Thorsten  Wagener1,2,  Riddhi  Singh1,  Denis  Hughes3,  Evison  Katsangawiri3  1Civil  &  Environmental  Engineering,  Penn  State  University,  USA  2Soon:  Civil  Engineering,  University  of  Bristol,  UK  3Ins?tute  of  Water  Research,  Rhodes  University,  South  Africa  

1  

We need (climate) change impact projections at decision-making scales to guide adaptation

2  

What  is  an  alterna?ve  

scien?fic  method?  

Tradi?onal  View:  “Model  simula?ons  derive  credibility  by  reproducing  historical  

observa?ons”  

Wagener et al. (2010) Water Resources Research

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Trading-Space-for-Time

Can we transfer models and their projections in space and time?

3  

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Historically Calibrated Model

How can we best use observations in a non-stationary world?

Are model projections robust given that boundary conditions might be highly uncertain?

4  

What possible (though unlikely) events are not considered in our models?

Can we estimate the uncertainty (confidence) in our projections?

5  

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Olifants Basin, South Africa

What controls the uncertainty (confidence) in our projections?

What is our ‘margin of error’?

How consistent with (equivalent to) the underlying system is our environmental model?

6  

Are expected and simulated dependencies (controls) identical under unobserved conditions?

1942 1989

Santa Cruz River near Tucson, Arizona

So instead of asking whether our impact projections can be validated (they cannot) …

…  we  should  ask  whether  they  are  T.R.U.E.!    Transferable    Robust    Uncertain    Equivalent  

 

We  need  to  rethink  the  scien?fic  method  from  which  we  derive  projec?on  credibility  in  a  non-­‐sta?onary  world!  

7  

Wagener and Forest (In Review)