Elevated heat indices resulting from hurricane-related defoliation: a case study

Area of Science:

• Environmental Science
• Atmospheric Science
• Public Health

Background:

• Tropical cyclones cause significant land surface defoliation, altering energy balance.
• Previous research indicates hurricane defoliation warms near-surface air temperatures.
• Human heat stress, measured by the heat index (HI), is a critical public health concern.

Purpose of the Study:

• To quantify the impact of hurricane-induced defoliation on human heat stress.
• To contextualize warming effects specifically through the lens of the heat index (HI).
• To assess the sensitivity of these HI changes to varying synoptic conditions.

Main Methods:

• Characterized defoliation extent and duration using normalized difference vegetation index (NDVI) after Hurricane Laura (2020).
• Assimilated defoliated land surface data into the Weather Research and Forecasting (WRF) model version 4.2.
• Compared defoliation simulation results with a control simulation for 30 days post-landfall.
• Performed additional WRF experiments using hypothetical landfall years (2017, 2018) to test synoptic condition sensitivity.

Main Results:

• Defoliation led to increased heat index (HI) values, particularly overnight.
• In southwest Louisiana, HI exposure time above 30°C increased by 8.1%.
• Cameron, Louisiana, experienced an additional 33 hours of HI exceeding 26°C and a 1.2°C mean HI increase at 0300 UTC.
• Statistically significant HI increases were observed even when accounting for different synoptic conditions in 2017 and 2018.

Conclusions:

• Hurricane-induced defoliation demonstrably exacerbates human heat stress.
• Increased overnight HI poses a significant risk, as minimum temperatures are key indicators of heat mortality.
• Findings are crucial for emergency managers and public health officials in preparing for and mitigating heat-related risks post-cyclone.