Changes In Large-scale Circulation Research Articles

Recent wetting trend over Taklamakan and Gobi Desert dominated by internal variability

The Taklamakan and Gobi Desert (TGD) region has experienced a pronounced increase in summer precipitation, including high-impact extreme events, over recent decades. Despite identifying large-scale circulation changes as a key driver of the wetting trend, understanding the relative contributions of internal variability and external forcings remains limited. Here, we approach this problem by using a hierarchy of numerical simulations, complemented by diverse statistical analysis tools. Our results offer strong evidence that the atmospheric internal variations primarily drive this observed trend. Specifically, recent changes in the North Atlantic Oscillation have redirected the storm track, leading to increased extratropical storms entering TGD and subsequently more precipitation. A clustering analysis further demonstrates that these linkages predominantly operate at the synoptic scale, with larger contributions from large precipitation events. Our analysis highlights the crucial role of internal variability, in addition to anthropogenic forcing, when seeking a comprehensive understanding of future precipitation trends in TGD.

Modeling the timing of Patagonian Ice Sheet retreat in the Chilean Lake District from 22–10 ka

Abstract. Studying the retreat of the Patagonian Ice Sheet (PIS) during the last deglaciation represents an important opportunity to understand how ice sheets outside the polar regions have responded to deglacial changes in temperature and large-scale atmospheric circulation. At the northernmost extension of the PIS during the Last Glacial Maximum (LGM), the Chilean Lake District (CLD) was influenced by the southern westerly winds (SWW), which strongly modulated the hydrologic and heat budgets of the region. Despite progress in constraining the nature and timing of deglacial ice retreat across this area, considerable uncertainty in the glacial history still exists due to a lack of geologic constraints on past ice margin change. Where the glacial chronology is lacking, ice sheet models can provide important insight into our understanding of the characteristics and drivers of deglacial ice retreat. Here we apply the Ice Sheet and Sea-level System Model (ISSM) to simulate the LGM and last deglacial ice history of the PIS across the CLD at high spatial resolution (450 m). We present a transient simulation of ice margin change across the last deglaciation using climate inputs from the National Center for Atmospheric Research Community Climate System Model (CCSM3) Trace-21ka experiment. At the LGM, the simulated ice extent across the CLD agrees well with the most comprehensive reconstruction of PIS ice history (PATICE). Coincident with deglacial warming, ice retreat ensues after 19 ka, with large-scale ice retreat occurring across the CLD between 18 and 16.5 ka. By 17 ka, the northern portion of the CLD becomes ice free, and by 15 ka, ice only persists at high elevations as mountain glaciers and small ice caps. Our simulated ice history agrees well with PATICE for early deglacial ice retreat but diverges at and after 15 ka, where the geologic reconstruction suggests the persistence of an ice cap across the southern CLD until 10 ka. However, given the high uncertainty in the geologic reconstruction of the PIS across the CLD during the later deglaciation, this work emphasizes a need for improved geologic constraints on past ice margin change. While deglacial warming drove the ice retreat across this region, sensitivity tests reveal that modest variations in wintertime precipitation (∼10 %) can modulate the pacing of ice retreat by up to 2 ka, which has implications when comparing simulated outputs of ice margin change to geologic reconstructions. While we find that TraCE-21ka simulates large-scale changes in the SWW across the CLD that are consistent with regional paleoclimate reconstructions, the magnitude of the simulated precipitation changes is smaller than what is found in proxy records. From our sensitivity analysis, we can deduce that larger anomalies in precipitation, as found in paleoclimate proxies, may have had a large impact on modulating the magnitude and timing of deglacial ice retreat. This fact highlights an additional need for better constraints on the deglacial change in strength, position, and extent of the SWW as it relates to understanding the drivers of deglacial PIS behavior.

