Development of climate-dependent pedotransfer functions for predicting soil hydraulic properties

Climate exercises considerable influence on the soil fabric (i.e., the arrangement of soil pores and particles) and, thus, soil hydraulic properties. Recent evidence suggests that soil hydraulic properties are changing in response to precipitation variations on shorter time scales than has been generally recognized―potentially as rapidly as years to decades. This evidence indicates that climate-induced changes to soil macroporosity cause a reduction in soil saturated hydraulic conductivity (Ksat) in areas subjected to increasingly humid climates; conversely, Ksat is enhanced under increasingly drier climates. To date, however, the relationship between climate and soil hydraulic properties is poorly understood. This is unfortunate because the rapid rate of change in soil hydraulic properties suggests that land-atmospheric feedbacks could be affected on time scales relevant to end-of-century climate simulations. The development of pedotransfer functions (PTFs) that describe these relationships will permit evaluation of these feedbacks, thus allowing the effects of climate-induced changes to soil hydraulic properties to be incorporated into simulation models. The goal of this work, therefore, was to develop climate-dependent PTFs to predict climatic effects on soil hydraulic properties. We assembled a large subset of the National Cooperative Soil Survey, Soil Characterization Database maintained by the Natural Resources Conservation Service, US Department of Agriculture. This soil database contains pedon-level data from across the US, allowing relationships between soil physical, chemical, biological, and hydraulic properties to be examined over a wide range of climatic regimes. A variety of exploratory multivariate statistical approaches to examine relationships between climatic variables such as mean annual precipitation and temperature, soil properties such as particle-size distribution and organic carbon content, and hydraulic properties such as macroporosity, water retention, and Ksat, reveal the importance of climate-induced influences on the soil fabric over diverse timescales. Ultimately, the development of empirically-based, climate-dependent PTFs will allow potential feedbacks associated with dynamic soil properties to be examined and described.