Panmao Zhai’s research while affiliated with Chinese Academy of Meteorological Sciences and other places

In a rapidly changing climate, evidence-based decision-making benefits from up-to-date and timely information. Here we compile monitoring datasets (published at 10.5281/zenodo.15639576; Smith et al., 2025a) to produce updated estimates for key indicators of the state of the climate system: net emissions of greenhouse gases and short-lived climate forcers, greenhouse gas concentrations, radiative forcing, the Earth's energy imbalance, surface temperature changes, warming attributed to human activities, the remaining carbon budget, and estimates of global temperature extremes. This year, we additionally include indicators for sea-level rise and land precipitation change. We follow methods as closely as possible to those used in the IPCC Sixth Assessment Report (AR6) Working Group One report. The indicators show that human activities are increasing the Earth's energy imbalance and driving faster sea-level rise compared to the AR6 assessment. For the 2015–2024 decade average, observed warming relative to 1850–1900 was 1.24 [1.11 to 1.35] °C, of which 1.22 [1.0 to 1.5] °C was human-induced. The 2024-observed best estimate of global surface temperature (1.52 °C) is well above the best estimate of human-caused warming (1.36 °C). However, the 2024 observed warming can still be regarded as a typical year, considering the human-induced warming level and the state of internal variability associated with the phase of El Niño and Atlantic variability. Human-induced warming has been increasing at a rate that is unprecedented in the instrumental record, reaching 0.27 [0.2–0.4] °C per decade over 2015–2024. This high rate of warming is caused by a combination of greenhouse gas emissions being at an all-time high of 53.6±5.2 Gt CO2e yr⁻¹ over the last decade (2014–2023), as well as reductions in the strength of aerosol cooling. Despite this, there is evidence that the rate of increase in CO2 emissions over the last decade has slowed compared to the 2000s, and depending on societal choices, a continued series of these annual updates over the critical 2020s decade could track decreases or increases in the rate of the climatic changes presented here.

Persistent extreme precipitation events (PEPEs) have dramatic socioeconomic impacts in the Yangtze–Huaihe River basin (YHRB). However, the possible role of the Northeast China cold vortex (NEC-CV) in modulating the PEPEs over the YHRB remains unresolved. In this study, the contribution of NEC-CVs to summer precipitation is first examined over central-eastern China, which is characterized by a local and long-distance effect, along with distinct geographic variability. Limited influence is found for the areas outside a threshold of 4× radius of NEC-CV. The YHRB is one of the regions significantly affected by the NEC-CVs, which accounts for about 35%–40% of the total extreme precipitation. During 1961–2022, about 27.7% of the total PEPEs are found to be closely related to the NEC-CVs. In addition, two types of PEPEs (type W/type E) are identified based on the position of corresponding NEC-CV tracks. Significant impacts are found for the opportune configurations of NEC-CVs. The PEPEs are found to be located more westward/eastward for type W/type E, with the anomalous moisture mainly coming from the western North Pacific/South China Sea. The two PEPEs exhibit the anomalous eastward/westward extension of the South Asian high/western North Pacific subtropical high and anomalous southward shift of the upper-level jet with respect to the climatology. Meanwhile, the lower troposphere is dominated by a large-scale low pressure, strong wind shear, and intense moisture transport in the YHRB. The concurrent combinations of the upstream Ural blocking and the downstream Okhotsk blocking are favorable for the development and southward intrusion of NEC-CVs to the YHRB in type W. However, the counterparts in type E are closely associated with the upstream Baikal blocking. The precursor signals of the NEC-CVs can be detected 12/8 days prior to the peak PEPE occurrence at 500 hPa for type W/type E. Significance Statement Persistent extreme precipitation events (PEPEs) can cause catastrophic flooding. This study demonstrates the role of the Northeast China cold vortex (NEC-CV) in influencing such high-impact weather events in the Yangtze–Huaihe River basin (YHRB). Using the latest reanalysis datasets and neural network technology, we quantitatively conclude that the NEC-CVs have contributed to about 35%–40% of the total extreme precipitation and 27.7% of the total PEPEs in the YHRB over the past 60 years. The relevant PEPEs are dominated by the NEC-CVs, with the opportune configuration of the upper and lower circulation systems. These key findings present a new perspective on the meteorology of the PEPEs with implications for the medium-range weather forecasts.