Effects of idealized land cover and land management changes on the atmospheric water cycle

Abstract. Land cover and land management changes (LCLMCs) play an important role in achieving low-end warming scenarios through land-based mitigation. However, their effects on moisture fluxes and recycling remain uncertain, although they have important implications for the future viability of such strategies. Here, we analyse the impact of idealized LCLMC scenarios on atmospheric moisture transport in three different Earth system model (ESMs): the Community Earth System Model (CESM), the Max Planck Institute Earth System Model (MPI-ESM), and the European Consortium Earth System Model (EC-EARTH). The LCLMC scenarios comprise of a full cropland world, a fully afforested world, and a cropland world with unlimited irrigation expansion. The effects of these LCLMC in the different ESMs are analysed for precipitation, evaporation, and vertically integrated moisture flux convergence to understand the LCLMC-induced changes in the atmospheric moisture cycle. Then, a moisture tracking algorithm is applied to assess the effects of LCLMC on moisture recycling at the local (grid cell level) and the global scale (continental moisture recycling). By applying a moisture tracking algorithm on fully coupled ESM simulations we are able to quantify the complete effects of LCLMC on moisture recycling (including circulation changes), which are generally not considered in moisture recycling studies. Our results indicate that cropland expansion is generally causing a drying and reduced local moisture recycling, while afforestation and irrigation expansion generally cause wetting and increased local moisture recycling. However, the strength of this effect varies across ESMs and shows a large dependency on the dominant driver. Some ESMs show a dominance of large-scale atmospheric circulation changes while other ESMs show a dominance of local to regional changes in the atmospheric water cycle only within the vicinity of the LCLMC. Overall, these results corroborate that LCLMC can induce substantial effects on the atmospheric water cycle and moisture recycling, both through local effects and changes in atmospheric circulation. However, more research is needed to constrain the uncertainty of these effects within ESMs to better inform future land-based mitigation strategies.

Two distinct declining trend of autumn Arctic sea ice concentration before and after 2002

This study investigates the Arctic sea ice concentration trend during 1979–2021 and explores why the autumn Arctic sea ice loss is accelerated after 2002 and its trend declining center shifts from the Chukchi Sea to the Barents-Kara-Laptev Seas. Attribution analysis reveals that the enhanced summer sea ice concentration negative trend in large part explains the autumn sea ice concentration accelerating reduction, whereas it is the trend center shift of increased downward longwave radiation that accounts for mostly of the autumn sea ice concentration decline center shift. Further analysis suggests the downward longwave radiation trend is closely related to large-scale atmospheric circulation changes. A tendency towards a dipole structure with an anticyclonic circulation over Greenland and the Arctic Ocean and a cyclonic circulation over Barents-Kara Seas enhances (suppresses) the downward longwave radiation over Western (Eastern) Arctic by warming and moistening (cooling and drying) the lower troposphere during 1979–2001. In comparison, a tendency towards a stronger Ural anticyclone combined with positive phase of the North Atlantic Oscillation pattern significantly promotes the increase of downward longwave radiation over Barents-Kara-Laptev Seas during 2002–2021. Our results set new insights into the Arctic sea ice variability and deepen our understanding of the climate change.

Projected Changes in the Onset of the Summer Monsoon over the South Asian Marginal Seas Modulated by Intraseasonal Oscillation

Abstract The onset of the summer monsoon associated with global warming is of great concern to the scientific community. While observational data diagnosis has shown the impact of intraseasonal oscillation (ISO) on the monsoon onset, how the ISO may affect the onset of monsoon under global warming remains unknown. Here, by analyzing the onset of the summer monsoon over the South Asian marginal seas projected by models in phase 6 of the Coupled Model Intercomparison Project (CMIP6) under the SSP5–8.5 scenario, we show evidence that the majority of models (>70%) project an earlier onset over the Arabian Sea (ArS) but a delayed onset over the Bay of Bengal (BoB) and the South China Sea (SCS). The temporal shifts of the monsoon onset are attributed to the changes in the premonsoon northward migration of equatorial ISO (NMISO), which is a trigger of monsoon onset and will be advanced (postponed) over the ArS (BoB and SCS). The subtropical upper-level westerly anomaly, inducing delayed occurrence of easterly shear, acts to delay the NMISO over the entire Indian Ocean. However, the intensified low-level southerly wind over the ArS, as well as its induced asymmetric pattern of boundary layer moisture work together to advance the premonsoon NMISO in the area, outweighing the delayed impact from vertical shear. These large-scale circulation changes are driven by tropical warming in the upper troposphere, land warming over the Arabian Peninsula, and ocean warming over the eastern Pacific. This analysis enriches monsoon onset projections by highlighting the role of ISO in influencing the future changes in monsoon onset.

