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Fine root phenology is controlled by complex mechanisms associated with aboveground phenological events and environmental conditions, and therefore, elucidating fine root responses to changing environments remains difficult without considering the dynamics within and among years. This study evaluated the response of fine root growth at variable time scales to the surrounding environments of soil temperature and moisture at ecosystem scales. Optical scanners were used to measure fine root production over 4 years in two forests dominated by either cypress or deciduous oak trees. Correlations between fine root production and soil temperature and moisture were analyzed using the state‐space model. Fine root phenology varied among years in the cypress stand and showed stable growth patterns in the oak stand as production peaked in spring every year. Soil temperature had a dominant influence on fine root production, while soil moisture enhanced fine root growth especially in the oak stand. Fine root responses to both soil temperature and moisture peaked during the early growing season, indicating its own temperature hysteresis that means different responses under same temperature within a year. The time‐varying response of fine root growth to external factors is a key perspective to explain fine root growth mechanisms, and whether evergreen or deciduous habits differentiates the fine root phenology due to a linkage between above‐ and belowground resource dynamics. [ABSTRACT FROM AUTHOR]

It is well known that the El Niño‐Southern Oscillation (ENSO) has a profound impact on climate over southern China (SC). This study indicates that independent from the ENSO variability, a meridional tripolar sea surface temperature (SST) pattern over tropical‐North Pacific in February has a close relationship with interannual variations in the frequency of spring extreme consecutive dry days (extreme‐CDDs) over SC. Further analyses suggest that the tripolar SST pattern has a good persistence from February to the following spring and could influence the variations of SC extreme‐CDDs through two ways. On one hand, the extratropical SST anomalies of the tripolar pattern can cause the meridional shift of the North Pacific subarctic oceanic front, resulting in a meridional dipole atmospheric pattern over the region from the North Pacific to East Asia through eddy‐mean flow interaction. The meridional atmospheric pattern can influence the East Asian upper‐level jet and western Pacific subtropical high (WPSH), leading to anomalous vertical motion and moisture transport over SC. On the other hand, the SST anomalies of the tripolar pattern over the tropical western Pacific can excite an overturning circulation and influence the WPSH through the Matsuno‐Gill response, also contributing to anomalous vertical motion and moisture transport over SC. These physical processes are further confirmed by numerical simulations. Therefore, through the aforementioned two physical ways, the February tripolar SST pattern can influence the moisture and dynamical conditions associated with the occurrence of extreme‐CDDs, consequently providing a factor and predictor for the variations of SC spring extreme‐CDDs. Key Points: The interannual variations of spring southern China (SC) extreme consecutive dry days (extreme‐CDDs) are related to a tripolar sea surface temperature (SST) pattern over tropical‐North Pacific in FebruaryThe tripolar SST pattern affects SC extreme‐CDDs through mid‐latitude eddy‐mean flow interaction and tropical overturning circulationThe February tripolar SST pattern provides a prediction source for the interannual variations of SC spring extreme‐CDDs [ABSTRACT FROM AUTHOR]

This study reveals that the interannual variability of the western edge of the western North Pacific (WNP) subtropical high (WNPSH) in early summer experienced an interdecadal decrease around 1990. Correspondingly, the zonal movement of the WNPSH and the zonal extension of the high-pressure anomaly over the WNP (WNPHA) in abnormal years possess smaller ranges after 1990. The different influences of the tropical SSTAs are important for this interdecadal change, which exhibit slow El Niño decaying pattern before 1990 while rapid transformation from El Niño to La Niña after 1990. The early summer tropical SSTAs and the relevant atmospheric circulation anomalies present obvious interdecadal differences. Before 1990, the warm SSTAs over the northern Indian Ocean and southern South China Sea favor the WNPHA through eastward-propagating Kelvin wave and meridional-vertical circulation, respectively. Meanwhile, the warm SSTA over the tropical central Pacific induces anomalous ascent to its northwest through the Gill response, which could strengthen the anomalous descent over the WNP through meridional-vertical circulation and further favor the eastward extension of the WNPHA to central Pacific. After 1990, the warm SSTAs over the Maritime Continent and northern Indian Ocean cause the WNPHA through meridional-vertical and zonal-vertical circulation, respectively. Overall, the anomalous warm SSTs and ascent and the resultant anomalous descent over the WNP are located more westward and southward after 1990 than before 1990. Consequently, the WNPHA features narrower zonal range and less eastward extension after 1990, corresponding to the interdecadal decease in the interannual variability of the western edge of the WNPSH. On the other hand, the dominant oscillation period of ENSO experienced an interdecadal reduction around 1990, contributing to the change of the El Niño SSTA associated with the anomalous WNPSH from slow decaying type to rapid transformation type. [ABSTRACT FROM AUTHOR]

