SWOT Measurements for Improving Understanding of

Mid-Latitude Hydrology

Franklin W. Schwartz

School of Earth Sciences

The Ohio State University

September 15, 2008Acknowledgements: 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

• TThousands of small lakeshousands of small lakes• Pothole lakes and wetlands occur Pothole lakes and wetlands occur together with few large recreational lakestogether with few large recreational lakes• Entire watershed area is hydrologically Entire watershed area is hydrologically closedclosed

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 - 1988-92 2rd drought century- 1993-1997 greatest deluge- observable by Landsat

Precipitation Waubay Lakes Area

2nd Drought 1st 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. 2500 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 m2

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

1939

2003

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 ~106 lake basin

realizations to provide power laws

0.6 0.8 1 2 4 6 8 10

10

100

08/193908/198608/199008/2002

Nu

mb

er

of L

ake

s

Lake area (ha)

0.4 0.6 0.8 1 2 4 6 8

10

100

1000 04/1992 09/1992 04/2002 09/2002

Num

ber

of la

kes

Lake area (ha)

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