Landsliding related to land-cover change:: A diachronic analysis of hillslope instability distribution in the Sierra Norte, Puebla, Mexico

This study examines mass movement associated with land use change, particularly deforestation, from multiple perspectives. The significance of such understanding is related to the degree of impact landsliding may cause on human settlements and economic activities, and on forest ecosystems. In this paper, the distribution of hillslope instability in the Sierra Norte, Puebla, Mexico is addressed by means of a diachronic analysis, which involves the development of vegetation indexes, as well as vegetation fragmentation derived from Landsat-5 (TM) and Landsat-7 (ETM+) satellite images from 1989 and 1999, respectively. The time period was chosen to compare vegetation cover conditions prior and after the extreme October 1999 rainfall event that triggered hundreds of slope failures in the study area. Results suggested there was a significant vegetation reduction from 1989 to 1999, which was strongly expressed by an increase of 809 km(2) of bare surfaces. Additionally, areas with highest vegetation density (91-100%) decreased considerably, from 1245 to 363 km(2), resulting in a net vegetation reduction of 70%. Furthermore, it was possible to highlight that landslide concentration was much higher on surfaces that were bare and had low vegetation density (0-50%), representing 85% of hillslope instability, than on surfaces having a greater density of vegetation cover. Land use change and land degradation are precursors to environmental hazards, such as mass movement events, that pose serious threats to regional population distributions and economic vitality. (c) 2005 Elsevier B.V. All rights reserved.