Climate Models
  • This chart shows number of Extreme Heat days in a year for the selected location on map under the RCP 4.5 scenario. An Extreme Heat day is defined as a day in April through October when the Maximum Temperature exceeds the location's Extreme Heat Threshold, which is calculated as the 98th percentile of historical maximum temperatures between April 1 and October 31 based on observed daily temperature data from 1961–1990).
  • * These models have been selected by California state agencies as priority models for research contributing to California’s Fourth Climate Change Assessment.
  • The gray line (1950–2005) is observed data. The colored lines (2006–2100) are projections from 10 LOCA downscaled climate models selected for California. Use year sliders to get means for different time periods. The projected mean is calculated for all models with a ☑. Use slider below the chart to zoom and pan different time periods in the chart.

Timing of Extreme Heat Days

Days above derived from HadGEM2-ES model


Scenario... ()

This chart displays a point for each day that exceeds the extreme heat threshold. Time of year between April through October is plotted along the y axis and each year 1950-2100 along the x axis. For most areas around the state, the models project not only an increase in the number of days expected to exceed the extreme heat threshold, but also their occurrence both earlier and later in the season. Near the end of the century you may find long periods meeting heat wave conditions.

About the Tool

With this tool you can explore how the frequency and timing of extreme heat days and warm nights is expected to change under different emission scenarios. This data is derived from daily climate projections which have been downscaled from global climate models from the CMIP5 archive, using the Localized Constructed Analogs (LOCA) statistical technique developed by Scripps Institution Of Oceanography. LOCA is a statistical downscaling technique that uses past history to add improved fine-scale detail to global climate models.

As the climate changes in California, one of the more serious threats to the public health of Californians will stem primarily from the higher frequency of extreme conditions, principally more frequent, more intense, and longer heat waves. An increase in heat waves may increase the risk of heat stroke and dehydration. Find out how you can become better prepared and more resilient to increasing temperature and extreme heat events at Preparing California for Extreme Heat, a report put together by California Environmental Protection Agency (CalEPA) and the California Department of Public Health (CDPH).

What is an extreme heat day?

For the purposes of this tool, an extreme heat day is defined as a day in April through October where the maximum temperature (Tmax) exceeds the 98th historical percentile of maximum temperatures based on daily temperature data between 1961-1990.

What is warm night?

For the purposes of this tool, a warm nigh is defined as a day in April through October where the minimum temperature (Tmin) exceeds the 98th historical percentile of minimum temperatures based on daily temperature data between 1961-1990.

What is a heat wave?

A heat wave is defined as 5 or more consecutive extreme heat days.

Data Sources

scripps logo

LOCA Downscaled Climate Projections for Temperature & Precipitation

Scripps Institution Of Oceanography - University of California, San Diego

Projected daily minimum and maximum temperature and daily precipitation data. These data were statistically downscaled from 32 global climate models from the CMIP5 archive at a 1/16º (approximately 6 km) spatial resolution on a daily timescale using the LOCA technique. The historical period is 1950–2005, and there are two future scenarios available: RCP 4.5 and RCP 8.5 over the period 2006–2100 (although some models stop in 2099). Details are described in Pierce et al., 2014.

university of colorado boulder logo

Gridded Historical Observed Meteorological and Hydrological Data

University of Colorado, Boulder

Historical observed daily temperature and precipitation data from approximately 20,000 NOAA Cooperative Observer (COOP) stations form the basis of this gridded dataset from 1950–2013 at a spatial resolution of 1/16º (approximately 6 km). Observation-based meteorological data sets offer insights into changes to the hydro-climatic system by diagnosing spatio-temporal characteristics and providing a historical baseline for future projections. Details are described in Livneh et al., 2015.