Trends of precipitation over the Iberian Peninsula and the North Atlantic Oscillation under climate change conditions

The trends of precipitation over the Iberian Peninsula (IF) and the North Atlantic Oscillation (NAO) index from December to March are compared using observations and model simulations from the Coupled Model Intercomparison Project phase 3 (CMIP3). The evaluation is performed in two multi-models as derived by averaging simulations corresponding to two experiments: one represents climate in the 20th century (20C3M) and the other the scenario with medium forcing IPCC SRES AIB in the 21st century. The NAO index shows a trend to more positive phases and precipitation tends to decrease in the case of observations, with greater significance in the NAO than in precipitation. The simulations in the 20th century underestimate the trend both in the NAO and in precipitation compared to observations. The multi-model in the 21st century indicates a change in the NAO regimes to being more positive: this leads to a reduction of precipitation over the IF. To explain the precipitation trend changes we consider the response of precipitation to the NAO. the regression between sea level pressure (SLP) over the Euro-Atlantic area onto precipitation averaged over the IF and the composite of precipitation for years with greater and lower NAO. Copyright (C) 2009 Royal Meteorological Society