Using isopleth mapping to evaluate landslide activity in relation to agricultural practices

In comparison to urban or suburban areas, agricultural lands generally have a lower landslide risk. This does not necessarily reflect a lower degree of landslide hazard. The lower risk is more often due to the sparser population and lower property values of rural areas. Population and property values influence methods applicable to assessing landslide hazard in rural areas. The cost of data and size of areas over which assessments must be made for agricultural lands render many assessment procedures uneconomic. Their use is only justified in populous, high-value areas. Many agricultural practices may have the same potential for initiating landslide activity recognized for some land uses in urban areas. Like their urban counterparts, residents dependant onagriculture for their livelihood suffer from the consequences of landslides. For these reasons, a method for landslide hazard assessment suitable for rural areas is needed. This need is satisfied by isopleth mapping of landslides. Isopleth mapping provides an economical means for assessing the degree of landslide hazard present within a large area. Data needs are limited to topographic and landslide maps. Isopleth maps facilitate comparison of landslide data to other information for developing a better understanding of how agricultural practices affect landslide activity. Their use in the Tuscany region of Italy provide insight on how changing agricultural practices altered landslide activity. Isopleth maps serve as a simple way to accomplish landslide hazard zonation. Landslide hazard zonation identifies locations where land use controls should be applied to achieve hazard reduction. Hazard reduction based on isopleth mapping is illustrated by their use in timber sale planning in California, USA.