Large-scale photovoltaic solar farms in the Sahara affect solar power generation potential globally

Globally, solar projects are being rapidly built or planned, particularly in high solar potential regions with high energy demand. However, their energy generation potential is highly related to the weather condition. Here we use state-of-the-art Earth system model simulations to investigate how large photovoltaic solar farms in the Sahara Desert could impact the global cloud cover and solar generation potential through disturbed atmospheric teleconnections. The results indicate negative impacts on solar potential in North Africa (locally), Middle East, Southern Europe, India, Eastern China, Japan, Eastern Australia, and Southwestern US, and positive impacts in Central and South America, the Caribbean, Central & Eastern US, Scandinavia and South Africa, reaching a magnitude of ±5% in remote regions seasonally. Diagnostics suggest that large-scale atmospheric circulation changes are responsible for the global impacts. International cooperation is essential to mitigate the potential risks of future large-scale solar projects in drylands, which could impact energy production.

Recent European drying and its link to prevailing large-scale atmospheric patterns

The extreme 2018 and 2022 droughts pose as recent examples of a series of drought events that have hit Europe over the last decades with wide ranging social, environmental and economic impacts. Although the link between atmospheric circulation and meteorological drought is clear and often highlighted during major drought events, there is a lack of in-depth studies linking historical changes in meteorological drought indices and prevailing large-scale atmospheric patterns in Europe. To meet this shortfall, we investigated the relation between changes in large-scale atmospheric patterns and meteorological drought, as indicated by the geopotential height at 500mb (Z500) and the Standardised Precipitation-Evapotranspiration Index (SPEI), respectively. Calculations were done separately for four climate regions (North, West, Central-East and Mediterranean) over the growing season (March–September). Coherent patterns of significant changes towards higher pressure (increasing Z500) and drier conditions (decreasing SPEI) over 1979–2021 are found over West in spring and Central-East in summer. Z500 and SPEI are strongly linked, reflected by both significant (1979–2021) correlations and high co-occurrences (69-96%) between meteorological drought and high-pressure anomaly occurrences since 1900. North shows the most heterogeneous trend patterns and weakest links, but constitutes a hotspot of significantly increasing Z500 in September. Finally, we performed an ensemble-based, European wide analysis of future Z500, based on CMIP6 low-end (SSP126) and high-end (SSP585) 21st century emission scenarios. According to the projected changes, anomalously high-pressure systems will be the new normal regardless of scenario, and well exceeding the 2018 and 2022 levels in the case of the high-end emission scenario. However, due to the limitations of the model ensemble to represent the spatial heterogeneity in historical Z500 variability and trends (1979–2014), projected changes in large-scale circulation, and associated meteorological droughts, are highly uncertain. This paper provides new insight into significant trends in atmospheric circulation over Europe, their strong links to the observed drying trends, and the inability of a CMIP6 ensemble to reproduce the spatial heterogeneity of the circulation changes.

Projections of winter polynyas and their biophysical impacts in the Ross Sea Antarctica

This study investigates winter polynyas in the southern Ross Sea, Antarctica where several polynyas are known to form. Coastal polynyas are areas of lower sea ice concentration and/or thickness along the coast that are otherwise surrounded by more extensive, thicker sea ice pack. Polynyas are also locations where organisms can exploit both the ice substrate and pelagic resources. Using a self organizing map algorithm, we identify polynya events in the Community Earth System Model Version 2 Large Ensemble (CESM2-LE). The neural network algorithm is able to identify polynya events without imposing an ice concentration or thickness threshold, as is often done when identifying polynyas. The CESM2-LE produces a wintertime polynya feature comparable in size and location to the Ross Sea polynya, and during polynya events there are large turbulent heat fluxes and export of sea ice from the Ross Sea. In the CESM2-LE polynya event frequency is projected to decrease sharply in the later twentyfirst century, leading to increasing sea ice concentrations and thicknesses in the region. The drivers of the polynya frequency decline are likely both large scale circulation changes and local atmosphere and ocean feedbacks. If declines in wintertime polynya frequency over the twentyfirst century do occur they may impact Antarctic Bottom Water formation and local net primary productivity. Thus, better understanding potential local and unexpected sea ice changes in the Ross Sea is important for both assessing climate system impacts and ecological impacts on the Ross Sea ecosystem, which is currently protected by an internationally recognized marine protected area.

