# Contrasting boundary-layer energy budgets during daytime, nighttime, and compound heatwaves in eastern China

## TL;DR

The study explores how different types of heatwaves affect energy budgets in eastern China, revealing how daytime and nighttime factors combine to intensify heatwaves.

## Contribution

The paper identifies distinct boundary-layer energy mechanisms for daytime, nighttime, and compound heatwaves in a rapidly urbanizing region.

## Key findings

- Daytime heatwaves are driven by reduced cloudiness and increased shortwave radiation.
- Nighttime heatwaves involve moisture-cloud feedbacks that enhance longwave radiation.
- Compound heatwaves combine daytime heating and nighttime cooling inhibition to produce extreme temperatures.

## Abstract

Heatwaves over the Yangtze River Delta (YRD) have intensified in frequency and diversity amid rapid urbanization and climate change, yet their underlying boundary-layer processes remain insufficiently understood. This study examines boundary-layer energy budgets of three heatwave types across the YRD using observations from 186 meteorological stations and reanalysis data covering 2002–2022. Daytime-only heatwaves exhibited reduced cloudiness (−37%), enhancing shortwave radiation (+201 W/m2), while efficient nocturnal cooling limited nighttime warming. Nighttime-only events were characterized by greater cloudiness (+6%) and humidity, increasing longwave radiation and suppressing cooling, with rice paddies buffering daytime temperature extremes more effectively than forests. Compound heatwaves combined both mechanisms—enhanced daytime solar heating and inhibited nocturnal cooling—producing the most intense temperature anomalies (>10 °C) concentrated in coastal-urban areas. Enhanced thermal turbulence deepened the boundary layer during daytime and compound events, whereas mechanical turbulence weakened under subsidence. These findings clarify heatwave boundary-layer processes and support region-specific climate adaptation strategies.

•Daytime heatwaves driven by reduced clouds and enhanced shortwave radiation•Nighttime heatwaves caused by moisture-cloud feedback enhancing longwave radiation•Compound heatwaves combine solar heating and inhibited cooling to maximize intensity•Land surface heterogeneity modulates heatwave energy budgets

Daytime heatwaves driven by reduced clouds and enhanced shortwave radiation

Nighttime heatwaves caused by moisture-cloud feedback enhancing longwave radiation

Compound heatwaves combine solar heating and inhibited cooling to maximize intensity

Land surface heterogeneity modulates heatwave energy budgets

Earth sciences; Environmental science; Heat transfer