The occurrence of drought in Mexico has brought to light the large vulnerability of the northern part of this country to water shortages. However, it is not clear what produces a meteorological drought spanning for more than one year. Based on gridded monthly precipitation data for the last forty years, the spatial structure of significant reductions in summer precipitation are documented. Low frequency variations in precipitation are examined to identify potential forcing mechanisms.

Meteorological drought is defined as a rare event based with low probability of occurrence as obtained from a Gamma probability distribution function for precipitation in every grid point. The magnitude of probability and the precipitation anomaly are used to define the severity of drought. This definition turns particularly useful to identify intense and prolonged drought events as the one associated to the “dust bowl” in the forties. It may be observed that this drought period manifested as far as central Mexico.

Based on the diagnosis of drought with observed data, some hypothesis are examined considering some numerical experiments with the Community Climate Model 3. Preliminary results and conclusions are discussed.