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Drought: The ‘dry’ face of climate variability

Nate Engle's picture

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Drought is not a new problem. People and ecosystems have been dealing with it for millennia; some successfully, and others not so successfully. Scientists have attributed past migrations to wetter regions—and even the decline of entire civilizations—to extremely dry periods lasting for several years or decades. A 1998 World Bank Report by Benson and Clay shows how the 1991-1992 Sub-Saharan African drought affected entire national economies, costing millions of dollars and thousands of jobs.

While people are largely well adapted to the ‘natural’ climate variability of their region (of which drought is one half of the equation, and abnormally wet periods the other), droughts can pose very serious risks when their severity exceeds expected levels, or when they strike in areas which are not used to coping with them. And this is likely to happen more frequently with climate change.

In the simplest terms, drought is a period of less than normal levels of precipitation. By this definition, virtually every place on the planet experiences drought at some time. Drought begins to be ugly when dry conditions in a given place for a given period of time begin to depart further and further from normal or average conditions. Some places are used to experiencing large departures from average conditions and greater drought intensity as part of their normal climate variability. Others are not. For example, Northeast Brazil historically sees large swings in climate variability (driven mainly by El Niño/La Niña cycles), and as a result, extreme droughts and serious flooding episodes are frequent, and people expect them. However, such large fluctuations are not part of normal climate variability just to the west, in the Amazon. Here, the conditions are consistently wet and humid, and as a result, people are not used to living with significant periods of dryness.

Abnormal drought is not an easy phenomenon to manage. Even though we can define drought generically, defining it specifically is quite a difficult task. Unlike other climate stresses, drought can extend over months, years, or even decades. Often, people do not even know they have entered into a drought until it is well into the drought period; which has as much to do with insufficient monitoring and reporting as it does with having regional consensus about what constitutes a drought. Further, there are many local factors other than climate that contribute to drought. People influence water availability through activities such as irrigation, land-use decisions, and damming and diverting rivers, to name a few. Ecosystems also contribute to the amount of water available, particularly through evapotranspiration. Given the number of factors contributing to drought, and the interaction between these factors, it is difficult to define what normal levels precipitation and water availability might be for a specific area.

People and the ecosystems on which they depend have developed in tandem with droughts, being both influenced by them and also contributing to them. We have seen countless examples of when our ability to successfully plan for, cope with, and adapt to the most serious droughts has been sadly exceeded. Climate change now presents an even greater threat to our ability to successfully manage droughts. Scientists anticipate varying drought impacts from climate across the world, but increases in drought severity in already variable regions and the expansion of extreme drought into new regions will further tax our ability to manage droughts. Therefore, communities need help to ready themselves for droughts of greater severity, frequency, and duration.

My next post will focus on how we might manage drought in the face of climate change.

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