Simulating lake and wetland areal coverage under future groundwater recharge projections: The Nebraska Sand Hills system

In a semi-arid climate, groundwater-fed endorheic lakes often have shallow depths and large areas of associated wetlands. These lake-wetland-aquifer systems are sensitive to land use and climate changes. Difficulties of modeling such systems include (a) tracking several thousand lakes and wetlands (LWs), and (b) evaluating major drivers of trends and fluctuations in LW areal coverage. Integrated hydrologic modeling of such systems is prohibitively expensive. We combine traditional groundwater flow modeling (MODFLOW), driven by modern and projected groundwater recharge (GR) estimates, with digital elevation model (DEM)-based geographic information system (GIS) terrain analyses. This approach can be a useful diagnostic tool for estimates of decade-averaged LW areas and numbers, and stream baseflow, facilitating conceptualization and design of more detailed modeling studies. We apply the approach to simulate dynamics of thousands of groundwater-fed LWs in the Nebraska Sand Hills, USA, under GCM-projected GR changes. Compared to the baseline period of 2000–2009, the model indicates an increase by 35% (from 2083 to 2804 km²) of decade-averaged LW area by the end of the 21st century under the Median GR projection, with GR averaging 55.3 mm/yr from 2010 through 2099 (5% increase). Under the same GR projection, the overall numbers of LW is simulated to increase by 18% (from 7331 to 8666). The uncertainty range in the hydrologic response of the system caused by differences among GR projections (Wet and Dry) are also evaluated.