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Hálfdán Ágústsson, Ólafur Rögnvaldsson, Haraldur Ólafsson and Einar Magnús Einarsson

Precipitation over Iceland simulated in a future climate scenario at various horizontal resolutions. Hálfdán Ágústsson, Ólafur Rögnvaldsson, Haraldur Ólafsson and Einar Magnús Einarsson.

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Hálfdán Ágústsson, Ólafur Rögnvaldsson, Haraldur Ólafsson and Einar Magnús Einarsson

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  1. Precipitation over Iceland simulated in a future climate scenario at various horizontal resolutions Hálfdán Ágústsson, Ólafur Rögnvaldsson, Haraldur Ólafsson and Einar Magnús Einarsson Institute for Meteorological Research, University of Iceland, University of Bergen and Icelandic Meteorological Office

  2. Downscaling to high horizontal resolution • Dynamical downscaling is done with the state of the art WRF numerical atmospheric model, which is widely used for research and operational forecasting. • Three datasets are downscaled to 27, 9 and 3 km resolution: • Actual climate of 1961-1990 based atmospheric reanalysis from the ECMWF. • Control climate of 1961-1990 based on atmospheric climate simulations with the Arpege model. • Future climate of 2021-2050 based on atmospheric climate projections with the Arpege model. • The Arpege model is run by the Bergen group on a T159c3 irregular grid. The scenario chosen is the SRES A1B. • Here we focus on precipitation and the relevant physics are parameterized using the WSM3-scheme.

  3. Downscaling to high horizontal resolution Approx. 125 km wide gridcells in global model 9 km 3 km

  4. Why is high horizontal resolution important? 27 km 9 km 3 km

  5. Mean annual precipitation in downscaled climate at 9 km resolution Actual climate Control climate Future climate

  6. Mean annual precipitation in control climate 3 km resolution

  7. Mean annual precipitation in future climate 3 km resolution

  8. Histogram of 24 hour precipitation at 9 km Red - Future Black - Control Fewer large events in future climate

  9. Histogram of 24 hour precipitation at 3 km Red - Future Black - Control Fewer medium size events in future climate No change in large events!

  10. Spatial distribution of 24 hour precipitation at 3 km Control climate 50 mm bins in histogram

  11. Spatial distribution of 24 hour precipitation at 3 km Future climate Decrease everywhere Increase in Southeast-Iceland, decrease elsewhere

  12. Spatial distribution of 24 hour precipitation at 9 km Control climate Future climate Decrease throughout Iceland

  13. Temporal distribution of 24 hour precipitation at 3 km Control climate

  14. Temporal distribution of 24 hour precipitation at 3 km Future climate Shift in precipitation from winter and spring to summer and autumn

  15. Temporal distribution of 24 hour precipitation at 9 km Control climate Future climate Same as at 3 km. Shift from winter and spring to summer and autumn

  16. Different regional models give different results Nawri and Björnsson, 2010

  17. Conclusions and final remarks • Resolution is important!!! • A major shift in precipitation regime can occur with improved resolution of simulations of local climate change. • Time of largest precipitation events may shift from winter to autumn. • Extreme precipitation events may become more frequent in Southeast-Iceland but less frequent in other parts of Iceland.

  18. Actual climate Temporal distribution of 24 hour precipitation at 9 km Control climate Future climate Fewer windstorms

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