Tool for Quantitative Assessment of Temperature Sensitivity under Future Climates and Legacy Impacts (QUAL2Kw)

This modeling framework simulating river and stream water quality was developed by the EPA as a pilot for climate change analysis.

The Total Maximum Daily Load (TMDL) program, established by the Clean Water Act, has frequently been used to develop management plans intended to achieve temperature criteria and protect cold water fisheries. Most of these analyses, however, have been conducted using assumptions of a stationary climate under which historical data on flow and temperature can be assumed to be an adequate guide to future conditions. The Environmental Protection Agency launched a pilot research project to consider how projected climate change impacts can be incorporated into a TMDL and influence restoration plans, using the temperature TMDL for the South Fork Nooksack River in northwest Washington as the pilot.

Table with flow scenarios from the tool

7Q10 flow multiplicative change factors (unitless) for tributary flow from VIC model for low-, medium-, and high-impact scenarios (columns) and 2020s, 2040s, and 2080s time horizons (rows).

The research plan provided for the development of both a Quantitative Assessment and a Qualitative Assessment. The Quantitative Assessment (the subject of this tool) uses the draft temperature TMDL Implementation Plan developed for the South Fork Nooksack River as the pilot for climate change analysis. It provides a comparison of modeled stream temperatures, with and without proposed allocations such as increased riparian shading, for critical conditions under projected climate conditions for the 2020s, 2040s, and 2080s. The pollutant in this case is thermal load and allocations to reduce the load often involve restoration of stream shading, which reduces the solar input.

The companion Qualitative Assessment is a comprehensive analysis of freshwater habitat for Endangered Species Act salmon restoration in the South Fork Nooksack River under climate change. Together, these assessments identify comprehensive actions to protect Clean Water Act beneficial uses (salmon habitat) and Endangered Species Act Recovery goals under climate change. Results indicate that pre-emptive mitigation strategies implemented now to establish cold water refuges and mature riparian forest canopy shading will be critical to reduce the accelerating threat of extended lethal summer water temperature extremes.


Qual2Kw is a modeling framework written in Excel/VBA for simulating river and stream water quality. The QUAL2Kw framework is a one-dimensional, non-uniform, steady-flow model with Diel (daily cycle) heat flow budget simulation. The heat budget and temperature are simulated as a function of meteorology on a Diel time scale with Diel water-quality kinetics. The channel is assumed to be well-mixed vertically and laterally. All water quality state variables are simulated on a Diel time scale for biogeochemical processes. Point and non-point loads and abstractions are simulated. Phytoplankton and bottom algae in the water column, as well as sediment diagenesis and heterotrophic metabolism in the hyporheic zone, are simulated. The model has variable stoichiometry and the luxury uptake of nutrients by the bottom algae (periphyton) is simulated with variable stoichiometry of N and P.


Surface water: temperature data, flow data, channel morphological data, solar radiation, meteorological data, continuous and instantaneous water quality data (pH, DO, conductivity, nutrients, etc).


Longitudinal profiles of flow, hydraulic properties, temperature, water quality and biological parameters. Temporal daily profiles also available.

Linkage to Other Models

A series of support models provide input to Qual2Kw.

Level of Effort

An intensive monitoring effort is required for the entire the model period. The model is complicated and requires an understanding of modeling, hydrology, and stream ecology.

Last modified
30 January 2018 - 2:36pm