Slide 30: Changes in precipitation
Globally, an increase in precipitation over land of approximately 2% has been observed over the last century (Jones and Hulme, 1996; Hulme et al., 1998).
However, this effect is localized, and such areas as the Sahel and sub-Saharan Africa have actually seen a decrease in rainfall.
Precipitation over the ocean can only properly be estimated from satellite observations, and as such, full records have only been available since 1987.
Current indications are that oceanic precipitation has increased as well, but it is too early to say with statistical certainty.
There may be a trend towards more intense rainfall events - whilst much of sub-Saharan Africa is getting less rain, it is also getting it in short bursts, rather than spread evenly over a season.
Jones, P.D. and M. Hulme, 1996: Calculating regional climatic time series for temperature and precipitation: methods and illustrations. Int. J. Climatol., 16, 361-377.
Hulme,M., T.J. Osborn and T.C. Johns, 1998: Precipitation sensitivity to global warming: Comparison of observations with HadCM2 simulations. Geophys. Res. Lett., 25, 3379-3382.