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Explaining Extreme Events of 2020 from a Climate Perspective


We estimate that anthropogenic forcing caused half of the observed temperature anomaly during the August 2022 heatwave in southern China. Thermodynamical processes, especially soil moisture–SAT feedback, amplified the heatwave.

Attribution of the August 2022 Extreme Heatwave in Southern China: Role of Dynamical and Thermodynamical Processes

The stratospheric contribution to tropospheric ozone has long been a topic of much debate over the past few decades. In this study, we leveraged multiple datasets from surface, sounding and satellite observations to reanalysis datasets, along with a global chemical transport model (Global Nested Air Quality Prediction Modelling System, GNAQPMS) to investigate the impact of a stratospheric-to-tropospheric transport (STT) event characterized by long duration and wide range in the summer on surface high ozone episodes over heavily industrialized regions in northern China. In 14–18 August 2019, the ERA5 reanalysis datasets showed a potential vorticity (PV) tongue and a deep, upper-level trough penetrate towards 35° N over the North China Plain (NCP), indicating the occurrence of a stratospheric intrusion. From Atmospheric Infrared Sounder (AIRS) measurements, we found that the ozone-rich, stratospheric air mass had been injected into the lower altitudes. The GNAQPMS generally captured the featured layers, although there was a slight underestimation in the low troposphere. The averaged magnitudes of stratospheric contribution (O3S) and percentage (O3F) simulated by GNAQPMS were 3–20 μg m−3 and 6%–20%, respectively, while the Whole Atmosphere Community Climate Model (WACCM) indicated a higher stratospheric contribution by 3–5 μg m−3. Through this study, we give our opinions on the controversial topic of a more thorough understanding of the influence of natural processes apart from anthropogenic emissions, even in a heavily polluted region during summer.

Influences of stratospheric intrusions to high summer surface ozone over a heavily industrialized region in northern China

With climate warming, eastern China has experienced a significant increase in temperature accompanied by intensified ozone pollution. We aimed to investigate the spatiotemporal patterns and relationships between ozone levels and temperature in eastern China using observation-based ozone data from 418 air quality monitoring stations and temperature data from ERA5. The summer maximum temperature and annual ozone concentration in eastern China increased significantly between 2015 and 2022, with increases rate of 10% and 2.84 μg/m3 yr-1, respectively. The baseline ozone concentration was increasing over time. The average difference in MDA8 O3 concentration in spring, summer, and autumn decreased, with more ozone pollution spreading into spring and autumn, indicating a trend of prolonging the ozone season. During the June-July-August (JJA) period of 2015-2022, heatwaves increased significantly in eastern China. The frequency of heatwave events >10 days played a vital role in exacerbating ozone pollution. During the JJA period, the increase rate in MDA8 O3 concentration was 9.31 μg/m3 yr-1 during heatwave periods, significantly higher than that during non-heatwave periods (4.01 μg/m3 yr-1). The correlation between MDA8 O3 concentration and temperature was as high as 0.99, indicating that temperature was vital in ozone formation during the JJA period in eastern China. This study suggests that more stringent actions are needed to control ozone-precursor compounds during frequent summertime heatwaves in eastern China. 

Evolution of surface ozone pollution pattern in eastern China and its relationship with different intensity heatwaves.

Precipitation is crucial for managing water resources in the Three River Headwaters (TRH) region of the Tibetan Plateau (TP). Gridded precipitation datasets across the TRH region exhibit significant discrepancies in their results. Previous studies have primarily focused on assessing average or extreme precipitation for a single dataset or several datasets. In this study, based on the observed gridded precipitation dataset (CN05.1), a comprehensive evaluation of the climatic features and extreme precipitation across the TRH region from 1983 to 2014 is performed by employing two gauge-based gridded datasets (GPCC and CRU), two satellite-derived precipitation datasets (P-CDR and IMERG), and two reanalysis precipitation datasets (ERA5 and CRA40). The results show that all datasets are consistent in reproducing the climatology, interannual variability, and annual cycle of precipitation in the TRH region. However, the different datasets exhibit significant discrepancies in characterizing the long-term trends and extreme precipitation events. P-CDR and GPCC provide a good representation of the spatial variability of the annual mean climatology. ERA5 and CRU are more reliable in capturing interannual variabilities. The long-term trends can be closely described by employing CRU. P-CDR and GPCC exhibit higher skills in terms of the annual cycle. P-CDR performs better than IMERG for daily precipitation in terms of probability distributions and other assessment metrics. P-CDR and IMERG have advantages and disadvantages in characterizing the nine extreme precipitation indices. This study demonstrates a comprehensive comparison method using multiple precipitation datasets to gain essential insight into the strengths and weaknesses of various datasets across the TRH region.

/pdf/precipitation-characteristics-across-the-three-river-2iwtifmr.pdf

Precipitation Characteristics across the Three River Headwaters Region of the Tibetan Plateau: A Comparison between Multiple Datasets

Northeast China (105°–135°E, 37°–55°N) is an important agricultural production area for wheat, soybean, and maize, among other crops (Lu et al. 2017; http://country.cnr.cn/gundong/20160303/ t20160303_521524231_1.shtml), making a substantial contribution to the food security of China. Late boreal spring (mid-April to mid-May) is a transition period when most crops are at their critical growing stage. Under climate change, a widespread shift toward earlier spring greening, triggered by warmer temperature, has been documented (Schwartz et al. 2006; Piao et al. 2015; Tan et al. 2018). Extreme cold events occurred at growth stage are more likely to cause serious damage to crop yields and large economic loss (Wheeler et al. 2000; X. Li et al. 2015). In the recent decades, regional cold extremes, superimposed on a warmer climate, recurred throughout the Northern Hemisphere (Cattiaux et al. 2015; Qian et al. 2018; Christidis and Stott 2020; Zhang et al. 2021). April 2020 was the second hottest April (following April 2016) in the records, being 1.06°C above the twentieth-century average (www.noaa.gov/news/april-2020was-earth-s-2nd-hottest-april-on-record). However, Northeast China witnessed an exceptional cold spell from 19th to 25th April 2020, mainly affecting the provinces of Heilongjiang, Jilin, Liaoning, Inner Mongolia, Hebei, Hongyong Yu, Xiaojing Yu, Ziwei Zhou, Yu Wang, Yingxin Li, Nergui Nanding, Nicolas Freychet, Buwen Dong, Dongqian Wang, Fraser C. Lott, Simon F. B. Tett, and Sarah Sparrow

/pdf/attribution-of-april-2020-exceptional-cold-spell-over-3fwjgpbi.pdf

Attribution of April 2020 Exceptional Cold Spell over Northeast China

Satellite monitoring of stratospheric ozone intrusion exceptional events- a typical case of China in 2019

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Attribution of April 2020 Exceptional Cold Spell over Northeast China

Satellite monitoring of stratospheric ozone intrusion exceptional events- a typical case of China in 2019