Hymenaea stignocarpa Mart. ex Hayne growth–climate relationships are regulated by soil water saturation in Cerrado-Pantanal ecotone

The expected intensification of the dry season, and concentration of rainfall during the wet season, can disrupt tree growth and regional biodiversity in the Cerrado-Pantanal transition zone. Thus, this study aims to assess the climatic responses of Hymenaea stigonocarpa tree growth, a common tree species in this region. Incremental cores were collected at breast height (ca. 1.3 m) from 67 trees to construct a dendrochronological series to correlate annual growth with local meteorological variables and large-scale atmospheric circulation indices from the Pacific and Atlantic Oceans. Significant positive correlations were observed between tree growth and the Pacific Ocean indices. Maximum and average air temperatures of the previous dry season negatively influenced growth, while precipitation at the beginning of the growth season (November) positively influenced growth. Tree growth was not correlated with temperature or rainfall during the wet season. However, at the end of the wet season (February), tree growth was negatively correlated with air temperature and positively correlated with rainfall, but the relationship shifted in the next month (March) suggesting that soil water saturation reduced growth. Our results indicate that dendrochronological studies of H. stignocarpa are useful for assessing the environmental change on the Cerrado-Pantanal ecotone. Furthermore, variations in water availability and temperature associated with changes in large-scale oceanic circulation and local meteorological conditions will impact the growth dynamics of this important Cerrado tree species.

Source attribution of near-surface ozone trends in the United States during 1995–2019

Abstract. Emissions of ozone (O3) precursors in the United States have decreased in recent decades, and near-surface O3 concentrations showed a significant decrease in summer but an increase in winter. In this study, an O3 source tagging technique is utilized in a chemistry–climate model to investigate the source contributions to O3 mixing ratios in the US from various emitting sectors and regions of nitrogen oxides (NOx) and reactive carbon species during 1995–2019. We show that domestic emission reductions from energy and surface transportation are primarily responsible for the decrease in summertime O3 during 1995–2019. However, in winter, the emission control also weakens the NOx titration process, resulting in considerable increases in O3 levels from natural sources. Additionally, increases in aviation and shipping emissions and transpacific transport of O3 from Asia largely contribute to the winter O3 increase. We also found that changes in large-scale circulation favoring O3 transport from the upper atmosphere and foreign transport from Asia also explain 15 % of the increase in the US near-surface O3 levels in winter.

The contribution of large-scale atmospheric circulation to variations of observed near-surface wind speed across Sweden since 1926

This study investigates the centennial-scale (i.e., since 1926) variability of observed near-surface wind speed across Sweden. Results show that wind speed underwent various phases of change during 1926–2019, i.e., (a) a clear slowdown during 1926–1960; (b) a stabilization from 1960 to 1990; (c) another clear slowdown during 1990–2003; (d) a slight recovery/stabilization period for 2003–2014, which may continue with a possible new slowdown. Furthermore, the performance of three reanalysis products in representing past wind variations is evaluated. The observed low-frequency variability is properly simulated by the selected reanalyses and is linked to the variations of different large-scale atmospheric circulation patterns (e.g., the North Atlantic Oscillation). However, the evident periods of decreasing trend during 1926–1960 and 1990–2003, which drive most of the stilling in the last century, are missing in the reanalyses and cannot be realistically modeled through multiple linear regression by only using indexes of atmospheric circulation. Therefore, this study reveals that changes in large-scale atmospheric circulation mainly drive the low-frequency variability of observed near-surface wind speed, while other factors (e.g., changes in surface roughness) are crucial for explaining the periods of strong terrestrial stilling across Sweden.