In a rapidly changing climate, evidence-based decision-making benefits from up-to-date and timely information. Here we compile monitoring datasets (published here https://doi.org/10.5281/zenodo.15327155 Smith et al., 2025a) to produce updated estimates for key indicators of the state of the climate system: net emissions of greenhouse gases and short-lived climate forcers, greenhouse gas concentrations, radiative forcing, the Earth's energy imbalance, surface temperature changes, warming attributed to human activities, the remaining carbon budget, and estimates of global temperature extremes. This year, we additionally include indicators for sea-level rise and land precipitation change. We follow methods as closely as possible to those used in the IPCC Sixth Assessment Report (AR6) Working Group One (WGI) report. The indicators show that human activities are increasing the Earth’s energy imbalance and driving faster sea-level rise compared to the AR6 assessment. For the 2015–2024 decade average, observed warming relative to 1850–1900 was 1.24 [1.11 to 1.35] °C, of which 1.23 [1.0 to 1.5] °C was human-induced. The 2024 observed record in global surface temperature (1.52°C best estimate) is well above the best estimate of human-caused warming (1.36°C). However, the 2024 observed warming can still be regarded as a typical year, considering the human induced warming level and the state of internal variability associated with the phase of El Niño and Atlantic variability. Human-induced warming has been increasing at a rate that is unprecedented in the instrumental record, reaching 0.27 [0.2–0.4] °C per decade over 2015–2024. This high rate of warming is caused by a combination of greenhouse gas emissions being at an all-time high of 53.6 ± 5.2 GtCO2e per year over the last decade (2014–2023), as well as reductions in the strength of aerosol cooling. Despite this, there is evidence that the rate of increase in CO2 emissions over the last decade has slowed compared to the 2000s, and depending on societal choices, a continued series of these annual updates over the critical 2020s decade could track decreases or increases in the rate of the climatic changes presented here.

In this study, we objectively identified rain belts of persistent precipitation processes over the Yangtze River basin during 1961–2021 based on an improved rotating calipers algorithm. Considering the accumulated precipitation volume as the flood-inducing indicator, persistent heavy precipitation events were identified and categorized into three types—along, north, and south of the Yangtze River—by applying k-means clustering for spatial similarity. Results showed that events along and in the south of Yangtze are more persistent and more flood inducing than events in the north of Yangtze. Composite analysis revealed the relevant three-dimensional stable circulation patterns and indicated that the location of their rain belts is determined by circulation configurations. For events along the Yangtze, an eastward-propagating wave train facilitates a single-blocking high and deepens the East Asian trough. A southeastward-positioned South Asian high (SAH) and intensified westerly jet support a strong divergence in the Yangtze River basin at 200 hPa. The western Pacific subtropical high (WPSH) stretches southwestward with a strong low-level jet, inducing warm and humid air to converge with cold air along the Yangtze. For events in the south of the Yangtze, a relatively southeastward wave train maintains under double-blocking highs. The northeast sector of the SAH, the westerly jet, WPSH, and low-level jet are located more to the south. Last, events in the north of the Yangtze are associated with the development of a blocking high and a dominant belt of low pressure to the south. The unfavorable circulation pattern inhibits cold air invasion, resulting in relatively weaker precipitation with shorter duration. Significance Statement Considering the location, spatial coverage, and intensity of persistent precipitation processes in the Yangtze River basin, this study objectively classified rain belts of persistent heavy precipitation (PHP) events, investigated the corresponding stable circulation patterns, and constructed three-dimensional conceptual models for three types of PHP events. This study may help to better understand the formation mechanisms of PHP events and serve as a reference for improving the forecasting of such events operationally.

The integration of weather and climate prediction represents the current frontier in the development of numerical modeling in China. Dynamic downscaling serves as a pivotal approach, improving the performance and resolution of global climate models to the weather scale. Focusing on the ‘23.7’ extreme rainstorm (July 29, 00:00–August 2, 00:00 UTC) in the Beijing‐Tianjin‐Hebei region, this study assesses predictions from the China Meteorological Administration Climate Prediction System version 3 (CMA‐CPSv3, 45 km resolution) and 9‐km dynamic downscaling hindcasts from the Weather Research and Forecasting model (WRF‐9 km). In contrast to the conventional climate anomaly approaches, direct outputs are used for evaluation, similar to weather forecasting tests. By examining, both the CMA‐CPSv3 predictions and the WRF‐9 km hindcasts provide a 5‐day prediction window for this rainstorm. They successfully predict the rainstorms and related atmospheric circulations from July 24th onward, aligning with observed and reanalyzed data. WRF‐9 km, with the higher resolution and optimised physical processes, outperforms CMA‐CPSv3, especially in precipitation spatial distribution and center intensity. The WRF‐9 km 7/24 hindcast demonstrates the most significant enhancement compared to the corresponding CMA‐CPSv3 prediction. This improvement is notably reflected in the substantial increase in spatial correlation, from 0.68 to 0.79, as well as a reduction in the difference of center values, decreasing from −51% to −20%. Furthermore, the WRF‐9 km 7/24 hindcast improves the Critical Success Index by 0.08, the Success Rate by 0.08, and the Probability of Detection by 0.29 for heavy rainfall (over 25.0 mm/d). However, improvements in large‐scale circulations with WRF‐9 km are limited, which may restrict advancements in predictability. In conclusion, the WRF‐9 km enhances the performance and resolution of CMA‐CPSv3 predictions, which can be regarded as a viable pathway for CMA‐CPSv3 to achieve weather‐climate integration.