This paper analyses and discusses the monthly and annual changes of chemical oxygen demand (COD), total nitrogen (TN), and total phosphorus (TP) concentrations from main sewage discharge ports in Xiangshan Bay. Using monitoring data obtained from 2010 to 2019, it systematically examines the monthly variation characteristics of the sewage discharge ports and the interannual changes in the fluxes of major pollutants into the sea. The concentrations of COD, TN, and TP, which were relatively high in November and January-March, generally declined. The annual and monthly changes fluctuated, but the flux into the sea generally decreased. The ecological environment of the nearby sea area is adversely affected, chiefly by land-based pollutants. During the five-year period, COD mainly came from soil erosion and domestic pollution, while TN and TP mainly came from agricultural activities and soil erosion. Hence, it is both necessary and urgent to improve the management of the sewage outfalls from land sources into the sea. [ABSTRACT FROM AUTHOR]

Through an analysis of station observations and reanalysis data, in this study, we investigate the variations of dust activity during 1979–2015 in western and southwestern Iran and their associated mechanisms. The dust day frequency (DDF) is used to identify dust activities. The results show larger interannual variabilities in the DDF in spring and summer, with standard deviations (σ) of 10% and 13%, respectively. Correlation analyses reveal that the interannual variability of DDF in western Iran is largely regulated by wind speed, precipitation and soil moisture in the region. The regional mean spring (March–May) DDF shows strong negative correlations with spring precipitation (correlation coefficient R = −0.5) and soil moisture (R = −0.6) over western to southwestern Iran, but strong positive correlations between the springtime DDF and surface winds can be found with the R reaching 0.4–0.6. Dust activity in the summer dry season (June–August) is mainly associated with surface winds over southwestern Iran, especially in regions near the Persian Gulf, where the R between the DDF and surface winds reaches 0.5. Meanwhile, the summer DDF also shows strong negative correlations (R < −0.4) with soil moisture of the top layer in the middle to southern part of the region. These results highlight the key roles of wind speed, precipitation and soil moisture in determining the interannual variation of dust activities in western and southwestern Iran.

Global changes are inducing migratory birds to advance their annual cycle. However, changes in the time of arrival at their breeding grounds have significant fitness implications. This study aims to identify factors affecting the variability in arrival time of migratory white storks (Ciconia ciconia L.) and to determine if their arrival at North African breeding grounds is occurring earlier. We monitored the arrival of ringed white storks at a breeding colony in Algeria between 2017 and 2021. The birds arrived at this breeding colony over an extended period spanning mid-December to mid-June each year. We found that stork arrival was negatively correlated with age and year of arrival, with older birds arriving first and stragglers consisting of first- and second-year birds arriving later. Notably, arrivals have been shifting toward earlier dates at this breeding ground. Furthermore, cluster analysis of arrival dates for each age-class revealed two distinct groups comprising early and late arrivals. Advancement of the annual cycle of the North African white stork population is consistent with phenological shifts induced by global changes and that have been recorded globally in a wide range of living organisms.

