Abstract : 2E.16
Numerical simulations of precipitation in Iceland - Comparison with hydrological and glaciological data

Ólafur Rögnvaldsson, Finndís Jóna Jónsdóttir, Haraldur Ólafsson
Institute for Meteorological Research

Atmospheric flow over Iceland has been simulated for the period September 1987 through June 2003, using the PSU/NCAR MM5 mesoscale model driven by initial and boundary data from the European Centre for Medium range Weather Forecasts (ECMWF). The simulated precipitation is compared with two types of indirect precipitation observations. Firstly, snow accumulation on two large glaciers in SE-Iceland and on two large ice caps in central Iceland. Secondly, model output is used as input to the WaSiMETH hydrological model to calculate and compare the runoff with observed runoff from six watersheds in Iceland for the water years 1987–2002. Model precipitation compares favourably with both types of validation data.

The seasonal and interannual variability of precipitation is investigated at low as well as high altitudes. The simulations reveal a negative trend in the winter precipitation in W-Iceland, but a positive trend in the ratio of lowland precipitation to mountain precipitation in E-Iceland. There is in general a substantial interannual variability in the ratio of lowland precipitation to precipitation in the mountains, especially in E-Iceland, emphasizing the limitation of precipitation observations in the lowlands as a proxy for precipitation in the mountains.