FETCH the umbrella 鈥� global warming and cleaner skies are making it rain more.
of the Swiss Federal Institute of Technology in Zurich and his colleagues analysed global measurements of solar radiation and rainfall taken between 1986 and 2000. On average, surface solar radiation has increased by 0.21 watts per square metre per year over land, and rainfall has increased by 3.5 millimetres per year (Geophysical Research Letters, ).
In recent decades, air pollution has dropped, so more sunlight is penetrating the atmosphere, says Wild. Meanwhile, rising levels of greenhouse gases are bouncing radiation back to Earth鈥檚 surface.
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The extra energy has fuelled an increase in evaporation. 鈥淭his intensification of the water cycle means more heavy precipitation events, more flooding, and more landslides, erosion and overloading of water management systems,鈥� says Wild. The analysis only covers land areas, so it isn鈥檛 clear whether the extra rain is coming from increased evaporation over land or oceans.
The effects have not been distributed evenly, says Wild. Local factors, such as winds that carry rain elsewhere, mean some places have become drier, such as the south-west US and southern Asia.
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