Drought, an athmospheric hazard

By: Eli Marie Smedsrud

Drought; a temporary shortfall of water supply with hydrological and agricultural impacts.

A long term hazard which develops slowly. Droughts are linked with aridity and desertification. Aridity; a permanent and natural condition. Desertification; associated with human activity and

in degrading ecosystems.

Four ways to describe a drought: Meterological; a measure of rain due to climate. A drought

in one place may not be a drought in a different place. Agricultural; is when the moisture in the soil does not meet

the needs of a particular.

Hydrological; occurs when water supplies are low.

Socioeconomic; is when it starts to affect people,the cummunities and the economcy.

Characterised by deficiency below normal levels for the environment affected.

Impact depends on lack of rainfall, amount of evapotranspiration, runoff and infiltration.

For a drought to develop the lack of rainfall must be enough to cause the soil and groundwater to decline, and result in a reduction in hydrological process producing steamflow.

Initial cause; change in average conditions. A drought in UK does not have to be a drought in Ethipoia.

Droughts are assosiated with three main causes Persistent sub-tropical high-preassure system; if sub-tropical high-

preassure cells increase in area and persistence, droughts may develop and winds may be blocked.

El Niño and ocean-surface temperature changes; If ocean-surface temp. differs from unusual temp. and wind are affected.

Changes in mid-latitude depression tracks; 1. upper westerly winds extend into lower latitudes which result in rain-

bearing depression moving south. 2. changes in the meandering paths of the upper westerlies which are

the result of changes in heat transferfrom low to higher latitudes.

Drought; not confined to any geographical location.

Severity of droughts, a feedback effect in natural systems? Overcropping, overgrazing and tree cover remotion of fragile soils.

No scale of drought magnitude excists. Drought periods may have rainfall, but overall

amounts will be below average and water storage will decline.

Agricultural droughts, when soil moisture is reduced and cannot maintain crop yields, will effect national food production and economic exporting crops.

Impossible to prevent or end droughts. Water storage; building of dams, reservoirs; multipurpose for

irrigation,flood control, water supply and Hazard Eliminating Program(HEP)

Prediction and warning; crop failures, reduced vegetation growth, food and nutrition survey systems.

Community preparedness; In urban areas people are encouraged to adopt water-conservation measures. In rural areas, especially in LEDCs, community preparedness is most critical.

In reality there are little or no strategy; induvidual level, selling stock, praying and govnt. Aid.

Land-use planning; better land management, soil conservation measurements.

Ethiopia; Environmental Educational Program reduce environmental degredation, unfortunately it can not tackle the

wider environmental and political factors involved.

Sharing losses by aid; governmental aid, international aid, non-govnt. Org. Such as Red Cross.

Different kinds of aid; food, money and material…

Risk; ’aid culture’, food not reach those in most need.

Long term; aid help farmers to re-establish, improve communication and health facilities.

Case study; Zambia, drought 1991-1992 Zambia; large

manufacturing and mining sector centered upon copper.

58% of pop. Living in rural areas.

Big maize production, but constantly threatened food supply by droughts.

Population: 10 millions.

1991-92 drought, at the end of a dry decade. Tot. Rainfall 450 mm in 1991-1992 compared to 850 med mer in

the 1970s. 2 millions were affected in the rural areas, while people in the

cities maintained their income and could buy imported food. Due to the flood the maize production fell 40-100%. Farmers

tried to plant later crops, but it all failed. Water stores were already low from the dry years. Flow on the

River Kafue were lowest since 1905 and power generation reduced to 30%.

Wetland and streams quickly dried up, reducing water availability.

The 1992-93 rains brought quickly recoveryon the nature and vegatation, but the effects on the people were long-term.

The drought stripped people for what they had, and they had to sell what they could to survive.

The government in Zambia informed aid donors of the coming

crisis, and there were enough food arriving to prevent famine. People got food, and in return they helped re-building schools,

repairing roads and wells.