Extreme rainfall over land exacerbated by marine heatwaves

Area of Science:

• Oceanography
• Atmospheric Science
• Climate Science

Background:

• Marine heatwaves (MHWs) are periods of exceptionally high sea surface temperatures (SSTs).
• MHWs significantly impact marine ecosystems.
• The influence of MHWs on coastal precipitation remains largely unknown.

Purpose of the Study:

• To investigate the impact of MHWs on extreme rainfall in coastal regions.
• To understand the physical mechanisms linking MHWs to precipitation anomalies.
• To quantify the contribution of MHWs to coastal extreme rainfall events.

Main Methods:

• Utilized multi-platform observational data from 2000 onwards.
• Analyzed sea surface temperature (SST) gradients during MHWs.
• Investigated surface wind speed, convergence, and upward motion anomalies.
• Assessed precipitation changes in coastal areas downwind of MHWs.

Main Results:

• MHW SST gradients intensify surface winds and enhance vertical turbulent flux.
• This leads to increased local precipitation, peaking one day after the MHW.
• 5%-25% of global coastal extreme rainfall events occur downwind of MHWs.
• Land precipitation during these events increases by 20%-30% (4-8 mm/day).

Conclusions:

• MHWs significantly contribute to coastal extreme rainfall events.
• These events can exacerbate flood-related fatalities.
• Projected increases in MHWs under greenhouse warming will amplify these risks.