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The impact of the positive and negative phase of the Indian Ocean dipole (IOD) on the Pacific blocking frequency (PBF) during boreal autumn is investigated based on the ERA5 daily reanalysis data from 1979 to 2021. It is found that the IOD index are characterized by an obvious interannual variation, and the most obvious dipole feature appears in boreal autumn, which is agree with previous studies. Strong 8 positive and 8 negative phases in boreal autumn are selected to further reveal the regulation of different IOD phases on PBF. The results show that the PBF exhibits negative (positive) anomaly in the North Pacific (East Siberia and Central Siberia) during the positive (negative) IOD phase. During the positive (negative) phase, the cold sea surface temperature anomaly (SSTA) in the tropical southeastern (western) Indian Ocean forces teleconnection wave trains, which are likely results of the northeastward propagation of Rossby wave energy. With such a wave train, a geopotential height anomaly of ‘north negative–south positive’ (‘north positive–south negative’) appears around the Bering Strait (Central Siberia) during the positive (negative) phase, which causes negative (positive) PBF anomalies, based on the ERA5 daily reanalysis data and ECHAM4.6 climate model output from 1979 to 2021. [ABSTRACT FROM AUTHOR]

One prominent mode of interannual variability in the number of persistent extreme high-temperature days (PEHDs) in midsummer (July–August) over southern China exhibits a dipole mode between South China (SC) and Southwest China (SWC), whose underlying mechanism remains unknown. Utilizing observations, reanalysis datasets, and numerical experiments, this study shows that this dipole mode is primarily contributed by local anomalous diabatic processes and is further related to the anomalies of the western North Pacific subtropical high (WNPSH), South Asian high (SAH), and East Asian westerly jet (EAJ). Meanwhile, midsummer sea surface temperature (SST) anomalies in the North Indian Ocean (NIO) and the central Pacific–type El Niño–Southern Oscillation play crucial roles, with the former making a relatively larger contribution and the latter being influenced by the Pacific meridional mode in the preceding April via wind–evaporation–SST feedback. Warmer NIO SST leads to the WNPSH extending southwestward via an eastward-propagating Kelvin wave and further causes a southward-displacing EAJ through the associated East Asia–Pacific/Pacific–Japan wave train. Additionally, it also favors an eastward-extending SAH by heating the troposphere over the NIO and its surrounding areas. A midsummer central Pacific–type La Niña contributes to a southwestward-extending WNPSH through a Gill response and influences the vertical velocity anomalies over SC and SWC by modulating the Walker circulation and associated local meridional circulations. Consequently, warmer NIO SST and a central Pacific–type La Niña lead to an increase (decrease) in PEHDs over SC (SWC) during midsummer, and vice versa. [ABSTRACT FROM AUTHOR]

In climatology, the tropical cyclones become active and shift northward over the western North Pacific (WNP) around pentad 41 (20–24 July), corresponding to the WNP summer monsoon onset, which is a phenomenon characterized by the abrupt northeastward extension of strong convection. This study investigates the change in tropical cyclone genesis during El Niño summers, which have been confirmed to coincide with a delayed onset of the summer monsoon. The results show that the spring-up of tropical cyclones is delayed for the El Niño summers. Specifically, there are negative tropical cyclone genesis frequency and genesis potential index anomalies over the region (15°–30°N, 110°–160°E) during pentads 41–44. Accordingly, the average number and genesis latitude of tropical cyclones decreases significantly. The diagnosis of the genesis potential index further reveals that the key factors affecting the tropical cyclone genesis lie in the mid-tropospheric relative humidity and vertical wind shear. [ABSTRACT FROM AUTHOR]

The South Asian summer monsoon (SASM) is of considerable scientific and social importance to the densely populated South Asia. Existing literature signified that the interannual variation of the SASM can be reflected by multiple dynamical and radiative processes. However, quantifying their relative contributions remains inadequate, particular for the contribution of aerosol process. Here, the land-sea thermal contrast index (LSTCI) is employed to represent the large-scale thermal driving at the mid–upper troposphere associated with the SASM, which is defined as temperature difference between the southern Eurasia (SE) and the tropical Indian Ocean (TIO) at the mid–upper troposphere. Based on the coupled atmosphere-surface climate feedback-response analysis method, this study linearly decomposes the total temperature change associated with the LSTCI into several partial temperature changes associated with individual dynamical and radiative processes. Our result demonstrates that the LSTCI is mainly explained by the positive contributions of atmospheric dynamic (69%), water vapor (35%), and aerosol (11%) processes, which are partially offset by a negative contribution of cloud process (-18%). Surface dynamic process play a neglectable role in the LSTCI, because it exerts similar effects on the temperature anomalies over the SE and the TIO. Further analysis indicates that the total effect of aerosols is dominated by change in black carbon. As two important components, the temperature anomalies over the SE and the TIO separately account for about 55% and 45% to the LSTCI. Our finding provides a new insight onto quantitatively understanding the relevant processes involved in the SASM variation. [ABSTRACT FROM AUTHOR]

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The El Niño‐Southern Oscillation (ENSO)‐related interannual variability of the Kuroshio in the East China Sea (ECS) was revisited based on reanalysis outputs during 1993–2018. Unlike the synchronized variations from 2006 to 2018, the period of 1993–2005 showed regional differences in how the ECS‐Kuroshio responded to ENSO events. Specifically, from the upstream region to the midway of the continental slope, the ECS‐Kuroshio exhibited distinct six‐year interannual modulation during 1993–2005. In contrast, downstream Kuroshio variability primarily followed a four‐year cycle, aligning with ENSO variability during the same period. Further analysis suggested that the sea surface height anomaly (SSHA) east of the Kerama Gap, near the midpoint of the Ryukyu Island chain, extended inside the ECS until the southern side of the Tokara Strait along the ECS‐Kuroshio path and was well correlated with the Kuroshio in the Tokara Strait during 1993–2005. The cause of this SSHA signal was attributed to forcing by ENSO‐related wind stress curl changes in the interior region. There was an obvious difference in the ENSO‐related atmospheric circulation before and after 2005. The wind stress curl pattern in the North Pacific during 1993–2005, characterized by a maximum in the Kerama Gap latitude band, shifted northward compared to that during 2006–2018. The relative northward shift of the ENSO‐related wind stress curl, which stimulates the long baroclinic Rossby wave propagating westward and arriving east of the Kerama Gap, affect the interannual variabilities of both the upstream and downstream Kuroshio. Plain Language Summary: The Kuroshio is the western boundary current of the North Pacific Ocean. It plays a significant role in the marine ecosystem and the global heat budget of the East China Sea (ECS). This study revealed that the responses of the Kuroshio in the ECS to the El Niño‐Southern Oscillation (ENSO) show distinctive regional differences from upstream to downstream region during 1993–2005, which is different from the synchronized response during 2006–2018. The sea surface height anomaly (SSHA) east of the Kerama Gap, which is forced by ENSO‐related wind stress curl changes in the North Pacific, could extend inside the ECS until the Tokara Strait along the ECS‐Kuroshio path and is well correlated with the Kuroshio in the Tokara Strait before 2005. Key Points: Upstream and downstream ECS‐Kuroshio exhibited inconsistent (consistent) responses to the ENSO variation before (and after) 2005Variation of the Kuroshio in the Tokara Strait is related to the SSHA east of the Kerama Gap, which may be attributed to the El Niño state before 2005The ENSO‐related wind stress pattern shifted northward during 1993–2005 compared with that during 2006–2018 [ABSTRACT FROM AUTHOR]

This study investigates the interannual variations in regional mean sea levels (MSLs) of the northeast Asian marginal seas (NEAMS) during August, focusing on the role of typhoon activity from 1993 to 2019. The NEAMS are connected to the Pacific through the East China Sea (ECS) and narrow, shallow straits in the east, where inflow from the southern boundary (ECS), unless balanced by eastern outflow, leads to significant convergence or divergence, as well as subsequent changes in regional MSLs. Satellite altimetry and tide-gauge data reveal that typhoon-induced Ekman transport plays a key role in MSL variability, with increased inflow raising MSLs during active typhoon seasons. In contrast, weak typhoon activity reduces inflow, resulting in lower MSLs. This study's findings have significant implications for coastal management, as the projected changes in tropical cyclone frequency and intensity due to climate change could exacerbate sea level rise and flooding risks. Coastal communities in the NEAMS region will need to prioritize enhanced flood defenses, early warning systems, and adaptive land use strategies to mitigate these risks. This is the first study to link typhoon frequency directly to NEAMS MSL variability, highlighting the critical role of wind-driven processes in regional sea level changes. [ABSTRACT FROM AUTHOR]

