Lower Colorado River Mainstream Evaporation and Riparian Evapotranspiration Losses Report

On August 16, 2022, the Bureau of Reclamation (Reclamation) and Department of the Interior announced several administrative actions for consideration to improve and protect the long-term sustainability of the Colorado River System. The System is currently experiencing prolonged drought and low runoff conditions accelerated by climate change that have led to historically low water levels in Lakes Powell and Mead (Reclamation, 2021). One of the actions included reviewing and prioritizing additional administrative initiatives to address system losses in the lower Colorado River mainstream. As part of that action, this report provides an overview of historical mainstream evaporation and riparian evapotranspiration (ET) losses along the lower Colorado River and presents methodologies used to develop those datasets. This report does not make recommendations on how to account for system losses in the lower Colorado River mainstream.

Supplemental documents:

• Appendix 1 – Reaches Identified in the Lower Colorado River Mainstream Evaporation and Riparian Evapotranspiration Losses Report
• Appendix 2 – LCRAS Open Water Monthly Evaporative
  Losses
• Appendix 3 – Lake Mead, Lake Mohave, and Lake Havasu Evaporation from Reclamation’s Hydrologic Database (HDB)
• Appendix 4 – LCRAS Riparian Monthly Evapotranspiration Losses by Vegetation
• Appendix 5 – Evaporation and Riparian Evapotranspiration (ET) Coefficients
• Appendix 6 – Evaporation and Riparian Evapotranspiration (ET) Rates