Impact of Land use Changes on Landslides Occurrence in Urban Area: The Case of the Constantine City (NE Algeria)

The city of Constantine (NE Algeria), the third largest city of the country (2.374 inhabitants/km(2)) is facing frequent damaging landslides that constitute a constraint to future development and land use planning. The main goals of this study are to evaluate the effect of land use changes on the spatial distribution of landslide hazard occurrence and give an example of landslide hazard assessment as useful tool within the context of long-term land use planning in the urban area of Constantine. For this purpose, the adopted methodology requires four steps: (i) Data collection and construction of a spatial database related to the historical landslides, land use, building and population inventory; (ii) landslide inventory and land use mapping for the period of 1970 to 2011 based on the analysis of aerial photographs, high resolution satellite images, historical records verified and completed by extensive field observations, (iii) analysis of the effects of land use changes on the spatial distribution of landslide occurrence for different periods 1970 and 2011; (iv) landslide hazard map, obtained by using the frequency ration (FR) under GIS and (v) evaluate the impact of human-induced land use changes on hazard occurrence. For that, we, firstly, compared the landslide inventory map with land use maps of different periods of 1970 and 2011 that showed that since 1970, the density of landslides increases with increasing of urban areas. In 2011, the high landslide density is concentrated on the following four layers: the urban area layer (41%), the agriculture land layer (39%), the grass area layer (15%) and the forest land layer (5%). The effect of the expansion of urban zone in agriculture, grass and pasture area have increase landslide densities over time. Secondly, we compared the landslide hazard map to these land use maps and we found that 40% of the high hazard zones and 50% of the moderate hazard zones fall in the urbanized area. The obtained results show a clear impact of the changed land use where human action is an important triggering and/or accelerating factor of landslides in the urban area of Constantine. Nowadays, about 72,749 inhabitants and 25,255 buildings are located in landslides threatened area. Therefore, landslide hazard maps should, always, guide the land use and urbanization in landslides prone areas.