Changes in Summer Precipitation Modes over Eastern China in Simulated Warm Intervals of the Last Interglacial, Mid-Holocene, and Twenty-First Century

Abstract The East Asian summer monsoon (EASM) and associated summer precipitation patterns over eastern China have exhibited interannual and interdecadal variations in recent decades, but whether the precipitation modes vary with climate conditions remains unclear. In this study, we investigate the changes in summer precipitation modes over eastern China and associated mechanisms in simulated past and future warm periods, namely, the last interglacial (LIG), mid-Holocene, and the twenty-first century under the Shared Socioeconomic Pathway (SSP) based on representative concentration pathway 8.5 (SSP5–8.5) scenario, using Coupled Model Intercomparison Project Phase 6 (CMIP6) models. The model evaluation indicates that only one out of nine CMIP6 models, specifically the Community Earth System Model, version 2 (CESM2), can well reproduce the observed summer precipitation modes at the present. The empirical orthogonal function (EOF) analyses of the CESM2 simulations reveal that during the warm periods induced by either orbital parameters or greenhouse gas concentrations, the first leading mode of summer precipitation switches from its present meridional tripolar structure to a dipole pattern, and the second leading mode is generally a meridional tripolar mode that differs from the present dipole pattern. This summer precipitation regime interchange in the warm intervals is associated with the formation of the dipole and tripolar circulation patterns. The large-scale circulation changes responsible for the altered precipitation modes are attributed to the enhanced EASM and relevant southerly winds due to intensified land–sea thermal contrast, although the external forcings and the magnitude of EASM enhancement are different in the interglacial and future periods.

Modulation of daily PM2.5 concentrations over China in winter by large-scale circulation and climate change

Abstract. We use the United Kingdom Earth System Model, UKESM1, to investigate the influence of the winter large-scale circulation on daily concentrations of PM2.5 (particulate matter with an aerodynamic diameter of 2.5 µm or less) and their sensitivity to emissions over major populated regions of China over the period 1999–2019. We focus on the Yangtze River delta (YRD), where weak flow of cold, dry air from the north and weak inflow of maritime air are particularly conducive to air pollution. These provide favourable conditions for the accumulation of local pollution but limit the transport of air pollutants into the region from the north. Based on the dominant large-scale circulation, we construct a new index using the north–south pressure gradient and apply it to characterise PM2.5 concentrations over the region. We show that this index can effectively distinguish different levels of pollution over YRD and explain changes in PM2.5 sensitivity to emissions from local and surrounding regions. We then project future changes in PM2.5 concentrations using this index and find an increase in PM2.5 concentrations over the region due to climate change that is likely to partially offset the effect of emission control measures in the near-term future. To benefit from future emission reductions, more stringent emission controls are required to offset the effects of climate change.

Long-term variations of cloud top patterns associated with heavy rainfall over the Korean peninsula

Study regionKorean peninsula Study focusAlthough heavy rainfall systems over Korea were known to be characterized by warm-type heavy rainfall associated with a relatively low cloud top, this feature can vary under climate change. This study primarily investigated the mean climatology and linear trends of heavy rainfall and cloud top distributions over the Korean peninsula. The rainy seasons from June to September for the period of 1983–2021 were analyzed in this study. To understand the climatology and changes of heavy rainfall events, thermodynamic variables and synoptic forcings were analyzed. New hydrological insights for the regionLong-term consistent geostationary satellite data provides a unique opportunity to understand the global cloud variations associated with climate change. This study examined the mean climatology and decadal trends of cloud tops inferred from geostationary satellite observations, along with heavy rainfall events over the Korean Peninsula. Rainfall and cloud top heights exhibited a decreasing trend in June, whereas an increase in vigorous deep convection was observed in August/September, mainly in southern Korea. The decadal trends in August and September were associated with large-scale circulation changes, while the trend in September was attributed to increasing typhoon visits over the Korean Peninsula. The cloud top changes, with lowered cloud tops in June and elevated cloud tops in August, suggested a shift of deep convective systems toward the late summer over Korea.

