Where Norway receives its water from

Water in its various states is a key element of the climate system. Yet, to date no research has been done at NILU on this most important of all atmospheric trace gases and how it relates to climate. The SIP proposed here shall change this situation and e stablish hydrometeorology as a new research discipline at NILU, around which other climate research activities will cluster. A particular aspect of hydrometeorology, transport of water in the atmosphere from its evaporation sources to its precipitation si nks, has been selected as the research topic of this SIP for two reasons: Firstly, because NILU can already play a leading role internationally in this niche. Secondly, recent research has shown how important it is to understand where the water falling as precipitation in a given region is coming from, in order to identify the relevant processes determining the precipitation amount - and the changes that may result as a consequence of changing climatic conditions. The SIP will use and further develop a m ethod recently developed by the applicants. It will use a Lagrangian particle dispersion model driven with (re-)analysis data from the European Centre for Medium-Range Weather Forecasts. The transport of millions of air parcels will be simulated over a 45 -year period and the change of specific humidity along the particle trajectories will be recorded. This will allow to connect regions of evaporation with such of precipitation. Focus will be on diagnosing the moisture transport towards Norway and the Arct ic Ocean and finding out where the precipitation in these regions comes from, how the source regions vary with time, and how the precipitation in Norway responds to climatic changes in the water's source regions. The project will also co-operate with two external groups, one at the Norwegian Meteorological Institute, the other at NOAA in Boulder, USA. It will also make a contribution to the International Polar Year.