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ARS Home » Midwest Area » West Lafayette, Indiana » National Soil Erosion Research Laboratory » Research » Publications at this Location » Publication #331683

Title: Quantifying the effects of future climate conditions on runoff, sediment and chemical losses at different watershed sizes

item WALLACE, CARLINGTON - Purdue University
item Flanagan, Dennis
item ENGEL, BERNARD - Purdue University

Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/30/2016
Publication Date: 2/1/2017
Citation: Wallace, C., Flanagan, D.C., Engel, B. 2017. Quantifying the effects of future climate conditions on runoff, sediment and chemical losses at different watershed sizes. Transactions of the ASABE. 60(3):915-929.

Interpretive Summary: Globally, mean surface temperatures have been slowly increasing over the past century, most likely due to increases in greenhouse gas (carbon dioxide, methane, nitrous oxide, etc.) levels in the atmosphere from human activities. This increase in temperature has resulted in global climate changes and increasing variability in weather patterns, which may result in increases or decreases in precipitation, drought periods, flooding, etc. Projected climate changes are location specific, and information from large-scale atmospheric general circulation models (GCMs) needs to be downscaled to specific small-scale areas. In this study, we downscaled GCM projections of future climate change for a region in northeastern Indiana containing several small watersheds, where flow and chemical losses are measured on a regular basis. We used the measured weather, land management, soil, flow, and pollutant data to test how well the SWAT (Soil and Water Assessment Tool) model could estimate the water flow and pollutant losses from 4 watersheds ranging in size from 20 to 679 km2 (8 to 262 mi2). SWAT performed well after calibration in predicting flow, soluble nitrogen (N) and phosphorus (P) losses, and total N and P losses. We then applied the calibrated model to determine the effect of projected climate changes on flow and pollutant losses. The results showed that surface flow is predicted to decrease by 9-22% while subsurface tile flow is predicted to increase by 20-26% across the four watersheds. Sediment losses were predicted to increase by 13-139% by the end of the century across all watersheds. Soluble and total N losses, and total P losses, did not change much between current levels and those projected at the end of the century. However, soluble P losses were predicted to decrease by 10-26% in the two larger watersheds. These results impact scientists, faculty members, students, conservation agency personnel and others concerned with the effects that climate change may have on effectiveness of current land management systems at controlling runoff, tile flow, and nutrient losses. In particular in the Lake Erie Basin, losses of soluble P are of high concern, as they affect algal blooms and eutrophication in the Lake.

Technical Abstract: Assessing the sensitivity of agricultural watersheds to possible changes in future climate is imperative when developing appropriate management practices. Agricultural management practices are often assessed at the watershed scale, and therefore, understanding the influence of climate change at different watershed sizes will provide insight into the effectiveness of watershed management strategies under future climate conditions, especially in highly agricultural watersheds with modified hydrologic landscapes. In this study, the Soil and Water Assessment Tool (SWAT) and downscaled weather data generated using the MarkSim weather file generator were used to evaluate the potential impact of climate change on surface flow, tile flow, sediment and chemical losses in the hydrologically modified Cedar Creek, F34, AXL and ALG watersheds located in northeastern Indiana. There was no clear evidence to suggest watershed size will have an impact on the simulation of climate change effects. Results of this study indicate that surface flow will decrease significantly towards the end of this century (ranging from 9% in CCW to 22% in ALG), while subsurface tile flow will increase significantly (ranging from 20% in CCW to 26% in AXL). The percentage increases in predicted sediment loss for the CCW, AXL and ALG watersheds were significant at a = 0.05, though the magnitudes of overall sediment loss were low, especially in the CEAP monitored watersheds (F34, AXL and ALG) in which several best management practices are implemented. Differences in predicted atrazine, soluble N, total N, and total P losses between the baseline period and the end of the century were not significant for any of the watersheds, while increased soluble P losses were only significant for the larger CCW and F34 watersheds.