ARS | Publication request: Can an ecohydrologic analysis distinguish land-use and climate-change effects on watershed hydrology?

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: October 2, 2008
Publication Date: October 2, 2008
Citation: Tomer, M.D., Schilling, K. 2008. Can an Ecohydrologic Analysis Distinguish Land-use and Climate-change Effects on Watershed Hydrology? [abstract]. p. 37.

Technical Abstract: Impacts of climate change on watershed hydrology are subtle compared to differences among years of drought and surplus rainfall, and not easily separated from effects of land use change. In the Midwest, trends such as increasing baseflow can be attributed to changes in agricultural practices as easily as to climate change. In a 25-year small watershed study in Iowa, when annual hydrologic budgets were accrued between major droughts (inter-drought periods), an eco-hydrologic water budget analysis suggested effects of agricultural practices and climate trends could be separated. Both effects resulted in increased stream discharge as a fraction of precipitation, but unsatisfied evaporative demand increased under conservation tillage yet decreased with time. We investigated records from larger watersheds in the Midwest to determine whether this interpretation could inform a wide-scale analysis. We selected records from five agricultural watersheds with minimal development of dams and urbanization, where both hydrologic and weather (daily max/min temperatures and precipitation) records extended to prior to 1950 (four had records to before 1930). All five watersheds showed significant increases in discharge, baseflow, and ratio of precipitation to potential evapotranspiration (PET) ratios (p<0.05). Four showed significant trends of decreasing PET and/or increasing precipitation. All five showed trends of increased fractional discharge, four being significant. Unsatisfied evaporative demand showed a decreasing trend in four of five watersheds. Although only one of these was significant, extension of small watershed results suggests climate change impact on hydrologic budgets in the Midwest exceeds that of conservation tillage practices at current extent.