Rapid-Response Unsaturated Zone Hydrology: Small-Scale Data, Small-Scale Theory, Big Problems

The unsaturated zone (UZ) extends across the Earth’s terrestrial surface and is central to many problems related land water resource management. Flow of through UZ typically thought be slow diffusive, such that it could attenuate fluxes dampen variability between atmospheric inputs underlying aquifer systems. This would reduce vulnerability contaminants water-related hazards. Reducing or negating effect, however, spatially concentrated rapid flow transport surprisingly common becoming more so with increasing frequency magnitude extreme hydroclimatic events. Arising from wide range in rates complex modes nonlinear processes, these effects are among most poorly characterized hydrologic phenomena. Issues scale present additional difficulties. Equations representing processes have been developed tested on basis field laboratory measurements made at scales pore size plot size. In contrast, significant interest society, including floods, recharge, landslides, groundwater contamination, watershed regional scales. disparity our understanding for societal has spurred application model equations increasingly coarse resolutions over larger areas than can justified by existing theory. mismatch requires an assumption averaging diffusive preferential effectively represent influence both vast areas. Given currently inadequate recognition quantitative characterization focused flow, phenomena critically need expanded attention effort.