Compound extremes. Quantifying interactions between catchment flooding and storm tides in the coastal zone. Seth Westra

Transcription

1 School of Civil, Environmental and Mining Engineering Monday, 16 th July 2012 Compound extremes Quantifying interactions between catchment flooding and storm tides in the coastal zone Seth Westra Life Impact The University of Adelaide

2 Slide 1

3 Quantifying the risk of extreme events Large diversity in extremes, in terms of climate processes, land surface responses and human impacts (Almost) all extremes can be regarded as compound events: Two or more extreme events occurring simultaneously or successively Combination of extreme events with underlying conditions which will amplify the events Combinations of events which are not themselves extreme but lead to an extreme event or impact when combined. Operate over a variety of (interacting) spatial and temporal scales The perspective of the stakeholder is key if we are to understand the system boundaries and define the event whose risk is to be quantified Slide 2

4 Quantifying the risk of extreme events Large diversity in extremes, in terms of climate processes, land surface responses and human impacts (Almost) all extremes can be regarded as compound events: Two or more extreme events occurring simultaneously or successively Combination of extreme events with underlying conditions which will amplify the events Combinations of events which are not themselves extreme but lead to an extreme event or impact when combined. Operate over a variety of (interacting) spatial and temporal scales The perspective of the stakeholder is key if we are to understand the system boundaries and define the event whose risk is to be quantified Slide 3

5 The role of the stakeholder defining the event Hazard Impact event Synoptic event Heat wave Event 1 heat impact Stakeholder A Wild fire Event 2 fire impact Stakeholder B Slide 4

6 Relationship between climate forcing and the impact Slide 5

7 Human systems can induce interactions! Physical system fall Flow Water level Astron. Tide Slide 6

8 Why focus on the compound nature of extremes now? Non-stationarity! Slide 7

9 The increasing complexity of quantifying risk 1. Flood 1. Inferring risk from historical observations Slide 8

10 The increasing complexity of quantifying risk 2. storm surge 1. Flood flow estuary model astr. tide 2. Accounting non-stationarity in the estaury by modelling the immediate boundary conditions Slide 9

11 The increasing complexity of quantifying risk 3. low P amt. ante cedent hydrological model dur. area Soil store 2. storm surge 1. Flood flow astr. tide estuary model Inferring Accounting risk for from non-stationarity historical observations in the rainfall-runoff transformation Slide 10

12 The increasing complexity of quantifying risk Climate forcing 4. SST climate model wind Physical event wave run up wave set up 3. low P vol. ante cedent hydrological model dur. area Soil store 2. storm surge 1. Flood flow astr. tide estuary model Inferring Accounting risk for from non-stationarity historical observations in the climate forcing Slide 11

13 The increasing complexity of quantifying risk Climate forcing Physical event Impact event 4. SST climate model wind wave run up wave set up 3. low P vol. ante cedent hydrological model dur. area Soil store 2. storm surge 1. Flood flow astr. tide estuary model $$$ loss lives Inferring Accounting risk for from other historical (non-climatic) observations factors Slide 12

14 The challenge of addressing compound extremes Almost all extremes of importance to society are compound, consisting of multiple interacting processes occurring at various spatial and temporal scales Both catchment change and climate change are challenging many conventional methods for quantifying the risk of extremes Need to think about methodology to identify which processes and interactions are important for any given situation and then ensure we can model those processes and interactions Slide 13

15 Acknowledgements This project is supported by the CSIRO Adaptation Flagship Collaboration Fund. Thanks also to the following individuals for contributing to this work: Michael Leonard, Aloke Phatak, Martin Lambert, Bart van den Hurk, Kathleen McInness, James Risbey, Doerte Jakob Slide 14