Tianjin Meteorological Bureau

Coupled climate models integrate atmospheric, oceanic, and land submodels, while the uncertainty of model parameters from different parameterization schemes or empirically derived parameters inevitably introduces systematic biases. Coupled parameter optimization (CPO) can reduce these biases to improve weather forecast and climate prediction, but must address strong nonlinearities inherent in coupled models. The analytical four-dimensional ensemble variational (A-4DEnVar) data assimilation method retains the nonlinear processing capability of the four-dimensional variational (4D-Var) data assimilation method but gets rid of the dependence on the adjoint model. In this study, a novel dynamic independent point (DIP) scheme is introduced to the improved A-4DEnVar, which reduces computational dimensionality and further explores a broader parameter space of dimensionality reduction through the outer loop. Based on the improved A-4DEnVar, a series of geographic-dependent CPO experiments with an idealized 2D coupled model are carried out. Results show that A-4DEnVar accurately captures the geographical characteristics of parameters and effectively optimizes cross-component parameters despite strong nonlinearity. Additionally, the DIP scheme presents significant advantages compared to the static independent point scheme, especially with fewer independent points. This work is offering a new perspective for parameter optimization in coupled general circulation models used for climate estimation and prediction.

Abstract Frequent droughts in the Sichuan Basin (SCB) have caused severe socioeconomic impacts and significantly altered the regional water cycle. However, the connection between these droughts and the atmospheric water cycle remains unclear. Here, we applied two process‐based models—the Dynamic Recycling Model (DRM) and the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model—to investigate the characteristics and mechanisms of atmospheric water cycles during SCB summer droughts from 1979 to 2022. The results show that the climatological mean precipitation recycling ratios for June, July, and August were 12.92%, 13.04%, and 12.63%, respectively, indicating the SCB's strong dependence on externally transported moisture. Most droughts are linked to deficits in external moisture transport. However, in the later stages of the most severe droughts (e.g., August 2006 and 2022), the drought evolves from preceding external moisture reduction into an internal‐moisture‐depletion regime. This shift is driven by extreme soil moisture depletion, which markedly intensifies land–atmosphere coupling and ultimately leads to the collapse of local moisture recycling. Moisture tracking further reveals that droughts with external deficits are associated with reduced oceanic inflow, while those with internal deficits exhibit reduced terrestrial moisture contributions despite sufficient oceanic supply, reflecting low efficiency in converting available moisture into rainfall. Large‐scale circulation systems, especially the Western Pacific Subtropical High and mid‐latitude westerlies, play a key role in shaping these drought‐related anomalies by regulating moisture transport and precipitation efficiency, while land–atmosphere coupling further amplifies these anomalies. These findings provide new insights into summer drought dynamics in the SCB and inform improved drought prediction under a changing climate.

Abstract Transport plays a significant role in non‐regional new particle formation (NPF) events but is often overlooked in regional NPF events, particularly in typical banana‐shaped NPF events. This study applied a population balance method incorporating the transport (TR) effect to examine transport influence in three distinct regional (banana‐shaped) NPF events and one non‐regional NPF event in the Pearl River Delta region. In the non‐regional NPF event, particle changes due to transport closely align with observed particle concentration trends. In regional NPF events, the role of transport is also significant and cannot be overlooked. During the initial phase of NPF, transport exerts a positive effect, leading to an increase in particle concentration. However, as the boundary layer height increases, possible enhanced dilution led to a transition to a negative effect, resulting in particle loss. Ultimately, transport has a net positive effect in local new particle formation events, with the average contribution to particle concentration changes ranging from 47% to 68% across different cases. Incorporating the transport (TR) term reduced the root mean square error (RMSE) between simulated and observed particle number concentrations ( N CN ) by 28%–55% and increased the average coefficient of determination ( R 2 ) from 0.82 to 0.93 across the three cases. Moreover, including the TR term improved estimates of CCN concentration at 1.0% supersaturation (SS), though deviations persisted due to variations in background particle concentrations. Future studies should further investigate the size‐dependent influence of transport and its potential impact on CCN activation under lower SS to better constrain transport‐related processes in regional NPF events.