The climatological connection between tropical cyclones (TCs) and boreal summer intraseasonal oscillation (BSISO) over the western North Pacific (WNP) is known, but here we additionally find that the influences of May–October BSISO on TC genesis and intensification at the interannual timescale reveal distinctive regional features. The strengthened BSISO variability over the subtropical WNP (7.5°–27.5°N, 145°E–165°W) contributes positively to the basin-total TC genesis count, while the BSISO amplitude over the central-western equatorial Pacific (5°S–5°N, 140°E–160°W) is significantly correlated with the average intensity that TCs can reach. The physical processes causing the differences in TC behavior associated with interannual changes in BSISO are quantified from the viewpoint of eddy energetics. During summers with enhanced BSISO over the subtropical WNP, more TCs form there. Composite diagnostic analysis results for TC genesis days show that local synoptic eddies (or TC embryos) gain more kinetic energy to grow into TCs from both the seasonal-mean and BSISO anomalies via barotropic energy conversion. Eddy self-augmentation processes related to baroclinic conversion and eddy geopotential flux also aid the generation of TCs. During summers with enhanced central-western equatorial BSISO, TCs stay longer over the open ocean before they reach maximum intensity. Further diagnosis along the TC tracks shows that these eddies may grow faster (with a larger kinetic energy tendency) and reach a higher intensity with the help of enhanced barotropic and baroclinic energy conversion processes. [ABSTRACT FROM AUTHOR]

To test the potential of high‐resolution satellite image analysis for assessing and predicting the mesoscale (<10 km in this study) effects of climate and environmental change on temperature and primary productivity in fishing grounds, we conducted satellite image analysis around an island in a coastal strait west of Japan from 2018 to 2023. We observed a distinct north–south gradient in sea surface temperature (SST) and chlorophyll a concentration (CHL) over approximately 20 km of the transect, which was likely affected by the current system. The model configuration suggests that the frequency of southward currents during winter–spring can control the magnitude of spring phytoplankton blooms. In the study region, an increase in SST at a rate of 0.06–0.13°C y−1 occurred during the study period, accompanied by a decrease in CHL. The north–south gradient in the rate of change suggests that the variation in the temperature and flow rate of the Kuroshio Current into the study area was due to these abrupt changes. The relationship between the annual mean SST and CHL was also spatially heterogeneous, showing a higher sensitivity of CHL to SST in the southwest of the island than in the north. In addition to the intrusion of warm and oligotrophic Kuroshio waters, the spread of less saline and more eutrophic coastal waters likely influenced this spatial heterogeneity. The satellite image analysis in the present study successfully revealed mesoscale mosaics of environmental conditions in coastal fishery grounds. [ABSTRACT FROM AUTHOR]

Abstract Background Tree rings play an important role in reconstructing past climate. Growth differences among individual trees due to microclimatic conditions and local disturbances are averaged in developing tree-ring chronologies. Here, we addressed the problem of averaging by investigating growth synchrony in individual trees. We used tree-ring data of 1046 juniper trees from 32 sites on the Tibetan Plateau and 538 pine trees from 20 sites in the subtropical region of eastern China and calculated the tree-growth synchrony index (TGS). Results Our results showed that both the TGS index and tree-ring index could be indicators of interannual variation of climatic factors. The TGS index identified 20% more climatic extremes than tree-ring index over the last 50 years that high synchrony indicates extreme climate forcing in controlling forest growth. Conclusions The TGS index can identify extreme climatic events effectively than tree-ring index. This study provides a novel perspective for climate reconstruction, especially in the realm of tree growth response to extreme climate. Our findings contribute to understanding of the spatiotemporal dynamics and the causes of historical climate extremes and provide guidance for protecting trees from climate extremes in the future.

Background: Tree rings play an important role in reconstructing past climate. Growth differences among individual trees due to microclimatic conditions and local disturbances are averaged in developing tree-ring chronologies. Here, we addressed the problem of averaging by investigating growth synchrony in individual trees. We used tree-ring data of 1046 juniper trees from 32 sites on the Tibetan Plateau and 538 pine trees from 20 sites in the subtropical region of eastern China and calculated the tree-growth synchrony index (TGS). Results: Our results showed that both the TGS index and tree-ring index could be indicators of interannual variation of climatic factors. The TGS index identified 20% more climatic extremes than tree-ring index over the last 50 years that high synchrony indicates extreme climate forcing in controlling forest growth. Conclusions: The TGS index can identify extreme climatic events effectively than tree-ring index. This study provides a novel perspective for climate reconstruction, especially in the realm of tree growth response to extreme climate. Our findings contribute to understanding of the spatiotemporal dynamics and the causes of historical climate extremes and provide guidance for protecting trees from climate extremes in the future. [ABSTRACT FROM AUTHOR]

Periodic eddies are a type of eddy that occur almost annually in fixed timeframes with similar patterns and trajectories. Nearly every year from April to June, under the combined effect of the barotropic instability of the mean flow and wind work, a cyclonic eddy (the Taiwan Cyclonic Eddy, TCE) forms in the southwest of Taiwan, then propagates westward, and finally dissipates near the Dongsha Islands. TCE exerts a significant impact on the Kuroshio intrusion into the South China Sea (SCS) and water exchange. Based on multi‐year in situ and satellite observations, this study reveals the thermohaline structure and evolutionary process of the TCE. The evolutions of the three‐dimensional structures of temperature, salinity, and geostrophic velocity of the TCE are analyzed based on reconstructed data. The TCE shows important interannual variations associated with El Niño–Southern Oscillation (ENSO), and the relationship between ENSO and the TCE is modulated by the Pacific Decadal Oscillation (PDO). In the negative phase of the PDO, the intensity of the TCE is significantly correlated with the Niño‐3.4 index. In contrast, in the positive phase, the ENSO–TCE relationship becomes weak and non‐significant. Further investigations indicate that these differences are related to the establishment of the low‐latitude Pacific–East Asian Teleconnection, influencing local wind stress curl in the region. This offers a new perspective on understanding the interannual variation of periodic mesoscale eddies in the SCS. Plain Language Summary: The Taiwan Cyclonic Eddy (TCE) represents a significant periodic mesoscale eddy in the South China Sea (SCS), demonstrating annual occurrences and profound impacts on regional oceanography and climatological dynamics. This study expands on multi‐year in situ and satellite observations to elaborate the three‐dimensional thermohaline structure and dynamic behavior of the TCE, emphasizing its seasonal consistency and interannual variability influenced by major climatic oscillations such as El Niño–Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO). The TCE's formation is primarily driven by the instability of the background current and significant wind forcing. Its interannual variation shows a non‐stationary relationship with ENSO, which is significantly modulated by the PDO. The study enhances our understanding of the interannual dynamics of the TCE by highlighting how shifts in large‐scale climatic conditions can directly alter the local structural and dynamic characteristics of the eddy. Understanding the TCE's formation and variation is vital as it affects water exchange in the SCS, and thus influences local marine ecosystems in the region. By studying this phenomenon, scientists can better predict the impacts of such eddies on marine and climatic environments. Key Points: The Taiwan Cyclonic Eddy (TCE) forms annually from April to June southwest of Taiwan due to current instability and wind forcingMulti‐year observations show the TCE has significant vertical extensions and temperature/salinity anomalies, impacting local conditionsThe TCE's evolution is tied to El Niño–Southern Oscillation and influenced by Pacific Decadal Oscillation phases, being stronger in negative phases due to enhanced teleconnections and wind adjustments [ABSTRACT FROM AUTHOR]

Hourly extreme precipitation is expected to intensify with global warming following a Clausius–Clapeyron (CC) relationship. While extensive research has investigated the relationship between hourly precipitation and temperature, inconsistencies in this relationship across the diurnal cycle affect all-hours scaling. This study uses hourly gauge observations and reanalysis data from mainland China to analyze the scaling and explore its diurnal cycle for the first time. Our results reveal that 88.7% of the stations exhibit super-CC scaling, which is significantly underestimated by reanalysis data. Notably, the scaling shows a pronounced diurnal cycle and exceeds all-hour scaling, indicating that the mix of precipitation from different hours ultimately affects the overall scaling results. Over a 39 year period, changes in extreme precipitation intensity were closely aligned with dew-point temperatures throughout the diurnal cycle in inland regions. The above results provide a valuable insight into the shift of extreme precipitation to morning/night in some regions under climate change.

