New study of soil moisture and storm generation could improve rainfall prediction in West Africa

Published: Thursday January 19 2012, 13:29:38

A new study of how storms are generated could improve rainfall prediction in dry regions of Africa where drought and short growing seasons are common. A team of international scientist used satellite observations to demonstrate that short lived changes in soil moisture over tens of kilometres can affect storm generation. Observational data was created using high resolution satellite images every 15 minutes over few kilometres on a daily basis for wet season of 2006-2010.

In the Sahel region monsoons can arrive abruptly which has important consequences on corps. The timing of planting and the start of the wet season can mean the difference between a good crop and no crop at all. Better predictive modelling could make a huge difference to the people for whom rains can be a matter of life or death.

The researchers analysed 3765 storms across a region of around 2.5 million kilometres to see how often and when and where convection (or cloud formation) was triggered. The aim was to determined the role of soil moisture on cloud formation in the Sahel, West Africa. One of the results showed strong soil moisture gradients have greater probability of initiating storm formation than uniform soil moisture conditions. Observation revealed rainfall event can induce further rainfall events because of positive feedback mechanism.

Lead author Dr Chris Taylor from the UK’s Centre for Ecology & Hydrology said, “Rainfall is difficult to predict, particularly in regions such as the Sahel where huge storms can grow from nothing in a matter of hours. 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 1 in 8 storms, in a region particularly prone to droughts and associated crop failures.”
The study concludes that rain storms are twice as likely to form over strong gradients in soil moisture compared with uniform soil-moisture conditions.
Dr Taylor added, “By exploiting data from satellites, we hope to be able to improve model predictions of both weather and future climate.”
The key conclusions revealed heterogeneity (differences) in soil moisture on the scale of a few kilometres has a strong impact on rainfall in the Sahel, meaning similar processes may be important throughout the semi-arid subtropical regions of the world. Now we can quantify this, climate models can be improved to use the right conditions and increase prediction of storm generation.

The research was carried out by scientists from Centre for Ecology & Hydrology in the UK, CNRM in France and Macquarie University in Australia.
This is a summary of the paper published in Nature Geoscience:
Frequency of Sahelian storm initiation enhanced over mesoscale soil-moisture patterns
Christopher M. Taylor, Amanda Gounou, Françoise Guichard, Phil P. Harris, Richard J. Ellis,Fleur Couvreux & Martin De Kauwe
Nature Geoscience 4, 430–433 (2011) doi:10.1038/ngeo1173

This publication was also commented on in the News and views piece in Nature Geoscience

The publication of this paper was accompanied by a press release prepared by
CEH and available from their website