Last update: March 30, 2012 08:36:58 AM E-mail Print

 

TOWARDS A BETTER UNDERSTANDING OF DROUGHT

 

J Booysen

 

Science has not yet come to grips with the phenomenon of drought. Nor have scientists yet been able to describe drought adequately, says Mr Johann Booysen, Head of the Agro-meteorology Section at the Grootfontein College of Agriculture.

Mr Booysen is researching the subject of drought as it occurs in the Karoo. He hopes to throw more light on the nature and incidence of this phenomenon which is a perpetual cause for concern among farmers in these areas.

In his recent address at the Congress of the Grassland Society of Southern Africa, held at the Grootfontein College of Agriculture, he said that the effects of drought have given rise to a number of investigations such as the Drought Investigation Commission of 1923, the Desert Encroachment Committee of 1951, and the Agricultural Investigation Commission of 1968, 1970 and 1972.

To minimise the effects of droughts, numerous recommendations have been made, including the resting of veld and the planting of drought-hardy species. Various financial measures have also been employed, such as the Veld Reclamation Scheme of 1966, the Stock Reduction Scheme of 1969 and the Drought Relief Plan of 1983.

Financial aid for farmers in terms of fodder loans, subsidies and rebate on transport of fodder in drought-stricken areas has amounted to R11,5 million in 1979/80, R28,1 million in 1980/81 and R23,1 million in 1981/82.

Mr Booysen also pointed out that droughts not only take their toll of the vegetation, but also have economic implications which may lead to the depopulation of extensive farming areas and give rise to unemployment and impoverishment of certain sections of the population.

Although the phenomenon of drought has been subjected to much scrutiny over the years, it has remained elusive and most attempts to evaluate it have been too subjective as well as too difficult to implement.

Mr Booysen has therefore set out to find a suitable definition of drought so as to identify and assess it objectively.

It is foreseen that Mr Booysen's method of drought evaluation could play a valuable role in the assessment of drought intensity for the purposes of the new Drought Relief Plan.

At the Congress Mr Booysen explained that a drought should be seen as a period in which there has been a decline in the amount of rainfall that is normally expected in a given area.

He said that farmers should not become confused between drought and natural aridity. An area is considered arid if low rainfall is a natural climatic feature of that area. On the other hand, a drought condition implies that uncharacteristically low rainfall is being experienced.

Mr Booysen defines drought as “a period during which the actual moisture supply at a given place rather constantly falls short of the climatically expected moisture supply". The severity of such a drought, however, depends upon preceding weather conditions and the time aspect involved.

Using 'Real Time' data collected from many weather stations all over the Karoo, Mr Booysen is able to produce maps depicting the extent and degree of drought conditions over this area. Wetter and drier areas are indicated on the maps by 13 different tones of grey.

Mr Booysen's drought map is derived from an analysis of such information as water budgets, water balance, precipitation and severity indices.

Evaluation of the drought situation is usually done on a monthly basis, but, since the whole system is computerised, it is possible to look at the effect of any individual shower on the current situation.

An index of -1 in a given area indicates that a drought situation is already establishing, but such a drought only becomes disastrous when the index drops to -4.

From the monthly drought maps produced over the past 2 years, it is clear that the northwestern parts of the Karoo have constantly been subjected to disastrous drought conditions during this period.

On comparing the Karoo Region with other summer and all-year rainfall areas, Mr Booysen found that the drought problem is without doubt concentrated within the Karoo and the northwestern parts of the country.

He explains that there are many reasons for the high frequency of droughts in the Karoo areas. These include the up to 35% variability of seasonal rainfall, the natural aridity of the region, the uniformly low topography, the low moisture content of the atmosphere and the unfavourable geographical position of these parts in relation to the general air circulation patterns passing from west to east over South Africa.

He also notes that it appears as if the Karoo goes into some sort of dormant state with no significant change in drought conditions during autumn and the beginning of spring.

On studying other areas of the country, he says it is striking to observe the greater sensitivity of the crop production areas to drought, compared with the livestock production areas.

 

 

Published

Karoo Regional Newsletter Autumn