K . F L Y N N , L . D O L A N , C . D A L B Y , R . N A G I S E T T Y

EVALUATING CLIMATE CHANGE IMPACTS ON WATER QUALITY USING

MECHANISTIC RECEIVING-WATER MODELS

EXPLORATORY – Caveat Emptor

OVERVIEW

• Introduction • Summary of basic literature regarding potential impacts of

climate change on water quality

• How mechanistic water-quality model frameworks can be used to inform climate change science

• Methods • Project site description

• GCM downscaling

• Representing climate change emission scenarios in a WQ model

• Results

• Discussion

10/14/2016 Exploratory 2

BASIC LITERATURE REVIEW

• Expected impacts of climate change on surface

WQ are widespread (Murdoch et al. 2000;

Whitehead et al. 2009)

• Warmer water temperatures

• Higher evapotranspiration

• Flow alteration

• Reductions in transport/increased residence time

• Reduced dilution

• Lower DO and pH

• Changes in kinetic/metabolic rates

• Increased biological productivity/eutrophication

10/14/2016 Exploratory 3

EVALUATING CLIMATE CHANGE EFFECTS ON WATER QUALITY

10/14/2016 Exploratory 4

General Circulation Model

Spatial Downscaling

Hydrologic Model

Water Quality Model

CLIMATE CHANGE THROUGH THE LENS OF A WATER-QUALITY MODEL

• Computational network (control-volume)

• Reaches/elements

• Meteorological Forcing Functions

• Air Temperature

• Relative Humidity/Dew Point

• Wind

• Cloud Cover

• Boundary Conditions

• Streamflow

• Water Temperature/Loading

10/14/2016 Exploratory 5

iinflow outflow

dispersion dispersion

mass load mass withdrawal

atmospheric

transfer

sediments bottom algae

n = 4n = 4

ReachReach ElementsElements

1

2

3

4

5

6

8

7

Non - point

withdrawal

Non - point

source

Point source

Point source

Point withdrawal

Headwater boundary

Downstream boundary

Point source

PROJECT SITE

10/14/2016 Exploratory 6

335 km

Location - Upper

Yellowstone River

MODEL, CALIBRATION DATA, AND CLIMATE SCENARIOS

• QUAL2K: 1-D ADR (heat, mass transport)

• Synoptic survey during 2012

• Critical flow conditions (Aug/September timeframe)

• Not fully calibrated yet; using lower river rates (Flynn et al. 2015)

• Approach – adjust model to reflect 2099 conditions

under two emission scenarios

• Air temperature, dew point, wind speed, cloud cover,

tributary and headwater flows, temperatures, dissolved

oxygen, point source inflows

10/14/2016 Exploratory 7

GCM DOWNSCALING

• General Circulation Models

(GCMs) cannot simulate

climate at the local to

regional scale

• Downscaling

• Dynamic

• Statistical

• Downscaled CMIP5 multi-

model ensemble median

• Two emission scenarios

• (medium/high)

10/14/2016 Exploratory 8

General Circulation

Model

Spatial Downscaling

Hydrologic Model

AIR TEMPERATURE ESTIMATES

• Downscaled CMIP5 BCSD climate/hydro projections (Reclamation 2013; 2014) upstream of Billings

• Two greenhouse gas emission scenarios (medium/high) • Representative

concentration pathway (RCP) RCP 4.5 (560 ppm by 2100) and RCP 8.5 (1370 ppm by 2100).

• Air Temp. Median Ensemble (2012-2099) • RCP 4.5 ≈ 2.5C increase

• RCP 8.5 ≈ 5C increase

similar to Chang and

Hansen (2014) for GYE 10/14/2016 Exploratory 9

http://gdo-dcp.ucllnl.org/downscaled_cmip_projections/

REL. HUMIDITY

• Pierce et al. (2013) projected changes in humidity via CMIP5 • RH predicted to change

−0.2 to −0.8 percentage points per decade

• 1.8–7.2% from 2010-2099 (9 decades)

• Decrease is accomplished by ambient air temperature warming faster than increasing moisture content of the atmosphere (both increase)

10/14/2016 Exploratory 10

WIND SPEED/CLOUD

• No statistical downscaling procedures have been

tested with wind speed (Pierce et al. 2013)

• % cloud cover expected to remain relatively

constant (Zelinka et al. 2012)

10/14/2016 Exploratory 11

Apply un-adjusted

wind and cloud

cover data from

2012 (for now)

STREAMFLOW BOUNDARIES

• CMIP5 projected

decadal Aug./Sept.

streamflow declines over 2012–2099

from VIC

• RCP4.5

• Livingston ≈ 10%

• Billings ≈ 7%

• RCP8.5

• Livingston ≈ 20%

• Billings ≈ 11%

10/14/2016 Exploratory 12

Billings

Adjust headwater −10/20%; remaining tributaries and

groundwater equitably

T99

T90

T50

T1

T10

Q99

Q95

Q90

Q50

Q20

Q5

Q1

Q80

Q10

OTHER BOUNDARY CONDITIONS

• WQ concentrations same as

2012 synoptic survey

• Based on temperature and

streamflow percentiles

• Other assumptions:

• Water temperature scales with

air temperature (surface and

groundwater)

• DO reduced on a percentage

basis

• No pH adjustment due to

complexity

10/14/2016 Exploratory 13

POINT SOURCES

• Point source flow increases based on per capita flow and historical population growth (1950–2015)

• Billings = 2%, Laurel = 1%, Livingston = 0%

• One scenario at projected 2099 flows

• No change in concentration/treatment

10/14/2016 Exploratory 14

RESULTS

10/14/2016 Exploratory 15

SUMMARY

10/14/2016 Exploratory 16

• Flow ↓

• Temp ↑

• SC ↑

• DO ↑↓

• pH ↓

• TN/TP ↑

• Balg ↑

DISCUSSION

• Water temperature expected to increase roughly proportionally to air temperature (thermal stress)

• Larger GPP cycles should occur • Upstream of Billings (B-1, B-2) freshwater aquatic standards

potentially not met for DO (> 8 mg/L). Likely would be met downstream (B-3 use class, 5 ppm).

• Reductions in pH (acidity) partially offset by increases in primary productivity if enriched. pH mostly within DEQ requirements (6.5–9 SU).

• Dilution greatly reduced as evidenced by concentration increases at Billings, MT

• Benthic biomass stimulated when enriched

10/14/2016 Exploratory 17

FUTURE WORK

• Refinement of boundary conditions (statistical

approaches vs. other approaches?)

• Temperature and mass loadings

• Groundwater vs. surface water effects

• Better understanding of the temperature

dependency of rates (theta value)

• Assemblage shifts?

10/14/2016 Exploratory 18

10/14/2016 19 Exploratory

Q U E S T I O N S | C O M M E N T S

THANK YOU