Uncertainty as to effects Mattias Alveteg, Harald Sverdrup

Acknowledge uncertainties Specifying types of uncertainties Quantitative estimates Understanding policy relevance Unc. management in decision process Funding Uncertainty in singular datavalues/events, ”thin air” sensitivity analysis Assessing uncertainty in structurally complex feedbacksystems of uncertain components Paradigm shift

Uncertainty vs Sensitivity A sensitivity assessment is relatively simple An uncertainty assessment demands detailed knowledge on input uncertainty

Uncertainty assessment Estimating uncertainty range –replicates, spatial heterogeneity, literature, etc. Estimating uncertainty distribution –lower pedigree => thicker tails (rectangular?) –bounded/non bounded distributions? Estimating interdependencies –ensure consistent input, additional submodels needed?, move system boundary?

Site specific unc.

Changing perspective Create one set of input for all sites taking interdependencies into account Calculate critical load for all sites => One CDF for the region Repeat over and over again =>Several independent CDFs for the region Calculate confidence intervals for the different percentiles of the region CDF

Site specific unc. (157 sites in the grid)

Site/percentile specific unc.

Comments Shifting our view from sites to percentiles –makes us more certain about the excedance in the region –we loose all information on where within the grid CL is exceeded

Number of sites?

Fewer sites = larger uncertainty

Fewer sites = less representativity

Thus: Increasing the number of sites up to sites per grid reduces uncertainty and increases representativity Increasing the number of sites increases the 95%-ile exceedance Taking uncertainty into account increases the exceedance

Dynamic uncertainties A flexible tool, UNSAFE, has been developed –creates input to dynamic soil chem. models –effective sampling (Latin Hypercube) –option to specify explicit distributions –handles input databases of different quality –is being tested in Switzerland

Future work or end of the road? Most of our work so far has not been funded Uncertainty assessment requires substantial funding No funding => No future work

Where do the uncertainties come from ?