Urban Heat Pollution in the Capital Region

The urban heat island (UHI) effect is the warming of urbanized areas relative to their surrounding, vegetated, rural regions. Traditional building and infrastructure materials — like concrete and asphalt pavements — retain more heat during the day and release it back into the environment, increasing surrounding temperatures. Coupled with summer heat, urban heat has implications for all of us, because excessive heat:

  • Negatively impacts health and well-being by exacerbating chronic and acute conditions (which increase emergency room visits and death rates, particularly for the most vulnerable populations);
  • Increases electricity use — which can increase the costs for cooling, stress power generation and transmission systems, and increase greenhouse gas emissions;
  • Negatively impacts our economy by reducing agricultural and labor productivity, among other factors;
  • Impairs water quality and increases the volume of water required to keep trees and landscape alive and healthy.

What is Regional Heat Pollution?

Although the traditional term “urban heat island” implies that the effects are isolated to urban city centers, the Capital Region is unique. Due to the Delta Breeze — a movement of cooler, ocean air via the Delta into hotter valley air — heat is not confined to the urban areas. The excess heat produced from the built environment and the use of internal combustion engines migrates to the surrounding areas in the northern and eastern parts of the region, including:

  • Citrus Heights
  • Arden-Arcade
  • Carmichael
  • North Highlands
  • Rio Linda
  • Fair Oaks
  • El Dorado Hills
  • Roseville
  • Folsom
  • Rocklin

The urban heat island effect is therefore a regional heat pollution problem. In other words, addressing the impacts of heat in the region requires a multi-agency and multi-jurisdictional collaborative effort.

In 2012, the California Legislature tasked the California Environmental Protection Agency to develop an Urban Heat Island Index that would quantify the extent and severity of the urban heat island for cities. The resulting (above) maps reflect the increase in temperatures caused by the urban heat island and not the total heat. Among other things, the study found that the index tends to increase during heat waves. The study also found that wind and topography can move the generated urban heat to surrounding areas. Looking at the map for the Sacramento region, the generated heat moves to areas including North Highlands, Roseville, Auburn, and El Dorado Hills.

We are currently working to expand awareness of the urgent need to address heat pollution in multiple sectors to protect the health and vitality of our region, both now and in the future. One key initiative is a project focused on identifying the most effective urban cooling strategies for the region, creating a map of polluting sources contributing to the urban heat, and developing a plan to reduce regional heat pollution.