The relative importance of interannual environmental changes in shaping phytoplankton community structure remains unclear in the East China Sea (ECS), which is the largest marginal sea in the western North Pacific Ocean. Based on high-performance liquid chromatography (HPLC) analysis of a variety of photosynthetic pigments, we investigated spatiotemporal variations in the phytoplankton community in the northern East China Sea (NECS) from 2018 to 2020 to understand biomass and compositional responses to environmental conditions in a complex current system. Correlation heatmaps and generalized additive models (GAMs) were used to explore the variations in major phytoplankton groups and their relationships to temperature, salinity, depth, and nutrients. The results indicated that the phytoplankton community structure was significantly different between 2018/2019 and 2020. Under the conditions of high dissolved inorganic nitrogen (DIN) and low dissolved inorganic phosphate (DIP) concentrations in winter 2020, cryptophytes replaced diatoms as the dominant species and were observed for the first time in this study area. Dinoflagellates predominated throughout the euphotic zone in spring 2020, and statistical analysis showed that dinoflagellates tended to prevail at low DIP and high DIN conditions compared with diatoms. Summer was the only season with strong water stratification that reoccurred every year, and diatoms were mainly concentrated at nutrient-enriched 1% light depths in the summers of 2018/2019. However, a large amount of Changjiang River Diluted Water (CDW) from the surface and western part of the study area affected all sampling sites eastward to 126°E in 2020, allowing diatoms to be dominant at 100% and 30% light depths in the westernmost stations in the NECS. In autumn 2020, diatoms decreased significantly because of DIP-limited environmental conditions and were replaced by small phytoplankton. Under expected warming ocean scenarios with human-induced nutrient inputs, small phytoplankton will become dominant, while spring dinoflagellate blooms will occur more frequently in the NECS. International monitoring programs for marine ecosystems are currently needed in the ECS.

Understanding how environmental factors impact the interannual variation in scallop growth and subsequently developing an easily obtained parameter to indicate this variation could provide a scientific basis for optimizing their aquaculture. In this study, we have set a growth scenario of uniformly sowed scallops of the same initial size in the Changhai sea area. The Yesso scallop culture ecosystem model was used to simulate the growth of bottom-cultured Yesso scallop each year from December 1, 2006 to November 30, 2017. The results show that the annual growth rate was higher in the northwest than in the southeast, and there were obvious high-value areas near the islands. The scallop biomass was significantly lower in 2009–2010 and reached its highest point in 2013–2014. Based on the match-mismatch conditions of bottom-water temperature, food availability, and the Yesso scallop growth process, three factors were determined: suitable growth days (SGD), restricted growth days (RGD), and food accumulation (FA). Subsequently, a multiple regression relationship was proposed with scallop biomass to explore the reasons affecting the interannual variations in scallop growth. We found that the anomaly of the contribution of SGD and FA for the scallop growth was small, and the interannual variation in scallop biomass was mainly regulated by RGD in winter. Our results indicated that the interannual variation in RGD in winter was closely related to the regional averaged air temperature in early winter. The air temperature in early winter is easily obtained in practice. Consequently, it could be used to predict the interannual growth of bottom-cultured scallops to improve aquaculture planning and management.

In the mesosphere and lower thermosphere (MLT) region, residual circulations driven by gravity wave breaking and dissipation significantly impact constituent distribution and the height and temperature of the mesopause. The distribution of CO2 can be used as a proxy for the residual circulations. Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) CO2 volume mixing ratio (VMR) and temperature measurements from 2003 to 2020 are used to study the monthly climatology of MLT residual circulations and the mesopause height. Our analyses show that (a) mesopause height strongly correlates with the CO2 VMR vertical gradient during solstices; (b) mesopause height has a discontinuity at midlatitude in the summer hemisphere, with a lower mesopause height at mid‐to‐high latitudes as a result of adiabatic cooling driven by strong adiabatic upwelling; (c) the residual circulations have strong seasonal variations at mid‐to‐high latitudes, but they are more uniform at low latitudes; and (d) the interannual variability of the residual circulations and mesopause height is larger in the Southern Hemisphere (SH; 4–5 km) than in the Northern Hemisphere (NH; 0.5–1 km). Key Points: Monthly climatology of the mesopause height, and MLT CO2 gradients as signatures of the residual circulations are derived from SABER dataBoth the regions of maximum vertical CO2 gradients and mesopause height show strong seasonal variations at mid‐to‐high latitudesInterannual variations of the height of maximum vertical CO2 gradients and mesopause height are larger in the SH than in the NH [ABSTRACT FROM AUTHOR]

