Soil Moisture Feedback Amplified the Earlier Onset of the Record-Breaking Three-Day Consecutive Heatwave in 2023 in North China

Abstract

A record-breaking heatwave swept North China in the summer of 2023, with a regional average of daily maximum temperature exceeding 35°C on June 23, which was the hottest day since 1959. We use the dynamical adjustment approach to assess the contributions of atmospheric circulation and Soil moisture (SM) to this heatwave and find that they contributed 69.8% and 39.5%, respectively. The anomalous anticyclone that caused this heatwave was influenced by upstream signals. Easterly winds on the southern side of the anticyclone led to anomalous subsidence, which heated the air over North China. While such anomalous anticyclones over North China are not uncommon due to atmospheric circulation variability, the 2023 heatwave still broke records because the SM-temperature coupling during the heatwave was unprecedented, with a strength four times that of typical years. The dry soil conditions during the heatwave stemmed from a lack of precipitation beforehand, with cumulative rainfall in North China being the lowest since 1979. The early dryness of the soil provided favorable conditions for land-atmosphere feedback, and under the trigger of subsidence-induced warming from the early summer anticyclone, the strong SM-temperature coupling significantly amplified the intensity of this heatwave. For future projections, numerical experiment analysis shows that temperatures currently considered extreme during 2023 heatwave event will become commonplace in the future due to SM-atmosphere coupling. However, by the end of the century, the impact of land-atmosphere coupling on extreme high temperatures in North China will diminish compared to historical period, owing to increased SM.