climate change impact on drought risk and uncertainty in the willamette river basin dept. of...
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Climate change impact on drought risk and uncertainty in the Willamette River basin
Dept. of Geography, Portland State University, Portland, ORIl-Won Jung, Heejun Chang
The Oregon Water Conference 2011
Research questions
Will drought risk increase in the Willamette river basin? What drought index can give reliable results? Which region is most vulnerable to climate change impact?
Climate change in the Pacific Northwest
Source: Mote and Salathé (2010)
Source: Mote and Salathé (2010)
Temperature Precipitation
Incr
ease
Dec
reas
eIn
crea
seD
ecre
ase
Main drivers of Willamette’s hydrology
< 1000m
1000 - 2000m
> 2000m
Elevation
Raindominated
Snowdominated
Coast range
Willamettevalley
WesternCascade
HighCascade
Geology
Hydrologic response to climate change
12
3
Sub Psum (-20%) T (+3 )℃ Combined
1Marys River
2Lookout
Creek
3ClearLake
SPI vs. SRI
Standardized Precipitation index (SPI)
Standardized Runoff index (SRI)
Thomas McKee at Colorado State Univ. (1993)
Shukla and Wood at Univ. of Washington (2008)
A statistical method for assessing Rainfall
A statistical method for assessing runoff
Climatological drought index Hydrological drought index
Source: Shukla and Wood (2008)
USGS 14178000
USGS 14182500
0 60 120 180 240 300 360 420 480 540 600
Time
0
400
800
1200
Dep
th (
mm
)
Precip ita tionR unoff
0 60 120 180 240 300 360 420 480 540 600
Time
0
400
800
1200
Dep
th (
mm
)
High seasonality in precipitation and runoff
High seasonality in precipitation but low seasonality in runoff
High flow in summer
Distinct hydrologic regimes at North Santiam River
LITTLE NORTH SANTIAM RIVER NEAR MEHAMA, OR
NO SANTIAM R BLW BOULDER CRK, NR DETROIT, OR
USGS 14178000
USGS 14182500
- 4 - 2 0 2 4U SG S141780 00
- 4
- 2
0
2
4
US
GS
14
18
25
00
SPI (1-m onth)
R 2 = 0.80
- 4 - 2 0 2 4U SG S14178000
- 4
- 2
0
2
4
US
GS
14
18
25
00
SPI (3-m onth)
R 2 = 0.83
- 4 - 2 0 2 4U SG S141780 00
- 4
- 2
0
2
4
US
GS
14
18
25
00
SPI (6-m onth)
R 2 = 0.83
- 4 - 2 0 2 4U SG S141780 00
- 4
- 2
0
2
4
US
GS
14
18
25
00
SPI (12-m onth)
R 2 = 0.82
- 4 - 2 0 2 4U SG S141780 00
- 4
- 2
0
2
4
US
GS
14
18
25
00
SPI (24-m onth)
R 2 = 0.82
- 4 - 2 0 2 4U SG S14178000
- 4
- 2
0
2
4
6
US
GS
14
18
25
00
SRI (1-m onth)
R 2 = 0.54
- 4 - 2 0 2 4U SG S141780 00
- 4
- 2
0
2
4
US
GS
14
18
25
00
SRI (3-m onth)
R 2 = 0.60
- 4 - 2 0 2 4U SG S14178000
- 4
- 2
0
2
4
US
GS
14
18
25
00
SRI (6-m onth)
R 2 = 0.69
- 4 - 2 0 2 4U SG S141780 00
- 4
- 2
0
2
4
US
GS
14
18
25
00
SRI (12-m onth)
R 2 = 0.78
- 4 - 2 0 2 4U SG S141780 00
- 4
- 2
0
2
4
US
GS
14
18
25
00
SRI (24-m onth)
R 2 = 0.81W
este
rn
High
Wes
tern
High
- 4 - 2 0 2 4USG S14178000
- 4
- 2
0
2
4
US
GS
14
18
25
00
SPI (1-m onth)
R 2 = 0.80
- 4 - 2 0 2 4USG S14178000
- 4
- 2
0
2
4U
SG
S1
41
82
50
0
SPI (3-m onth)
R 2 = 0.83
- 4 - 2 0 2 4USG S14178000
- 4
- 2
0
2
4
US
GS
14
18
25
00
SPI (6-m onth)
R 2 = 0.83
- 4 - 2 0 2 4USG S14178000
- 4
- 2
0
2
4
US
GS
14
18
25
00
SPI (12-month)
R 2 = 0.82
- 4 - 2 0 2 4USG S14178000
- 4
- 2
0
2
4
US
GS
14
18
25
00
SPI (24-month)
R 2 = 0.82
- 4 - 2 0 2 4USG S14178000
- 4
- 2
0
2
4
6
US
GS
14
18
25
00
SRI (1-m onth)
R 2 = 0.54
- 4 - 2 0 2 4USG S14178000
- 4
- 2
0
2
4
US
GS
14
18
25
00
SRI (3-m onth)
R 2 = 0.60
- 4 - 2 0 2 4USG S14178000
- 4
- 2
0
2
4
US
GS
14
18
25
00
SRI (6-m onth)
R 2 = 0.69
- 4 - 2 0 2 4USG S14178000
- 4
- 2
0
2
4
US
GS
14
18
25
00
SRI (12-month)
R 2 = 0.78
- 4 - 2 0 2 4USG S14178000
- 4
- 2
0
2
4
US
GS
14
18
25
00
SRI (24-month)
R 2 = 0.81
SPI vs. SRI between two distinct watersheds
Short-term drought Long-term drought
Wes
tern
High
Downscaled GCM simulations by CIG
Source: Mote and Salathé (2010)
Precipitation Runoff Modeling System
PRMS model is physically based, semi-distributed hydrologic modelDeveloped by USGS (Leavesley et al., 1983)
Frequency of extreme drought (1-month)
2 4 6 8 10 12 14 18 2016
Frequency of extreme drought (3-month)
2 4 6 8 10 12 14 18 2016
Frequency of extreme drought (6-month)
2 4 6 8 10 12 14 18 2016
Frequency of extreme drought (12-month)
2 4 6 8 10 12 14 18 2016
Frequency of extreme drought (24-month)
2 4 6 8 10 12 14 18 2016
3) Multi-model results show an increase in the short-term fre-quency of extreme drought, but long-term drought shows no change or a slight decrease pattern
2) The Willamette Valley region has relatively high drought vulner-ability, but the High Cascade region has low drought risk be-cause of a deep groundwater system that help sustain summer flow
Conclusions
4) To cope with possible drought risk, more efficient water re-source management will be needed. (e.g., new reservoir opera-tion rules, drought forecasting capability, transfer water system between water-rich and water-poor regions)
1) SRI is a more appropriate index than SPI for assessing the po-tential impact of climate change on short-term droughts in the Willamette River Basin
Acknowledgements: This research was supported by Institute for Sustain-able Solutions (ISS) at Portland State University. We appreciate John Ris-ley of the US Geological Survey for this countless help on the PRMS model setup and Eric Salathé at the Climate Impacts Group of University of Wash-ington who provided downscaled climate change simulations.
Drought impact based on time-scales
1-month 3-month 6-month 9-month 12-month 24-month
Agricultural
Ecosystem
Water supply
Socioeconomic system