This project is funded by an NSF INSPIRE grant to facilitate collaborations between hydrologists/CZ scientists and global Earth system modelers to improve hydrologic process representations in ESMs.
Our limited ability to predict the water cycle in weather, climate, and Earth System models is at least partially attributed to inadequate representations of the land branch of the water cycle. The hydrology community has traditionally focused on plot, hillslope and catchment scales, and thus their collective wisdom has not been fully tapped to advance large-scale water cycle research. To bridge this community and knowledge gap, we began a collaborative project between CUAHSI (Consortium of Universities for the Advancement of Hydrologic Science, Inc.) representing the academic hydrology community, and NCAR (National Center for Atmospheric Research) leading weather, climate and ESM development and applications.
The heart of the project is community synthesis activities, through a series of workshops, meetings at AGU, white paper contributions, webinars, writing synthesis papers with recommendations, and experimenting/testing different approaches to represent hillslope hydrology concepts in the NCAR version of the Community Land Model (CLM).
A first synthesis paper, led by Martyn Clark at NCAR, reviewed the hydrologic schemes in current global climate and ESMs, articulated the scientific needs for a community level effort to improve some of the elements in current schemes, and argued for the need for systematic model testing ad benchmarking.
Clark, M. P., Y. Fan, D. M. Lawrence, J. C. Adam, D. Bolster, D. J. Gochis, R. P. Hooper, M. Kumar, L. R. Leung, D. S. Mackay, R. M. Maxwell, C. Shen, S. C. Swenson, and X. Zeng (2015), Improving the representation of hydrologic processes in Earth System Models, Water Resour. Res., 51, doi:10.1002/2015WR017096.
In the fall of 2015, we held a first synthesis workshop at NCAR with >40 scientists from the hydrology and atmospheric science communities; the objective was to develop state-of-science synthesis of hydrologic processes and recommend best ways to represent them in large-scale models. A major recommendation from the workshop is to test the importance of lateral surface and groundwater flow from uplands to lowlands to simulating evapotranspiration (ET) fluxes.
Preliminary tests in CLM, using Reynolds Creek CZO as the test bed, suggest implementing lateral flow improves the simulated ET fluxes in the dry season, allowing continued ET from the riparian forests as observed by the flux tower. These results were presented to the community at the workshops held at the 2016 and 2017 AGU meeting.
After the 2016 AGU meeting, CUAHSI initiated a call for white paper contributions from the broader community, and over 20 contributions were received. Based on these contributions, CUAHSI facilitated a series of five webinars, where the white paper contributors presented their approaches to represent hillslope hydrology in large ESM grids. These activities have led to the development of a second synthesis paper to prioritize the processes that are deemed most basic and well understood yet still missing in ESMs, such as lateral flow from high to low lands (Fig 1), and the slope aspect difference in energy and water balance (Fig 2). The manuscript, led by Ying Fan Reinfelder at Rutgers University and includes over 50 coauthors, is in preparation.
Fig 1. Google Earth image of trees growing along drainage lines, CA
Fig 2. Google Earth image of trees growing on shady slopes, CA
Our objectives are:
(1) Energize the hydrology and CZ communities to synthesize our best process understanding at hillslope and catchment scales, and to recommend the best ways to represent them in global models.
(2) Implement synthesis recommendations in the Community Land Model (CLM), and test the sensitivities of model simulated ET globally to the inclusion of hillslope hydrology concepts.
(3) Test/benchmark progress in CLM water cycle simulations with observations, bringing in the rich set of hydrologic observations yet to be tapped for testing large-scale water cycle models, e.g., from the NSF-funded Critical Zone Observatories (CZOs), and the research watersheds of USDA, USGS and USFS.
(4) Conduct CLM/CESM simulations to demonstrate new model capabilities in addressing long-standing science questions related to global water, energy and carbon cycles.
(5) Hold a final synthesis workshop; based on the results of benchmarking and demonstration of new science capabilities (or lack of), the synthesis team will analyze model deficiencies and recommend future model development and observation priorities.
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Contributors / Acknowledgements
Over 75 members from the hydrology, CZ and ESM communities have participated in our workshops, webinars, contributed white papers and presentations, and contributed to synthesis papers and general discussions.
We thank NSF for support through CUAHSI cooperative agreement (NSF-EAR-0753521) and an INSPIRE grant (NSF-EAR-1528298). We thank NCAR leadership for their support of the project, and we thank CUAHSI leadership for their support and CUAHSI staff for coordinating the many workshops and webinars.