CalHeatScore creates heat wave warnings for every zip code in California, using temperature data, socioeconomic indicators, and the history of emergency room visits, to predict heat-related health risk. A new tool aims to do for heat waves what Saffir and Simpson did for hurricanes. CalHeatScore, an online mapping tool developed by the California Office of Environmental Health Hazard Assessment, ranks heat wave risk on a straightforward scale of 0 to 4.