Sand and dust storms are regular occurrences around the world and more common in arid and semi-arid regions, such as the Middle East. Dust storms play an important role in global dust cycle, and can alter the radiative balance. It can damage agricultural crops and retard plant growth and alter the life cycle of the marine benthic organisms due to less sun light penetration into the sea floor. Dust storms can cause social disruption, economic loss and adverse impact on human health.
When the visibility is below 1000 meters on a dusty day, it is considered that dust storm is occurring. Sand and dust storms should not be confused with other types of dusts such as rising dust, suspended dust and haze. The former are mostly associated with dry and hot northerly and north-westerly winds locally whereas the latter are mostly caused by human activities. Many studies have shown that dust oscillation at local level is associated with strengthening and weakening of low level tropospheric wind. The dust storm occurs at any place when there is an interaction of weather event with soil and land management such as soil structure and vegetation cover.
Sand and Dust Storms in Arid Countries
The major source of sand storm in arid countries are the presence of desert itself. The Sahara Desert itself accounts for 25% of the suspended micro particles in the atmosphere. The total worldwide annual production of dust by deflation of soils and sediments was estimated to be 61 to 366 million tonnes. From Africa alone it is estimated that more than 100 million tonnes of dust per annum is blown westward over the Atlantic. Arabian Peninsula is also recognised as one of the major dust sources of the world.
The major source of present day sand and dust storms are the subtropical desert regions and the semi-arid and sub-humid regions, where dry exposed soil is subject to severe winds at the dry period of the year, i.e. the summer time. In the Gulf region, the regional sources of dust and sand are alluvial plains of southern Mesopotamia, Syrian Desert, Jordan and North Saudi Arabia. The dust storms in the region are dominated by Shamal winds, which is the local name for the northerly and north-westerly winds.
In the desert regions, there are two main factors that have been identified as causing sand and dust storms. These are geographic condition and climatic conditions. Some of the components of these two conditions are;
- Loose and dry sand, dirt, lack of vegetation or land cover
- strong seasonal wind speed on the ground
- Surface air turbulence due to huge amounts of radiation in the region
- Vertical and unstable weather conditions,
- Dry surfaces due to lack of rain.
- Decrease in soil moisture and the soil/ sand binding capacity due to reduced or lack of rainfall
- Anthropogenic factors such as land clearing and desertification
The frequency of dust storms during the summer time are more as it provides the most favourable climatic conditions for the same. Human induced changes are also considered as significant factors in increase in occurrences of dust storms in some non-arid regions.
Local and Global Impact of Dust Storm on Climate
Dust particles in the air, also known as dust aerosols, cause a shielding effect similar to rain cloud. Hence, dust aerosols can alter the climate by intercepting incoming radiation from the sunlight, reducing the net radiation at the surface during its occurrence. Net radiation is equal to absorbed sunlight minus thermal radiation emitted by the surface back to the atmosphere. This causes a local cooling effect for a temporary period of time. The temperature can reduce by 10C due to diminished sunlight falling onto the surface. However, dust aerosols differ from sulphate aerosols emitted from volcanic eruption activities.
Sulphate aerosols are lofted into the stratosphere following the eruption. They reflect sunlight back into space and reduce the amount of radiative heating both within the atmosphere and at the surface. However, the displacement of solar heat away from surface at local level due to dust aerosol alters the Earth’s climate. The cooling effect can only remain for a short period of time as heat from surrounding warmer region gets transferred to the dust affected region to bring an equilibriumin temperature distribution and hence offsetting the cooing effect. Therefore, the local temperature returns to normal after a short period of time.
Cooling effect of Arabian dust cloud can sometimes be extended from northern Asia to the Pacific and North America when the atmospheric circulation that connects the regions downwind to beneath the dust cloud.
Effect on Sustainability
Sand and dust storm can cause negative impacts on three pillars of sustainability; society, economy and environment. As the dust cloud rises, it reduces the horizontal visibility. Low visibility can affect human life in many ways. The fine suspended particles also contain contaminants, bacteria, pollens, which cause negative health impacts such as allergies and respiratory diseases. Dust also carries air borne pollutants such as toxins, heavy metals, salt, sulphur, pesticides etc. They cause significant health impacts when people inhale the contaminated dust. Dusts can corrode buildings and other built infrastructure since it is contains high level of salts particularly in the dust storms of deserted gulf region.