What happens when the Degree Heating Week index exceeds 8 degrees C?

Degree Heating Week (DHW) index shows how much heat stress has piled up or accumulated in an area over the past twelve weeks (3 months). This is usually done by adding up any temperature above the bleaching threshold during that time period.

When heat stress reaches 8 degree Celsius-weeks or higher, there would an experience of severe, widespread bleaching and significant mortality.