Predicting the ecological consequences of hydrologic and thermal modification in wadeable streams: The climatic context

Project ID: 8224
Principal Investigator: Mark Nelson
Research Topic: Ecosystem Needs
Funded Fiscal Years: 2014
Keywords: climate change, flow modification, benthic invertebrates, rocky mountains, thermal modification

Research Question

The proposed research investigates how present-day flow management/regulation modifies the natural hydrologic and thermal regimes and the ecological integrity of Rocky Mountain streams. This understanding of current conditions is key to predicting the ecological consequences of future adaptive flow management in response to a changing climate. The research focuses on small (wadeable) streams because relative to large rivers influenced by Reclamation Projects, small streams are studied less, yet constitute a geographically large resource that is influenced by water-management operations.

Two research questions will be addressed. First, how are the ecological integrity and thermal regime of streams related to the modification of natural hydrologic regimes that result from flow management/regulation? Second, what are the expected responses of ecological integrity to future changes--both natural and anthropogenic--to the thermal or hydrologic regime of streams?

This proposed study has three objectives:

1). Identify the long-term (1900-present) natural baseline conditions of the hydrologic and thermal regimes for each stream segment in the Southern Rockies Ecoregion,
2). Quantify present-day modification of hydrologic and thermal regimes at select stream sites currently influenced by various forms of water management,
3). Develop empirical models that relate thermal modification to streamflow modification, and subsequently to biological integrity (as indicated by benthic invertebrate and fish communities).

Need and Benefit

Whether the future climate warms or becomes more variable, water-management operations will likely be affected. Because current water-management operations in the West were designed to operate under historic climatic conditions, climate-induced changes to runoff patterns may require adjustments to the operations of diversions and dams in order to meet water-delivery commitments. In addition, because stream thermal regimes are tightly linked to air temperature, a warming climate is likely to increase stream water temperatures, which could threaten cold-water species in streams with managed flows. In either case, it will be important to anticipate the effects of alternative water management scenarios on stream hydrology, temperature, and ecological integrity.

The proposed study aims to develop tools that can be used to assess the ecological responses of streams and rivers to climate change and the resulting water management adaptations to climate change. The study emphasizes the development and dissemination of web-based tools that can be readily used by water managers and stakeholders.

Obtained information from this study will benefit Reclamation and other water managers and stakeholders in several ways.
• The focus is on wadeable streams rather than large heavily-managed rivers. The majority of stream kilometers affected by water management are wadeable, but little is known about how ecological health is related to operational-driven changes to streamflow and thermal conditions in these smaller streams.
• A web-based information delivery system will be built, similar to USGS WaterWatch (, that is intended for the public and decision makers concerned with stream ecosystems throughout the Rocky Mountains. This tool would be navigated via a map interface, where users can select stream segments of interest. The user would then select the streamflow and temperature characteristics of concern, and the tool would graphically display the long-term temporal natural variation over a specified time period (1900-2010). With this information, scientists and managers can assess how current and projected future streamflow and temperature compare to long-term natural variation. Managers can also use the data to set management targets or benchmarks intended to protect ecological health. This study and web-based tool development can then be replicated in other subregions of interest.
• Specific statistical models that predict the thermal and biological consequences of streamflow modification will be produced. This type of information enables managers to make operational decisions with knowledge of the likely consequences on ecological systems. For example, a model developed for Utah mountains (Carlisle et al., 2012) revealed that depletion of average winter flows in excess of 30% (relative to natural baseline) dramatically increased the likeliness that stream biological integrity was in poor condition. This model can be used to understand the ecological effects of current water operations, but could also be used to predict ecological consequences of future operations in the Utah mountains.
• Finally, resulting models could be integrated into basin-wide network models of management operations, coupled with expected water availability models under various climatic and use scenarios. Such models could form the basis of a decision-support tool that allows managers to evaluate expected ecological consequences of water operation decisions under alternative climatic and water-use scenarios.

Contributing Partners

Contact the Principal Investigator for information about partners.

Research Products

Independent Peer Review

The following documents were reviewed by qualified Bureau of Reclamation employees. The findings were determined to be achieved using valid means.

Is detection of long-term impacts using aquatic macroinvertebrates seasonally dependent? (final, PDF, 1.1MB)
By Mark Nelson
Report completed on September 25, 2014

Aquatic invertebrates have been utilized as ecological indicators of short and long-term (pulse and press) disturbances to streams for many years. Pulse disturbance recovery of communities is rapid (< 18 months). Press disturbances, such as altered flows below a dam, are repetitive and persistent in nature, resulting in a permanent non-normative community adapted to these enduring environmental modifications. Theoretically, community sampling at any time of the year should allow for press im

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Last Updated: 6/22/20