Abstract
Conclusions on the General Circulation Models (GCMs) horizontal and temporal optimum resolution for dynamical downscaling of rainfall in Mediterranean Spain are derived based on the statistical analysis of mesoscale simulations of past events. These events correspond to the 165 heavy rainfall days during 1984–1993, which are simulated with the HIRLAM mesoscale model. The model is nested within the European Centre for Medium-Range Weather Forecasts atmospheric grid analyses. We represent the spectrum of GCMs resolutions currently applied in climate change research by using varying horizontal and temporal resolutions of these analyses. Three sets of simulations are designed using input data with 1°, 2° and 3° horizontal resolutions (available at 6 h intervals), and three additional sets are designed using 1° horizontal resolution with less frequent boundary conditions updated every 12, 24 and 48 h. The quality of the daily rainfall forecasts is verified against rain-gauge observations using correlation and root mean square error analysis as well as Relative Operating Characteristic curves. Spatial distribution of average precipitation fields are also computed and verified against observations. For the whole Mediterranean Spain, model skill is not appreciably improved when using enhanced spatial input data, suggesting that there is no clear benefit in using high resolution data from General Circulation Model for the regional downscaling of precipitation under the conditions tested. However, significant differences are found in verification scores when boundary conditions are interpolated less frequently than 12 h apart. The analysis is particularized for six major rain bearing flow regimes that affect the region, and differences in model performance are found among the flow types, with slightly better forecasts for Atlantic and cold front passage flows. A remarkable spatial variability in forecast quality is found in the domain, with an overall tendency for higher Relative Operating Characteristic scores in the west and north of the region and over highlands, where the two previous flow regimes are quite influential. The findings of this study could be of help for dynamical downscaling design applied to future precipitation scenarios in the region, as well as to better establish confidence intervals on its results.
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Acknowledgements
The authors would like to express their thanks and appreciation to Dr. Charles A. Doswell III, Visiting Professor at UIB under grant SAB2002-0084, for his valuable comments and suggestions on this work, as well as the reviewers for their efforts and help to improve the quality of the study. The authors also wish to acknowledge the Spanish Instituto Nacional de Meteorología (INM) for providing the ECMWF gridded data analysis and precipitation data. This work has been sponsored by CICYT CLI99-0269 (FIRME) and EU EVK1-2001-00042 (MEDIS) grants.
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Amengual, A., Romero, R., Homar, V. et al. Impact of the lateral boundary conditions resolution on dynamical downscaling of precipitation in mediterranean spain. Clim Dyn 29, 487–499 (2007). https://doi.org/10.1007/s00382-007-0242-0
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DOI: https://doi.org/10.1007/s00382-007-0242-0