Quantifying the Benefits of Integrated Surface Water-Ground Water Modeling for Climate Impact Analyses
Project ID: 9048
Principal Investigator: Ian Ferguson
Research Topic: Water Resource Data Analysis
Priority Area Assignments: 2012 (Climate Change and Variability Research), 2013 (Climate Change and Variability Research)
Funded Fiscal Years: 2012
Keywords: climate change, hydrologic modeling, groundwater-surface water interaction
The Bureau of Reclamation (Reclamation) relies on hydrologic models for a variety of planning and operations support activities including assessing climate change impacts on water resources. Ground water-surface water (GW-SW) interactions play a key role in runoff generation and, thus, in governing surface water resources; however, most hydrologic models used in climate change risk assessments represent surface water and ground water as separate and independent.
This project evaluates the limitations of traditional surface water models, defined here as models lacking physically based representation of ground water flow, compared to coupled GW-SW models for simulating streamflow under historical and projected climate conditions, focusing on basins where baseflow provides a significant contribution to runoff. This proposal addresses the following research questions:
(1) Are biases in historical streamflow simulated by traditional surface water models greater in watersheds where baseflow makes up a significant fraction of total streamflow compared to watersheds where streamflow is dominated by direct (surface) runoff?
(2) For watersheds with high baseflow, can biases in streamflow simulated by traditional surface water models be adequately reduced through model calibration or are biases irreducible due to model structure (i.e., due to model conceptualization that lacks physically based representation of ground water flow)?
(3) To what extent does simulated streamflow response to projected climate depend on model structure specifically with respect to model representation of ground water flow, baseflow, and stream-aquifer interactions?
(4) Do integrated GW-SW models provide significant benefits to Reclamation with respect to climate change risk assessments, compared to traditional modeling approaches, and do benefits outweigh the costs of increased complexity and computational demands.
Need and Benefit
While many hydrologic and watershed models are available, more information is needed to guide Reclamation's model selection for specific studies. In particular, there is little information regarding what situations traditional modeling approaches are adequate and what situations require models that represent ground water flow GW-SW interaction. In the context of climate change, recent studies suggest that GW-SW interaction will have a first-order influence on streamflow response to climate change in basins where a large fraction of streamflow occurs as baseflow.
The proposed research addresses the following research gaps identified in the document Addressing Climate Change in Long-Term Water Resources Planning and Management: User Needs for Improving Tools and Information:
Gap 4.01 (WH): Guidance on strengths and weaknesses of watershed hydrologic models/methods to support scoping decisions in planning.
Gap 4.05 (WH): Understanding how climate change should impact ground water recharge and ground water interaction with surface water supplies.
The proposed research also addresses draft recommendations detailed in the white paper titled Integrated Ground water-Surface Water Management in a Changing Climate, which is currently under review by Reclamation's Research and Development Office. Furthermore, the recent technical report to support the SECURE Water Act Report to Congress identifies important limitations of hydrologic model calibration and hydrologic model structure. The proposed research addresses the recommendation of the technical report to investigate the use of improved model structure that accounts for ground water-surface water interaction in future climate risk assessment studies.