Precipitation Dynamical Downscaling Over the Great Plains

• Published in: Journal of advances in modeling earth systems 2018-02, Vol.10 (2), p.421-447
• Main Authors: Hu, Xiao‐Ming, Xue, Ming, McPherson, Renee A., Martin, Elinor, Rosendahl, Derek H., Qiao, Lei
• Format: Article
• Language: English
• Subjects: Anticyclonic circulation; Circulation anomalies; Climate; Climate models; Climatology; Clouds; Discrete Cosine Transform (DCT); dynamic downscaling; Dynamics; Physics; Plains; Precipitation; Regional climate models; Regional climates; Simulation; Spatial distribution; spectral nudging; Stage IV and PRISM precipitation data; Warm seasons; Watersheds; Weather forecasting
• ISSN: 1942-2466; 1942-2466
• DOI: 10.1002/2017MS001154

Detailed, regional climate projections, particularly for precipitation, are critical for many applications. Accurate precipitation downscaling in the United States Great Plains remains a great challenge for most Regional Climate Models, particularly for warm months. Most previous dynamic downscaling simulations significantly underestimate warm‐season precipitation in the region. This study aims to achieve a better precipitation downscaling in the Great Plains with the Weather Research and Forecast (WRF) model. To this end, WRF simulations with different physics schemes and nudging strategies are first conducted for a representative warm season. Results show that different cumulus schemes lead to more pronounced difference in simulated precipitation than other tested physics schemes. Simply choosing different physics schemes is not enough to alleviate the dry bias over the southern Great Plains, which is related to an anticyclonic circulation anomaly over the central and western parts of continental U.S. in the simulations. Spectral nudging emerges as an effective solution for alleviating the precipitation bias. Spectral nudging ensures that large and synoptic‐scale circulations are faithfully reproduced while still allowing WRF to develop small‐scale dynamics, thus effectively suppressing the large‐scale circulation anomaly in the downscaling. As a result, a better precipitation downscaling is achieved. With the carefully validated configurations, WRF downscaling is conducted for 1980–2015. The downscaling captures well the spatial distribution of monthly climatology precipitation and the monthly/yearly variability, showing improvement over at least two previously published precipitation downscaling studies. With the improved precipitation downscaling, a better hydrological simulation over the trans‐state Oologah watershed is also achieved. Key Points The downscaling obtained from this study captures well the spatial/temporal variation of monthly climatology precipitation Different cumulus schemes lead to more pronounced difference in simulated rainfall than other tested physics schemes at a 20 km resolution Spectral nudging is important for correctly downscaling precipitation over the Great Plains