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Using the daily precipitation data from surface observation stations in China, the global atmospheric multi-factor and SST monthly analysis data from 1961 to 2017, the present study analyzed the climatic characteristics of the persistent heavy precipitation processes in South China and diagnosed and compared the characteristics of atmospheric circulation and sea surface temperature (SST) anomalies related to the interannual variation of persistent heavy precipitation in the rainy seasons in South China. The results showed that persistent heavy precipitation processes in South China might occur from March to December, of which 94.4% occurred in rainy seasons (April—September). The significant anomaly of local vertical upward movement in South China was a common feature of the two rainy seasons each year, associated with the interannual variation of regional persistent heavy precipitation. However, there were some differences between the two rainy seasons in terms of circulation anomalies, water vapor transport sources and abnormal distribution of SST. When the persistent heavy precipitation in the annually first rainy season was strong, SST anomalies was negative in the equatorial western Pacific region (145～170 ° E, 10 ° S～13 °N). Because of the strong subtropical high of the western Pacific due to the atmospheric Rossby wave response, the water vapor transport from tropical western Pacific to the southern China region was strengthened. This was favorable to regional persistent heavy precipitation. When the persistent heavy precipitation in the annually second rainy season was strong, the SST anomaly was positive in the equatorial Middle and East Pacific (175～140 °W, 5 °S～15 °N) and negative in the warm pool from the Eastern Indian Ocean to the Western Pacific. Through the subtropical high in the Northwest Pacific, the intensity of the tropical monsoon in the South China Sea, the water vapor transport, and the vertical circulation, the SST anomalies resulted in the heavy rainfall in South China in the annually second rainy season. [ABSTRACT FROM AUTHOR]

Yearly changes in tropical carbon‐cycling have been a major biotic determinant of the interannual variation in the rise of atmospheric carbon dioxide ([CO2]). The environmental responses underlying these changes remain poorly understood. A 21‐year field study (1997–2018) in a Costa Rican rainforest has produced the first multi‐decade record of landscape‐scale annual aboveground productivity for a tropical ecosystem. While none of the four production components (wood production; leaf‐, twig‐, and reproductive litterfall) increased over two decades, all significantly varied among years. Multi‐factor environmental models explained a large fraction of the inter‐year changes in two production components. Annual changes in three climatic factors and [CO2] jointly accounted for 84% of the variation in annual wood production. While the strongest response of wood production was to decline in years of slightly warmer nights, it also significantly declined in years with more dry‐season hours hotter than 28°C. The yearly changes in reproductive litterfall were largely (52%) determined by the combined effects of increasing [CO2] and declining annual radiation. Twig litterfall declined over the 21 years. Annual leaf litterfall, the largest component of field‐assessed aboveground production, showed no significant environmental responses. An extreme storm in the study's final year disrupted the environmental controls on production that prevailed through the prior 20 years. While important uncertainties are introduced by some of the field methods for assessing aboveground forest production, the findings of this first long‐term field study of annual landscape‐scale productivity raise deep concerns for the future of tropical forests as global warming proceeds. Plain Language Summary: The rate at which carbon dioxide (CO2) is increasing in the atmosphere is determined both by humans (fossil‐fuel emissions, deforestation) and by how the natural world processes CO2. The yearly increases in atmospheric CO2 have been significantly affected by tropical ecosystems. Changes in the balance between their uptake of huge amounts of CO2 through photosynthesis and their also very large CO2 emissions through respiration have been affecting the rate of accumulation of atmospheric CO2. Through two decades we studied annual plant productivity, the net result of photosynthesis and plant respiration, in a tropical rainforest. We found that tree growth (=wood production) declined with slightly hotter nights and when more daytime hours were above the optimum temperature for photosynthesis. Also, the expected benefits for forest productivity from the increase in atmospheric CO2 were quite limited. While both wood production and tree reproductive litterfall positively responded to the increase in atmospheric CO2, most of aboveground productivity did not. No productivity component increased over the two decades. Together these findings raise the prospect of declining tropical‐forest productivity as global warming intensifies. This would in turn speed up the rate of increase of CO2 in our atmosphere, a positive feedback to warming. Key Points: Interannual productivity changes dominated by negative temperature impactsMost of aboveground productivity unresponsive to increasing carbon dioxideDisruption of environmental controls by an extreme storm [ABSTRACT FROM AUTHOR]

