Although many impacts of climate change remain uncertain, climate models robustly project that land surfaces become drier in warmer climate conditions. General circulation models (GCMs) almost universally show reduced soil moisture over much of the globe, even in locations where average rainfall increases (Figure 1). This change is a significant societal concern both because of potential effects on food production and because drier soils feed back on local weather conditions, exacerbating heat waves. (In wetter conditions, evaporative cooling buffers extreme temperatures.) These adverse consequences make understanding the surface-atmosphere interactions that control soil moisture a research priority.
While the model projections of drying are plausible, the model representation of soil moisture dynamics have not been fully validated. Soil moisture observations are sparse and controversial, and there is as yet no consensus on whether the historical record suggests that droughts are increasing. The RDCEP soil moisture project is using a unique observational resource to characterize soil dynamics and test the representation of soil moisture in models. We make use of the Department of Energy’s Atmospheric Radiation Measurement Climate Research Facility at the Southern Great Plains site in Kansas and Oklahoma (ARM-SGP), where soil moisture, moisture fluxes, and meteorological variables have been measured at hourly intervals over more than a decade, as a test-bed for characterizing statistical relationships between soil moisture and moisture fluxes and local forcing variables (e.g. temperature, precipitation, wind speed, and relative humidity). We then compare to output from the soil moisture model (CLM) used in the Community Earth System Model, one of the most widely-used climate models, to understand how well models capture the physics controlling soil moisture.
This project is supported in part by a University of Chicago - Argonne National Laboratory Strategic Collaboration Initiative seed grant.
Shanshan Sun. Statistical exploration of processes controlling soil moisture in present and future climates. Poster presented at: ARM/ASR Joint User Facility/PI Meeting, Tyson’s Corner, VA. March 16-19, 2015.