Dallas-Fort Worth heat waves are getting longer

Data: EPA ; Note: Includes 50 most populated metros; New York City, Houston, Minneapolis-St. Paul and Denver were excluded for incomplete data in this period; Chart: Axios Visuals

Heat waves in Dallas-Fort Worth now last an average of four days longer than they did in the 1960s, per a new Environmental Protection Agency analysis of U.S. heat trends.

Why it matters: Prolonged heat can strain power grids and lead to heat illnesses and death, particularly among vulnerable populations.

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• Heat wave seasons are lengthening across the country meaning excessive temperatures can occur at times when people aren't expecting it, like in early spring and late fall, per the EPA report .

The big picture: Heat waves nationwide are becoming longer, more frequent and more intense. The average number of heat waves has increased from two per year in the 1960s to six per year in this decade.

• And they last about a day longer now than they did in the 1960s.

How it works: The EPA analyzed climate trends in the 50 largest U.S. metro areas.

• Heat waves are defined as two or more consecutive days with a daily temperature above the 85th percentile of historical July and August temperatures for the city. The metric adjusts for how hot it is due to humidity.
• The 85th percentile is equivalent to the "nine hottest days during the hottest two months of the year."

Zoom in: Dallas-Fort Worth area heat waves last about four days longer than they did, an increase double that of the national average of major U.S. cities.

• Temperatures during heat waves are about 0.7 degrees hotter now than they were in the 1960s.

The bottom line: Even small increases in heat can be catastrophic, the report says.