Boston is under its third heat emergency of the summer

The city of Boston declared a heat emergency lasting from Monday through Wednesday, marking the third time this summer the city has issued such a warning.

The heat index, or the "feels like" temperature, is predicted to be in the mid- to high-90s for the first half of the week. Boston declares heat emergencies when two or more days are forecast to have a heat index of 95 degrees or above.

Boston issued previous emergencies in June and July. Human-caused global warming has increased the frequency, size, intensity and duration of extreme heat events. Heat waves were once rare in this area, but are becoming more common.

City officials urged residents to stay hydrated and in air conditioning when possible. Splash pads and pools around the city are open, and officials noted public library locations are available for those in need of air conditioning.

Much of eastern and central Massachusetts was also under an air quality advisory Monday. The state Department of Environmental Protection issued the advisory due to high ozone levels, making the air unhealthy for older adults, children, and those with lung or heart disease.

The department advised that people reduce time outside, especially when doing intense activities.

With reporting from WBUR's Barbara Moran.