Annual Number of Extreme Heat Days

The raw temperature data is sourced from the North American Land Data Assimilation System (NLDAS-2) (https://ldas.gsfc.nasa.gov/nldas/v2/forcing.) database's air temperature (K) at 2 meters above the surface, with a spatial resolution of 14*14 km. The gridded raw temperatures are aggregated to the county level. The threshold is set using the 90th percentile of daily average temperatures from May to September over the years 1979 to 2019, and the number of days that exceed this threshold is considered the annual number of extreme heat days. This calculation method is provided by the CDC National Environmental Public Health Tracking (https://ephtracking.cdc.gov/indicatorPages )