CalHeatScore API Documentation
The CalHeatScore API provides daily heat-health risk scores for every California ZIP code through a public ArcGIS Feature Service. No API key, token, or account is required. You can start making requests immediately.
What is CalHeatScore?
CalHeatScore is a public health tool developed by the California Environmental Protection Agency (CalEPA) and the Office of Environmental Health Hazard Assessment (OEHHA).
CalHeatScore assigns every California ZIP code a daily score from 0 to 4 based on forecasted temperatures and historical rates of heat-related emergency room visits. Because California's climate and health response to heat varies across the state, and even within counties, risk is calculated at the ZIP code level.
| CalHeatScore | Impact Level | Meaning |
|---|---|---|
| 0 | Low | Little to no heat-related health impacts are expected. |
| 1 | Mild | Warm day. A minor increase in heat-related health impacts is expected among those sensitive to heat. |
| 2 | Moderate | Very warm day. A moderate increase in heat-related health impacts is expected among those sensitive to heat. |
| 3 | High | Hot day. An increase in heat-related health impacts is expected for everyone, especially those without access to adequate cooling and hydration or those engaged in strenuous physical activity outdoors. This level of heat can pose a significant risk to health. |
| 4 | Severe | Extreme heat day. A major increase in heat-related health impacts is expected for everyone, especially those without access to adequate cooling and hydration or those engaged in strenuous physical activity outdoors. This level of heat can pose a very serious risk to health. |
What the API returns
The API returns a 7-day rolling forecast in wide format — one row per ZIP code with a separate column for each forecast day:
| Field | Description |
|---|---|
ZIP_CODE |
California ZIP code |
DATE |
Reference date for the forecast (YYYY-MM-DD) |
CHS_Day_0 |
Heat score for today (0–4) |
CHS_Day_1 through CHS_Day_6 |
Heat scores for the next 1–6 days (0–4) |
Shape__Area |
ZIP code polygon area in square meters |
Shape__Length |
ZIP code polygon perimeter in meters |
Score fields (CHS_Day_0 through CHS_Day_6) are returned as strings, not numbers. Convert them to integers in your code before performing numeric comparisons.
Data is updated automatically at 5:00AM and 8:00AM Pacific Time each morning, with the 8:00AM forecast serving as the definitive rankings for the current day.