AGU 2016 Conference Poster

1. Accounting for wetlands loss in a changing climate in the estimation
of long-term flood risks of Devils Lake in North Dakota
Sergey Gulbin1 , Andrei Kirilenko2, Xiaodong Zhang1
1University of North Dakota, Grand Forks ND; sergey.gulbin@und.edu, 2University of Florida, Gainesville, FL; andrei.kirilenko@ufl.edu
ABSTRACT
Endorheic (terminal) lakes with no water outlets are sensitive indicators of
changes in climate and land cover in the watershed. Regional variation in
precipitation pattern in the US Northern Great Plaines lead to a long term
flooding of Devils Lake (DL), ND, leading to a 10-m water level rise in just two
decades, with estimated flood mitigation costs of over $1 billion. While the
climate change contribution to flooding has been established, the role of large
scale land conversion to agriculture has not been researched. Wetlands play a
very important part in hydrological balance by storing, absorbing and slowing
peak water discharge. In ND, 49 % of wetlands are drained and converted to
agriculture. We investigated the role of wetlands loss in DL flooding in current
and future climate.
The Soil and Water Assessment Tool (SWAT) was used to simulate streamflow in
all DL watershed sub-basins. The model was calibrated using the 1991-2000 USGS
gauge data for the first 10 years of study period and validated for the second 10
years (2001-2010), resulting in a satisfactory model performance compared
against the measured water discharge in 8 streams in the watershed and against
observed DL water level. A set of wetland loss and restoration scenarios were
created based on the historical data and the Compound Topographic Index. To
emulate the future climate conditions, an ensemble of CMIP5 weather
integrations based on IPCC AR5 RCP scenarios was downscaled with the MarkSim
weather simulator.
Model simulations indicate that the land use change in the DL watershed
increased the impacts of climate change on hydrology by further elevating DL
water level. Conversely, wetland restoration reduce the flooding and moderates
risks of a potential high-impact DL overspill to the Sheyenne River watershed.
Simulations for the period from 2011 to 2040 indicate that with increasing area of
wetlands, probability of DL overspill to Sheyenne River decreases.
SWAT MODEL
• We used 17 Global Climate Models (GCM), each with 4 Representative
Concentration Pathways (RCP), so total is 68 scenarios, representing future
climate for the period 2011-2040.
• Every land cover model(scenario) was simulated under 68 climate scenarios and
evaluated on natural overspill to Sheyenne River, which correspond to elevation
444.4 meters.
• Finally, we can say how likely DL would overspill in every scenario. In the model
with no wetlands DL overflows in 54 scenarios out of 68, in a model with 5%
wetlands, DL would overspill under 40 climate scenario. In a business as usual
scenario, when area of wetlands wouldn’t change, DL would overflow in 29
scenarios in the period from 2011 to 2040. If area of wetlands would be
increased by 50% and would make 16% of basin, the lake would overflow in 20
scenarios out of 68, and, finally, when area of wetlands would reach 20% of DL
watershed, DL would overspill to Sheyenne River only in 11 scenarios.
• Thus, this research proves that wetlands restoration would reduce water level in
Devils Lake and it’s flood risks. However, currently we simulated only original
future climate scenarios, which may have a period with consequent high
precipitation, so to reduce the influence of such bias, we plan to shuffle years in
climate scenarios 100 times, so we would have 100 shuffled versions of each
climate scenario (6,800 scenarios total).
DEVILS LAKE HISTORY
RMSE = 0.22 m
Currently wetlands occupy around 11% of DL basin area (based on NLCD2006
estimation), 4 hypothetical scenarios were created to test how wetlands influence on
DL: two scenarios with reduced area of wetlands (absolutely no wetlands and 5% of DL
watershed under wetlands), and two scenarios with wetlands coverage higher than
currently (16% and 20% of basin occupied by wetlands).
For hydrologic simulation, location of wetlands is as important as its amount and area.
To simulate the most likely location of wetlands in DL basin, a Compound Topographic
Index (CTI) was used: 𝐶𝑇𝐼 = 𝑙𝑛
𝛼
𝑡𝑎𝑛𝛽
, where
α is an upland contributing area and β is a slope in radians. Basically, CTI shows
measure of area “wetness”. It is commonly used to recreate historical wetlands location.