The North China Plain, a major grain production base in China, is facing the chronic threat of climate-change-induced delays in winter wheat sowing, with late sowing constraining yields by shortening the pre-winter growth period, and soil moisture at sowing potentially serving as a key factor to alleviate late-sowing losses. However, previous studies have mostly independently analyzed the effects of sowing time or water stress, and there is still a lack of systematic quantitative evaluation on how the interaction effects between the two determine long-term yield potential and risk. To fill this gap, this study aims to quantify, in the context of long-term climate change, the independent and interactive effects of different sowing dates and baseline soil moisture on the growth, yield, and production risk of winter wheat in the North China Plain, and to propose regionally adaptive management strategies. We selected three representative stations—Beijing (BJ), Wuqiao (WQ), and Zhengzhou (ZZ)—and, using long-term meteorological data (1981–2025) and field trial data, undertook local calibration and validation of the APSIM-Wheat model. Based on the validated model, we simulated 20 management scenarios comprising four sowing dates and five baseline soil moisture levels to examine the responses of phenology, aboveground dry matter, and yield, and further defined yield-reduction risk probability and expected yield loss indicators to assess long-term production risk. The results show that the APSIM-Wheat model can reliably simulate the winter wheat growing period (RMSE 4.6 days), yield (RMSE 727.1 kg ha−1), and soil moisture dynamics for the North China Plain. Long-term trend analysis indicates that cumulative rainfall and the number of rainy days within the conventional sowing window have risen at all three sites. Delayed sowing leads to substantial yield reductions; specifically, compared with S1, the S4 treatment yields about 6.9%, 16.2%, and 16.0% less at BJ, WQ, and ZZ, respectively. Moreover, increasing the baseline soil moisture can effectively compensate for the losses caused by late sowing, although the effect is regionally heterogeneous. In BJ and WQ, raising the baseline moisture to a high level (P85) continues to promote biomass accumulation, whereas in ZZ this promotion diminishes as growth progresses. The risk assessment indicates that increasing baseline moisture can notably reduce the probability of yield loss; for example, in BJ under S4, elevating the baseline moisture from P45 to P85 can reduce risk from 93.2% to 0%. However, in ZZ, even the optimal management (S1P85) still carries a 22.7% risk of yield reduction, and under late sowing (S4P85) the risk reaches 68.2%, suggesting that moisture management alone cannot fully overcome late-sowing constraints in this region. Optimizing baseline soil moisture management is an effective adaptive strategy to mitigate late-sowing losses in winter wheat across the North China Plain, but the optimal approach must be region-specific: for BJ and WQ, irrigation should raise baseline moisture to high levels (P75-P85); for ZZ, the key lies in ensuring baseline moisture crosses a critical threshold (P65) and should be coupled with cultivar selection and fertilizer management to stabilize yields. The study thus provides a scientific basis for regionally differentiated adaptation of winter wheat in the North China Plain to address climate change and achieve stable production gains.

Land subsidence is widely present across the globe and brings catastrophic hazards. The well-acknowledged mechanism of subsidence is groundwater pumping, which leads to the reduction of hydraulic head and hence increases the effective stress, resulting in the vertical compaction of unconsolidated sediment. Here, we propose a hypothesis that subsidence in the coastal areas might be caused by osmotic effects, given the presence of seawater intrusion. The hypothesis is corroborated by simulating fluid flow, solute transport, and elastic deformation of multi-layered aquifer-aquitard systems. The simulations potentially cover a variety of natural environments by varying concentration, hydraulic head, thickness of aquitard, and hydraulic conductivity. We find that osmotic effects due to seawater intrusion play a non-negligible role in controlling subsidence in our studied cases, suggesting that future work on subsidence in areas impacted by seawater intrusion should fully incorporate osmotic effects to improve our understanding and prediction of subsidence.