Climate Impacts on Arrow Reservoir
by Se-Yeun Lee and Alan Hamlet
1. Introduction
Pacific Northwest temperature has increased for 20th century and is predicted to
further increase in the 21st century in response to greenhouse forcing. The temperature
increase and resultant streamflow timing shifts are likely to decrease the reliability of
reservoir refill in Columbia River Basin (Payne et al. 2004; Lee et al., 2009). Lee et al.
(2009) developed optimized flood control curves to migrate the hydrologic impacts of
global warming and showed that storage deficits decreased without increasing flood risk
when the optimized flood control curves were used. As an extension of the Lee et al.
(2009) study, we examine potential climate change impacts on the Arrow Lakes from
simulated results.
2. Methods
The climate change scenario assuming an annual average 2° C warming combined
with historical precipitation values was simulated using the Variable Infiltration Capacity
hydrologic simulation model (Liang et al. 1994) implemented at 1/8th degree
latitude/longitude resolution. The monthly time step Columbia reservoir simulation
(ColSim) model, described in more detail by Hamlet and Lettenmaier (1999) is used to
examine the impacts of the warming scenario alone, and with adaptive changes in flood
control operations based on optimization developed by Lee et al. (2009). Note that we
report the effects to storage levels as average “storage deficits”, which are equivalent to
the full volume of the reservoir minus the volume of water simulated by the ColSim
model in each month. If storage deficit increases on average, this means that the
reservoir either successfully fills on that date less frequently, or that the lake levels are
lower when the reservoir does not refill (or both).
3. Results
Figure 1 shows simulated average end of month storage deficits of Arrow dam
from July to September when reservoir refill is important. When the current flood control
curves are used for both 20th century climate and the climate change scenario, storage
deficits increase for the climate change scenario in comparison to the 20th century
climate. When flood control curves are changed from “current flood control curves” to
“optimized flood control curves” for the climate change scenario, the storage deficits
decrease for all months. For July, storage deficits for the climate change are restored the
similar level of those for 20th century, when optimized flood control curves are used.
Average Storage Deficit (KAF)
3,000
20th Cent_Cur FC
CC_Scen_CurFC
CC_Scen_OptFC
2,000
1,000
0
Jul
Aug
Sep
Figure 1. Simulated average end of month storage deficit of Arrow Reservoir for
simulated 20th century climate using current flood control curves (20th_Cent_CurFC) and
the climate change scenario climate using current flood control curves (CC_Scen_CurFC)
and HEC-PRM derived flood control curves (CC_Scen_HecFC).
4. Conclusions
In the absence of precipitation changes, streamflow timing shifts related to
warmer temperatures are likely to increase storage deficits in the Arrow Lakes.
Adaptation measures that revise current flood control operations can potentially reduce
these impacts to those consistent with historical values in July. Storage deficits in
August and September, however, cannot be fully mitigated by flood control adaptation.
This suggests that some impacts in late summer are to be expected even if flood rule
curves are revised.
Potential impacts to precipitation (and changes in precipitation from decade to
decade) may affect these results, and are not considered in this preliminary study.
5. References
Hamlet, A. F., and Lettenmaier, D. P. _1999_. “Effects of climate change on hydrology
and water resources in the Columbia River Basin.” J.Am. Water Resour. Assoc., 35(6),
1597–1623.
Lee, S-Y., Hamlet, A. F., Fitzgerald, C. J., and Burges, S. J. (2009). “Optimized Flood
Control in the Columbia River Basin for a Global Warming Scenario.” Journal of Water
Resources Planning and Management, DOI 10.1061/(ASCE)0733-9496(2009)135:6(440),
135(6) 440-450.
Liang, X., Lettenmaier, D.P., Wood, E.F., and Burges, S.J. (1994). “A simple
hydrologically based model of land surface water and energy fluxes for general
circulation models.” Journal of Geophysical Research, 99(D7), 14415-14428.
Payne, J. T., Wood, A. W., Hamlet, A. F., Palmer, R. N., and Lettenmaier,D. P. (2004).
“Mitigating the effects of climate change on the water resources of the Columbia River
Basin.” Clim. Change, 62 (1–3), 233–256.