Hydrological response surfaces in the Nordic Region for use in probabilistic

assessment of climate change

Phil Graham

Sara-Sofia Hellström

Fredrik Wetterhall

Swedish Meteorological and Hydrological Institute, Norrköping

Our contribution to workpackage

objectives

• Hydrological rainfall-runoff models to

investigate impacts of climate change

on stream discharge

• Using the climate change signal from

RCMs

Our contribution to workpackage

objectives

• Response surfaces for selected

applications

• Direct use of multiple regional model

projections

• Comparison of outcomes from the two

methods

What have we achieved since Lund?

• In Lund, we showed some preliminary

response surfaces

• Now, we have produced many more

• In Lund, we discussed the question of

seasonality

• Now, we have investigated the details

of representing seasonality

Response Surfaces – Annual Runoff

no seasonality

Lake Vänern

Lake Vänern

Response Surfaces – Annual Runoff

with seasonality

Lake Vänern

Lake Vänern

RS – Representing Seasonality

Method 1

2 4 6 8 10 120

1

2

3

4

5

6

7

8

9

10

Tem

pera

ture

cha

nge

Month2 4 6 8 10 12

0.6

0.8

1

1.2

1.4

1.6

1.8

2

Pre

cipi

tatio

n ch

ange

Month

Temperature Precipitation

RS - Extended Period with Maximum

Discharge

Current regulation rules

Lake Vänern

RS - Extended Period with Maximum

Discharge

Current regulation rules

Lake Vänern

RS - Extended Period with Maximum

Discharge with Modified Regulation

Modified regulation can help reduce risk of high discharge

Lake Vänern

Response Surfaces – Monthly Runoff

Lake Vänern

Lake Vänern

Response Surfaces – Annual Runoff

Lake Mälaren

Response Surfaces – Annual Runoff

seasonality 1Lake Mälaren

Response Surfaces – Annual Runoff

seasonality 2Lake Mälaren

RS – Representing Seasonality

Method 2

Precipitation method 1

Precipitation method 2

2 4 6 8 10 12

0.6

0.8

1

1.2

1.4

1.6

1.8

2

Precipitation change type 1

%-c

hang

e pr

ecip

itatio

n

Month2 4 6 8 10 12

0.6

0.8

1

1.2

1.4

1.6

1.8

2

Precipitation change type 2

Month

%-c

hang

e pr

ecip

itatio

n

RS – Lake Levels

Low levelsLake Mälaren

RS – Lake Levels, seasonality 1

Low levelsLake Mälaren

RS – Lake Levels, seasonality 2

Low levelsLake Mälaren

Response Surfaces – Monthly Runoff

Lake Mälaren

Monthly Runoff – compared to

previous results

0

50

100

150

200

250

300

350

400

1 2 3 4 5 6 7 8 9 10 11 12

month

run

off

(m

3/s

)

0

50

100

150

200

250

300

350

400

ctrl

RCAO-EA2

RCAO-EB2

RCAO-HA2

RCAO-HB2

RCAO-EA2-rs

RCAO-EB2-rs

RCAO-HA2-rs

RCAO-HB2-rs

Lake Mälaren

Some Conclusions

• Seasonal differences not so apparent for annual runoff

• Shows up in monthly results, and even more for thresholds, although not all basins are equally sensitive

• Different methods for representing seasonality have an impact

• Representation of evapotranspiration is problematic (as usual!)

Coming Work

• Contribution to del. 6.7 (RS Report)

• Not too much more on response surfaces before data starts coming

• Next major effort will be to work with direct modelling of RCM simulations (the “Matrix,” as soon as they are

available)

Questions for Discussion

• Critical thresholds, we use experience

from critical past events, better ideas?

• What if there is widely differing

seasonality from the climate models?

• What will we actually get from the

climate models (i.e. probabilistic info.)?

• How many simulations will be available

(perturbed vs. RCM results)?