Response of Soil Effective Porosity to Prevailing Climates.

Understanding the coupling of climate to the land surface is important for predicting the response of hydrology, land-atmospheric dynamics, terrestrial ecology, geomorphology, and soil erosion to climatic forcings at regional and global scales. Previous research examining this response often assumed that the soil physical properties controlling water flux through the vadose zone remain static. Thus, total porosity and available water holding capacity are commonly used properties that are expected to vary only with soil texture. Pedogenic studies indicate, however, that soil structure develops under prevailing soil climatic conditions. This structure controls macroporosity, which is important for determining infiltration, runoff potential, and evaporation and, thus, the water cycle, land-atmosphere dynamics, surficial hydrology, soil erosion, and vegetation responses to climate change. Since climate is a factor controlling soil fabric, another variable describing soil structure and its concomitant effect on macroporosity should be incorporated into models examining the effects of climate change on the land surface. In this work, we propose the use of soil effective porosity (EP) to predict soil-landscape response to shifts in the earth's climate. Soil EP is defined as the difference between total porosity and field capacity. The objective of our work was to examine the relationship between soil climate and EP. We used a database compiled by the NRCS containing over 14000 samples that were measured for total porosity, field capacity, and wilting point. In addition, these samples were identified with one of five soil climates: aquic, udic, ustic, xeric, and aridic moisture regimes. Approximately 1000 weather stations across the US were located within regions containing udic, ustic, xeric, or aridic moisture conditions. Data from these stations were used to inversely solve for precipitation timing and magnitude and median values were used to represent each of these regions. Relationships between EP and climate will be presented and discussed.