An index of regional summertime heat wave activity that reflects intensity, duration and spatial extent of heat waves over California and Nevada. The index is computed using nighttime (minimum) temperatures for local durations of at least one, two and three consecutive days/nights. Credit: Scripps Institution of Oceanography, UC San Diego

An index of regional summertime heat wave activity that reflects intensity, duration and spatial extent of heat waves over California and Nevada. The index is computed using nighttime (minimum) temperatures for local durations of at least one, two and three consecutive days/nights.

Deadly heat waves are becoming more frequent in California