The interannual variation of intraseasonal (10–30-day) oscillation (ISO) intensity for the eastward- and westward- propagating types over the mid-high latitudes in austral summer is studied. It indicates that during strong ISO years, the wave train has a larger amplitude and wider zonal influencing range. The wave train propagates eastward in both strong and weak eastward-propagating ISO years, while it propagates westward only in strong westward-propagating ISO years. One possible explanation for the larger magnitude of the wave train in strong ISO years is that the ISO perturbation acquires more energy from the mean flow through the barotropic kinetic energy and potential energy conversion. Based on the diagnostic results of the geopotential height trend, the maximum contributor to the eastward propagation is the same during strong and weak ISO years, as well as for the westward propagation. However, the relative contribution of the relative vorticity's meridional advection in weak years is smaller than that in strong years, which may be the reason why there is no significant westward propagation in weak ISO years. Due to the difference in amplitude and influencing range of the wave train during strong and weak ISO years, the two ISO types have different effects on the surface air temperate over land areas at the Southern Hemisphere. The interannual variation of the eastward-propagating ISO intensity appears to be linked to the El Niño-Southern Oscillation and Southern Annular Mode, while the westward-propagating ISO appears unrelated to them. [ABSTRACT FROM AUTHOR]

Changes in land cover by rapid urbanization have diminished the cooling effect of urban green spaces (UGS), exacerbating the upward trend of land surface temperature (LST). A thorough and precise understanding of the spatio-temporal characteristics of UGS and LST is essential for mitigating localized high temperatures in cities. This study identified the spatio-temporal changes in UGS configuration and LST in Shanghai from 2003 to 2022. The correlation between UGS configuration and LST was explored using spatial autocorrelation analysis and causal inference. The results show that (1) the high-temperature space had grown from 721 km2 in 2003 to 3059 km2 in 2022; (2) in suburbs, the largest area of UGS tended to decrease, while the number of patches tended to increase, indicating a distinct feature of suburbanization; (3) changes in the largest area of UGS had more significant spatial correlation, indicating that urban sprawl primarily impacts large UGSs; and (4) compared to the number and shape of UGS, changes in the largest area are the key factor influencing regional LST. These findings enrich the knowledge of the spatio−temporal relationship between the UGS configuration and its cooling effect in urbanization, offering valuable insights for building cooler cities. [ABSTRACT FROM AUTHOR]

Upscaling flux tower measurements based on machine learning (ML) algorithms is an essential approach for large‐scale net ecosystem CO2 exchange (NEE) estimation, but existing ML upscaling methods face some challenges, particularly in capturing NEE interannual variations (IAVs) that may relate to lagged effects. With the capacity to characterize temporal memory effects, the Long Short‐Term Memory (LSTM) networks are expected to help solve this problem. Here we explored the potential of LSTM for predicting NEE across various ecosystems using flux tower data over 82 sites in North America. The LSTM model with differentiated plant function types (PFTs) demonstrates the capability to explain 79.19% (R2 = 0.79) of the monthly variations in NEE within the testing set, with RMSE and Mean Absolute Error values of 0.89 and 0.57 g C m−2 d−1 respectively (r = 0.89, p < 0.001). Moreover, the LSTM model performed robustly in predicting cross‐site variability, with 67.19% of the sites that can be predicted by both LSTM models with and without distinguished PFTs showing improved predictive ability. Most importantly, the IAV of predicted NEE highly correlated with that in flux observations (r = 0.81, p < 0.001), clearly outperforming that by the random forest model (r = −0.21, p = 0.011). Among all nine PFTs, solar‐induced chlorophyll fluorescence, downward shortwave radiation, and leaf area index are the most important variables for explaining NEE variations, collectively accounting for approximately 54.01% in total. This study highlights the great potential of LSTM for improving carbon flux upscaling with multi‐source remote sensing data. Plain Language Summary: Net ecosystem exchange (NEE) of CO2 is a crucial process that regulates carbon exchange between terrestrial ecosystems and the atmosphere. Currently, the growing availability of flux tower measurements and the rapid development of artificial intelligence technology, have made the machine learning‐based data‐driven flux upscaling approach a popular way for estimating carbon fluxes over large scales. Several upscaling NEE data sets have been derived with different machine learning methods; however, the lack of representing memory effects of climate and environmental factors in the modeling remains an important source of uncertainty for NEE estimates. To address this issue, we constructed site‐level Long Short‐Term Memory (LSTM) training models by plant function types in North America to improve the simulation of monthly scale NEE and its interannual variations. The established LSTM model improves the prediction of the temporal variability of NEE, showing great potential for improving carbon flux upscaling. Key Points: The Long Short‐Term Memory (LSTM) model with differentiated plant function types (PFTs) demonstrates the capability to explain 79.19% of the monthly variations in net ecosystem exchange (NEE)The LSTM model exhibited clear advantages over the RF model in capturing the interannual variations of NEEThe relative importance of feature variables for predicting monthly NEE dynamics across different PFTs in North America was quantified [ABSTRACT FROM AUTHOR]

Parameters of surface marine heatwaves (MHWs) in the Northwest Pacific during 1993-2019 are derived from two sea surface temperature (SST) products: the Optimum Interpolation SST based on satellite remote sensing (OISST V2.1) and the Global Ocean Physics Reanalysis based on data-assimilative global ocean model (GLORYS12V1). Similarities and differences between the MHW parameters derived from the two datasets are identified. The spatial distributions of the mean annual MHW total days, frequency, duration, mean intensity and cumulative intensity, and interannual variations of these parameters are generally similar, while the MHW total days and duration from GLORYS12V1 are usually higher than that from OISST V2.1. Based on seasonal-mean values from GLORYS12V1, longer MHW total days (>7) have the largest spatial coverage in both the shelf and deep waters in summer, while the smallest coverage in spring. In selected representative regions, interannual variations of the MHW total days are positively correlated with the SST anomalies. In summer, the MHW total days have positive correlations with the Western Pacific Subtropical High intensity, and negative correlations with the East Asia Monsoon intensity, over nearly the whole South China Sea (SCS) and the low-latitude Pacific. In winter, positive correlations with both the Subtropical High and Monsoon intensities present over the western part of SCS. Strong El Niño is followed by longerMHWtotal days over the western half of SCS in winter, and over the whole SCS and low-latitude Pacific in summer of the next year. These correlation relationships are valuable for developing forecasts of MHWs in the region. [ABSTRACT FROM AUTHOR]

This study scrutinizes interannual (2003–2023) variations in coastal upwelling along the Guangdong Province during summers (June–August) in the northeastern South China Sea (NESCS) by comprehensively applying the moderate-resolution imaging spectroradiometer (MODIS) remote sensing sea surface temperature (SST) and chlorophyll concentration (CHL) data and the model reanalysis product. The results show that SST and upwelling intensity in the sea area have significant (p < 0.05) rising trends in the last 21 years. The CHL shows an upward but insignificant trend, which is affected simultaneously by the rise in SST and the enhancement of upwelling. Further analysis reveals that the interannual variations in upwelling are robustly related to the wind fields' variations in the coastal region. A clockwise/counter-clockwise anomaly in the wind field centered on the NESCS facilitates alongshore/onshore winds near the Guangdong coast, which can strengthen/weaken coastal upwelling. Based on the correlation between wind field variations and large-scale climate factors, long-term variations in the upwelling intensity can be primarily predicted by the Oceanic Niño Index. [ABSTRACT FROM AUTHOR]

Child trafficking is a serious social problem in China that has led to numerous family tragedies and drawn considerable attention. Here, we used a new database to investigate child trafficking in Henan Province in central China from a geographical perspective to help researchers better understand and explain trafficking activity. We discovered that trafficking cases involved more male than female children and that the trafficking rate was the highest for younger age groups. Child trafficking presented an interannual variation of 'rise and fall' between 1949 and 2018. An increasing trend in trafficking cases was observed after 1981, peaking in 1991, followed by a rapid decline in trafficking cases in subsequent years. Trafficking occurs more frequently during the summer than in the winter. The geographic hotspots of trafficking have continuously expanded over time from central to southwestern to southeastern Henan Province, thus revealing a triangular trafficking pattern of decentralization. The spatial pattern of child trafficking is strongly influenced by transportation. We expect these findings to provide a valuable reference for local governments in their efforts to prevent and combat child trafficking. [ABSTRACT FROM AUTHOR]

