Simulation of climate change over europe using a nested regional‐climate model. II: Comparison of driving and regional model responses to a doubling of carbon dioxide

Abstract

Results are assessed from a 10‐year simulation of the equilibrium response to doubled carbon dioxide (CO2) over Europe made with a nested high‐resolution regional‐climate model (RCM). the simulated changes are compared against those produced by the driving global general‐circulation model (GCM). the domain‐averaged increases in temperature and moisture content are similar in both models. Because of a stronger hydrological cycle the increases in precipitation and evaporation are larger in the RCM than in the GCM, whereas the reductions in lower and middle tropospheric relative humidity and cloud cover are smaller. The frequency of intense precipitation events increases substantially in both models; however, the fractional changes are significantly smaller in the RCM. the proportion of precipitation associated with convection also increases in both models; however, much of the increase in intense events is explained simply by increased atmospheric moisture concentrations, especially in the RCM. The time‐averaged precipitation changes in the RCM contain a substantial mesoscale component on scales not resolved by the GCM. Attempts are made to reconstruct this component from the changes in the large‐scale atmospheric circulation using empirical relationships calibrated from the 1 x CO2 integration. These are largely unsuccessful, indicating that simple downscaling schemes to generate high‐resolution scenarios of climate change from coarse‐grid GCM data may be of only limited applicability. Further statistical calculations suggest that longer integrations (∼ 30 years) are needed to reduce the sampling uncertainty associated with the simulated mesoscale component to an acceptable level. The large‐scale patterns of change of surface temperature and precipitation reveal significant regional contrasts which are influenced both by changes in atmospheric circulation and regional physical feedbacks. the RCM changes are similar to those of the driving GCM except in summer. the differences in the summer changes are traced to differences between the 1 x CO2 integrations, in which the influence of the lateral boundary forcing on the RCM simulation is found to be anomalously weak. It is argued that any development of significant divergence between the RCM and GCM solutions on scales resolved by the latter may imply the need to refine or replace the one‐way nesting technique currently used in many regional modelling experiments.

An assessment of temperature and precipitation change projections over Italy from recent global and regional climate model simulations

“…Also reported in the precipitation change panels are the mean changes in low-level (850 hPa) wind. This figure is available in colour online at www.interscience.wiley.com/ijoc agreement with previous generation model experiments (Jones et al, 1997;Kittel et al, 1998;Giorgi et al, 2001;Räisänen et al, 2002;Deque et al, 2007) and this adds robustness to the reliability of the signals. In this regard, however, we stress the caveat that the signal obtained from ensembles of model, as in this paper, filters out multi-decadal variability.…”

“…During the last two decades or so, mostly as a result of a series of European projects, a number of climate change simulations over Europe have been completed by several groups using a grid spacing of about 50 km (e.g. Giorgi et al, 1992Giorgi et al, , 1997Giorgi et al, , 2004bJones et al, 1997;Rotach et al, 1997;Machenhauer et al, 1998;Räisänen et al, 1999Räisänen et al, , 2004Christensen and Christensen, 2003;Kjellström, 2004;Schär et al, 2004;Semmler and Jacob, 2004;Déqué et al, 2005Déqué et al, , 2007, which allows a crude but realistic description of the Italian territory. In particular, as part of the most recent European Union (EU) project, PRU-DENCE ten RCMs were used to produce climate change scenarios over the European region for two different GHG emission scenarios of IPCC (2000).…”

Seasonal/Regional Variation of Variability Characteristic of Daily Maximum/Minimum Temperatures in Japan Observed and Reproduced by RegCM Nested in NCAR-CSM

“…As mentioned in their paper, the two 10-year simulations are not intended to provide actual predictions of climate change, but to clarify the problems of this nesting method in the prediction of regional climate change in East Asia. The purpose of the series of studies using RegCM, is almost the same as that of the regional climate change simulation studies recently conducted (e.g., Jones et al 1997;Giorgi et al 1998;Renwick et al 1998;Deque et al 1998;Laprise et al 1998;Leung and Ghan 1999).…”

Climate version of the ETA regional forecast model

“…The running of RCM with the horizontal resolution of a few tens of kilometers over an area of interest with boundary conditions of AOGCM for the periods of 10-30 years in the present and in the future can give additional information about the regional-scale climate and climatechange effects in this area. Such downscaling studies related to climate change have been made already for various parts of Europe, North America, Australia, and Africa; see for example the references cited by Jones et al (1997), Laprise et al (2003), Giorgi et al (2004), Duffy et al (2006). Currently some large projects such as (PRUDENCE (Christensen et al 2002) and NARCCAP (http://www.narccap.ucar.edu)), launched to investigate uncertainties in the RCM climate-change simulations over Europe and North America, are underway.…”