Different types of drought
There are no agreed definitions of drought. However, the consensus of opinion is that a drought is not an environmental condition which occurs instantaneously, but rather a creeping phenomenon which affects an area over a number of years, with devastating results on livestock, farming and the all essential water supplies crucial to life.
Droughts are a constant threat to mankind – creating famine, war, fires and pestilence (just like the four horsemen of the apocalypse rolled into one). In order to combat drought we first need to understand it.
Types of drought
The National Drought Mitigation Center (based at the University of Nebraska-Lincoln in the US) has defined four types of drought as follows:
Meteorological drought is region specific; it occurs when dry weather patterns occur. The continuity of these altered atmospheric conditions results in a lack of precipitation. The reasons why people often consider drought to be an area-based phenomenon are as follows:
- Great Britain 1936. Drought occurred with 15 consecutive days of daily precipitation of less than 0.25 mm.
- United States 1942. Drought occurred with less than 2.5 mm of rainfall in 48 hours.
- Bali 1964. Drought occurred when there was a period of 6 days without rain.
- Libya 1964. Drought occurred when there was less than 180 mm of rain annually.
Most people are familiar with meteorological drought since media weather reports tend to focus on this type of drought in most regional areas.
Hydrological drought occurs when there are persistent low water levels in streams and reservoirs; it is seen to be a natural phenomenon for the most part and is closely related to meteorological drought. However, it can occur as a result of human activity too. For instance, changes in land use can cause the onset of drought.
Agricultural drought happens when crops are affected due to a lack of moisture, or when there is not enough moisture to support grass production on rangelands, leading to shortage of food for cattle. The changing moisture requirements during the cultivation of crops should also be taken into account. Low topsoil moisture can lead to sparse crops and a reduction of yield. Additionally, the high incidence of wildfires during dry spells such as the latest California drought are a threat to people and agriculture.
Socioeconomic drought occurs when the demand for water outweighs the supply. Meteorological, hydrological and agricultural droughts play a contributing part in this, but this type of drought specifically relates to when certain goods cannot be provided due to a shortage in rainfall.
So, what can we do about droughts?
Agricultural drought primarily affects farmers and ranchers, which in turn affects businesses which depend on agricultural produce to survive – restaurants, grocers, bakers and butchers are examples of such businesses.
In brief, soil and water conservation is paramount in combating drought, as is close monitoring of dry spells, clear assessments of the impact of drought on a given region, accurate predictions of future drought and above all, the correct response to minimise the damage caused by drought. We will discuss how to mitigate the effects of drought in more detail in a future blog.
Meanwhile, here is a statement on humanity’s relationship with nature to reflect on:
“I think we are bound to, and by, nature. We may want to deny this connection and try to believe we control the external world, but every time there’s a snowstorm or drought, we know our fate is tied to the world around us.” Alice Hoffman
(Photos by James Marvin Phelps and Alex Pink)
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