Use of very high resolution climate model data for hydrological modelling: estimation of potential evaporation

Climate model data are increasingly used to drive hydrological models, to assess the possible\udimpacts of climate change on river flows. Hydrological models often require potential evaporation\ud(PE) from vegetation, alongside precipitation, but PE is not usually output by climate models so has to\udbe estimated from other meteorological variables. Here, the Penman-Monteith formula is applied to\udestimate PE using data from a 12 km Regional Climate Model (RCM) and a nested very high resolution\ud(1.5 km) RCM covering southern Britain. PE estimates from RCM runs driven by reanalysis boundary\udconditions are compared to observation-based PE data, to assess performance. The comparison\udshows that both the 1.5 and 12 km RCMs reproduce observation-based PE well, on daily and monthly\udtime-steps, and enables choices to be made about application of the formula using the available\uddata. Data from Current and Future RCM runs driven by boundary conditions from a Global Climate\udModel are then used to investigate potential future changes in PE, and how certain factors affect\udthose changes. In particular, the importance of including changes in canopy resistance is\uddemonstrated. PE projections are also shown to vary to some extent according to how aerosols are\udmodelled in the RCMs