The Impact of Future Climate Variability on the Hydrology ... · The Impact of Future Climate...

The Impact of Future Climate Variability on the Hydrology of the

Delaware River Basin

Timothy W. Hawkins

Shippensburg University

2018 AWRA Annual Meeting

Outline

• Delaware River Watershed

• Model description

• Climate projections

• Model assessment

• Hydrologic projections

Delaware Bay and Watershed

• Watershed: 35,066 km2

• Bay: 2,025 km2

• Main Stem: 330 miles (undammed)

• Tributaries: 216; 14,057 miles

• States: NY, PA, NJ, DE

• Counties: 42; Municipalities: 838

• Water supply: 15 million people

• Watershed: $22.5 billion/year

• Port: $19 billion/ year

https://www.state.nj.us/drbc/

Climate Change and the Watershed

9

11

13

15

1950 2000 2050 2100

Tem

per

atu

re (

°C)

rcp2.6

rcp4.5

rcp6.0

rcp8.5

Modeling the Watershed

• 864 grid cells– 1/8° (~12 km x 12 km)– 141 water cells– 225 watershed cells

• Monthly time step• Development: 1950 – 1999 • Projections: 1950-2099

Gridded Parameters and Constants

• Lat, Lon, area

• Average monthly day length

• Elevation

• Subsurface storage

• Land use land cover

Outputs

• Monthly average temperature (T; °C)

• Monthly total precipitation (P; mm)

• Rainfall (Prain)• Snowfall (Psnow)• Snowmelt (Melt)• Snowcover (Snow)• Available water (Pavail)• Potential ET (PE)• Actual ET (AE)• Subsurface Moisture (SM)• Surplus water (S)• Runoff (RO)

All outputs in mm

Inputs

Monthly Gridded Inputs

• 231 CMIP5 projections

– 1/8° (~12 km x 12 km) statistically downscaled T & P

– Monthly 1950 – 2099

– 37 models; 4 RCP; several runs

• Observed T and P 1950 – 1999 for validation

– Used for hydrologic model development

Model Workflow

1. Differentiate rainfall/snowfall f (T)

Model Workflow


2. Snowmelt based on f (T)

Model Workflow



3. Accumulate snow water storage

Model Workflow




4. Available water from melt and rainfall

Model Workflow





5. Hamon PE constrained

Model Workflow






6. Subsurface moisture f (PE, Pavail , capacity, LULC)

Model Workflow






6. Subsurface moisture f (PE, Pavail, capacity, LULC)

7. Surplus water

Model Workflow






6. Subsurface moisture f (PE, Pavail, capacity , LULC)

7. Surplus water

8. AE f (PE, Pavail , SM)

Model Workflow







7. Surplus water

8. AE f (PE, Pavail, SM)

9. Runoff f (surplus, LULC)

Model Workflow







7. Surplus water

8. AE f (PE, Pavail, SM)

9. Runoff f (surplus, LULC)

10. Aggregate RO for subwatersheds

8

10

Model Evaluation

Gage 8 Gage 10 Whole Basin

Model Evaluation

Gag

e 8

Gag

e 1

0

12

-gag

e a

vg

Monthly r 0.896 0.912 0.855

r sig 0.000 0.000 0.000

NS 0.803 0.824 0.593

Annual r 0.981 0.972 0.944

r sig 0.000 0.000 0.000

NS 0.962 0.918 0.721

8

10

Model Results

Percent Change between Future

and BaselineRCP

2.6

RCP

4.5

RCP

6.0

RCP

8.5

T (°C) 1.9 2.8 3.1 4.5

PE (mm) 58.4 78.4 107.1 99.5

AE (mm) 49.1 64.5 84.0 76.7

SM (%) -2.1 -3.3 -5.4 -5.0

RO (mm) 48.9 51.5 41.0 72.7

P (mm) 98.1 116.3 125.6 150.0

Pr (mm) 132.4 162.1 172.1 212.6

Ps (mm) -34.3 -45.7 -46.5 -62.5

SWE (mm) -3.9 -4.8 -4.8 -5.9

Melt (mm) -34.3 -45.7 -46.5 -62.5

Trends per Century

Modeled DJF Snow Cover

Distribution of Modeled Runoff

Conclusions

• Basin-wide increases– T, P, Pr , PE, AE, RO

• Basin-wide decreases– Ps , SWE, melt, SM

• High spatial variability

• Runoff as an integrator– Increasing 3.5 – 17.4%

• most under rcp 8.5

– Increasing in winter

– Range in projections

– PE calculation matters

Future Work

• Impact on flood hydrology

• Impact on tree species

• Repeat analysis at 800 m resolution

• Examine drought and surplus conditions

Questions?

Tim [email protected]

https://centerforlanduse.org/projects/drb/

AcknowledgementsAlfonso Yáñez, Jonathon Chester, Troy Pomeroy, Antonia Price, Claire Jantz, Christopher Woltemade, Scott Drzyzga, Patrick Jantz

Impact of Constraining PE

• Energy Only– Simple proportion

based on LE and H

• 7 traditional ET’s

• ET calculations reasonable

• ET future changes not reasonable except for energy only

Milly and Dunne (2017)


• Calculate Hamon and Energy only for GCM’s– 1 cell for DRB, monthly 1950-2099

• Calculate Hamon diff between future downscaled and historic GCM

• If Hamon difference > GCM Energy Only:– PE = Historic Hamon + Energy Only diff +

diff btw downscaled PE and running mean

• Take home message: – Statistically constrained runaway PE– Accounts for increased stomatal resistance w/

warmer temperatures.

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