The causes of drought can be divided into two main categories namely natural causes and anthropogenic causes. Natural causes will include the shifting of rain belts, the El Nino/ Southern Oscillation effect and lastly, global warming. Anthropogenic factors on the other hand will include rise in population densities and the rapid conversion of natural ecosystems to farmlands.
The ITCZ can shift in position depending on the movement of the overhead sun thus, locations that lie within this fluctuating zone will experience wet and dry seasons with rainfall lasting for 5 to 6 months a year on average. The dry seasons will tend to occur with the period where the sub-tropical high-pressure belts lies across a particular area (20-30° North and South) due to the shifting of the ITCZ. This area will experience high pressure which prevents the formation of rain clouds thus, leading to the formation of deserts. The size of these areas will also vary from year to year and in years where the areas are larger, droughts along the desert edges will occur.
El Nino is the term used to describe an extensive warming of the upper ocean in the tropical eastern Pacific lasting up to a year or even more. They are normally linked with a change in atmospheric pressure known as the Southern Oscillation (SO).Under normal atmospheric conditions, pressure rises over the eastern Pacific Ocean and falls over the western Pacific Ocean. This creates a circulation system where the upper air moves from west to east and the surface air from east to west as the trade winds. During El Nino, there is a reversal in these conditions and this allows the ITCZ to migrate southwards and causes the trade winds to weaken in strength or even to be reversed in direction. The air will now descend over South East Asia instead of the eastern pacific, giving us much drier conditions and even droughts at times.
Global warming is the result of the escalation of the greenhouse effect and rising global temperatures. This may cause climate boundaries to shift their positions, making some regions wetter while others become drier and it may also cause the frequency of El Nino to increase, which will worsen drought conditions.
A rise in population densities will cause droughts as the population far outstrips food production. The rise in demand leads to the progressive conversion of natural ecosystems into farmland which has given rise to desertification when the cropland are over cultivated, fallow seasons are shortening and mismanagement of irrigated croplands. Desertification is the permanent transformation of the land surface by human activities to resemble a desert. An example would be the Sahel Region at the edge of the Sahara Desert where the annual precipitation is only 250-500mm.
Thus, as we can see, a combination of anthropogenic factors and natural factors are responsible for causing droughts to occur and worsen over the years.
Having seen the factors that cause drought, we will have to analyze how to manage droughts by studying the impacts, the mitigation, the prediction and the response of drought disasters. We will find that often, the management of droughts is made more difficult by the poverty factors and uneducated farmers.
The impacts of droughts can be studied from four directions namely, economic, mortality and the impact of drought on the physical environment itself.
Economically, droughts leads to not only crop loss but it also has an effect on smallholder agricultural households and the effects can be felt indirectly when the market price of food increases as it becomes more scarce. People who depend upon income from farm work, food processing or food transport and marketing will lose their income when food production is affected by droughts. What we have to note is that the economic impacts for relatively simple and predominantly agricultural economies are greater than a developed economy which is well-diversified into different industries and markets. In the Sahel region in East Africa, up to 90% of harvests were lost as a result of the drought.
Crop loss as a result of the drought causes wide-spread famine and high mortality rates as people die from hunger related diseases. This is often made worse by bad government planning and civil wars which drive people out of their land. In the 1973 drought in Sahel, over 100 000 people were killed as a result of starvation. In America, in the 1930s, during the Dust Bowl years, every one in ten farmers was forced to change land at the height of the drought. The drought also leads to the loss of livestock as there is insufficient grazing ground for the animals to feed on. In the Sahel, over 25% of cattle have died as a result of droughts.
Lastly, droughts have a huge impact on the land surface as the lands that were previously arable are being turned into desert slowly through desertification. Desertification occurs when the lands are over-cultivated and not given time to fallow, This leads to the land being stripped of its moisture and nutrients faster than usual, rendering the land useless and under persistent drought, the land will eventually dry up to form deserts. Desertification has worsened the existing hunger problems as there is now less arable land available for cultivation and this has also led to an increasing mortality rate. The Sahel region in particular, is facing this imminent problem of desertification where droughts in the 20th century covered close to 6.7 million square kilometers, affecting a total of 24 million people.