Ulva prolifera (U. prolifera) green tide outbreaks have occurred in the Yellow Sea of China for many years, causing serious losses to marine ecology and the marine economy. The monitoring and tracking of U. prolifera green tide is a crucial aspect of marine ecological disaster prevention and control management. This paper aims to investigate the spatiotemporal distribution changes in U. prolifera green tide in the Yellow Sea throughout its life cycle. A survey of the Yellow Sea from 2008 to 2023 was conducted using multi-source remote sensing images. Long-term monitoring and analysis of U. prolifera revealed the evolution process of the green tide, including the early development, outbreak, decline, and extinction stages, considering time, space, and frequency of occurrence. Additionally, this study examined peak coverage change patterns over the past 16 years and analyzed the influence of environmental factors such as sea surface temperature and sea surface wind field on the development of U. prolifera. The research results serve as a valuable reference for the monitoring, early warning, and scientific prevention and control of U. prolifera green tide in the Yellow Sea, as well as other similar marine disaster areas. [ABSTRACT FROM AUTHOR]

Rivers in arid regions serve as crucial freshwater resources for local communities and play an essential role in global hydrological and biogeochemical cycles. The Aral Sea Basin (ASB) in Central Asia is characterized by an arid climate and river dynamics that are sensitive to climate change and human activities. Monitoring the spatiotemporal variations in river water extent in the ASB is essential to maintain an ecological balance and ensure water security. In this study, we extracted data regarding monthly river water bodies in the ASB from 2017 to 2022 by synthesizing monthly Sentinel-2 images. The water extents on the Sentinel images were automatically mapped using the Otsu method, and the river widths for all river channels were calculated using the RivWidth algorithm. We investigated the relationships between the river dynamics and the geomorphology, climatic change, human activities, and the annual and interannual variations in the river width in different reaches of the basin. The results show a seasonal variability in the river width, with most rivers reaching the largest width in the warm season and a few rivers in the middle and lower areas reaching the valley value in the warm season. Compared to their tributaries, the mainstem in the middle/lower regions showed less seasonal variability. According to interannual analysis, most of the rivers in the ASB significantly narrowed between 2017 and 2022, a phenomenon which is generally impacted by temperature and evapotranspiration variations. Comparisons show that our results provide improved information about the narrow river reaches and denser river networks compared to the previous global dataset, demonstrating the advantageous properties of high spatial resolution in Sentinel-2 imagery. [ABSTRACT FROM AUTHOR]

This study investigates the interannual variations in regional mean sea levels (MSLs) of the northeast Asian marginal seas (NEAMS) during August, focusing on the role of typhoon activity from 1993 to 2019. The NEAMS are connected to the Pacific through the East China Sea (ECS) and narrow, shallow straits in the east, where inflow from the southern boundary (ECS), unless balanced by eastern outflow, leads to significant convergence or divergence, as well as subsequent changes in regional MSLs. Satellite altimetry and tide-gauge data reveal that typhoon-induced Ekman transport plays a key role in MSL variability, with increased inflow raising MSLs during active typhoon seasons. In contrast, weak typhoon activity reduces inflow, resulting in lower MSLs. This study’s findings have significant implications for coastal management, as the projected changes in tropical cyclone frequency and intensity due to climate change could exacerbate sea level rise and flooding risks. Coastal communities in the NEAMS region will need to prioritize enhanced flood defenses, early warning systems, and adaptive land use strategies to mitigate these risks. This is the first study to link typhoon frequency directly to NEAMS MSL variability, highlighting the critical role of wind-driven processes in regional sea level changes.

Beijing, Tianjin, Hebei and neighbouring areas (34°-43°N, 113°-123°E) are located at the north edge of the East Asian summer monsoon, and they are also the main heavy-rain areas in northern China. The hourly precipitation data of 87 national meteorological stations from 1966 to 2021 are used for the analysis of spatial distribution and interannual variations, while the data of 298 stations from 1980 to 2021 are used to statistically analyze the diurnal variations and interannual variations of light precipitation (0.1-20 mm·h-1) and short-time heavy precipitation (no less than 20 mm·h-1) for the warm season (May-September) over the region. The results show that the annual average light precipitation and frequency in Beijing, Tianjin, Hebei and neighbouring areas during the warm season are much higher than those of short-time heavy precipitation. However, there is an area in the west of the Bohai Sea Region (37°-41°N, 115°-119.5°E) with high short-time heavy rainfall intensity but weak rainfall amount and frequency, which means the convective characteristics of short-time precipitation over this area are more extreme and significant. The interannual variations of two kinds of precipitation amount, frequency, and intensity in Beijing, Tianjin, Hebei and neighbouring areas excluding the west of Bohai Sea Region both present an overall growing trend in the warm season, in which the increasing trend of short-time heavy precipitation is more obvious, but the trend in the west of the Bohai Sea Region is not obvious. The diurnal variation amplitudes of light precipitation amount and frequency in Beijing, Tianjin, Hebei and neighbouring areas excluding the west of the Bohai Sea Region are significantly weaker than those of short-time heavy precipitation, but the peak durations are significantly longer. Compared to Beijing, Tianjin, Hebei and neighbouring areas excluding the west of the Bohai Sea Region, two types of precipitation in the west of the Bohai Sea Region from July to September are more frequent and the rainfall peak durations are longer. The interannual variations of precipitation in different periods of the whole day show that the light precipitation in two regions both decrease in the afternoon, while the short-time heavy precipitation has weakened significantly in the afternoon since 2005, but increased significantly from midnight to early morning.

The cloud type product 2B-CLDCLASS-LIDAR based on CloudSat and CALIPSO from June 2006 to May 2017 is used to examine the temporal and spatial distribution characteristics and interannual variability of eight cloud types (high cloud, altostratus, altocumulus, stratus, stratocumulus, cumulus, nimbostratus, and deep convection) and three phases (ice, mixed, and water) in the Arctic. Possible reasons for the observed interannual variability are also discussed. The main conclusions are as follows: (1) More water clouds occur on the Atlantic side, and more ice clouds occur over continents. (2) The average spatial and seasonal distributions of cloud types show three patterns: high clouds and most cumuliform clouds are concentrated in low-latitude locations and peak in summer; altostratus and nimbostratus are concentrated over and around continents and are less abundant in summer; stratocumulus and stratus are concentrated near the inner Arctic and peak during spring and autumn. (3) Regional averaged interannual frequencies of ice clouds and altostratus clouds significantly decrease, while those of water clouds, altocumulus, and cumulus clouds increase significantly. (4) Significant features of the linear trends of cloud frequencies are mainly located over ocean areas. (5) The monthly water cloud frequency anomalies are positively correlated with air temperature in most of the troposphere, while those for ice clouds are negatively correlated. (6) The decrease in altostratus clouds is associated with the weakening of the Arctic front due to Arctic warming, while increased water vapor transport into the Arctic and higher atmospheric instability lead to more cumulus and altocumulus clouds. [ABSTRACT FROM AUTHOR]

Atmosphere clearness is the single most essential parameter determining surface solar radiation. However, few studies have investigated the interannual variations in China's atmosphere clearness and the impacts of El Niño–Southern Oscillation on it. This study aims to fill the knowledge gap by calculating the clearness index using the China Meteorological Forcing Dataset version 1.7 and then analyzing the correlations between the interannual anomaly and the Niño-3.4 index. The results show that there is a significantly negative correlation in the southeastern coastal regions, northern Xinjiang, northeastern Xizang, and areas from northern Hebei to middle Inner Mongolia. In these areas, the higher the ENSO index, the lower the clearness index, and, coincidingly, positive precipitation anomalies are reported in previous studies. The impacts of El Niño and La Niña vary with seasons. The ENSO events have generally opposite impacts in the seasons other than summer. El Niño tends to decrease the clearness index, while La Niña tends to decrease the atmosphere clearness in most territories of China. The impacts are different in the places of statistical significance. The negative impacts of El Niño are significant in the southeastern coastal regions of China in winter and in northeast China in autumn. The positive impacts of La Niña are significant in the southwestern and northeastern China in the autumn. In these seasons, ENSO's impacts scale with the strength of the event. Stronger events amplify the magnitude of the anomalies, while the spatial patterns of the anomalies are kept almost invariant. In summer, ENSO's impacts exhibit different characteristics than in the other seasons and between the El Niño and La Niña events. For the El Niño events, the impacts are insignificant in most territories of China, even for the strong ones. La Niña has a larger influence on the summertime clearness than El Niña, and the spatial pattern of the La Niña's impacts varies with the event strength. The anomalies during strong La Niña events have a tripolar pattern with a positive anomaly in south and north China and a negative anomaly in between. The pattern suggests that the relationship between the clearness index and precipitation is different during strong La Niña events. These findings would provide valuable insights into the interannual variations of atmosphere clearness in China and could be clues to further investigation. The revealed impacts of El Niño–Southern Oscillation should be important for developing solar energy. [ABSTRACT FROM AUTHOR]