WETLANDS AREA CHANGE
• All hydrological simulations were conducted in SWAT (Soil and Water Assessment
Tool; Arnold et al., 1998), model calibration – in SWAT_CUP
• Watershed delineation is based on DEM (Digital Elevation Model) of Devils Lake basin
(source – USGS; resolution 30 m)
• Soil data was obtained from STATSGO2 database (250 m resolution)
• Land cover data is from NLCD 2006 (National Land Cover Dataset; resolution 30 m)
• Wetlands data - NWI2 (National Wetlands Inventory)
• For weather simulation in SWAT, data from 4 USDA weather stations was used
• Calibration and validation of the model was made with help of 8 river gages
observation data from USGS
• In 2007 first outlet that pumps water from DL was launched. Later, second outlet
started to operate, their total maximum capacity is 17m3/s. We incorporated outlets
in our model, but since the real outlet has never operated on their maximum capacity,
we used their average rate: 11.2 m3/s
http://earthobservatory.nasa.gov/IOTD/view.php?id=42624
http://earthobservatory.nasa.gov/IOTD/view.php?id=42624
• After comparing 5 scenarios, including current one, in scenarios with lower area of
wetlands, Lake level is higher than in scenarios with increased area of wetlands
(comparing to current coverage)
• Mean difference between scenarios is 0.44 meters with lowest at the start of study
period and highest at the end – in 2010.
0.00%
10.00%
20.00%
30.00%
40.00%
50.00%
60.00%
70.00%
80.00%
Open Water Developed Deciduous Forest Grassland/Herbaceous Pasture/Hay Cultivated Crops Herbaceous Wetlands
Area,%
No wetlands 5% wetlands Current 16% wetlands 20% wetlands
SCENARIO rcp26 rcp45 rcp60 rcp85
No wetlands 15 15 10 14
5% 9 10 9 12
Current (11%) 4 8 7 10
16% 2 6 4 8
20% 1 4 2 4
PRECIPITATION
(MM/DAY) 1.57 1.58 1.55 1.60
TEMPERATURE C 4.08 4.10 3.88 4.19
DL expansion has multiple
consequences, from obvious flooding
of adjacent areas to pollution of Red
River and Lake Winnipeg. It should be
mentioned that to the South of Devils
Lake, Spirit Lake tribe territory is
located. Tribe’s population is directly
affected by flooding. Also, Devils Lake,
as wetlands located in its watershed
are important attractions for hunters,
fishermen and bird watchers. This
natural disaster is causing loss to a
county and even state budget. Finally,
with overspill of DL to Sheyenne River
water from DL goes up to Canada and
Lake Winnipeg. The quality of water in
DL is very poor, so overflowing to
Sheyenne River would lead to pollution
of Red River, Lake Winnipeg and its
eutrophication. All this makes DL
flooding an international problem.
Currently, most of the wetlands is concentrated in the Southern part of the DL basin,
with the highest density on the South-East. In hypothetical scenarios with higher area
of wetlands, the highest density of wetlands is located in the Northern and Central
parts of the basin.
One of the SWAT limitations is that this tool can represent wetlands only on sub-basin
level, that means that wetlands parameters, such as area, volume and drainage area
are summarized for all wetlands in sub-basin. Since there is no data on volume and
drainage area of wetlands in North Dakota, these parameters were calculated using a
method from Gleason et al., 2011. The following model was used and tested on
wetlands in our study area: V = 0.25𝐴1.4742
; 𝑈𝐴 = 2.24𝐴0.4647
, where 𝑉 is a volume
of wetland, 𝐴 – its area and 𝑈𝐴 is upland area (or contributing area).
ACKNOWLEDGEMENTS
This study was partially funded by NSF RII EPSCoR (1355466) grant
KEY REFERENCES
• Gleason, Robert A., and Brian A. Tangen. "Chapter D: floodwater storage."
Ecosystem Services Derived from Wetland Conservation Practices in the United
States Prairie Pothole Region with an Emphasis on the US Department of
Agriculture Conservation Reserve and Wetlands Reserve Programs (2008): 31.
• Arnold, Jeffrey G., et al. "Large area hydrologic modeling and assessment part I:
Model development1." (1998): 73-89.
• Dahl, Thomas E. Status and trends of wetlands in the conterminous United States
2004 to 2009. US Department of the Interior, US Fish and Wildlife Service,
Fisheries and Habitat Conservation, 2011.
Overspill Frequency under Different RCPs
CTD.: DEVILS LAKE HISTORY
CONCLUSIONS
• Land cover change in DL basin, in particular, wetlands loss due to agricultural
expansion, impacted DL system. Our results suggest that with higher area of
wetlands, DL level would drop, and as consequence, flooding severity would
decrease. At the same time, if agricultural expansion would have been more intense,
and less wetlands would exist in DL watershed, the lake would rise.
• If until 2040 area of wetlands wouldn’t change, DL would overflow to Sheyenne River
in 29 CMIP5 climate scenarios out of 68.
• Restoration of some wetlands may help to reduce consequences of climate change
for Devils Lake. The results of our study indicate that if wetlands coverage in DL
watershed would be increased to 20%, DL would experience natural overflow to
Sheyenne River only in 11 CMIP5 climate scenarios out of 68 for the period 2011-
2040. The contrary is also true: if all wetlands in DL would be drained, DL would
overspill to Sheyenne River in 54 scenarios out of 68.
FUTURE CLIMATE
Acquired August 11, 1984
Red River & Devils Lake Basin
Acquired September 1, 2009
Study Area
Simulated and Observed DL Water Level
Land Cover Fractions