Extreme Heat Days & Warm Nights

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 purposes of this tool, an extreme heat day or warm night is defined as a day in a year when the daily maximum/minimum temperature exceeds the 98th historical percentile of daily maximum/minimum temperatures based on observed historical data from 1961–1990 between April and October. Users have the option of setting a different value for threshold temperature or reset back to the 98th percentile value.

What is a warm night?

For purposes of this tool, a warm night is defined as a day in April through October when the daily minimum temperature exceeds the 98th historical percentile of daily minimum temperatures based on observed data from 1961–1990. Users have the option of setting a different value for threshold temperature or reset back to the 98th percentile value.

What is a heat wave?

Heat waves are characterized as durations of sustained, extreme heat, although there is no universal definition of a heat wave. For purposes of this tool, a heat wave is defined as a duration of 4 consecutive extreme heat days or warm nights when the daily maximum/minimum temperature is above the extreme heat threshold. Each 4 day/night duration is counted, so that if extreme temperatures persist for 10 consecutive days/nights, it counts as 2 Heat Waves. Users have the option of choosing a different value for number of consecutive days/nights.