The interannual variation of the North Equatorial Current (NEC) across the North Pacific Ocean and the modulation of the Pacific Decadal Oscillation (PDO) are investigated based on both observations and reduced gravity model experiments. Results reveal that the interannual variation of the NEC is highly related to El Niño‐Southern Oscillation (ENSO) with unsynchronized variations both in zonal and meridional structure. The tropical and subtropical gyre branches of the NEC (NEC‐S and NEC‐N) behave antiphase variation during El Niño events with the transport of the former being enhanced and the latter being weakened across the Pacific. The NEC axis in the western/eastern Pacific shifts northward/southward during El Niño events, consistent with the meridional shift of the zero‐line of wind stress curl. Model experiments indicate that Rossby waves mainly modulate the NEC near the western boundary and the NEC‐N, while Ekman pumping modulates NEC‐S in the western basin. Meanwhile, the relationship between the interannual variation of the NEC and ENSO events is significantly modulated by different PDO phases. The PDO cold phase favors a much closer connection between the NEC and the Niño 3.4 index. The dynamics lie in that PDO‐related wind stress curl and sea level anomalies are consistent with that of El Niño, favoring the enhanced correlation between NEC and El Niño. The reverse is true for the warm phase. These results will contribute to a better understanding of the behavior of the tropical Pacific Ocean circulation and its role in climate change. Plain Language Summary: Serving as the boundary of tropical and subtropical gyres, the North Equatorial Current plays an important role in the exchanging of mass, heat, and salt between the mid‐ and low‐latitude oceans. It is a very broad current and behaves quite differently in both zonal and meridional directions across the Pacific due to the phase lag of propagated Rossby waves. This study reveals that the interannual variation of the North Equatorial Current is highly related to El Niño‐Southern Oscillation (ENSO) with unsynchronized variations in zonal and meridional structure. The tropical and subtropical gyre branches of the North Equatorial Current behave antiphase variation during El Niños with the transport of the former is enhanced and the latter weakened across the Pacific. Rossby waves excited west of the dateline modulate the North Equatorial Current near the western boundary, while those excited in the eastern Pacific modulate the subtropical branches. Local Ekman pumping plays a dominant role in tropical branches in the western Pacific. Further analysis indicates that the ENSO‐related air‐sea state in the tropical Pacific Ocean is modulated by Pacific Decadal Oscillation phases. The cold phase favors a much closer connection between the North Equatorial Current and ENSO events. Key Points: Interannual variation of the North Equatorial Current (NEC) is highly related to El Niño‐Southern Oscillation (ENSO) with unsynchronized variations both in zonal and meridional structureRossby waves mainly modulate the NEC near the western boundary and subtropical gyre branch, while Ekman pumping modulates the tropical gyre branchThe relationship between the NEC and ENSO is nonstationary and significantly modulated by different phases of the Pacific Decadal Oscillation [ABSTRACT FROM AUTHOR]

Restoring valuable timber trees is a necessary part of regaining many ecosystem services and products provided by degraded tropical forests. However, knowledge of seed production, a regeneration prerequisite, is limited for many tropical timber tree species. We studied the fruit production of African mahogany (Khaya anthotheca) in a semi-deciduous rainforest in East Africa, to provide information for ecological restoration programs. First, we quantified population variability and synchrony in fruit production. Then, we assessed how reproductive status and output were influenced by tree size, neighbourhood crowding, exchangeable cations, liana presence, and crown exposure. We found fruit production at the population level was weakly synchronised, with high interannual variability at the population and individual levels. Tree size determined reproductive status. Individual quantity of fruit produced increased with tree size but decreased with neighbourhood crowding. Our results indicate that K. anthotheca does not meet the criteria for mast fruiting. Our findings suggest that reproductive output in mahogany is regulated by tree size and competition. In addition to active protection, thinning to reduce competition around seed trees may boost fruit production at the individual tree level to provide seed for forest enrichment. [ABSTRACT FROM AUTHOR]

Spatiotemporal variation of seed rain reflects the response of plants in terms of their reproductive strategy to environmental gradients. In this study, we collected seeds from four sites in the Dalaoling Nature Reserve, Hubei Province, China, between 2011 and 2014, measured seed output and seed mass as seed rain traits, and compared their interannual and elevational variation. Then, we ran phylogenetic generalized mixed linear models (PGLMMs) to explore the effects of temperature and precipitation as well as interspecific differences on seed rain, and fitted the best regression models for seed rain vs. weather of canopy and understory species. The results showed no correlation between values of seed output and seed mass. However, the variation of the two traits showed significantly positive correlation. Seed output of canopy species generally decreased with increasing elevation, and showed significant interannual difference; however, seed output of understory species and seed mass for both canopy and understory species did not show consistency tends along elevational or in interannual variation. Seed output was significantly affected by temperature and precipitation, while seed mass mainly varied due to interspecific differences. Weather explained more the variation of the seed output of canopy species than that of understory species, with R² values of 43.0% and 29.9%, respectively. These results suggested that canopy plants contributed more to the reproductive dynamics of the whole communities, and the canopy's buffer effect on the underground weakened the response of understory plants to weather variation in terms of their reproductive strategy. [ABSTRACT FROM AUTHOR]

Antarctic coastal polynyas are biological hotspots in the Southern Ocean that support the abundance of high-trophic-level predators and are important for carbon cycling in the high-latitude oceans. In this study, we examined the interannual variation of summertime phytoplankton biomass in the Marguerite Bay polynya (MBP) in the western Antarctic Peninsula area, and linked such variability to the Southern Annular Mode (SAM) that dominated the southern hemisphere extratropical climate variability. Combining satellite data, atmosphere reanalysis products and numerical simulations, we found that the interannual variation of summer chlorophyll-a (Chl-a) concentration in the MBP is significantly and negatively correlated with the spring SAM index, and weakly correlated with the summer SAM index. The negative relation between summer Chl-a and spring SAM is due to weaker spring vertical mixing under a more positive SAM condition, which would inhibit the supply of iron from deep layers into the surface euphotic layer. The negative relation between spring mixing and spring SAM results from greater precipitation rate over the MBP region in positive SAM phase, which leads to lower salinity in the ocean surface layer. The coupled physical-biological mechanisms between SAM and phytoplankton biomass revealed in this study is important for us to predict the future variations of phytoplankton biomasses in Antarctic polynyas under climate change. [ABSTRACT FROM AUTHOR]

Atmospheric cloud radiative effect (ACRE) is a critical heat source in the atmosphere, with pronounced regional distributions. Here, we investigate seasonal and interannual characteristics of ACRE over South China (SC) and neighbouring ocean regions using 2001–2020 satellite and reanalysis data. Annual mean net ACRE shows a warming role over most of SC, its eastern ocean (ESCO), and the South China Sea and western North Pacific (SWNP), with domain‐mean values of 6.0, 14.9, and 32.8 W m−2, respectively. Over SC, the shortwave ACRE warming dominates annual mean net ACRE, and considerable low‐middle clouds with small particle size and large water content reflect shortwave radiation and enhance shortwave absorption, especially in spring. Notably, winter longwave ACRE over SC, with a cooling role, strongly offsets its summer counterpart's warming role. In contrast, longwave ACRE mainly accounts for net ACRE over ESCO and SWNP, especially the latter where high clouds prevail. The Asian summer monsoon enhances summer high clouds and longwave (net) ACRE. Cloud types and complex vertical distribution associated with continental environments and the Tibetan Plateau's topography forcing enable seasonal behaviours of ACRE over SC to be different from the other two regions. Longwave ACRE dominates the interannual variation of net ACRE, with a larger interannual variability over SWNP, while a larger annual variability of shortwave ACRE occurs over SC. There are no significant interannual trends of ACRE except for annual and spring mean longwave (net) ACRE over SC. Moreover, the interannual variation of longwave (net) ACRE relates well to 500‐hPa vertical velocity, indicating the strong influence of large‐scale circulation on regional ACRE. [ABSTRACT FROM AUTHOR]

