Mean Annual Precipitation

For the purpose of Desertification Atlas map production, the GRID-Nairobi data analysts required data from a fairly dense network of global climate stations. They therefore obtained both precipitation and temperature station data from UEA/CRU for two 30-year periods, 1930-59 and 1960-89. While the CRU database contained 950 precipitation station values, this number was not sufficient for interpolating two separate global surfaces to be used in a climate change study, for reasons of both temporal instability and inaccuracies of eventual area estimates.

Thus, GRID decided in conjunction with UEA/CRU to produce a single, high-resolution preci- pitation surface for one time period only, using the maximum number of station means available. For this surface, data from the time period 1951-1980 were selected, both in order to avoid creation of a "timeless" data set, and to better match the period of the GLASOD study whose data were compiled in the late 1980s.