Understanding the role of heterogeneous land cover and hydrologic regime on watershed function
- Principal Investigator: Eric Pierce
- Annual reports: 2023
Watersheds are complex systems that provide important freshwater resources for energy production, irrigated agriculture, industry, and human consumption. The economic and societal importance of watersheds—and their vulnerability to environmental stresses—is exemplified in the southeastern region of the United States, which includes the Tennessee River Basin.
Water resources in the southeastern region are vulnerable to changes in land use and land cover (LULC) and a range of climate-induced disturbances. The National Climate Assessment 5 indicates that the southeastern United States will experience higher temperatures, more extreme heat events, and an intensifying hydrologic cycle with more frequent and severe storm and drought events over time. Changes in LULC can alter water storage and partitioning of rainfall into runoff with a host of cascading consequences for ecosystems and their services, while climate change simultaneously changes the frequency and intensity of precipitation events. The impact of these disturbances is exacerbated by existing regional socioeconomic stressors and inequalities.
Predicting the interactive consequences of hydrologic intensification and LULC change on watershed function at local to regional scales first requires an improved understanding of the coupled hydro-biogeochemical processes and feedbacks that link uplands, the shallow subsurface, and stream corridors. Predictions also require an improved understanding of how those processes aggregate and exert control on watershed function along a stream network.
To address this challenge, the U.S. Department of Energy’s (DOE) Biological and Environmental Research (BER) program supports the Watershed Dynamics and Evolution (WaDE) Science Focus Area (SFA) led by Oak Ridge National Laboratory (ORNL). WaDE will advance predictive understanding of how dominant processes controlling watershed hydro-biogeochemical function operate under a range of hydrologic regimes and vary along stream networks that drain heterogeneous land covers.
WaDE aims to create a multiscale, model-observation-experiment framework to enable hypothesis-driven research addressing 5 critical knowledge gaps.
- Land Cover Effects on Watershed Function. Insights are needed about if, how, or at what scale land cover influences the generation and export of water and solutes from the landscape to the stream network and how this affects local and emergent hydro-biogeochemical function within the stream network.
- Hillslope-Catchment Interactions. The mechanisms controlling upland-stream interactions are not fully understood, nor is how these interactions vary under different hydrologic regimes and land covers.
- Integrated Measures of Watershed Function. Better understanding is needed about how measures of stream function, such as stream metabolism, integrate complex watershed properties that vary in space and time.
- Stream Observational Networks in the United States. Existing observational networks are skewed to higher-order streams and end- member systems with either forested, agricultural, or highly urbanized land covers, leading to insufficient observations of low- to mid-order streams and systems with heterogeneous land cover.
- Integrated Modeling. Model predictions of watershed function at the scale of basins or the continental United States under changing climate scenarios are uncertain because of incomplete mechanistic understanding of how key processes depend on land cover and hydrologic regimes.
Integrated Model-Observation-Experiment Framework
During WaDE’s 9-year, phased plan, researchers will focus successively on three mid-order watersheds to support systematically translating, applying, and refining the process understanding and virtual watershed modeling capabilities gained from one watershed to increasingly disparate systems. Study watersheds are evaluated and selected to be broadly representative of the Tennessee River Basin. The WaDE SFA is organized around 3 integrated research themes and a crosscutting modeling activity.
- Dynamic Headwaters: Evaluate how biogeochemical processes respond to variable saturation in non-perennial channels.
- Stream Corridor Processes: Assess the resilience and resistance of metabolism to disruptions either directly or indirectly associated with land cover and in response to seasons and hydrologic events.
- Network Function: Resolve the network-scale organizational controls on metabolic regimes in watersheds with heterogeneous land cover.
- Virtual Watershed Capability: Provide a configurable virtual watershed capability focused on watershed hydrology, water temperature, and stream metabolism that can support a variety of numerical experiments and aid in designing and interpreting empirical experimental approaches.
Collaborative Science and Alignment with Grand Challenges
This multidisciplinary, multi-institutional project led by ORNL spans 6 partner institutions and takes advantage of expertise in environmental subsurface science, climate change science, biological systems science, ecohydrology, hydrology, computational science, and world-class high-performance computing facilities. The research directly contributes to 3 of 5 scientific grand challenge topics developed by BER’s Earth and Environmental Systems Sciences Division: integrated water cycle, biogeochemistry, and model-data integration.