Precipitation-use efficiency (PUE) is an important ecosystem indicator of the efficiency of carbon–water conversion. The trend and interannual variation of precipitation-use efficiency (PUE) response to climatic factors provide a theoretical foundation for understanding how Eurasian grasslands adapt to climate change. However, the long-term trends and regulating factors of PUE in Eurasian grasslands at the continental scale are still unclear. Here, we integrated long-term Global Inventory Monitoring and Modeling System (GIMMS) Normalized Difference Vegetation Index (NDVI), field surveys of aboveground net primary production (ANPP) and meteorological datasets during 1982–2015 to reveal the temporal variations and controls of PUE in Eurasian grasslands. We found that there was an overall uptrend of PUE (3 × 10−3 g C m−2 mm−1/10 yr) in Eurasian grasslands. The greatest increasing trends of PUE was found in forest steppe at the rate of 13 × 10−3 g C m−2 mm−1/10 yr, while greatest decreasing trend presented in alpine steppe at the rate of −2.6 × 10−3 g C m−2 mm−1/10 yr. The PUE showed linearly decreasing patterns with precipitation at the biome and continental scales, while it was uncorrelated with temperature at the continental scale and showed diverse patterns of linear increase, concave-down and no correlation with temperature for different biomes. The temporal variation of PUE was mainly controlled by precipitation in Eurasian grasslands. This result further revealed that climatic factors shaped the temporal pattern of PUE by the cascading effects networks of climatic factors (precipitation and temperature) − vapor pressure deficit (VPD) – leaf area index (LAI) – ANPP – PUE (CVLP-CENet). This study identified the long-term trends, interannual variations and controls of PUE in Eurasian grasslands over the past three decades, and provided crucial insights into understanding grassland ecosystems dynamics and response to climate change.

China has increased its vegetation coverage and enhanced its terrestrial carbon sink through ecological restoration since the end of the 20th century. However, the temporal variation in vegetation carbon sequestration remains unclear, and the relative effects of climate change and ecological restoration efforts are under debate. By integrating remote sensing and machine learning with a modelling approach, we explored the biological and physical pathways by which both climate change and human activities (e.g., ecological restoration, cropland expansion, and urbanization) have altered Chinese terrestrial ecosystem structures and functions, including vegetation cover, surface heat fluxes, water flux, and vegetation carbon sequestration (defined by gross and net primary production, GPP and NPP). Our study indicated that during 2001–2018, GPP in China increased significantly at a rate of 49.1–53.1 TgC/yr2, and the climatic and anthropogenic contributions to GPP gains were comparable (48%–56% and 44%–52%, respectively). Spatially, afforestation was the dominant mechanism behind forest cover expansions in the farming‐pastoral ecotone in northern China, on the Loess Plateau and in the southwest karst region, whereas climate change promoted vegetation cover in most parts of southeastern China. At the same time, the increasing trend in NPP (22.4–24.9 TgC/yr2) during 2001–2018 was highly attributed to human activities (71%–81%), particularly in southern, eastern, and northeastern China. Both GPP and NPP showed accelerated increases after 2010 because the anthropogenic NPP gains during 2001–2010 were generally offset by the climate‐induced NPP losses in southern China. However, after 2010, the climatic influence reversed, thus highlighting the vegetation carbon sequestration that occurs with ecological restoration. [ABSTRACT FROM AUTHOR]

