Extreme rainfall (ER) produced by convective storms moving from mountains to plain areas in North China has long been a great challenge in short-term forecasting, since the production of rainfall is closely related to the fine structure of convection. This type of ER event struck northern Beijing on 26 July 2025, causing widespread community concern. Based on multi-source observations and convection-permitting simulation, this study attempts to reveal the thermodynamic and microphysical structures in the meso-β-scale convection system (MCS-k) that produced the ER. Observational facts show that the weakening of cold outflow together with the southeast wind in the warm sector hindered the movement of the MCS-k after travelling downhill, and the more abundant water vapor and stronger convective instability in plain areas led to its back-building development. The content of liquid water significantly increased, and more large raindrops were produced by coalescence, indicating more intense warm-rain processes. Simulation experiments show that direct contribution of the warm-rain processes dominated the production of ER, since they provided 77.8
Wildfire danger in Southern California is strongly influenced by episodic offshore wind events and extreme atmospheric dryness, conditions that are not fully captured by the standard Canadian Fire Weather Index (CFWI), which was developed for boreal forest environments using noon-based meteorological inputs and has been widely applied by various climatic and ecological regimes. This study presents a regionally calibrated adaptation of the CFWI to improve representation of wind-driven fire danger in San Diego County’s chaparral-dominated landscapes. Using high-resolution observation-based meteorological data, the CFWI was recalibrated by replacing noon observations with daily maximum temperature and wind speed, and daily minimum relative humidity, applying a region-specific day-length factor, and introducing conditional modifiers based on wind direction and humidity thresholds. Evaluation over the 2000–09 period, including extreme fire years such as 2003 and 2007, shows that the recalibrated CFWI substantially improves the ability to distinguish large wildfire days, particularly during peak Santa Ana wind seasons. A conditional Initial Spread Index adjustment based on easterly (negative zonal) winds and low relative humidity improves model performance, particularly during autumn and winter. Results also highlight strong seasonal and spatial variability, supporting a seasonally adaptive calibration strategy. This work demonstrates that physically motivated regional recalibration improves the use of the CFWI to wind-dominated fire regimes, providing a more reliable tool for operational fire danger assessment and wildfire preparedness in locations prone to extreme wind-driven wildfires.
Achieving net-zero emissions is critical for the 2°C-target set forth by the Paris Agreement. This paper presents a dataset under a sector-specific combined scenario (SSP2-com), which integrates recent national climate commitments, including China’s carbon neutrality pledge. The simulation, performed with the Chinese Academy of Sciences Flexible Global Ocean–Atmosphere–Land System Model, finite-volume version 3 (CAS-FGOALS-f3-L) model, covers 2015–2100 and provides 52 variables at monthly, daily, and sub-daily resolutions, all interpolated onto a 1° × 1° grid. A preliminary analysis shows that under the SSP2-com scenario, global mean surface air temperature is projected to peak around midcentury, stabilizing at 2.02°C above pre-industrial levels by the end of this century, a 0.81°C reduction relative to SSP2-4.5 (2.83°C). Regional precipitation patterns show significant variability, with increases found mainly in the Intertropical Convergence Zone. Projected changes in the annual maximum temperature are more spatially homogeneous and of lesser magnitude than mean warming, whereas increases in extreme precipitation are widespread but exhibit fine-scale heterogeneity. Overall, under the SSP2-com scenario, the top-of-atmosphere net radiation and Atlantic Meridional Overturning Circulation are stronger than those under the SSP1-2.6 scenario but weaker than those under the SSP2-4.5 scenario, for both 2061–80 and 2081–2100. However, the evolution of the East Asian summer monsoon under the SSP2-com scenario shows little difference from that under the SSP1-2.6 and SSP2-4.5 scenarios. This dataset facilitates an understanding of the fundamental characteristics of future climate change under this scenario and thus serves as a reference for formulating near-term climate policies.
Previous studies have shown that both the instantaneous radiative forcing (IRF) and effective radiative forcing (ERF) of CO2 become larger in warmer climates. However, the increase in ERF is much smaller than that in IRF, indicating that atmospheric adjustments partially compensate for the initial IRF enhancement. This paper aims to quantify the processes responsible for this compensation. Using the Community Earth System Model version 1.2, we consistently evaluate how the IRF, stratosphere-adjusted radiative forcing (SARF), and ERF respond when the climate changes from the piControl state to the abrupt-4×CO2 state. By employing a radiative transfer model, we show that the IRF4×CO2 increases by 2.28 W m−2 (42
Understanding the variability of spring rainfall in South China (SCSR) is important for local agriculture and daily life. While the preceding boreal winter El Niño–Southem Oscillation (ENSO) and Southern Hemisphere Annular Mode (SAM) are recognized to influence subsequent SCSR, their potential combined effect remains unclear. This study indicates that the co-occurrence of El Niño and negative SAM (SAMN) exerts a combined effect on SCSR, with larger anomalies than those associated with single El Niño or SAMN events. To investigate the underlying mechanism, differences in sea surface temperature anomalies (SSTAs) between joint and single factor events are analyzed, given that SSTAs may serve as a bridge linking the cross-seasonal influence of both pre-winter ENSO and SAM on SCSR. Specifically, the Southern Ocean Dipole (SOD)—an inverse SSTA pattern between around 37.5°S and 60°S—appears to play a role in the cross-seasonal influence of SAM on SCSR. Diagnostic analysis suggests that the SAMN signal stored in the negative phase of SOD may influence meridional circulation, which in turn induces westerly wind anomalies that affect tropical central-eastern Pacific surface wind. Therefore, during joint El Niño SAMN events, the tropical central-eastern Pacific SST is warmer than in single El Niño or SAMN events, coinciding with an intensified anticyclone over the western North Pacific and enhanced southwesterly moisture transport over South China. Anomalous low-level convergence and upward motion are also observed over South China, consistent with the increased SCSR. These findings suggest a potential SOD-mediated pathway linking tropical ENSO and extratropical SAM to SCSR variability.
