Electrical resistivity monitoring of a collapsing meta-stable soil

A model of electrical conduction through clay-coated, silt-sized quartz-grains inter-connected by clay-bridges (e.g. brickearth) is developed. Underpinned by SEM studies of brickearth, the model predicts resistivity to be proportional to the size of the quartz-grains, where the resistance afforded by clay grain-coatings and clay-bridges is comparable. The model accommodates resistivity that increases through bridge breakage and decreases through bridge compression. The resistivity of in-situ undisturbed brickearth was found to be in the range 15 to 35 ohm-m. At such low values we demonstrate that electrical flow is dominated by conduction within clay-coatings and their interconnecting clay-bridges, rather than in mobile pore-water. A small electrode array, buried at shallow depth beneath the load plate (1.0m by 1.0m) of a field collapse experiment, monitored resistivity to a depth of 1.5m over a 260 hour period. While the water level beneath the load plate remained below 1.0m depth, the resulting 3D inverted resistivity models detected water injected immediately beneath the plate; recording rapid increases, in stages over 90 minutes, in the depth interval 0.45 to 0.75m directly under the plate, during what appears to be collapse. These increases are attributed to breaking of clay-bridges weakened by injected water

Climate shocks and migration: an agent-based modeling approach

This is a study of migration responses to climate shocks. We construct an agent-based model that incorporates dynamic linkages between demographic behaviors, such as migration, marriage, and births, and agriculture and land use, which depend on rainfall patterns. The rules and parameterization of our model are empirically derived from qualitative and quantitative analyses of a well-studied demographic field site, Nang Rong district, Northeast Thailand. With this model, we simulate patterns of migration under four weather regimes in a rice economy: 1) a reference, ‘normal’ scenario; 2) seven years of unusually wet weather; 3) seven years of unusually dry weather; and 4) seven years of extremely variable weather. Results show relatively small impacts on migration. Experiments with the model show that existing high migration rates and strong selection factors, which are unaffected by climate change, are likely responsible for the weak migration response