Better models for storm prediction emerge
Arid regions around the world long for rainstorms to come and replenish their thirsty soils. A new international investigation on the generation of storms could enhance the prediction of rainfall in arid regions, and in particular Africa where drought and short-growing seasons are the norm. The findings of the study, presented in the journal Nature Geoscience, are funded in part by an EU grant under the Sixth Framework Programme (FP6). Led by the Centre for Ecology & Hydrology in the United Kingdom, scientists from Australia, France and the United Kingdom evaluated the Sahel region of West Africa using high-resolution satellite images. They found that the generation of storms is impacted by brief changes in soil moisture over areas of just tens of kilometres. According to the researchers, the Sahel could be hit by a monsoon in the blink of an eye. So it is crucial for farmers to correctly gauge when the planting of crops should begin, and to forecast the start of the wet season. Having this information could mean the difference between a good crop or no crop at all, they say. In a nutshell, improved predictive modelling could prove instrumental for those who depend on knowing when the rains will come. A wrong move can lead to economic trouble and possibly even death. For the period 2006 to 2010, the team took satellite images every 15 minutes at a scale of a few kilometres in order to assess storm generation on each day of the wet seasons. A total of 3,765 storms were analysed across an expanse of 2.5 million kilometres, giving the team the data it needed to determine how often, when and where convection (i.e. cloud formation) was produced. The team found that variations in soil moisture on length scales of around 10 to 40 km exert a strong control on the generation of storms, confirmed by the appearance of convective clouds. They say the chance of rainstorms forming doubles over strong soil-moisture gradients compared with that over uniform soil-moisture conditions. Overall, 37 % of the storm initiations assessed by the researchers materialised over the steepest 25 % of soil-moisture gradients. 'Rainfall is difficult to predict, particularly in regions such as the Sahel where huge storms can grow from nothing in a matter of hours,' says lead author of the study Dr Chris Taylor of the Centre for Ecology & Hydrology. 'We found that areas with contrasting soil moisture play an important role in the creation of new storms, a factor not accounted for in current climate models. Our study shows that this effect is important for typically one in eight storms, in a region particularly prone to droughts and associated crop failures.' Dr Taylor goes on to say that using satellite-generated data gives scientists the means to improve model predictions of weather and future climate. Commenting on the results of the study, co-author Dr Phil Harris from the Centre for Ecology & Hydrology, says: 'Because this dataset is much larger than those from previous studies and covers several years we're much more confident of the results. Now that we can quantify this process, and give the climate models the right conditions to work with, they are more likely to initiate the storms in the right places.' Scientists from the Centre National de Researches Météorologiques (CNRM) in France and Macquarie University in Australia contributed to this study.For more information, please visit:Centre for Ecology & Hydrology:http://www.ceh.ac.uk/Nature Geoscience:http://www.nature.com/ngeo/index.html
Countries
Australia, France, United Kingdom