The frequent occurrence of dry and hot (DH) days in South China in summer has a negative impact on social development and human health. This study explored the variation characteristics of DH days and the possible reasons for this knotty problem. The findings revealed a notable increase in the number of DH days across most stations, indicating a significant upward trend. Additionally, DH events were observed to occur frequently. The number of DH days increased during 1970–1990, decreased from 1991 to 1997, and stayed stable after 1997. The key climate factors affecting the interannual variability of the number of DH days were the Indian Ocean Basin warming (IOBW) in spring and the East Asian Summer Monsoon (EASM). Compared with the negative phase of IOBW, in the positive phase of IOBW, 500 hPa and 850 hPa geopotential height enhanced, the West Pacific subtropical high strengthened and extended abnormally to the west, more solar radiation reached the surface, surface outgoing longwave radiation increased, and there was an anomalous anticyclone in eastern South China. The atmospheric circulation characteristics of the positive and negative phases of ESAM were opposite to those of IOBW, and the abnormal circulation of the positive (negative) phases of ESAM was unfavorable (favorable) for the increase in the number of DH days. A long-term prediction model for the number of summer DH days was established using multiple linear regression, incorporating the key climate factors. The correlation coefficient between the observed and predicted number of DH days was 0.65, and the root-mean-square error was 2.8. In addition, independent forecasts for 2019 showed a deviation of just 1 day. The results of the independent recovery test confirmed the stability of the model, providing evidence that climatic factors did have an impact on DH days in South China. [ABSTRACT FROM AUTHOR]

Abstract Based on station monthly observational statistics, the major rainfall in the Red River Delta (RRD) of Vietnam occurs in late summer (July–September) with conspicuous year-to-year variation. Using the ± 0.8 of the seasonal total rainfall standard deviation as criteria, seven wet and six dry years are identified over the period 1983–2015. In addition to the 70.5% of the seasonal total rainfall contributed by the heavy rainfall days, the distinct heavy rainfall accumulation difference between wet and dry years seems to fundamentally establish these two separated extreme wet and dry groups. As revealed from further analyses, the large variability in rainfall is attributed to the influence of tropical cyclones (TCs) and 7–24- and 30–60-day intraseasonal oscillations (ISOs); in particular, the number of TCs affecting the RRD and rainfall produced by TCs are more (less) during the wet (dry) years, and the amplitudes of ISOs are also enhanced (reduced). In many cases, heavy rainfall days are induced by the combined effect of both ISOs and TCs, while some heavy rainfall events are mainly triggered by ISOs. It is found from the water vapor budget analyses that an anomalous cyclone (anticyclone) dominates over the Indochina Peninsula in wet (dry) years, resulting in more (less) water vapor being transported to the RRD, whereas the anomalous convergence (divergence) of water vapor flux leads to the maintenance of excessive (insufficient) rainfall over the RRD. However, the El Niño–Southern Oscillation (ENSO) forcing shows minor effects on the interannual variation in rainfall in the RRD.

The traditional drought field studies are inadequate to study drought field characteristics from the perspective of trend and periodicity at the same time, especially to compare the interannual and interdecadal variations of different drought types in the drought field to reveal their similarity and difference patterns. The drought field in Pearl River Basin (PRB) was determined in this paper using the standardized precipitation evapotranspiration index (SPEI) and the empirical orthogonal function (EOF)/rotated empirical orthogonal function (REOF). Periodic characteristics and trend features of the drought field were recognized by extreme-point symmetric mode decomposition (ESMD) and other methods. The results showed that from the perspective of regional characteristics five different spatial modes may be used to categorize the interannual drought field of the PRB; there were interannual cycles associated with the southwest-type drought and the northwest-type drought. The central-south-, north-central- and eastern-type droughts had both interannual and interdecadal cycles; during the study period, the PRB's five types of drought revealed a changing tendency as opposed to a straightforward linear trend; from the interannual variation, the southwest-type drought was consistent with the northwest-type drought prior to 2000, and the north-central-type drought was consistent with the eastern-type drought before 2010. HIGHLIGHTS The spatial characteristics and periodic properties of the watershed were identified.; There are five spatial modes in the Pearl River Basin.; Southwestern and northwestern droughts have interannual cycles.; Five types of droughts in the Pearl River Basin showed a fluctuating trend.; The interannual similarity and variability of the five droughts were studied.;

Abstract A long-term fern demography study that included measurements of plant traits of three species in the dimorphic genus Danaea (1991-2009) was conducted in a rainforest in Puerto Rico beginning two years after the first major hurricane (Hugo) since the early 1930s. Both vegetative (sterile) leaves and spore-bearing (fertile) leaves on tagged plants were monitored repeatedly to document not only differences between two types of leaves, but also patterns of annual variation during a timespan that included the passage in 1998 of hurricane Georges. While all three species had fertile leaf lifespans of six mo or less, Danaea geniculata and D. polymorpha had much longer mean sterile leaf spans (54.4 mo, 52.7 mo) than D. nodosa (33.5 mo). All three species had significant year-to-year trait differences, often with immediate increases after Hurricane Georges levels returning to or below pre-hurricane levels in subsequent years. Long-term observations of annual variation in traits of herbaceous layer ferns that mainly follows the passage of a major hurricane highlight the importance of this study as the frequency and magnitude of hurricanes due to climate change are predicted to increase, although more experimental studies to identify specific causes of these long-term trends are needed.

The presence of yessotoxins (YTXs) was analyzed in 10,757 samples of Galician bivalves from 2014 to 2022. Only YTX and 45-OH YTX were found. YTX was detected in 31% of the samples, while 45-OH YTX was found in 11.6% of them. Among the samples containing YTX, 45-OH YTX was detected in 37.3% of cases. The maximum recorded levels were 1.4 and 0.16 mg of YTX-equivalentsg−1, for YTX and 45-OH YTX, respectively, which are well below the regulatory limit of the European Union. The YTX and 45-OH YTX toxicities in the raw extracts and extracts subjected to alkaline hydrolysis were strongly and linearly related. Due to the lack of homo-YTX in Galician samples, the effect of alkaline hydrolysis on homo-YTX and 45OH-Homo-YTX was only checked in 23 additional samples, observing no negative effect but a high correlation between raw and hydrolyzed extracts. Hydrolyzed samples can be used instead of raw ones to carry out YTXs determinations in monitoring systems, which may increase the efficiency of those systems where okadaic acid episodes are very frequent and therefore a higher number of hydrolyzed samples are routinely analyzed. The presence of YTX in the studied bivalves varied with the species, with mussels and cockles having the highest percentages of YTX-detected samples. The presence of 45-OH YTX was clearly related to YTX and was detected only in mussels and cockles. Wild populations of mussels contained proportionally more 45-OH YTX than those that were raft-cultured. Spatially, toxin toxicities varied across the sampling area, with higher levels in raft-cultured mussels except those of Ría de Arousa. Ría de Ares (ARE) was the most affected geographical area, although in other northern locations, lower toxin levels were detected. Seasonally, YTX and 45-OH YTX toxicities showed similar patterns, with higher levels in late summer and autumn but lower toxicities of the 45-OH toxin in August. The relationship between the two toxins also varied seasonally, in general with a minimum proportion of 45-OH YTX in July–August but with different maximum levels for raft-cultured and wild mussel populations. Interannually, the average toxicities of YTX decreased from 2014 to 2017 and newly increased from 2018 to 2021, but decreased slightly in 2022. The relationship between 45-OH YTX and YTX also varied over the years, but neither a clear trend nor a similar trend for wild and raft mussels was observed. [ABSTRACT FROM AUTHOR]

In this study, based on the ECMWF 20-year (1997 ~ 2016) hindcasts, the subseasonal prediction of the weekly summer rainfall anomaly over the middle and lower reaches of the Yangtze River (YR) were studied. The skill at 2-week lead time exhibits prominent interannual variation, which is significantly correlated with the preceding winter ENSO. That is, rainfall anomaly can be better predicted in El Niño decaying summer than in La Niña decaying summer. Observation analyses show that in El Niño decaying summer the intraseasonal variation of YR summer rainfall is featured by strong low-frequency (> 30 days) intraseasonal oscillation (ISO) partly associated with the first boreal summer ISO mode (BSISO1) activity, in comparison with La Niña decaying summer. This is possibly because El Niño-induced mean state western North Pacific (WNP) anti-cyclone blocks the northward propagation of convection over the WNP, resulting in BSISO1 stagnation in phases 3–4. The phase stagnation could force stable atmospheric teleconnection, which is favorable to sufficient moisture transportation to the YR and persistent rainfall formation. Finally, prediction verification showed that more accurate prediction for the middle-low-level circulation contribute to the better prediction of rainfall anomaly in El Niño decaying summer than in La Niña decaying summer. [ABSTRACT FROM AUTHOR]