Recovery time is critical for accurate assessment of drought impacts on vegetation growth and terrestrial carbon dynamics. However, the dominant factors driving the spatiotemporal variation of recovery time are still poorly understood; hardly any research has focused on the comparison of recovery time between general drought and compound dry-hot events. This study examined recovery time of vegetation greenness post different drought types during 1982–2016 and attempted to identify the predominant factors determining vegetation recovery time over the globe. Our findings demonstrated protracted recovery of vegetation greenness after compound drought and hot extreme (CDHE) event compared to general drought in 68% of global vegetated area. Deciduous broadleaved forest exhibited the most remarkable difference between recovery time post CDHE (13.8 ± 5.6 months) and post general drought (9.3 ± 4.7 months). We also revealed that post-event moisture condition and long-term precipitation were the chief impact factors of drought recovery time.

Plain Language Summary Southern China is a typical hotspot of heatwaves. In the recent decade of 2013–2022, the southern China experienced a marked transition from dry heatwaves to humid ones, with the occurrence frequency of humid heatwaves becoming more than 4 times that of dry counterpart. As the humid heatwaves usually lasting for 3–5 days are more directly associated with the intraseasonal (10–90‐day) variability, we have identified significant 10–30‐day intraseasonal oscillation (ISO) in temperature and humidity in southern China, and found their critical role in inducing the lethal humid heatwaves. This finding provides the scientific clues for extending the forecast lead time of humid heatwaves. The circulation configuration of the 10–30‐day atmospheric ISOs at mid–high latitudes and tropics leads to the concurrence of strong moisture convergence and anomalous descents over southern China. The increased downward longwave radiation in association with moisture enhancement, shortwave radiation and adiabatic heating in association with descents bring about the persisting hot and wet conditions in humid heatwaves. As more barotropic energy are transferred from mean flow to 10–30‐day circulation at mid–high latitudes, and tropical 10–30‐day convection activities get stronger, the occurrence of 10–30‐day circulation configuration induced humid heatwaves have increased from 39% in the period of 2003–2012 to 52.3% in the period of 2013–2022. Therefore, humid heatwaves become the predominant type.

The Tibetan Plateau (TP) has experienced accelerated warming in recent decades, especially in winter. However, a comprehensive quantitative study of its long-term warming processes during daytime and nighttime is lacking. This study quantifies the different processes driving the acceleration of winter daytime and nighttime warming over the TP during 1961–2022 using surface energy budget analysis. The results show that the surface warming over the TP is mainly controlled by two processes: (a) a decrease in snow cover leading to a decrease in albedo and an increase in net downward shortwave radiation (snow-albedo feedback), and (b) a warming in tropospheric temperature (850 − 200 hPa) leading to an increase in downward longwave radiation (air warming-longwave radiation effect). The latter has a greater impact on the spatial distribution of warming than the former, and both factors jointly influence the elevation dependent warming pattern. Snow-albedo feedback is the primary factor in daytime warming over the monsoon region, contributing to about 59% of the simulated warming trend. In contrast, nighttime warming over the monsoon region and daytime/nighttime warming in the westerly region are primarily caused by the air warming-longwave radiation effect, contributing up to 67% of the simulated warming trend. The trend in the near-surface temperature mirrors that of the surface temperature, and the same process can explain changes in both. However, there are some differences: an increase in sensible heat flux is driven by a rise in the ground-atmosphere temperature difference. The increase in latent heat flux is associated with enhanced evaporation due to increased soil temperature and is also controlled by soil moisture. Both of these processes regulate the temperature difference between ground and near-surface atmosphere.

Annex of the special report of climate change and land by IPCC, note that Mr. ALI GEATH ELJADID is not an Author of the Report, but he is one of the EXprt Reviewers of the Report.