Assessment on impacts of the 2022 extreme heatwave and drought on Camellia oleifera production in China

In 2022, southern China experienced an unprecedented summer-autumn extreme heatwave and drought, resulting in significant impacts on agricultural and forestry production. Camellia oleifera, a woody edible-oil-bearing species endemic to China and one of the world’s four major woody oil crops, is primarily cultivated in subtropical low mountain and hilly regions, with extensive distribution across 15 major production provinces in southern China. The period from July to October represents a critical stage for fruit enlargement and oil accumulation in C. oleifera. This study aims to assess the impact of the 2022 extreme heatwave and prolonged drought on C. oleifera production in China and to explore disaster thresholds for heat and drought affecting C. oleifera.

The study focuses on 15 major C. oleifera-producing provinces in China, utilizing meteorological data from the Tianqing Big Data Center (daily precipitation and maximum temperature from 1,307 weather stations) and identifying representative years significantly affected by summer-autumn heat and drought (2022, 2021, and 2013). We investigated the mortality rates of C. oleifera plants and flower buds in 2022, and collected data from three representative years including yield, affected areas, fruit oil content, plant phenotypic traits, and phenological phases. Meteorological disaster indices used in this study include the cumulative number of days with daily maximum temperature ≥35°C (D_Tm35) and ≥39°C (D_Tm39), extreme maximum temperature (T_max), the longest consecutive days with maximum temperature ≥35°C (CD_Tm35) and without effective rainfall (CD_nr).

Results indicate that, in 2022, most regions within the C. oleifera-producing areas experienced D_Tm35 ≥ 37d with localized D_Tm39 ≥ 20 d and T_max reaching 45.0°C. From July 21 to December 3, some areas experienced CD_nr ≥ 61 d. These conditions led to severe water deficits, with fresh fruit yields in severely affected areas decreased by more than 90%, flower bud mortality rates ranging from 10.6% to 37.2%, and fruit set rates in some regions dropping to below 1% in the following year. In extreme heat zones, fresh fruit oil content was reduced by more than 40%. New plantations experienced mortality rates of 71.0%–74.5%, young forests 15.2%–70.4%, and mature forests 9.2%–14.7% due to compounded heat and drought stress. Comprehensive analysis of the three representative years reveals that during the oil accumulation phase, CD_Tm35 ≥9 d combined with D_Tm39 ≥3 d leads to significant reductions in oil content, while CD_nr ≥46 d during the flower bud maturation phase significantly increases flower bud mortality. Furthermore, CD_Tm35 ≥18 d and CD_nr ≥31 d are critical thresholds for abnormal fruit drop and substantial reductions in fresh fruit yield. When CD_Tm35 ≥15 d and CD_nr ≥31 d, the mortality rate of young forests increases significantly. These findings provide valuable insights into the disaster thresholds for heat and drought impacts on C. oleifera and highlight the vulnerability of its production system to climate extremes.