The 950,000 km2 Prairie Pothole Region (PPR) of central North America contains millions of surface water bodies in the form of lakes, wetlands, and ponds. These water bodies provide irreplaceable services to maintain the stability and sustainability for the wildlife, ecosystems, water resources, agriculture, and the economy. Because most of them are hydrologically “closed”, the water bodies are extremely sensitive to climate variability and are highly dynamic in terms of their numbers, water levels, areas, and storage. The ultimate goal of this study is to provide a better understanding of the dynamic hydrologic response of the water bodies in the PPR to variability in climate. To achieve this goal, three individual studies have been conducted.
In the first study, a hydrologic model, capable of simulating surface water complexes comprised of tens-of-thousands or more individual closed-basin water bodies, was developed to simulate the hydrologic response of water bodies to climatic variability over a 105-year period (1901-2005) in an area of the PPR in North Dakota. Simulation results over the last century showed that the area-frequency power laws for water bodies changed intra-annually and interannually as a function of climate. Major droughts and deluges were shown to produce marked variability in the power-law functions. Analyses also revealed the frequency of occurrence of small potholes and puddles did not follow pure power-law behavior with the departure from linear behavior closely related to the climatic conditions.
Next, a space-for-time (SFT) substitution approach was developed for the hydrologic study of the PPR water bodies. Evidence from a suite of surface-water complexes along a climate gradient in the PPR was used to validate the SFT substitution. Comparison of spatial and temporal trends in water-body population dynamics revealed a common response to climate variability in space and time. Findings on the validity of SFT substitution in hydrologic systems not only answered an important science question in its own right, but improved my understanding of climate-forcing and hydrologic-response mechanisms. This study also has important regional-scale implications, for the first time, providing a complete picture of the heterogeneous spatial and temporal water-body distribution across the entire PPR and revealing how these distribution patterns vary with changing climate.
Third, a new concept on integrated climatic forcing was developed and applied to elucidate the controlling factors on lake/wetland hydrologic dynamics. Currently, the existing paradigm is that lakes/wetlands can accurately track climate variations. Data on several closed-basin lakes and wetlands, however, implied that disparities in timing and magnitude exist between lake/wetland and climate records. It was found that what is important in determining the hydrologic behavior of lakes or wetlands is not the present climate signal but the cumulative history, with a memory that fades following exponential-decay trajectory at scale-dependent rates as time passes. Findings from this study provide a better understanding of mechanisms on how lakes/wetlands respond as a function of climate and, therefore, hold considerable promise for improving the quality of climate reconstruction.