Quantifying the Impact of Subsurface‐Land Surface Physical Processes on the Predictive Skill of Subseasonal Mesoscale Atmospheric Simulations

• Published in: Journal of geophysical research. Atmospheres Vol. 123; no. 17; pp. 9131 - 9151
• Main Authors: Sulis, M., Keune, J., Shrestha, P., Simmer, C., Kollet, S. J.
• Format: Journal Article
• Language: English
• Published: 16.09.2018
• Subjects: boundary conditions; Earth observatories; hydrometeorological predictions; integrated terrestrial simulations; land‐atmosphere interactions; skill metrics
• ISSN: 2169-897X; 2169-8996
• DOI: 10.1029/2017JD028187

Integrated terrestrial system modeling platforms, which simulate the 3‐D flow of water both in the subsurface and the atmosphere, are expected to improve the realism of predictions through a more detailed physics‐based representation of hydrometeorological processes and feedbacks. We test this expectation by evaluating simulation results from different configurations of an atmospheric model with increasing complexity in the representation of land surface and subsurface physical processes. The evaluation is performed using observations during the (HD(CP)2) Observational Prototype Experiment field campaign in April–May 2013 over western Germany. The augmented model physics do not improve the prediction of daily cumulative precipitation and minimum temperature during this period. Moreover, a cold bias is introduced in the simulated daily maximum temperature, which decreases the performance of the atmospheric model with respect to its standard configuration. The decreased performance in the maximum temperature is traced in part to a higher simulated soil moisture, which shifts surface flux partitioning toward higher latent and lower sensible heat fluxes. The better reproduced air temperature profiles simulated by the standard atmospheric model comes, however, with an overestimated heat flux at the land surface caused by a warm bias in the simulated soil temperature. Simulated atmospheric states do not correlate significantly with differences in soil moisture and temperature; thus, different turbulent flux parameterizations dominate the propagation of the subsurface signal into the atmosphere. The strong influence of the lateral synoptic forcings on the results suggests, however, the need for further investigations encompassing different weather situations or regions with stronger land‐atmosphere coupling conditions. Plain Language Summary Terrestrial system models provide detailed information on states and fluxes of the integrated water and energy cycles that are of paramount importance for a wide range of environmental applications at subseasonal to seasonal time scale. The application of such modeling systems, which improve the representation of subsurface‐land surface physical processes in standard atmospheric simulations, has therefore the potential of generating an added value for weather predictions. In this study, we quantify how incorporating additional physical processes in an operational atmospheric model improve its skills. The analysis is carried out for a 2‐month period over a region located in western Germany. Results indicate that improvements in soil moisture dynamics and land surface energy fluxes achieved with a more complex model do not necessarily lead to better predictions of temperature and precipitation. Reasons for this trade‐off include the location of the study area in a region characterized by relatively weak control of land surface processes on atmospheric dynamics as well as the strong influence of large‐scale synoptic conditions on the internal model variability. In light of these findings we advocate future studies in order to arrive at more general conclusions on the potential of detailed terrestrial system models for operational purposes. Key Points This study assesses the impact of lower boundary conditions with increasing complexity on the predictive skill of a weather forecast model More detailed surface and subsurface processes improve soil moisture dynamics and energy partitioning but not necessarily ABL states Synoptic conditions control precipitable water and precipitation in small model domains under weakly coupled land‐atmosphere conditions