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Preview of Regional Moisture Balance Control of Landslide Motion: Implications for Landslide Forecasting in a Changing Climate, by Jeffrey A. Coe. Published in USGIS

Geology, v. 40, no. 4, p. 323-326; doi:10.1130/G32897.1. April 2012

How will active and dormant landslides respond to climate change? This is a challenging question for Earth scientists (e.g., Sidle, 2007; Briceno et al., 2007; Crozier, 2010; Winter et al., 2010) that has broad implications for population centers throughout the world. There are multiple issues that make this question difficult to answer, but two issues are prominent. First, landslide activity is difficult to forecast in a static climate (e.g., van Westen et al., 2006), so attempting to forecast activity in a changing climate seems challenging at best. Second, projections of future precipitation based on simulations from climate models tend to be available as monthly or annual precipitation for large areas, rather than as precipitation frequency, duration, and intensity at individual sites.

The responsiveness of individual landslides to precipitation is dependent on their geometry;  stratigraphic, structural, and hydraulic properties; soil moisture and groundwater characteristics; and the frequency, duration, and intensity of precipitation (e.g., van Asch et al., 1999). Large, deep-seated (>5 m in thickness), slow-moving landslides typically have complex boundaries, distinct kinematic elements, and materials with hydraulic conductivities of <10−4 m/s and diffusivities <10−4 m2/s (e.g., Iverson and Major, 1987; Baum and Reid, 1995; Schulz et al., 2009a; Calabro et al., 2010). The properties of deep-seated landslides make the timing of their movement with respect to precipitation complex; some landslides respond days after precipitation (Baum and Reid, 1995) and others respond weeks to months after precipitation (e.g., Iverson and Major, 1987). The magnitude of movement during each movement episode is dependent on pore pressures at basal shear surfaces, pressures that are functions of groundwater flow and propagating pressure waves from long-term precipitation integrated over time periods of weeks to months. Because long-term precipitation patterns are readily available from downscaled climate projections, the effects of climate change on landslide motion may be easier to forecast for deep-seated landslides than for shallow landslides, which are highly sensitive to individual precipitation events. This situation highlights a need for landslide forecasting tools that account for long-term moisture and groundwater conditions.