ed variations in river discharge deriving from altered rainfall distribution will dramatically affect both natural equilibriums and people, as some areas are liable to experience large increases in flood flows, whereas others will be subject to water stress.
We developed IRIS (Interactive River Scheme) which is a numeric tool to estimate river discharge from modelled total runoff fields. Runoff fields are computed by atmospheric models via a soil parameterization scheme, which accounts for energy and water fluxes at the atmosphere-biosphere-land interfaces, thus determining the moisture content of soil, the quantity of water returned to the atmosphere through evapo-transpiration and the excess rainfall that goes into runoff.
Fig.2 Mediterranean and Black Sea catchments in IRIS. Reconstruction based on TRIP datase
On sufficiently long time scales, vertical balance between the four components of the terrestrial hydrological cycle should be achieved:
where P is the cumulated precipitation, E is the cumulated evaporation, ΔS is the soil storage variation and R is the cumulated total runoff. Therefore, river discharge can be easily calculated by spatially integrating the simulated time mean total runoff field over distinct catchment basins. Such a simple approach is allowed only when climatic scales are concerned as the relevant variables can be derived as long term means of those computed for forecast purposes.
IRIS is based on the Total Runoff Integrated Pathway (TRIP) dataset, which maps information on land water flow directions onto a 0.5°x0.5° regular global grid.
The above figure shows the results of the hind-cast run. The blue line is the modelled seasonal cycle from the runoff fields of the hind-cast run of the Protheus coupled model, forced with the ERA-40 reanalysis , years 1958-1997. For comparison, we also show the observed climatology for the same years (red line), computed from river discharge time series. Only in the case of the Danube river the plotted climatology refers to the period 1958-1984, for wh