Climate change impacts on rainfall extremes and urban drainage & needs for climate adaptation

Transcription

1 Climate change impacts on rainfall extremes and urban drainage & needs for climate adaptation Patrick Willems KU Leuven hydraulics division

2 INTERNATIONAL GROUP ON URBAN RAINFALL (IGUR) IWA/IAHR Joint Committee on Urban Drainage Provides a state-of-the-art overview of existing methodologies and relevant results related to the assessment of the climate change impacts on urban rainfall extremes as well as on urban hydrology and hydraulics Content: 1. Climate change simulations 2. Modeling of urban rainfall extremes in a stationary context 3. Study of rainfall and urban runoff variability and trends in a non-stationary context 4. Statistical downscaling of rainfall extremes 5. Climate factors and changes in IDF relationships 6. Climate change impacts on urban drainage: results and regional differences 7. Needs for adaptation and flexible designs

3 Some key messages / conclusions from the review on: Historical trend analysis Future climate trends and impacts Adaptation needs

4 Historical trend analysis Historical trends are difficult to quantify because of: limited length of time series instrumental or environmental changes (site relocation, changes and deficiencies in monitoring program, improvement of instrumentation, urban heat island effect) strong inter-annual variations (weak signal-to-noise ratio) (multi-)decadal climate oscillations.

5 Historical trend analysis (Multi-)decadal climate oscillations: Summer (JJA) Willems (2013), J. Hydrol., 490, Willems (2013), Clim. Change, 120(4), Uccle (Brussels), , 10 minutes Anomalies in extreme rainfall int. quantiles

6 Historical trend analysis (Multi-)decadal climate oscillations: 30 Winter (DJF) anomaly in extremes [%] Willems (2013), J. Hydrol., 490, Willems (2013), Clim. Change, 120(4), 931 Uccle (Brussels), , 10 minutes Anomalies in extreme rainfall int. quantiles year [-] winter, 10-year window winter, 15-year window long-term average approximate cyclic variations cyclic variations plus climate change climate change effect separate climate change signal from natural variability (also long-term variations)

7 Multidecadal climate oscillations (Anti-)correlations of climate oscillations across Europe Daily rainfall ECA&D database: Anomaly [%] precipitation, Uccle precipitation, Bologna Willems (2013), Clim. Change, 120(4), 931

8 Historical trend analysis Future climate trends and oscillations? 30? anomaly in extremes [%] year [-] winter, 10-year window winter, 15-year window long-term average approximate cyclic variations cyclic variations plus climate change climate change effect

9 Some key messages / conclusions from the review on: Historical trend analysis Future climate trends and impacts Adaptation needs

10 Climate model projections : need for downscaling Large Scale km; seasonally monthly General Circulation Models (GCMs) Dynamical downscaling ± 50 km; weekly - daily ± 25 km; daily river catchment; hourly sewer system; 10-min Hydrological scale Regional Climate Models (RCMs) Statistical downscaling

11 Climate model projections Uccle (Brussels), extreme daily rainfall (summer, > ): Highest event in 10 years: up to +50%

12 Climate model projections Uccle (Brussels), extreme daily rainfall (summer, > ): Factor rainfall change [-] High Mean Low Return period [years]

13 Impact climate scenarios Caution must be exercised when interpreting climate change scenarios Order of magnitude of uncertainty assessed by ensemble approach with several: climate forcing scenarios GCMs RCMs initial states statistical downscaling assumptions and methods + real uncertainty is larger: models share the same level of process understanding and sometimes even the same parameterization schemes and code Whatever methods are adopted: resulting change should not be interpreted as an exact number but only as indicative of the expected magnitude of future change

14 Impact climate scenarios Urban drainage systems: (highly) non-linear responses to rainfall extremes: amplification of % changes Review (international references, at urban hydrology scales, till 2100): 10 to 60 % change in rainfall 0 to 400 % change in sewer flood and overflow frequencies and volumes (depending on systems characteristics)

15 Impact climate scenarios Increase of greenhouse gasses in atmosphere Temperature rise Saturation concentration of air vapour increases

