Project Overview

Evapotranspiration from wetlands buffers the impacts of short-term drought on upland grasslands through mesoscale (e.g., 10s1 to 10s2 km) climate effects.

T o test this hypothesis we will measure the water and energy balance of two interdunal valleys at UNL's Gudmundsen Sandhills Laboratory (GSL) using micrometeorological techniques (Bowen Ratio towers. Hydrologic fluxes of these wet meadows are measured with monitoring wells, providing an independent estimate of ET. Previous studies allow us to estimate the water and energy balance of SandHills lakes and wetlands. To make landscape-scale water and energy balance estimates, the wetland ET data, together with our upland ET measurements, will be combined with a satellite-based land cover classification of the Sand Hills using geospatial modeling techniques. Using aggregate estimates of energy and water balance for model grid cells (viz., 10km x 10km), we will use the mesoscale meteorological model MM5 to test for the presence of significant mesoscale circulation feedbacks caused by the wetlands.

Although frequent drought characterizes the Great Plains climate, the geologic record suggests that episodes of widespread dune destabilization in the Sand Hills have been uncommon and brief. Most areas contain evidence of only one major period of dune activity in the last millennium. Prolonged periods of "no-recharge" conditions would be required to drop the regional water table sufficiently to terminate the wetlands buffer effect on local and regional climate. The ratio of sensible to latent heat flux for the Sand Hills (both locally and regionally) would increase sharply as wet valleys desiccate. Would this generate a "desertification" feedback effect of land cover on mesoscale climate, intensifying the drought effect, the loss of grassland cover and dune destabilization? We hypothesize that this feedback plays a dominant role during periods when interdunal wetlands go dry during long-term droughts, and, perhaps, within subregions of the Sand Hills that lack wet interdunal valleys. Alternatively, the high albedo of dry sand may reflect most incoming radiation, reducing the magnitude of the increase in sensible heat flux while maintaining the shift in the Bowen ratio and enhancing drying similar to the feedbacks proposed for the African Sahel.