Phenology is an important factor indicating environmental changes and regulates the variations of carbon, water, and energy exchange. However, phenology models exhibit large uncertainties due to limited understanding of its mechanisms. In this study, we modified deciduous phenology scheme based on the evaluation of different phenological models using long‐term observations at Chinese Ecosystem Research Network with CLM4.5. The alternating leaf unfolding model and summer‐influenced autumn leaf falling model that we proposed, performed best in simulating leaf‐unfolding and leaf‐falling. Compared with the observed and remote‐sensed phenology, the modified model could better simulate the phenological dates at the site and regional scale. Moreover, the modified model improved the simulation of gross primary productivity (GPP) by decreasing the errors of modeled carbon uptake duration and amplitude. Furthermore, the advance in leaf‐unfolding slowed down from 0.20 days/year during 1981–2015 to 0.11 days/year during 2016–2100 under RCP4.5 because of the slowdown of climate warming, but the delay in leaf‐falling changed little. By the last decade of the twenty‐first century, the leaf‐unfolding would advance (8 days) and leaf‐falling would delay (16 days). The subtropical region had large interannual variation (IAV) in leaf‐unfolding because of the high sensitivity to temperature. The phenological dates IAV in the cold temperate region increased due to enhanced temperature IAV. We suggest that the deciduous phenology models, especially the leaf‐falling process, used in Community Land Model need to be improved to reduce the errors in predicting phenology and carbon flux in the future. Plain Language Summary: As an important factor indicating climate and environmental changes, phenology plays an important role in regulating the variation of carbon, water, and energy exchange. Due to limited understanding of phenology mechanisms, the simulation of phenology remains large uncertainties. In this study, we evaluated and modified the leaf unfolding and leaf falling models using the long‐term phenological observations with the Community Land Model (CLM4.5), validated the modified leaf‐unfolding and leaf‐falling models by observed phenology and remote‐sensing phenology data, examined the ability of CLM4.5 with modified deciduous phenology submodels in simulating gross primary productivity, and used the modified phenology models to predict the changes in phenological dates in the future. Our results suggest that the deciduous phenology models, especially the leaf‐falling process, used in the CLM is urgent to be improved to reduce the errors in predicting growing season length and carbon fluxes in deciduous forests in the context of climate change. Key Points: The involvement of chill accumulation with heat requirement in leaf unfolding models can improve the model performanceWe propose a new leaf falling model by considering the relationship between summer temperature and aging state threshold, which improves the model performanceThe revise of deciduous phenological model in CLM4.5 improves the simulation of gross primary productivity by influencing carbon uptake duration and amplitude [ABSTRACT FROM AUTHOR]

Nutrient recycling is one of the most important services that supports other processes in ecosystems. Changing litterfall patterns induced by climate change can cause imbalances in nutrient availability. In this study, we reported the long-term (28-year) interplay between environmental factors and variability among litterfall fractions (leaves, flowers, and fruit) in a tropical dry forest located in Kanchanaburi, Thailand. A long-term litter trap dataset was collected and analyzed by lagged generalized additive models. Strong seasonality was observed among the litter fractions. The greatest leaf and flower litterfall accumulated mostly during the cool, dry season, while fruit litterfall occurred mostly during the rainy season. For leaf litter, significant deviations in maximum temperature (Tmax), volumetric soil moisture content (SM), and evapotranspiration (ET) during the months prior to the current litterfall month were the most plausible factors affecting leaf litter production. Vapor pressure deficit (VPD) and ET were isolated as the most significant factors affecting flower litterfall. Interestingly, light, mean temperature (Tmean), and the southern oscillation index (SOI) were the most significant factors affecting fruit litterfall, and wetter years proved to be highly correlated with elevated fruit litterfall. Such environmental variability affects both the triggering of litterfall and its quantity. Shifting environmental conditions can therefore alter nutrient recycling rates through the changing characteristics and quantity of litter. [ABSTRACT FROM AUTHOR]

The interannual variations in salt flux on the 80°E section in the equatorial Indian Ocean were explored based on the ORAS5 data, which was quite consistent with the observational data among the four available reanalysis datasets. The results indicated that the area with significant interannual variations in salt flux coincided with that of significant climatological mean salt flux in general and was mainly located in the upper 150 m layer. Specifically, three important areas were identified in the north-south direction, i.e., (1) the Equatorial Indian Ocean Area (EIOA, 3°S–3°N), where the mean salt flux was eastward with the largest value on the section and associated with the most significant interannual variations mainly modulated by the Wyrtki Jets and the Equatorial Undercurrent; (2) the South Equatorial Indian Ocean Area (SEIOA, 3°S–6°S), where the mean salt flux changed in the vertical direction from strong eastward flux in the upper layer to weak westward flux in the subsurface layer and associated with significant interannual variations in the upper 100 m layer, which was affected by the South Equatorial Countercurrent; and (3) the North Equatorial Indian Ocean Area (NEIOA, 3°N–6°N), where the mean salt flux changed in the north-south direction from strong westward flux to the north of 5°N to weak eastward flux in the south and associated with relatively significant interannual variations, which was mainly influenced by the South Sri Lanka Coastal Current. Two leading interannual variation modes were revealed by the empirical orthogonal function decomposition. The first mode accounted for 39% of the total variance and had four significant spatial antinodes; two of those in-phase antinodes were located at SEIOA and upper 75 m of EIOA, and the other two opposite in-phase antinodes were located at NEIOA and below 75 m of EIOA. The second mode accounted for 17% of the total variance having four antinodes with two dominant out-of-phase antinodes located at the subsurface of EIOA and SEIOA. The temporal components of the two leading modes showed a 1–4 year variation with a main period of 2 years, in which the first mode showed a greater correlation with the Indian Ocean Dipole, while the second mode showed a weak correlation with the Indian Ocean Dipole and the El Niño-Southern Oscillation. Variance analysis showed that the interannual variations in salt flux were mainly determined by the variations in the current, and the spatial distribution was modulated by temporal mean salinity. Composite strong interannual events showed interannual variations in current, and so the salt flux was driven by the interannual anomaly of the wind field and sea surface temperature associated with the Indian Ocean Dipole. [ABSTRACT FROM AUTHOR]

There is a continuous and relatively stable rainy period every spring in southern China (SC). This spring precipitation process is a unique weather and climate phenomenon in East Asia. Previously, the variation characteristics and associated mechanisms of this precipitation process have been mostly discussed from the perspective of seasonal mean. Based on the observed and reanalysis datasets from 1982 to 2021, this study investigates the diversity of the interannual variations of monthly precipitation in spring in SC, and focuses on the potential influence of the tropical sea surface temperature (SST) anomalies. The results show that the interannual variations of monthly precipitation in spring in SC have significant differences, and the correlations between each two months are very weak. All the interannual variations of precipitation in three months are related to a similar western North Pacific anomalous anticyclone (WNPAC), and the southwesterlies at the western flank of WNPAC bring abundant water vapor for the precipitation in SC. However, the WNPAC is influenced by tropical SST anomalies in different regions each month. The interannual variation of precipitation in March in SC is mainly influenced by the signal of El Niño-Southern Oscillation, and the associated SST anomalies in the equatorial central-eastern Pacific regulate the WNPAC through the Pacific-East Asia (PEA) teleconnection. In contrast, the WNPAC associated with the interannual variation of precipitation in April can be affected by the SST anomalies in the northwestern equatorial Pacific through a thermally induced Rossby wave response. The interannual variation of precipitation in May is regulated by the SST anomalies around the western Maritime Continent, which stimulates the development of low-level anomalous anticyclones over the South China Sea and east of the Philippine Sea by driving anomalous meridional vertical circulation. [ABSTRACT FROM AUTHOR]

