Water Resour. Res. doi:10.1029/2007WR006514 (2008)

Monsoons are driven in large part by contrasts between land and sea temperatures, which are key to their prediction. However, other factors are also at play, such as soil moisture; higher moisture makes the transfer of heat from the land to the air through evaporation easier.

Eungul Lee, at the University of Wisconsin, Madison, and his colleagues show through analysis of satellite and other records that including this effect can improve monsoon forecasts. Taking into account the vegetation growth — which has a strong influence on soil moisture — in the months preceding the northern and southern East Asian summer monsoons allowed them to improve the reliability of forecasts by a factor of two for the northern and three for the southern monsoon.