Assessing the Future wind Energy Potential in Portugal Using a CMIP6 Model Ensemble and WRF High-Resolution Simulations

Future wind energy potential over Portugal is assessed, using wind speed data from a WRF regional simulation under the SSP5-8.5 scenario for 2046–2065 and 2081–2100. Data from a CMIP6 multi-model ensemble were also used to assess future changes in the Euro-Atlantic large-scale circulation. CMIP6 results have shown a southward displacement of the mid-latitude jet stream during winter, and a northward displacement during spring, summer, and autumn, which causes the northern winds to strengthen during summer along the north-western Iberian coast. Furthermore, in 2046–2065 the wind power density (WPD) should increase between 25% and 50% off the northwest coast of Portugal and in the Serra da Estrela mountain range during summer, which is in agreement with the CMIP6 global ensemble projections. Analyses of WPD’s 2046–2065 daily variability of offshore north-western Portugal reveal a variability increase during winter, spring and summer, as well as more intense extreme WPD events, and less intense extreme events during autumn. The WPD’s 2046–2065 inter-annual variability should increase off the northwest coast, and decrease along the central western and southern coasts, whereas it should increase in the entire studied area in 2081–2100, apart from the northern mountain regions and Cape Raso.

Modern-like deep water circulation in Indian Ocean caused by Central American Seaway closure

Global overturning circulation underwent significant changes in the late Miocene, driven by tectonic forcing, and impacted the global climate. Prevailing hypotheses related to the late Miocene deep water circulation (DWC) changes driven by the closure of the Central American Seaways (CAS) and its widespread impact remains untested due to the paucity of suitable records away from the CAS region. Here, we test the hypothesis of the large-scale circulation changes by providing a high-resolution record of DWC since the late Miocene (11.3 to ~2 Ma) from the north-western Indian Ocean. Our investigation reveals a progressive shift from Pacific-dominated DWC before ~9.0 Ma to the onset of a modern-like DWC system in the Indian Ocean comprising of Antarctic bottom water and northern component water during the Miocene-Pliocene transition (~6 Ma) caused by progressive shoaling of the CAS and suggests its widespread impact.

What caused the interdecadal shift in the El Niño–Southern Oscillation (ENSO) impact on dust mass concentration over northwestern South Asia?

Abstract. Changes in large-scale circulation, especially El Niño–Southern Oscillation (ENSO), have significant impacts on dust activities over the dust source and downwind regions. However, these impacts present an interdecadal pattern, and it remains less clear which factors lead to the interdecadal variability of the ENSO impact on dust activities over northwestern South Asia, although previous studies have discussed the response of interannual dust activities over northwestern South Asia to the ENSO circle. Based on the linear regression model and MERRA-2 atmospheric aerosol reanalysis data, this study investigated the interdecadal variability of the ENSO impact on dust activities as well as the associated possible atmospheric drivers under two different warming phases over northwestern South Asia. Results indicated that the relationship between ENSO and dust column mass density (DUCMASS) experienced an obvious shift from the accelerated global warming period (1982–1996) to the warming hiatus period (2000–2014). The change in Atlantic and Indian Ocean sea surface temperature anomaly (SSTA) patterns weakened the impact of ENSO on dust activities over northwestern South Asia during 1982–1996, while the change in Pacific Decadal Oscillation (PDO) strengthened ENSO's effect when it was in phase with ENSO. Both the Atlantic and Indian Ocean SSTA patterns were modulated by the duration of ENSO events (i.e., continuing and emerging ENSO). This study provides new insights into numerical simulation involving the influence of atmospheric teleconnections on the variability of dust activities and their influence mechanisms.

