An integrated observational and model-based analysis of the hydrologic response of prairie pothole systems to variability in climate

We developed a hydrologic model capable of simulating pothole complexes composed of tens of thousands or more individual closed-basin water bodies. It was applied to simulate the hydrologic response of a prairie pothole complex to climatic variability over a 105 year period (1901-2005) in an area of the Prairie Pothole Region in North Dakota. The model was calibrated and validated with a genetic algorithm by comparing the simulated results with observed power law relationships on water area-frequency derived from Landsat images and a 27 year record of water depths from six wetlands in the Cottonwood Lake area. The simulated behavior in water area and water body frequency showed good agreement with the observations under average, dry, and wet conditions. Analysis of simulation results over the last century showed that the power laws changed intra-annually and interannually as a function of climate. Major droughts and deluges can produce marked variability in the power law function (e. g., up to 1.5 orders of magnitude variability in intercept from the extreme Dust Bowl drought to the extreme 1993-2001 deluge). Analyses also revealed the frequency of occurrence of small potholes and puddles did not follow pure power law behavior and that details of the departure from linear behavior were closely related to the climatic conditions. A general equation, which encompasses both the linear power law segment for large potholes and nonlinear unimodal body for small potholes and puddles, was used to build conceptual models to describe how the numbers of water bodies as a function of water area respond to fluctuations in climate.