To prevent the situation from worsening, steps must be taken to combat against desertification and droughts and this can be done through mitigation and prediction. Prediction can be done by forecasting and monitoring conditions in drought-prone areas to look for early sign of an oncoming drought period. One way of predicting drought is to use weather records to forecast two fundamental meteorological variables: precipitation and temperature. The historical occurrence of drought will provide a better basis for us to make informed decisions. The PSDI is the most effective index in place currently in determining long term drought. A value of 0 means conditions are normal and any negative values represents the severity of the droughts. The historical frequency, duration and spatial extent of previous droughts will help people to prepare better by projecting possible situations. However, this prediction method only works for long term periods and is of little use in predicting short term drought. Prediction accuracy varies between region but a current project called The Tropical Ocean has produced results that suggest that it may be possible to predict certain climatic conditions associated with ENSO events more than a year in advance. For regions which are affected adversely by ENSO events, this will lead to more accurate forecasting and better preparation.
There are also two global warning systems in place to anticipate crop failure and food shortage: the UN-sponsored Global Information and Early Warning System (GIEWS) and the USA-sponsored Famine Early Warning System (FEWS NET). These were developed after the Sahel droughts of 1970s to 1980s. Both systems rely on multi-agency support and focus on large-scale monitoring and forecasting activities to support potential intervention at a more local level. The primary data they get comes from satellites that produce near real-time images on a 10 day basis. The rainfall and vegetation estimates are than processed into maps of current and forecast conditions for staple food and crops and pasture land. These reports are produced regularly and when danger threatens, local field reports will be done to assess the situation at hand. However, this large-scale system is not able to detect food security issues at the sub-national or local levels, when the prompt detection of failing supplies is necessary to prompt swift reactions from donors.
However, prediction is still rather undeveloped due to the fact that droughts are hard to identify as it is a creeping phenomenon, developing over time and area. This hinders efforts to identify drought thus, reducing the probability of alerting people of the danger months before, giving them sufficient time to prepare.
Another way of managing droughts is through mitigation. The first way is through increasing permanent vegetation cover so as to increase the ability of the land to retain moisture, so as not to exacerbate drought conditions. This can be done through planned crop rotation to minimize erosion and Xeriscaping, which involves the planting of drought-tolerant species. For example, in Mozambique, Oxfam has provided aid in the development of drought- resistant sweet potato production. This is also increasingly popular in West United States.
Population control is also essential so as to reduce the pressure on existing lands for food. Animal population control is essential and this can be done by reducing numbers, weaning the calves and segregating / diversifying herds. When there is insufficient food, less useful animals may have to be sold off to reduce pressure for food. Weaning of calves gives the cow a higher chance of living as the body’s resources are strained less by not producing milk. Herd diversification ensures that animals with different grazing habits are reared such that in the case of droughts, reducing the risk of pasture failure. These livestock are than eaten or sold off during the worse times of drought. Building aqueducts to transport water from a remote source to a desired location is another way. In Malawi, simple irrigation systems are being built to help provide water for the lands.
Mitigation is a more reliant and more useful prevention method in the management of drought. However, the problem we have to recognize is that many of the farmers are poor and uneducated, as such they may find it hard to adapt to new ways of farming and very often, the techniques may require expensive seed such as drought resistance crops.
For drought management to be successful, response is crucial as well. Resettlement is a way of evening out population densities such that the population pressure on a land will be reduced. This will prevent the problem of over- cultivation occurring which leads to desertification during periods of drought. Food aid is one of the most important humanitarian response of the international community towards drought. For many LDCs, they have become dependent on food aid during periods of drought. However, food aid is not necessarily useful as very often, corruption means not all the food reaches the needy people and moreover, the type of food provided may not be the most suitable for the dietary needs of the people there such as the young and the old. Charity programs such as Oxfam and Mercy relief also play important roles as they often provide long term help in the re-development of crop planting for the people affected, giving them a livelihood again. Response however often occurs only after the drought occurs, reducing its effectiveness as compared to mitigation which can prevent as well as reduce the impact of drought on the lands and crops.
Thus, as we can see, the successful management of droughts requires a three prong approach prediction, mitigation and response. The most useful and most reliant component of drought management is probably mitigation as it is not only easily implemented but it helps reduce the impact during a period of drought. Prediction of droughts is often difficult and inaccurate due to its slow-moving characteristics and response only takes place after the droughts occur, and often, the aftermath is hard to resolve efficiently.