A geography of dust storms in South‐West Asia

Mean annual dust storm frequencies are mapped for south-west Asia (Iran, Afghanistan, Pakistan and India) showing areas of greatest activity in two regions: an area at the convergence of the borders of Iran, Afghanistan and Pakistan that comprises the Seistan Basin, Registan and north-western Baluchistan; and the plains of Afghan Turkestan. The highest average annual number of dust storm days is 80.7 at Zabol in Iranian Seistan. Little dust-raising activity occurs on the Indian peninsula. Dust storms occur principally during the dry season months of spring and summer. Local and regional meteorological conditions associated with dust storms are described, ranging from the short-lived dust devil measuring tens of metres across to dust plumes visible on satellite imagery. Dust is transported from the region north to Asian states of the U.S.S.R., south over the Arabian Sea and east over south-east Asia. The importance of soils in the wind erosion system is indicated. Dust storms commonly occur on fine-grained material, particularly loess, alluvium, silt, clay and other outwash sediments. Dust storms have received a variety of names locally in the region. Dust storm frequency during the peak season in northern India is found to be poorly related to mean rainfall, mean wind speed and a climatic wind erosion factor, C developed by Chepil et al. (1962).