Top counties by heat wave risk
Heat is consistently the leading cause of weather-related mortality in the US, yet it remains underrepresented in federal disaster declarations relative to its actual impact. High scores reflect a combination of extreme temperature exposure, population vulnerability (elderly, outdoor workers), and limited access to cooling infrastructure.
Current ENSO status: Emerging El Niño (ONI +0.98, AMJ 2026) — ONI has been at or beyond ±0.5 for 2 consecutive seasons — NOAA's threshold for an official episode is 5.
Heat wave activity tracks the El Niño–Southern Oscillation (ENSO) phase. Comparing NOAA-recorded heat-wave events by year since 2016:
- El Niño years (2019, 2023): 4,372.5 events/year on average
- Neutral years (2016, 2017, 2018, 2020, 2024, 2025): 2,439.3 events/year on average
- La Niña years (2021, 2022): 1,983.5 events/year on average
Source: NOAA CPC Oceanic Niño Index (ONI). Episodes are classified using NOAA's official rule: ONI at or beyond ±0.5°C for 5+ consecutive overlapping 3-month seasons. Yearly buckets used in the heat-wave correlation use each calendar year's mean ONI across its seasons. Sample sizes are small (2–7 years per phase) — this is a directional pattern, not a statistically robust trend, and other factors (long-term warming, urbanization, reporting changes) also affect year-to-year event counts.
| # | County | State | NRI score | Rating | NOAA events 2016–2026 |
|---|---|---|---|---|---|
| 1 | Maricopa County | AZ | 100 | Very High | 99 |
| 2 | Philadelphia County | PA | 100 | Very High | 20 |
| 3 | St. Louis County | MO | 99.9 | Very High | 21 |
| 4 | Clark County | NV | 99.9 | Very High | 152 |
| 5 | Dallas County | TX | 99.9 | Very High | 55 |
| 6 | Pima County | AZ | 99.8 | Very High | 98 |
| 7 | Cook County | IL | 99.8 | Very High | 6 |
| 8 | St. Louis | MO | 99.8 | Very High | 19 |
| 9 | Kings County | NY | 99.7 | Very High | 0 |
| 10 | Queens County | NY | 99.7 | Very High | 6 |
| 11 | Harris County | TX | 99.7 | Very High | 13 |
| 12 | Bronx County | NY | 99.6 | Relatively High | 1 |
| 13 | New York County | NY | 99.6 | Relatively High | 5 |
| 14 | Tulsa County | OK | 99.6 | Relatively High | 42 |
| 15 | Shelby County | TN | 99.6 | Relatively High | 107 |
| 16 | Kern County | CA | 99.5 | Relatively High | 24 |
| 17 | Oklahoma County | OK | 99.5 | Relatively High | 93 |
| 18 | Tarrant County | TX | 99.5 | Relatively High | 56 |
| 19 | Washington County | AR | 99.4 | Relatively High | 1 |
| 20 | Baltimore | MD | 99.4 | Relatively High | 31 |
| 21 | Bexar County | TX | 99.4 | Relatively High | 13 |
| 22 | Los Angeles County | CA | 99.3 | Relatively High | 0 |
| 23 | Miami-Dade County | FL | 99.3 | Relatively High | 1 |
| 24 | Wayne County | MI | 99.3 | Relatively High | 2 |
| 25 | Tulare County | CA | 99.2 | Relatively High | 7 |
| 26 | District of Columbia | DC | 99.2 | Relatively High | 27 |
| 27 | Baltimore County | MD | 99.2 | Relatively High | 13 |
| 28 | Cochise County | AZ | 99.1 | Relatively High | 45 |
| 29 | Hennepin County | MN | 99.1 | Relatively High | 6 |
| 30 | Jackson County | MO | 99.1 | Relatively High | 1 |
| 31 | Santa Cruz County | AZ | 99 | Relatively High | 51 |
| 32 | Essex County | NJ | 99 | Relatively High | 5 |
| 33 | Milwaukee County | WI | 99 | Relatively High | 14 |
| 34 | Pinal County | AZ | 98.9 | Relatively High | 42 |
| 35 | Franklin County | OH | 98.9 | Relatively High | 2 |
| 36 | Hamilton County | OH | 98.9 | Relatively High | 4 |
| 37 | Broward County | FL | 98.8 | Relatively High | 0 |
| 38 | Hudson County | NJ | 98.8 | Relatively High | 0 |
| 39 | Hidalgo County | TX | 98.8 | Relatively High | 62 |
| 40 | San Diego County | CA | 98.7 | Relatively High | 53 |
| 41 | Marion County | IN | 98.7 | Relatively High | 2 |
| 42 | Caddo Parish | LA | 98.7 | Relatively High | 85 |
| 43 | El Paso County | TX | 98.7 | Relatively High | 1 |
| 44 | Mohave County | AZ | 98.6 | Relatively High | 0 |
| 45 | Santa Clara County | CA | 98.6 | Relatively High | 1 |
| 46 | Monmouth County | NJ | 98.6 | Relatively High | 17 |
| 47 | Riverside County | CA | 98.5 | Relatively High | 58 |
| 48 | Sedgwick County | KS | 98.5 | Relatively High | 1 |
| 49 | Travis County | TX | 98.5 | Relatively High | 8 |
| 50 | Mariposa County | CA | 98.4 | Relatively High | 6 |
Source: FEMA National Risk Index v1.20.0, December 2025. Scores are 0–100 percentile rankings among all US counties — a score of 95 means this county's expected annual loss from heat wave exceeds 95% of all other counties. See the methodology page for definitions. Download the full CSV for all 3,114 scored counties.
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