Climatic role in landslide occurrence in the Central Andes, Argentina

MOREIRAS S.M.

Mendoza

Simposio; Symposium on Climate Change: Organizing the Science in the American Cordillera; 2006

IAI (Inter American Institute for Global Climatic Change) - IANIGLA

Identification of landslides triggering mechanisms is a key for the prediction of these natural hazardous events. Although landslides are triggered by several causes; summer rainstorm is one of a major factor in their distribution and frequency in this arid region (200 mm mean annual precipitation). More than 200 historical rockfall and debris flows happened during the 1902-2002 period could be correlated with rainfall. The precipitation threshold value established from daily meteorological records was 6.5-12.9 mm, even though the net of meteorological stations is not dense enough in the region. What is more, the antecedent precipitation is important to be taken into account as 60% of these events showed previous rainfall. Total amount of rainfall increases notably and the mean value increases by 56% if antecedent rainfall is considered. Furthermore, climatic phenomena are forcing landslide occurrence in the Central Andes. Given that the ENSO warm episodes (El Niño) (Díaz and Kiladis, 1992) are characterised by major precipitation events; greater number of landslides has been recorded during these periods in Cordillera Frontal; whereas a decreasing number happened during cold episodes (La Niña). However, the slope instability in the Precordillera, located east of the Cordillera Frontal, seems to be mainly influenced by wet-cold periods linked to the Atlantic Anticyclone behaviour (Compagnucci et al. (2002). A higher number of landslides were recorded in years linked to wet periods than during dry periods. Moreover, the analysis of variance shows that there is no significant difference between landslide records and cold-warm episodes. The mean interval of landslide recurrence is 4 and 15 years in Cordillera Frontal and Precordillera, respectively (Moreiras, 2006). However, we suspect that this frequency may be higher in the future as climate models suggest an increase in both precipitation and temperature in the region. In addition, El Niño climatic phenomenon may be more frequent and severe in the future as a consequence of global climatic change. Likewise, the end of the present wet period starting in 1972 is yet unknown. Hence the importance of considering the climatic role in temporal distribution of landslides related to hazard and risk scenarios.