Impact Of Wetlands Loss On The Long-Term Flood Risks Of Devils Lake In A Changing Climate

Endorheic (terminal) lakes with no water outlets are sensitive indicators of changes in climate and land cover in the watershed. Since 1990 Devils Lake watershed in North Dakota experienced a dramatic change of local climate: wet phase. This change yielded in a 10-m water level rise in just two decades. The Lake’s water level increase caused flooding of adjacent areas, including towns, agriculture fields and houses of Native Americans, costing over $1 billion in mitigation. While the climate change contribution to flooding has been established, the role of large scale land conversion to agriculture has not been researched. The purpose of this study was to assess the influence of land cover change, in particular, wetlands drainage and/or restoration on Devils Lake flooding through modeling the Devils Lake watershed. The Soil and Water Assessment Tool (SWAT) was used to simulate streamflow in all DL watershed sub-basins. The model was calibrated using the 2001-2010 USGS lake level data for the second 10 years of the study period and validated for the first 10 years (1991-2000), resulting in a satisfactory model performance compared against observed DL water level. A set of wetland loss and restoration scenarios were created based on the historical data and the Compound Topographic Index. To emulate the future climate conditions, an ensemble of CMIP5 weather integrations based on IPCC AR5 RCP scenarios was downscaled with the MarkSim weather simulator. The results suggested that increase of wetlands area in the Devils Lake basin helps to lower lake level both under weather observed during the period 1991 – 2010 and under future climate projections up to 2040. On average, under historic climate, Lake’s water level reduces by 0.47 meters on every 5% increase in the fractional coverage of wetlands in the basin. The lake level descends as a result of a reduced streamflow of its two main inlets: the Big Coulee and the Channel A. Under predicted future climate scenarios, every 5% increase in the fractional coverage of wetlands in the basin decreases the probability of Lake’s natural overspill to the Sheyenne River by 2 – 10%, depending on the type of climate projection