CLIMATE scientists claim to have found a land-based equivalent of El Ni帽o. It could allow them to forecast droughts and floods months in advance.
Forecasting more than about a week ahead has usually proved impossible because the atmosphere is so chaotic. But there are some hidden influences that guide the world鈥檚 weather. For instance, changes in sea temperatures in the eastern Pacific occur months before the big flip in global climate that we call El Ni帽o.
Now a global research initiative headed by NASA鈥檚 Goddard Space Flight Center in Maryland has found something similar on land. According to NASA鈥檚 Randal Koster, researchers have located a series of 鈥渉otspots鈥� in the middle of continents, where subtle changes in the amount of moisture in soils may predict forthcoming droughts and floods.
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The thinking is that water evaporating from soil is often the main source of the water vapour that creates clouds and rain, and the drier the soil, the greater the chance of drought. Extremely wet soils may indicate future heavy rains. 鈥淚n these hotspots, soil moisture and precipitation are tightly linked,鈥� Koster says.
The method will not work everywhere. Near coasts plenty of moisture evaporates from the ocean, and in deserts there is rarely enough moisture in the soil to create rain. But in other regions, especially in the transition zones between wet and dry climates, evaporation from soil can make all the difference.
The Global Land-Atmosphere Coupling Experiment (GLACE) asked 12 climate-modelling teams to map regions where the influence of soil moisture is strongest. Several zones showed up in most forecasts. The three biggest are the African Sahel on the southern fringe of the Sahara desert, northern India, and the Great Plains of North America. There are others in central Asia, China and equatorial Africa (Science, vol 305, p 1139). Each is an area known for droughts that strike in clusters.
