A man has been charged after allegedly lighting a series of fires in bushland in Sydney's north, including on Wednesday when the temperature hit 33 degrees.

The 50-year-old man allegedly lit three fires in Berowra between August 24 and September 13.

Police said detectives were searching bushland in Berowra as part of an ongoing investigation when they saw a man standing near a fire on Wednesday morning, when a total fire ban was in place.

The man allegedly attempted to run off but officers chased him and arrested him.