and in some areas is still, the only economic activity.

Definition

A dry climate is defined simply as an area with perennial water deficit, little biological productivity, little carrying capacity, and restricted human [Page 429]activities. According to the Köppen classification, there are five major climate regimes: tropical rainy, dry, humid temperate, humid cool, and polar. Each regime has subdivisions based on precipitation distribution and/or temperature regimes. A dry climate is simply defined as that which has a substantial negative water balance (precipitation is much less than potential evaporation), either permanently or for the larger part of the year.

Figure 1 A schematic diagram showing the general circulation patterns along with latitudinal pressure distribution

Source: Author.

There is a clear difference between aridity and drought. The first term refers to a condition in which long and sustained conditions of low and highly variable precipitation are the norm in a given area. For instance, the Sahara in North Africa has been typified by very low precipitation for the past several thousand years, and thus, the climate of the Sahara is either arid or hyperarid. On the other hand, drought is a temporary weather condition in which precipitation ceases for a long enough time to cause agricultural, hydrological, and/or meteorological drought. Drought occurs almost everywhere, but its occurrence is more frequent and severe in marginal climates, where precipitation tends to fail more often (e.g., marginal areas separating two contrasting climates—the Great Plains and the Sahel region in Africa).