1. Eidgenössisches Departement des Innern EDI Bundesamt für Meteorologie und Klimatologie MeteoSchweiz Using seasonal forecasts to estimate current climate Jonas Bhend, Mark Liniger, Andreas Fischer, Christoph Spirig

2. 2 Using seasonal forecasts to estimate the current climate | CH2018 Workshop Jonas Bhend, Mark Liniger, Andreas Fischer, Christoph Spirig Estimates that are purely model based (e.g. RCMs or ESMs) -Limited relevance (systematic errors) -No ‘translation’ problems -Large sample Estimates that are purely based on observations -Relevance (real world) -Not seamless (models vs. obs.) -Limited sample size How to estimate current climate? Climate Change in Australia, 2015 RCP8.5 RCP4.5 RCP2.6 RCP0.0 ? Seasonal forecasts?

3. 3 Using seasonal forecasts to estimate the current climate | CH2018 Workshop Jonas Bhend, Mark Liniger, Andreas Fischer, Christoph Spirig Seasonal forecast fundamentals ECMWF System4 (older version of current NWP model) NEMO 1 x 1, IFS 36r4 (T255L91, ~ 0.7 x 0.7) Initialized on 1 st of every month 51 ensemble members 215 forecast days (7 months) 30+ years of hindcasts 1981- present

4. 4 Using seasonal forecasts to estimate the current climate | CH2018 Workshop Jonas Bhend, Mark Liniger, Andreas Fischer, Christoph Spirig Potential predictability

5. 5 Using seasonal forecasts to estimate the current climate | CH2018 Workshop Jonas Bhend, Mark Liniger, Andreas Fischer, Christoph Spirig Bias correction is necessary Mean de-biasing with smoothing of observed climatology (Mahlstein et al. 2015) Empirical quantile mapping

6. 6 Using seasonal forecasts to estimate the current climate | CH2018 Workshop Jonas Bhend, Mark Liniger, Andreas Fischer, Christoph Spirig Use SFC to estimate current climate Summer 2003

7. 7 Using seasonal forecasts to estimate the current climate | CH2018 Workshop Jonas Bhend, Mark Liniger, Andreas Fischer, Christoph Spirig Estimates of indices Heat days (tmax > 30)Ice days (tmax < 0) Consecutive dry daysMaximum 1-day precip.

8. 8 Using seasonal forecasts to estimate the current climate | CH2018 Workshop Jonas Bhend, Mark Liniger, Andreas Fischer, Christoph Spirig Statistical and internal variability uncertainty Simple mean de-biasing is not enough

9. 9 Using seasonal forecasts to estimate the current climate | CH2018 Workshop Jonas Bhend, Mark Liniger, Andreas Fischer, Christoph Spirig Statistical and internal variability uncertainty

10. 10 Using seasonal forecasts to estimate the current climate | CH2018 Workshop Jonas Bhend, Mark Liniger, Andreas Fischer, Christoph Spirig Summary and Outlook Lack of skill  SFC sample climatology (mainly) Bias correction necessary  circular reasoning? Large ensemble size adds to improved estimates Trade off between placing trust in the model (seasonal forecasts) and trust in the (few) observations No published literature on using SFC as surrogate climate

12. 12 Using seasonal forecasts to estimate the current climate | CH2018 Workshop Jonas Bhend, Mark Liniger, Andreas Fischer, Christoph Spirig Skill (2AFC) tasmax JJA tasmax DJF pr DJFpr JJA no resolution perfect discrimination

13. 13 Using seasonal forecasts to estimate the current climate | CH2018 Workshop Jonas Bhend, Mark Liniger, Andreas Fischer, Christoph Spirig Visualization