16 Impact climate scenarios Increased peak rainfall intensities in summer: more sewer floods Longer dry summer periods: lower water availability

17 Impact urbanization Land use Flanders 1976: 1976 PhD Lien Poelmans KU Leuven, % paved

18 Impact urbanization Land use Flanders 1988: 1988 PhD Lien Poelmans KU Leuven, % paved

19 Impact urbanization Land use Flanders 2000: 2000 PhD Lien Poelmans KU Leuven, % paved

20 Impact urbanization Land use Flanders 2050: 2050 PhD Lien Poelmans KU Leuven, 2010 business-as-usual scenario: ±20% paved (same trend in pavement increase)

21 Impact urbanization Same type of impact on water systems as climate change: Increased temporal variability / hydrological extremes: Increased runoff during storm periods Reduced water availability during dry periods

22 Some key messages / conclusions from the review Historical trend analysis Future climate trends and impacts Adaptation needs

23 Urban drainage adaptation needs: how to deal with the high uncertainties? The large uncertainties that currently exist should not be an argument for delaying climate change impact investigations or adaptation actions! for High pessimistic climate scenario Risk = Probability * Consequence high? very high Precautionary principle: take pessimistic scenario into account take climate insurance

24 Urban drainage adaptation needs: Uncertainties should be accounted for! Future designs: flexible and sustainable solutions avoid closing off options (reversibility) active learning, public debate o <-> traditional engineering approach, which is rather static and is often based on design rules set by engineering communities o recognize that flexibility is required as understanding increases

25 Climate change serves as a driver for changes in urban drainage paradigm Urban design and planning processes incorporating more sustainable approaches: In many cities in the world, the rate of renewal of urban infrastructure is currently low, but this may need to change in the future, in order for communities to cope with deteriorating pipe networks, population growth and climate change At the same time the changes need to be consistent with an increasing awareness of the environmental stress the end-of-pipe solution puts on the ecosystem of the city There will be a need for more natural urban drainage approaches and installation of blue-green stormwater infrastructure, all of which requires a change in design philosophy

26 Sustainable urban drainage: More local-upstream storage and infiltration Permeable pavements: Individual infiltration: Stormwater retention and re-use:

27 Sustainable urban drainage: More local-upstream storage and infiltration Stormwater storage and infiltration in public spaces: reduces sewer flood & overflow frequencies & feeds groundwater system before after RIONED 2009

28 Sustainable urban drainage: More local-upstream storage and infiltration Improved interfacing between urban water management and spatial planning / urban design: Multiple functions to open spaces (e.g. parks) in the city: RIONED 2009 Campus Park, Clichy sous Bois [Composante Urbaine, 2004]

29 Sustainable urban drainage: Reduce damage during urban flooding Road design: before after RIONED 2009

30 Sustainable urban drainage: Reduce damage during urban flooding Keep people away from the water and/or: Water proof buildings Food paths that automatically raise during flooding and act as flood barriers: Dry proof buildings: Water robust doors: Water robust doors:

31 Sustainable urban drainage: Increase preparedness for urban flooding Flood forecasting and warning: Fine-scale rainfall acquisition and nowcasting band on high resolution local radars in 4 pilots: Rotterdam (NL) Leuven (B) Paris (F) London (UK)

32 Sustainable urban drainage: Increase preparedness for urban flooding Flood forecasting and warning: Fine scale radar observations Small & local scale rainfall nowcasting 2D urban flood modelling Warning, risk communication Rain cells R(x,y) y u y Small meso-scale areas x Large meso- θ scale areas x

33 Sustainable urban drainage: Cooperation! Between: Urban drainage & Up- & Flood & Spatial planning / urban design & Agriculture & Ecological / nature & Centralized & Scientists & river management downstream river management low flow management storm water management flood/low flow management water management decentralized approaches practitioners / policy developers and implementers

34 INTERNATIONAL GROUP ON URBAN RAINFALL (IGUR) IWA/IAHR Joint Committee on Urban Drainage State-of-the-art review + analysis: IWA Publishing, 252 p. Print ISBN Ebook ISBN Water Wiki site: /Articles/ICCREUDS Contact: Patrick.Willems@bwk.kuleuven.be