Hazard assessment of rainfall-induced landsliding in Mexico

Rainfall-induced landsliding represents a major hazard in Mexico. About 200 municipalities in the states of Puebla, Veracruz and Hidalgo were affected by flooding and mass movement processes that resulted from a tropical depression from the Atlantic Ocean in October 1999. Hundreds of slope failures were triggered by intense precipitation, which in some localities reached 420 mm during a 24-h period. According to official information; 263 people died and 1475654 inhabitants were affected by flooding and landsliding. Rainfall event and cycle coefficient defined and the ratios between event and antecedent rainfalls, respectively, and the mean annual rainfall are summed to give a total coefficient. For landslide-triggering rainfalls in the Sierra Norte, values for the total coefficient of 0.8 and 0.4 for beginning and end of the wet season, respectively, appear to be important. In addition, a hazard assessment was carried out through the development of a landslide susceptibility indicator. This was elaborated by using aerial photographs, integrating field observations and the coupling of slope instability analysis within a digital elevation model framework. Field validation indicated that this approach provides a good representation of shallow translational failures; 81% of the observed landslides were satisfactorily predicted as potential unstable zones. Results suggested that: this type of DEM-based hazard assessment can be extremely valuable not only after, but also before any landslide-related event, so that disaster preparedness and planning could be adequately structured. (C) 2003 Elsevier B.V. All rights reserved.