Beijing commuters endure scorching heat as they brave the sun-drenched streets. Credit: Kexin Gui

This summer, much of North China has endured widespread temperatures above 35°C. Even typically cooler, high-latitude summer retreats like Harbin in Northeast China—usually a refuge from the heat—saw temperatures soar past 35°C in late June and July. As climate change accelerates, extreme heat events will become increasingly frequent.

Just two years earlier, in late June 2023, North China sweltered under a searing three-day heat wave that arrived weeks earlier than usual and broke six decades' worth of temperature records. Daily highs soared past 40°C in some areas, triggering , straining the region's power grid, and threatening crops during the growing season. For millions living in this vital agricultural and industrial heartland, the scorching conditions were a stark reminder of the mounting risks posed by climate extremes.

A study in Earth's Future by researchers Kexin Gui and Tianjun Zhou of the Institute of Atmospheric 鶹Ժics, Chinese Academy of Sciences, has pointed out the dual drivers behind this unprecedented heat: large-scale atmospheric circulation and an unusually strong soil moisture feedback.

Using advanced climate analysis techniques, the team found that while an anomalous accounted for nearly 70% of the heat wave's intensity, the early-season drought and dry soils added another 40%—amplifying the heat wave's severity far beyond what would have occurred otherwise.

Spatial characteristics of variables related to the 2023 North China heat wave. Spatial pattern of (a) Tmax anomalies, (b) 500 hPa geopotential height (Z500) anomalies, and (c) soil moisture (SM) anomalies. The dashed and solid boxes represent the regions used for the spatial-temporal analysis of record-breaking high temperature areas and the region defined as North China, respectively. The hatched areas indicate grid points with record-breaking temperatures. (d) Time series of Tmax anomalies, Z500 anomalies, and SM anomalies averaged over North China during heat wave periods from 1959 to 2023. The black star indicates the temperature anomaly during the 2023 heat wave. Credit: Earth's Future (2025). DOI: 10.1029/2024EF005561

"Dry soils, caused by the lowest rainfall in over four decades, acted like a giant amplifier," explained lead author Gui. "With little moisture left to evaporate, the heated up rapidly, pushing temperatures to extremes rarely seen in North China's early summer."

The study warns that such conditions may become more common under . Model projections suggest that heat waves with the same intensity as the 2023 event could become the new normal by the end of the century. While the influence of soil moisture feedback on extreme heat may weaken in the long term due to projected increases in soil moisture.

"Heat waves of this magnitude put enormous pressure on , agriculture, and public health," said Dr. Zhou. "Understanding how and atmospheric processes interact is crucial for better predicting and mitigating future extreme weather events."

The findings underscore the urgency of climate adaptation strategies in North China, where the increasing heat extremes pose a significant threat to livelihoods and ecosystems.

More information: Kexin Gui et al, Soil Moisture Feedback Amplified the Earlier Onset of the Record‐Breaking Three‐Day Consecutive Heatwave in 2023 in North China, Earth's Future (2025).

Journal information: Earth's Future