“Monsoon,” is Arabic in origin, their word for season. Wind systems are prone to seasonal reversals, the spawn of temperature variations between continents and oceans. Traders’ southeastern winds of the Indian Ocean produce a summer deluge as they move onshore, crossing the Indian continent before losing moisture on the slopes of the Aravalli Range. Monsoon deserts such as the Rajasthan of India and Thar Desert of Pakistan spread where dry regions are born west of the range.
Zephyrs near the Earth’s surface scatter the granules aloft as dust or haze. Parched atmospheres are crowded with fragments in suspension, held indefinitely in the biosphere by upward currents of air which support their weight. Saltation moves small particles in the direction of the wind in a series of short hops or skips. A saltating grain may hit other grains that jump up to continue the process. Eolian turbidity currents produce dust storms. Rain passes through and cools the desert. This sinks, chilled and dense, toward the surface and reaches hot ground, deflecting air forward. Turbulence sweeps up surface debris in its wake as a dust storm. Compact winds—dust devils whirl like dervishes over arid land, related to intense local heating and de-stabilization of the air mass. These can create gyrating funnels a kilometer in height.
On occasion, sand seas are wracked by violent storms. When a rare shower is imminent, the water can torrent. Dry stream beds, called arroyos or wadis quickly fill, making human crossings dangerous. Regal waters such as the Nile flow through hostile environments, their volumes derived from rain and snow accumulations from highlands at their origins. Sediments are picked up and deposited as these courtesans meander their way to the sea. Civilizations based on alluvial residues spring up and flower as ripples in their wake.
Desert plants are tolerant of drought and the salt content from small reservoirs of concentrated water that they store in leaves, roots and stems. In Mexico’s semi-arid central plateau regions, plant cover is typically lean, but of great diversity—as is the animal life that benefits from aquifers and springs. Cacti, deciduous trees and aquatic plants thrive, some reintroduced through conservation. Fauna includes species of birds, reptiles and mammals adapted to meager habitats. Reservoirs often support verdant shoreline growth, fish and varieties of birds. The dry chaparral represents a Mexican highland panorama of grasses, mesquite and huizache trees and the stately garambullo or candelabrum cactus. Summer rains turn these regions into palettes of greens interspersed with riots of multicolored blooms.
For the inhabitants of deserts and regions with water shortages, quarrels over allocations in newly appropriated eco-zones readily mushroom into structural conflicts between ethnic lines of demarcation. Equilibrium in vast tracts of the world’s arid and semi-desert areas is dependent upon environmental harmony and balanced equations of soils, climates, water, flora and fauna. Modern conditions such as global warming exacerbate persistent drought. The resulting is widespread famine. In the process of re-adapting to variant ecological habitats, environmental borders are created. Unfortunately for the millions of homeless and dispossessed, these often become ethnic and cultural identification criteria. Fragile ecology means fragile peace.
The supporting document, "Fossil Dunes, Monsoon Deserts" is also available as a separate downloadable product at :