Climate: dryness in one third of the earth

Even regions with more rain could be affected by D rre

Dehydrating soils could cause drought in up to 30 percent of the earth in the future © SXC
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More rain, nevertheless drought? Southern Europe, Southeast Asia and the Southwest of the US could be just that. A new study by US climate researchers concludes that by the end of the century, even regions could be affected by drought, where it rains more than before. The reason for this, according to the researchers in the magazine "Climate Dynamics", is a factor neglected to date in climate models: increased evaporation with rising temperatures.

The global climate will heat up significantly by the end of the century, so much is certain now. For many regions, the rising temperature will cause longer dry periods, while others are likely to get more rainfall. For the prediction of periods of drought in the future climate, mainly rainfall was the basis.

Rain alone is not crucial

A group of scientists around Benjamin Cook of Columbia University believe that the effect of temperature on precipitation has been neglected so far. Whether it rains more frequently or less often is not alone decisive for the drought risk, the researchers say: The temperature and thus the evaporation of moisture from the soil also plays a major role.

Increasing drought due to a warmer climate - that sounds obvious: "Fundamentals of physics tell us that warm temperatures make things dry faster, " says First author Cook. Therefore, in his study, he and his colleagues included the effect of evaporation in their predictions. Based on climate models from the IPCC Report of 2013, the scientists analyzed their predictions for both precipitation and evaporation of water from the soil. They encountered a surprising and disquieting effect: even areas with more rain than before could be more vulnerable to drought in the future.

Greater danger of drought in agricultural areas

For example, if the climatologists only considered the precipitation in their models, then there was no danger of drought for the areas in the midwestern US and southeast China - it is still raining enough. However, if the model also includes increasing evaporation, these agronomically important regions are on the brink of drought - despite sufficient rainfall. display

The summer dry seasons, as they already prevail in the Mediterranean and in Turkey, will continue to affect the north and thus to Central Europe. Similarly, drylands will increase in Central America, the Amazon, and southern Africa.

In it, the study agrees with the latest climate report of the IPCC. The IPCC also warns that soil moisture will decrease worldwide. Cook and colleagues estimate in their study that only twelve percent of Earth's land mass, excluding the Antarctic, will be threatened by D rre by the year 2100 due to changes in precipitation. However, this value even increases up to 30 percent, taking into account the increasing evaporation.

Price explosions in food?

This could have serious consequences for agriculture and thus for the production of food: if today's bad weather brings bad harvests to one area, other regions can normally compensate for this and a food shortage prevent. However, the authors of the study predict that in the harsher climate of the future crops in many regions could wither at the same time as drought spreads large. "Price explosions in food could become commonplace, " says climate specialist Richard Seager, one of the co-authors. Large cities, especially in dry areas, will need to carefully monitor their water balance, he adds.

"For agriculture, the water balance of the soil is the only thing that really counts, " summarizes co-author Jason Smerdon of Columbia University. "If it rains more, but the temperature also increases, it can be followed by a drought." That rain alone is not enough, also knows Steven Sherwood of the University of New South Wales in Australia, who in the journal "Science" to consider: "Many regions will receive more rain. But it seems as if only a few get enough to keep up with the increasing evaporation. "

(Climate Dynamics, 2014; doi: 10.1007 / s00382-014-2075-y)

(Springer, 02.04.2014 - AKR)