Amplification of non-stationary drought to heatwave duration and intensity in eastern China: Spatiotemporal pattern and causes

Amplifying the frequency and loss of weather and hydrological extremes under climate warming have aroused increasing human concerns in recent decades and it is particularly the case for compound drought-heatwave (CDH) events. The drought index based on the hypothesis of non-stationarity is of great significance for the study of CDH events. Here we presented spatiotemporal patterns of CDH, general heatwaves (GHW, he heatwave that does not occur in dry months) and relevant circulation backgrounds in eastern China. We found that heatwaves are starting earlier and ending later and later. While, the termination date of heatwaves in southern China is late than those in northern China. Significant increases since the 1980 s were detected in the frequency, duration, and intensity of heatwaves and the frequency of CDH events in eastern China. Besides, heatwaves were observed mainly in the middle and lower Yangtze River basin and in the Sichuan Basin as well. Most areas of eastern China were dominated by higher occurrence probability of CDHs in July and the probability was as high as 0.49. The duration and intensity of the CDHs were 0.28 days longer and 11.14℃ higher than GHWs. Further examinations show that the western Pacific subtropical high (WPSH) has a significant influence on the occurrence of heatwaves. The average position of the WPSH is shifted westward and its intensity is relatively stronger, thus favoring the occurrence of heatwave events. The occurrence of compound events in eastern China cannot be separated from the influence of large-scale circulation and atmospheric changes.

Projected changes and uncertainty in cold surges over northern China using the CMIP6 weighted multi-model ensemble

Cold surge (CS) events are the most serious extreme cold events in winter in China, causing large economic losses and casualties. The occurrence of CS events has slightly increased since the 1990s. However, the possible future changes in these events remain unclear, and quantifying robust projected changes in CS events is important for developing adaptation and policy planning. Here, we project the occurrence of CS events and strong CS (SCS) events using the weighted multi-model ensemble (MME) of the Coupled Model Intercomparison Project 6 (CMIP6) through the application of the rank-based weighting (RBW) approach under three shared socioeconomic pathway (SSP126, SSP245, and SSP585) scenarios. The corresponding weights of each model were obtained depending on the comprehensive historical performance from three aspects: climatology, spatial variation, and interannual variability. The results show that the RBW approach can reduce the relative bias by approximately 50% compared to the unweighted MME. The occurrence of CS and SCS events shows a decreasing trend during 2015–2099 over northern China under the three SSP scenarios. There are also robust change projections during the long-term (2080–2099) and 2015–2099 periods under SSP245 and SSP585, especially in the NEC region, which exhibits a signal-to-noise ratio (SNR) that is >1. However, the occurrence of SCS events shows slight increases of 1.18% and 3.55% over northern China (notably western and eastern Northwest China) during the near-term (2020–2039) under SSP126 and SSP245, respectively. Obvious reductions in projected uncertainty are widespread throughout northern China after applying the RBW approach compared to the unweighted MME, which mainly depends on the scenario, region, and term variation. Then, a robust decreased frequency may contribute to projected changes in large-scale atmospheric circulation (a more positive AO and weaker SH and EAT) under SSP585. Our results emphasize that the weighted MME can be taken into account when projecting future extreme climate change in some areas to enhance reliability.

Trend Changes of the Vegetation Activity in Northeastern East Asia and the Connections with Extreme Climate Indices

In the context of global warming, vegetation activity in northeastern East Asia (40–45°N, 105–130°E) (NEA) shows a significant growth trend on a multidecadal scale, but how vegetation changes on a decadal scale is unclear. In this study, we find a significant trend of vegetation greening in northeastern East Asia during 1982–1998 and a slowdown in the greening trend during 1998–2014. Trend analysis of the extreme climate indices reveals that the trends of precipitation-related extreme climate indices are similar to those of vegetation change, and further correlation analysis reveals that precipitation-related extreme climate indices have a strong positive correlation with the NDVI. The results indicate that the vegetation in northeastern East Asia is more sensitive to precipitation changes, especially extreme precipitation, compared with the temperature and related extreme indices. Furthermore, the analysis of large-scale atmospheric circulation changes suggests a role of Northwest Pacific subtropical high (NPSH) in the trend changes of precipitation-related extreme indices. The strengthening of NPSH before 1998 enhances the moisture transport to the NEA, providing abundant water vapor favorable for extreme precipitation events, while after 1998, the NPSH trend is much weakened, corresponding to a decrease in the moisture transport trend.