Climate change rivers and rainfall Vicky Pope Debbie

Climate change, rivers and rainfall Vicky Pope, Debbie Hemming Hadley Centre Side Event 7 Hadley Centre for Climate. Co. P 11 Prediction and Research th December 2005 1

Contents § Observed climate change § Temperature changes § Extreme rainfall changes § Changes in river flow § Predicting future climate § Temperature and rainfall changes § River flow changes § Changes in tropical storms § African case study Hadley Centre for Climate Prediction and Research 2

Global average surface air temperature change, relative to the end of the 19 th century 2004 was the 4 th warmest year on record Hadley Centre for Climate Prediction and Research 3

10 warmest years since 1860 Hadley Centre for Climate Prediction and Research 4

Temperature anomalies for Jan–Aug 2005, relative to the end of the 19 th century Hadley Centre for Climate Prediction and Research 5

Rainfall is also changing Portugal Hadley Centre for Climate Prediction and Research 6

Rainfall is also changing Change in number of heavy precipitation days The upper diagrams show the spatial distribution of significant trends while the lower diagrams show the spatial average anomolies (relative to 1961– 1990) for each year Change in number of days Hadley Centre for Climate Prediction and Research Year 7

Observed flow of freshwater into the Arctic Eurasian rivers Hadley Centre for Climate Prediction and Research 8

Observed & simulated flow of freshwater into the Arctic - Eurasian rivers Hadley Centre for Climate Prediction and Research 9

New Hadley Centre model – Had. GEM 1 Simulations for IPCC AR 4 ▬ A 1 B (13. 9 Gt. C/yr) to 2100 then fixed GHG ▬ A 2 (29 Gt. C/yr) Hadley Centre for Climate Prediction and Research 10

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Predicted temperature rise Late 21 st century – present day A 1 B Hadley Centre for Climate Prediction and Research 12

Predicted change in winter precipitation Late 21 st century – present day Latest IPCC simulations Hadley Centre for Climate Prediction and Research 13

The simulation of rivers is much improved in the new Hadley Centre climate model Debbie Hemming Hadley Centre for Climate Prediction and Research 14

Rivers simulated in the African continent using TRIP river routing scheme: • follows topography • major global river basins • improved timing of river flow Facility to validate flow against river gauging station data Assess potential flood risk Hadley Centre for Climate Prediction and Research 15

Change in global river flow during the 21 st century projected for SRES emissions scenarios A 1 B & A 2 Hadley Centre for Climate Prediction and Research 16

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Predicted change in global river flow between present day and the late 21 st century for SRES emissions scenario A 1 B Hadley Centre for Climate Prediction and Research 18

New approach to quantifying uncertainties QUMP - Quantifying Uncertainty in Model Predictions Motivation • Single model-projections provide only one realisation, where a range of probable realisations exist • Ensembles of projections are needed to produce probabilistic predictions & quantify uncertainties for risk assessments • Perturbing ill-constrained model parameters is a first step in generating ensembles Approach § HADCM 3 slab ocean, prescribed vegetation distribution § 30 parameters – variation range by expert opinion § 128 runs, 20 year averages, Control & doubled [CO 2] Hadley Centre for Climate Prediction and Research 19

Uncertainty in future river flow predictions for doubled CO 2 (units in mm/yr) Hadley Centre for Climate Prediction and Research 20

Interaction of vegetation in H 2 O cycle Transpiration Evaporation ↓ stomatal conductance → ↓ transpiration ↑ soil moisture & runoff ~98% of water taken up by roots is lost by transpiration through leaf stomata e. g. 15 m high Silver Maple (Acer saccharinum) can loose 220 litres water per hour through transpiration Hadley Centre for Climate Prediction and Research 21

Plant response to [CO 2] – physiological forcing stomatal conductance ↑ [CO 2] → ↓ stomatal conductance Precipitation Transpiration Surface evaporation Surface runoff Infiltration Subsurface runoff Hadley Centre for Climate Prediction and Research 22

Projected global average river flow with & without CO 2 effect on plants business-as-usual scenario Hadley Centre for Climate Prediction and Research 23

Projected changes in river flow with & without CO 2 effects on plants average 2071 -2100 minus 1971 -2000 Hadley Centre for Climate Prediction and Research 24

There is a growing concern that tropical cyclone numbers and strength may be changing Further changes may occur in the future Vicky Pope Hadley Centre for Climate Prediction and Research 25

Track of Hurricane Katrina GOES-12 satellite image 2045 GMT on 28 August 2005 Hadley Centre for Climate Prediction and Research 26

Observed number of North Atlantic tropical storms, including hurricanes No trend Significant increase since 1995 Hadley Centre for Climate Prediction and Research 27

Predicted change in number of storms Late 21 st century – present day Hadley Centre for Climate Prediction and Research 28

Predicted change in storms of different strengths Late 21 st century – present day Hadley Centre for Climate Prediction and Research 29

Predicted change in rainfall Late 21 st century – present day Hadley Centre for Climate Prediction and Research 30

African Case study - observations Temperature anomalies 12 -month period, Aug 2004 to July 2005, relative to the 1961– 1990 average Hadley Centre for Climate Prediction and Research 31

Change in rainfall June, July and August double pre-industrial CO 2 concentrations Daily maximum rainfall █ seasonal average █ wettest day of the season (99 th percentile) Hadley Centre for Climate Prediction and Research 32

Change in temperature June, July and August double pre-industrial CO 2 concentrations Daily maximum temperature █ seasonal average █ hottest day of the season (99 th percentile) Hadley Centre for Climate Prediction and Research 33

Conclusions Past and present § 2004 was the 4 th warmest year on record § 10 warmest years on record are since 1990 § Extremes of rainfall have changed § Evidence that human activity is changing river flows – e. g. Arctic Hadley Centre for Climate Prediction and Research 34

Conclusions Future § Increases in temperature, rainfall and river flow are expected globally § Patterns of rainfall change are uncertain § Decreases in rainfall and river flow in some regions § Changes in climate and vegetation affect river flow § Africa – further reductions in rainfall are likely in some regions Hadley Centre for Climate Prediction and Research 35