ERA‐40 reanalysis hydrological applications in the characterization of regional drought

The use of a land surface model (TESSEL) for drought characterization is proposed. The method is tested with the 1958–2001 ECMWF ERA‐40 reanalysis and its results are successfully compared with those obtained with other indices (SPI, PDSI) computed from observations in Iberia, a region highly vulnerable to drought. The proposed index, Normalized Soil Moisture (NSM), requires no local tuning, and, in principle, is readily computable from point observations, reanalysis, forecasts or climate scenarios. NSM from offline integrations has an enhanced consistency for drought analysis when compared with NSM computed directly from ERA‐40 soil moisture. Analysis of the NSM fields indicates that while the spatial heterogeneity of precipitation is the main driver of the spatial variability of drought, the spatial distribution of soil characteristics modulates its temporal variability. This suggests the need for better soil maps at the global scale.