Simulation of δ¹⁸O in precipitation by the regional circulation model REMOiso

The first results of a regional circulation model REMO iso fitted with water isotope diagnostics are compared with various isotope series from central Europe. A 2 year case study is conducted from March 1997 to February 1999 centred over Europe, analysing daily and monthly measurements. Isotope signals over Europe are dominated by the typical isotopic effects such as temperature, continental and altitude effects, both on annual and seasonal scales. These well‐known isotopic effects are successfully reproduced by REMO iso , using two different boundary data sets. In a first simulation, the European Centre for Medium‐range Weather Forecasts (ECMWF) analyses serve as boundary conditions, where water isotopes were parameterized by a simple temperature dependence. In a second simulation, boundary conditions both for climatic and isotopic variables are taken from the ECHAM iso general circulation model output. The comparison of both simulations shows a very high sensitivity of the simulated δ 18 O signal to boundary conditions. The ECMWF‐nested simulation shows an average offset of −4·5‰ in mean δ 18 O values and exaggerated seasonal amplitude. The ECHAM‐nested simulation represents correctly the observed mean δ 18 O values, although with a dampened seasonality. REMO iso 's isotope module is further validated against daily δ 18 O measurements at selected stations (Nordeney, Arkona and Hohenpeissenberg) situated in Germany.