Climate Change: Methodology to Evaluate the Influence of Joint Changes in Climate and Land Cover on Water Availability

Project ID: 2768
Principal Investigator: Levi Brekke
Research Topic: Water Operation Models and Decision Support Systems
Priority Area Assignments: 2010 (Climate Change and Variability Research), 2011 (Climate Change and Variability Research)
Funded Fiscal Years: 2009 and 2010
Keywords: None

Research Question

* How do land cover and ecosystem changes affect precipitation-runoff relationships?

Reclamation has limited understanding on how such changes would affect water supply in the context of past or future climate change. Having such understanding would benefit hydrologic assumptions framing longer-term operations and infrastructure planning. The proposed research involves:

A. Employing a novel method of hydrologic model calibration with respect to changing land cover and thereby permits assessment of the joint and relative influences from past climate and land cover changes on water supply; and,

B. Applying the hydrologic model from (A) to assess influences of projected climate and land cover changes on water supply.

Methods will be demonstrated on two southern Great Plains watersheds: Canadian River basin above Lake Meredith, Texas and Red River (North Fork) above Lake Altus, Oklahoma. Outcome will be a documented methodology transferrable to other Reclamation regions.

Need and Benefit

Reclamation typically uses surface water budget analyses to assess historical water supply variations and help establish related assumptions for longer-term planning. In many Western United States watersheds, evapo-transpiration (ET) from the land surface is a significant loss term in the surface water budget. When discussing ET in the context of climate change (past or projected), it is relevant to discuss coincidental land cover changes (natural or due to human activity) and their contribution to ET change.
Traditionally, Reclamation analysts have not jointly included climate and land cover changes in historical assessments of water supply or when establishing future water supply assumptions for longer-term planning. This is partially due to lack of a well-established method, and lack of understanding on how to apply surface water hydrologic simulation models to assist with these tasks.

Surface water hydrology models have typically been applied with land cover treated as a static condition during the period of model development. In other words, while historical period weather and runoff observations are time-varying during the calibration period, land cover conditions are typically cast as a period-representative static condition. The latter assumption is likely incorrect, understanding land cover evolves with climate. This raises issues for understanding past hydrologic variability and understanding the potential interacting and relative impacts of projected climate and land cover change.

The proposed research involves developing and demonstrating two related methodologies in two case study watersheds:

A. Employing a novel method of hydrologic model calibration with respect to changing land cover to reveal climate and land-use change influences on past surface water supplies

B. Assessing projected water availability as affected by projected changes in both factors, and the relative significance of these changes.

The case study watersheds are located above Reclamation reservoirs in the southern Great Plains: the Canadian River above Lake Meredith (near Lubbock, Texas), and the North Fork Red River above Lake Altus (near Altus, Oklahoma). The Lake Meredith watershed offers a particularly relevant case study region, given that reservoir yield since completion of Sanford Dam has been less than preconstruction estimates. Two suspected drivers are climate change (increased temperatures and associated ET) and land cover change (brush proliferation; construction of private impoundments); however, the relative potential role of each driver has not been well established.

The methodology produced through this research should benefit longer-term prospective planning by enabling water availability assumptions to be developed relative to past and projected changes in climate and land cover rather than climate change alone.
This work relates to the research recommendation "Improve Understanding of Surface water, Ground water and Land cover Interaction" offered (among others) in the Upper Colorado/Lower Colorado Regions Climate Technical Working Group report, "Review of Science and Methods for Incorporating Climate Change Information into Reclamation's Colorado River Basin Planning Studies" (Section U.10.3, Appendix U, Final EIS - Colorado River Interim Guidelines for Lower Basin Shortages and Coordinated Operations for Lake Powell and Lake Mead, 2007). This work also relates to a Reclamation capability gap on understanding land cover response to climate change as it affects hydrologic assumptions, as discussed under the heading "Element 4: Assess Natural Systems Response (e.g., Hydrology, Ecosystems)" at the Reclamation-NOAA-USGS February 2008 workshop "Managing Western Water as Climate Changes - Knowledge Gaps and Initial Research Strategies and Projects" (Handout 1, ).

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Last Updated: 4/4/17