12/10/2013
New Mathematical Method Uses Land-Atmosphere Interface Observations to Improve Land Model Hydrology Simulations
Summary
The exchange of water and energy between the atmosphere and land is among the most uncertain aspects of climate modeling. For example, when rain falls on the land, it is not known how much of that water evaporates back into the atmosphere and how much gets carried by groundwater to rivers and the ocean. The answer to this and similar questions could be estimated using climate models, but these models have numerous uncertain variables or “parameters” that must be adjusted based on what is observed in different regions of the Earth. One way to adjust these parameters is to run the model repeatedly, each time adjusting the parameters individually until a solution that matches observations is found. It is possible, however, that a different set of solutions would also match observations. New mathematically sophisticated “inverse” solutions are now being developed, in which a set of data can simultaneously and rapidly constrain a set of model parameters. This can be a difficult approach because there may be more than one solution, and some solutions may not be physically realistic. Therefore, some solution assumptions and constraints are required to obtain a realistic solution. A team led by U.S. Department of Energy researchers at Pacific Northwest National Laboratory has developed a new inversion method that includes enough constraint for effectively improving the Community Land Model under different climate and environmental conditions. The team evaluated inversion methodologies at select field sites based on global sensitivity analyses performed in previous studies. They found significant improvements in the model simulations that better match the observed heat flux and runoff by using the estimated parameters compared to using the default parameter values. Improvements in heat flux were found especially in areas with strong energy and water constraints.
References
Sun, Y., Z. Hou, M. Huang, F. Tian, and L. R. Leung. 2013. “Inverse Modeling of Hydrologic Parameters Using Surface Flux and Runoff Observations in the Community Land Model,” Hydrology and Earth System Sciences 17, 4995-5011. DOI: 10.5194/hess-17-4995-2013.