Potential effects of environmental change on landslide hazards in forest environments.

Abstract

The interactive roles of the natural factors that contribute to landslide initiation and potential climate changes are complex. Additional complexity is added when changing forest land uses are considered. Thus, while it is impossible to ascertain specific patterns of landslide response to possible climate change, certain generalizations can be made and scenarios can be discussed. Shallow, rapid landslides will only increase in scenarios of increasing rain event intensity, whereas, deep-seated mass movements will increase with seasonal increases in precipitation. Dry ravel may respond more directly to warming, increasing with sparse vegetation covers and increased frequency of fire. Climate change has the greatest impacts on landslide occurrence by modifying evapotranspiration and root strength of vegetation. Evapotranspiration affects soil water recharge and subsurface flow and thus influences slope stability. Climate change may alter canopy structure, soil runoff and evaporation, ground cover, and rooting depth; these in turn affect water storage and routing in unstable sites. Anthropogenic and climate-induced changes in vegetation cover particularly affect the potential for shallow landsliding due to modifications in root cohesion. While much attention has been placed on the impacts of forest harvesting practices on increased landslide erosion, the effects of permanent forest land conversion, particularly in the tropics, appear more problematic. Additionally, the increasing impacts of affluent recreation in the developing world need to be assessed. Agroforestry may offer some socioeconomic and natural resource advantages in selected cases, but cumulative off-site effects must be evaluated. Depending on the level of detail required and type of available data, landslide hazard can be assessed by several methods: (i) terrain stability classification; (ii) empirical landslide hazard assessment; and (iii) physically-based models. Including climatic change scenarios into landslide hazard models is a complex task because scenarios of climatic change are unclear even at regional levels. Also, most models only evaluate land use in a very general way. Thus, much progress is needed to predict these interactive climate-change and anthropogenic impacts on slope stability.

Erosion processes in steep terrain—Truths, myths, and uncertainties related to forest management in Southeast Asia

“…Land uses that contribute to the majority of the surface erosion and slope stability problems in tropical mountain uplands include: timber harvesting, roads and trails, various agroforestry practices; conversion of forest to agricultural land; and grazing (e.g., Sidle et al, 1985Sidle et al, , 2004aHashim et al, 1995;Lu et al, 2001;Bruijnzeel, 2004;Ziegler et al, 2004a,b). Recreation appears to be having an increasing impact on erosion, including smallscale mass wasting, but the effects are poorly documented and typically occur as the result of trails and off-road vehicle use Sidle and Dhakal, 2002). The conversion of tropical forests to commercial and noncommercial agricultural lands can have significant effects on water pathways and soil erosion, thus influencing site productivity (e.g., Harwood, 1996;Ross and Dykes, 1996).…”

Rainfall patterns and related landslide incidence in the Porretta-Vergato region, Italy

“…For example, Campbell (1975) identifies an intensity threshold above which landslides occur, Nilsen et al (1976) have equally ascertained an intensity/storm threshold, stipulating that failures are even more likely to occur if the storm takes place after a particularly rainy period. The analysis of precipitation, in terms of its intensity and duration, is frequently divided into two distinct phases: the preparatory period and the triggering event (Sidle and Dhakal 2002). Guidicini and Iwasa (1977) defined these phases as the Cycle Coefficient (C c ), the cumulative precipitation record up to the date of the event and the Event Coefficient (C e ), namely the precipitation record of the event.…”

Physically based modeling of rainfall-triggered landslides: a case study in the Luquillo forest, Puerto Rico

“…These movements are generally shallow and rapid when triggered by large precipitation events on slopes with wet antecedent conditions -deeper and slower when the accumulated precipitation volume gradually builds over an extended time period, eventually leading to stability failure. This study focuses primarily on very fast and shallow earth displacements triggered by intense and short rainfall events, such as debris slides (Sidle and Dhakal, 2002). For these movements, the assumption that the failure plane is oriented approximately parallel to the soil surface can be accepted, allowing for the use of the infinite slope hypothesis, which introduces greater simplification to the modeling process.…”