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Hadley Centre

Changes and uncertainty in global river flow under climate change

Pete FalloonWith thanks to Richard Betts, Cameron Rye, Chris Jones, Rob

Harrison, Debbie Hemming, Venkata Jogireddy, Nicola Gedney, Olivier Boucher, Taikan Oki (University of Japan)

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OutlineRiver routing model in HadGEM1River flow validation (vs HadCM3)Changes in river flow under climate changeUncertainty studies (QUMP)

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River routing in HadGEM1

TRIP (University of Japan) 1 degree gridboxes, daily timestepNetwork of global riversValidate against observed river flow gauge data Realistic time lag between precipitation and outflow to oceansGood agreement with observations, and an improvement over the previous GCM, HadCM3

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HadCM3: original scheme vs TRIP

Improved seasonality of flowNorthern hemisphere rivers (Mackenzie, Ob, Amur, Yukon) extremely good agreement in amount & phase of flowSouthern hemisphere rivers (Amazon and Orinoco) much improved seasonality but annual mean flow too lowHadCM3 precipitation and land hydrology scheme produced too little runoff

Obs TRIP HadCM3

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TRIP in HadCM3 vs TRIP in HadGEM1

In 28 out of 40 gauging stations total annual river flow was improved in HadGEM1 Considerable improvement in flow prediction for the Amazon mouth (largest flux of freshwater to the oceans, approximately 3x other rivers)HadGEM1 predictions for high latitude rivers were particularly goodSeasonality generally improved in many rivers

Obs HadCM3 TRIP

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Climate change: Global totals

% Change in river flow from 1961-1990 average, 2071-2100 SRES A2/A1B

4-8% =5800-11700 billion m3/s

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Climate change: Global patterns

% Change in river flow from 1961-1990 average, 2071-2100 SRES A1B

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Comparing with other studies

–75 –50 –25 –5 to 5 25 50 75

HadGEM1: % Change in river flow from 1961-1990 average, 2091-2100

SRES A1BArnell et al: % Change in river flow from 1961-1990 average, 2080s

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Comparing with other studies

HadGEM1: % Change in river flow from 1981-1990 average, 2091-2100

SRES A1B

Hosaka et al (2005)TRIP:

Weighted ensemble mean A1B15 AOGCMs

(2100 relative to 1980-2000)

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Climate change: basin level impacts

Lena

Chari Amazon

Orinoco

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Climate change: long-term trends

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Climate change: seasonality

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Climate change: QUMP uncertainty

QUMP 53 member single parameter perturbation -HadSM34 members chosen to cover range of climate sensitivities(equilibrium global response of global surface temperature to 2xCO2)As in Reading crop modelling work

7.0123.6112.944.13

Climate sensitivity

Member

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Uncertainty in climate impacts (QUMP)

% Change in river flow 2xCO2 – 1x CO2

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Uncertainty in climate impacts (QUMP)

% Change in river flow 2xCO2 – 1x CO2

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Uncertainty in seasonality (QUMP)

2070s river flow under 2xCO2

Obs Obs

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Uncertainty in seasonality (QUMP)

2070s river flow under 2xCO2

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ConclusionsTRIP/HADGEM1 is an improvement on HadCM3 (river scheme & climate)Climate change

Global mean increase 4-8%‘Drier’: Europe, Northern S America, S Africa, Midwest USA‘Wetter’: Mid/W Africa, Boreal zones, N China, S USASeasonality e.g. Russian rivers – earlier peak in runoff

UncertaintyQUMP: patterns generally similar but magnitudes very differentRange often > mean of ensemble membersAlso affects seasonality considerably

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Questions & Answers