precipitation over iceland simulated in a future climate scenario at various horizontal resolutions...
TRANSCRIPT
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
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.
Downscaling to high horizontal resolution
Approx. 125 km wide gridcells in global model
9 km3 km
Why is high horizontal resolution important?
27 km
3 km9 km
Mean annual precipitation in
downscaled climate at 9 km
resolution
Actual climate
Future climateControl climate
Mean annual precipitation in control climate
3 km resolution
3 km resolution
Mean annual precipitation in future climate
Histogram of 24 hour precipitation at 9 km
Fewer large events in future climate
Red - FutureBlack - Control
Histogram of 24 hour precipitation at 3 km
Red - FutureBlack - Control
Fewer medium size events in future climate
No change in large events!
Spatial distribution of 24 hour precipitation at 3 km
Control climate
50 mm bins in histogram
Future climate
Increase in Southeast-Iceland,
decrease elsewhere
Decrease everywhere
Spatial distribution of 24 hour precipitation at 3 km
Control climate
Spatial distribution of 24 hour precipitation at 9 km
Future climate
Decrease throughout
Iceland
Control climate
Temporal distribution of 24 hour precipitation at 3 km
Future climate
Shift in precipitation from winter and spring to summer
and autumn
Temporal distribution of 24 hour precipitation at 3 km
Control climate
Temporal distribution of 24 hour precipitation at 9 km
Future climate
Same as at 3 km. Shift from winter
and spring to summer and
autumn
Different regional models give different results
Nawri and Björnsson, 2010
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.
Control climate
Temporal distribution of 24 hour precipitation
at 9 km
Future climateFewer
windstorms
Actual climate