Large increase in global storm runoff extremes driven by climate and anthropogenic changes.

Area of Science:

• Climatology
• Hydrology
• Environmental Science

Background:

• Extreme weather events, particularly flash floods, cause substantial mortality and economic damage.
• Flash floods linked to storm runoff extremes are expected to intensify globally due to climate change and human activities.
• Prior research has not fully explored how surface temperature and atmospheric moisture influence storm runoff extremes.

Purpose of the Study:

• To investigate the response of storm runoff extremes to changes in surface temperature and atmospheric moisture.
• To assess whether current climate models accurately project the intensification of flash floods.

Main Methods:

• Analysis of historical climate data and hydrological models.
• Comparison of observed trends in storm runoff extremes with theoretical scaling laws (e.g., Clausius-Clapeyron scaling).
• Global-scale assessment of spatial and decadal variability in extreme runoff events.

Main Results:

• Storm runoff extremes are increasing in most regions at rates exceeding Clausius-Clapeyron scaling predictions.
• The rate of increase for storm runoff extremes often matches or surpasses that of precipitation extremes globally.
• Significant spatial and decadal variations in these extreme events were observed.

Conclusions:

• Current projections of storm runoff extremes may underestimate their future intensity and frequency.
• The findings highlight a critical need to revise impact assessments and adaptation strategies for flash floods.
• Increased resilience of ecosystems and communities is threatened by the underestimated risk of extreme runoff events under future warming.