SWOT Measurements for Improving Understanding of Mid-Latitude Hydrology Franklin W. Schwartz School of Earth Sciences The Ohio State University September 15, 2008 Acknowledgements: National Science Foundation, Ganming Liu, Bo Zhang, Jerry Allen

Example of pothole lake in South Dakota in Waubay Lakes chain Typically, a product of an extremely hummocky, glacial terrain Lakes are commonly found in closed basins, often saline, surrounded farmland

T housands of small lakes T housands of small lakes Pothole lakes and wetlands occur together with few large recreational lakes Pothole lakes and wetlands occur together with few large recreational lakes Entire watershed area is hydrologically closed Entire watershed area is hydrologically closed

Prairie Pothole Region Unique lake system Canada and USA Upwards of 6 million pothole lakes Most located around edges with more rainfall Important farming impacts

Hydrology Prairie Pothole Lakes Water primarily from snowmelt runoff with ground water and summer rains less important Water levels fluctuate tremendously depending upon variable climate Continental climate of prairies cycles between drought and deluge

Waterfowl Prairie Pothole region produces 50% primary game ducks in North America For seven species – e.g., mallard, blue- winged teal, redhead, and canvasback - region home to >60% N.A. breeding population Populations of some species of ducks rise and fall in response to deluges and droughts

Hydrology and biology of these lakes and wetlands well understood - more than 30 years of study at Cottonwood Lakes Study Area Important role ground-water and surface water interactions Long-term monitoring at a few sites explained how pothole lakes responded to periodic drought and deluge Why Study these Lakes?

New Challenges Emerging challenge for hydrologists is describing and understanding processes in large complex systems Conventional monitoring approaches inadequate and not commonly available Tremendous potential in linking regional- scale models, and space geodetic and remote sensing techniques SWOT provides important new capabilities

Regions of Interest Pothole lakes not uniformly distributed Prairie Coteau and Missouri Coteau M P

Lakes and Climate Variability Study area – tip of Prairie Coteau in SD Climate affects on water on landscape - change in numbers of lakes, size, volume rd drought century greatest deluge - observable by Landsat

Precipitation Waubay Lakes Area 2 nd Drought1 st Deluge

Lake Occurrences – 1990 vs. 1997

Lakes and Power Laws Known for many years that areas of lakes followed a power-law distribution e.g lakes by Kent and Wong [1982] Now commonly applied in global assessment What pattern of organization of lake systems? Can we use for analysis? Powerful because lake/wetland complexes rationalized by few parameters

Small Lakes Large Lakes Lakes and Power Laws Developed area versus frequency curves - one curve for each Landsat image – Spring - straight line - boundaries

Seasonal Effects Within any year considerable variability - spring to summer – small lakes impacted

Additional Imagery Lines extend 1.5 orders magnitude in area Colored digital aerial photography 1 meter resolution lets us measure lakes areas of the order of 100 m 2

Develop Test Area Landsat - Low res over big area DOQQ - Hi res over small area Next Step - power law for DOQQ - small area, fewer lakes

Are Lake Areas Self-Similar?

Dust Bowl Drought – 1930s Aerial photographs commonly available

Extrapolate 1939 Photography

Conceptual Model Area small lakes changes rapidly – season Area large lake changes slowly - cycles

Extensions Modeling now underway to simulate behavior of a lake complex 100,000 lakes Ganming Liu able to calibrate to power laws and long-term records for individual lakes Work will be helped when SWOT mission comes along - changes in storage great opportunity to recast power laws

Sample Simulation Results 100-year simulation of a pothole lake complex along Missouri Coteau, ND Stochastic analysis ~10 6 lake basin realizations to provide power laws

Important Findings Like others found that areas of lakes obey a power-law function – 3.5 orders No single power law because rapid shifts as a function of climate - seasonal effects important Small lakes and large lakes respond to different climate signals For this reason, small lakes could be robust for small periods in a long drought