A clear understanding of the spatial and temporal distribution characteristics of water resources is essential for the optimal allocation and sustainable utilization of water resources. In this paper, the spatial and temporal distribution characteristics of water resources in Henan Province were studied based on GIS, combining the Mann-Kendall (M-K) nonparametric test and rescaled range (R/S) analysis. In addition, SPSS software was used to analyze the influence of climate and land use type on water resources. The results indicated that (1) the hot spots of water resources were concentrated in the southwest, while the low values were concentrated in the northeast, and the distribution of water resources decreased from southwest to northeast. (2) In the past 21 years, spatiotemporal mutations in the water resource sequence occurred between 2010 and 2014. The Z-values of the M-K trend test were all less than 0, the H-values of groundwater resources (GWRs) were mostly greater than 0.5, and the h-values of surface water resources (SWRs) and total water resources (TWRs) were less than 0.5, showing an overall declining trend. However, this trend may change in the future. (3) From the correlation analysis, climate change had a greater impact on water resources than land use changes did. HIGHLIGHTS Combining the M-K method and R/S analysis to study water resource sequences and used GIS to visualize the analysis.; Both temporal and spatial characteristics of water resources had abrupt changes during the 21 years, and they occurred at similar times. Precipitation had a greater effect than temperature on water resources, while land use had no significant effect on water resources.;

[Objective] Based on different models, the spatiotemporal evolution characteristics of rainfall erosivity in the middle reaches of the Yellow River were explored, in order to providing a reference basis for the assessment of soil erosion hazards and planning of soil and water conservation measures in this area. [Methods] Daily rainfall data from 1981 to 2020 for the middle reaches of the Yellow River was used to explore the temporal and spatial variation characteristics of rainfall and rainfall erosivity based on two rainfall erosivity models. [Results] Average annual rainfall in the middle reaches of the Yellow River was between 349.90 mm and 699.90 mm. Spatial variation followed a fluctuating decreasing trend from southeast to northwest. Temporal variation exhibited a multi-peak insignificant upward fluctuation that had a 2-year main cycle change feature. There were some similarities between the two models of rainfall erosivity from the interannual trend characteristics and periodicity in the middle reaches of the Yellow River. However, areas with greater rainfall exhibited greater differences in rainfall erosivity estimated by the two models. The average annual rainfall erosivity in the middle reaches of the Yellow River was 767.00~3 003.40 MJ·mm/(hm2·h), exhibiting a high monthly concentration (concentrated in July-August) and showing a single peak shape. [Conclusion] There were significant vertical spatial differences from annual average rainfall erosivity in the middle reaches of the Yellow River, and there were spatial differences resulting from the influence of topography and landforms. The coefficient of variation in high-altitude areas was generally greater than in low-altitude areas. In the Qinling Mountains and the Guanzhong Plain in the southeast, the erosivity of rainfall decreased rapidly with increasing altitude. In in the northwest of the Loess Plateau region, the erosivity of rainfall increased gradually with increasing altitude. Therefore, in areas where erosivity of rainfall increases in the middle reaches of the Yellow River, appropriate measures should be taken to reduce the potential risk of soil erosion and to ensure the sustainable development of regional ecological security.

Interannual variation in net ecosystem carbon production (NEP) plays an important role in the carbon cycle processes. An agricultural ecosystem may fluctuate between carbon net source and carbon sink, or it may remain neutral. Thus, the long-term trends in NEP and the relevant meteorological, soil and biotic control of interannual variation in NEP remain unclear in farmland agroecosystems. To effectively assess the carbon sequestration potential of the farmland ecosystem, the eddy covariance dataset of rain-fed spring maize in Northeast China from 2005 to 2020 are used to investigate the interannual variations in NEP and the relevant meteorological, soil and biotic influences. NEP is partitioned into gross ecosystem productivity (GEP) and ecosystem respiration (RE) to explain the interannual variations of NEP and its influencing factors. The average annual NEP, GEP and RE are 272±109, 1086±177, 820±130 g·m-2·a-1, respectively, with no significant changes. The day-to-day dynamics of NEP, GEP and RE show single peak curves. NEP and GEP reach the maximums at the very time of maize tasseling, and the maximum value of RE occurs 13 days after NEP and GEP. Compared with RE, NEP variations are mainly caused by GEP. The redundancy analysis shows the interannual variations in NEP are mainly affected by precipitation as the meteorological factor and water use efficiency as the biotic factor, and the influence weights of the meteorological and biotic factors are 28.4% and 31.4%. Meanwhile, the influence weights of the meteorological factors (photosynthetically active radiation, carbon dioxide and precipitation), soil (soil volumetric water content and soil organic carbon) and biotic factors (leaf area index and water use efficiency) are 61.0%, 43.8% and 62.8% for the interannual variations in GEP. The interannual variations in RE are mainly affected by the soil (soil volumetric water content and soil organic carbon) and the biotic factors (leaf area index), and the influence weight of the soil factors (39.3%) is larger than that of the biotic factor (29.2%). The results indicate that, under the background of climate warming, interannual variations in NEP in rain-fed spring maize agroecosystems are likely to be more sensitive to changes in moisture, while radiation and temperature will contribute to interannual NEP variations by affecting vapor pressure difference and soil water content.

Based on 373 stations precipitation data in West China and National Centers for Environmental Prediction/National Center for Atmospheric Research（NCEP/NCAR）reanalysis data， variation characteristics of autumn rain in Western China are investigated， and associated atmospheric circulation systems affecting autumn rain in Western China and their interactiovemechanism are explored in this study.The results show that there are significant interannual variation characteristics of autumn rain in Western China.When more rainfall occurs in autumn in West China， there is an abnormal anticyclone at the low troposphere over the northern Philippines， and the associated southerly wind anomalies to the west side of this anticyclone anomaly carry warmer and wetter water vapor from northern Arabian Sea-Indian Peninsula-northern Bay of Bengal-China Peninsula to Western China.At the same time， the positive geopotential height anomaly， representing enhanced blocking activities， is observed over Europe， and the negative geopotential height anomaly， indicating enhanced low trough， is observed near Lake Balcosh in the middle troposphere.Therefore， this anomalous circulation configuration is conducive to the outbreak of cold air from higher latitude southward to West China.A clear atmospheric circulation teleconnection which plays an important role in the maintenance and development of blocking high in Europe and low-pressure trough near Lake Balcosh as well as circulation anomalies over East Asia， is seen over mid-high latitudes of Eurasia in the upper troposphere.Further analysis shows that the suppressed convection activities near the Philippines and Taiwan Island and the southern equatorial Indian Ocean play an important role in the maintenance of the anomalous anticyclone in the northern Philippines.On the other hand， when there is less rainfall in autumn in West China， the Eurasian wave train anomaly causes the positive height potential anomaly in Balkash Lake， which is not conducive to the establishment of low trough and the activity of cold air in West China.The active convection in the northern Philippines and the Equatorial East Indian Ocean and the negative height anomaly of Northeast Asia caused by Eurasian wave train lead to the formation of north wind anomaly in West China， which is unfavourable for the northward movement of warm air， and the divergence of water vapor flux in West China is unfavourable for precipitation.In shore， this configuration is not beneficial to precipitation.Therefore， the results in this study have certain application value for improving the understanding of the characteristics and mechanism of interannual variation of autumn rain in Western China and further improving its prediction level.

The Kuroshio-Oyashio confluence region (K/O region) plays a significant role in the global carbon cycle and climate change. In this study, we examined the concentration and composition of dissolved organic matter (DOM) in water samples collected from depths of 0 to 1000 meters between 2019 and 2021. The concentration of dissolved organic carbon (DOC) ranged from 30.54 to 113.21 μmol L-1, with higher concentrations observed in surface waters. The biological index (BIX) decreases with increasing depth, indicating decreasing in-situ production of plankton downwards. Additionally, the humification index (HIX) increased with depth, suggesting the transformation of labile to refractory DOC by bacteria. Using parallel factor analysis, we identified two humic-like (C1, C3) and one protein-like (C2) fluorescent components in 467 water samples. Water samples collected in 2020 exhibited significantly higher specific ultraviolet absorbance at 254 nm (SUVA254) (0.5 ± 0.2 L mg-1 m-1) and higher intensities of C1 (8.2 ± 2.69 *10-3 R.U.) and C3 (9.22 ± 4.39 *10-3 R.U.) compared to samples from 2019 and 2021. We found that water temperature had a positive correlation with C2 intensity (r = 0.33; p< 0.01), but negative correlations with C1 (r = −0.72; p< 0.01) and C3 intensity (r = −0.55; p< 0.01). Comparison of measured and theoretical values using a conservative physical mixing model revealed active biogeochemical processes of DOM during water mixing of the Kuroshio, Oyashio, and North Pacific Intermediate Water that change concentration and composition of DOM. Since the hydrology in the K/O region is sensitive for the ongoing climate warming, further investigation is needed to understand water mass mixing and associated DOM dynamics.