COMPILING REGIONAL-SCALE PERMEABILITY ESTIMATES FOR A GLOBAL MAP OF NEAR-SURFACE PERMEABILITY

Permeability is a key parameter necessary for integrating approaches to modeling geochemical, hydrological and ecological process in watersheds. Local-scale (<1 m to 1 km) permeability varies over more than 13 orders of magnitude and is often poorly defined because it is extremely heterogeneous and dependent on flow direction. The permeability of shallow soil has been mapped at continental scales. However, the regional-scale (>5 km) permeability of consolidated and unconsolidated geologic units (hydrolithologies) underlying soil is poorly understood and has not been previously mapped. Here we show that hydrolithologies have representative, regional-scale permeabilities that can be used to map the global distribution of near surface permeability. By compiling existing hydrogeological models we show that regional-scale permeability is not scale-dependent and the distribution for each hydrolithology is generally log normal with a standard deviation of 1-2 orders of magnitude. We also calculate a spatially-distributed, near-surface global mean of the logarithmic permeability of -13.2 ± 2.7 m². Our results resolve the near-surface permeability field, at new scales and at new depths. We anticipate the permeability compilation and maps will be invaluable resources for understanding and modeling diverse earth processes.