The thermal effect of the Tibetan Plateau (TP) on the northern hemisphere climate has long been a hot topic of scientific research. However, the global effects of the TP heat source are still unclear. We investigate the teleconnection patterns coincident with the TP heat source in boreal summer using both observational data and numerical models including a linearized baroclinic model and an atmospheric general circulation model. The western TP shows the most intense variability in atmospheric heating and the most active connection to atmospheric circulations. The surface sensible heating component of the western TP heat source is associated with a high-latitude wave train propagating from North Japan to central North America through the Bering Sea and Canada. The radiative heating component is accompanied by a wavenumber-4 wave train over Eurasia. We focus on the global zonally-oriented pattern that is connected with the latent heat release from the western TP, referred to here as the TP–circumglobal teleconnection (TP-CGT). The TP-CGT pattern is triggered by the western TP latent heating in two parts starting from the TP: an eastward-propagating wave train trapped in the westerly jet stream and a westward Rossby wave response. The TP-CGT accounts for above 18% of the total variance of the circumglobal teleconnection pattern and modulates mid-latitude precipitation by superimposition. The western TP is the key region in which diabatic heating can initiate the two atmospheric responses concurrently, and the heating over northeastern Asia or the Indian Peninsula is unable to induce the circumglobal pattern directly. The unique geographical location and strong tropospheric heating also make the western TP as a "transit area" of transferring the indirect impact of the Indian summer monsoon (ISM) to the TP-CGT. These results enhance our understanding of the relationship between the circumglobal teleconnection and the ISM and is helpful for improving the prediction of the circumglobal teleconnection variability. [ABSTRACT FROM AUTHOR]

Over 70% of the cities in China are experiencing urbanization, and urban heat island intensity (UHII) evaluation studies have been widely performed. However, under the rapid economic development in China, few studies on surface urban heat island (SUHI) interannual variations have been conducted in coastal cities in the leading economic region of the Yangtze River Delta. In this study, the long-term summer daytime SUHI from 2001 to 2019 is studied based on the remotely sensed land surface temperature (LST) in 11 coastal cities in the Yangtze River Delta. The results show that notable SUHIs occur in the study area with high spatial heterogeneity, particularly in the central area, including Shanghai, Hangzhou, and Ningbo. The SUHI trends are not synchronous across the study area, with suburban areas revealing higher trends than city center areas. In addition, all 11 cities show an increasing trend of the urban heat proportion index (UHPI) over 19 years, which is more profound in Shanghai and Zhoushan but less profound in Lianyungang and Wenzhou. The strong correlation between the UHPI and artificial impervious coverage indicates that artificial impervious coverage plays an important role in determining the spatial and temporal distributions of the summer daytime SUHI in the 11 coastal cities, which are especially notable in Ningbo and Taizhou. [ABSTRACT FROM AUTHOR]

Open biomass burning (BB) frequently occurs in spring over Southeast Asia (SEA). The concentration of fine particulate (PM 2.5) produced by BB and its impacts on air quality in downwind aeras exhibit significant interannual variations, which are controlled by emission intensity and meteorological circulation. In this study, a regional air quality model system (RAQMS) was applied to investigate the contributions of BB emissions in SEA to atmospheric PM 2.5 concentrations over South China in March (a spring month) during 2009–2018 and their interannual variations. Higher near-surface BB-PM 2.5 (refers to the PM 2.5 produced by BB in SEA) concentrations and contributions were mainly distributed in the source region and its vicinity, while the higher tropospheric BB-PM 2.5 concentrations and contributions were characterized by a long belt extending from BB source regions to Yangtze River Delta (YRD) in South China. Combined with the vertical distribution of BB-PM 2.5 on the transported path profile, it indicated that higher BB-PM 2.5 concentrations were mainly concentrated in 0∼1500 m above the ground over source regions, while the maximum BB-PM 2.5 concentrations in the downwind area were distributed in 1500∼3500 m above the ground. The monthly mean tropospheric BB-PM 2.5 concentrations were higher in March 2009, 2010, 2012, and 2013, with evident correlation with interannual variation of BB emissions. Sensitivity experiments suggested that the near-surface and tropospheric BB-PM 2.5 concentrations over South China had changed by-48.1%∼190.5% and −48.0%∼213.8%, respectively in March 2009–2018 by fixing BB emissions unchanged at the mean of the 10 years, being greater than the changes caused by meteorological conditions and other affecting factors (∼20%). In addition, the relative contributions of BB emission from various regions in SEA on the mean near-surface and tropospheric BB-PM 2.5 concentrations over South China were further identified. The spatial distribution for monthly mean tropospheric BB-PM 2.5 concentrations (fill color, mg m−2) and contributions (grey contour, %) of BB-PM 2.5 to total tropospheric PM 2.5 concentrations in March of 2009–2018. [Display omitted] • Interannual variation of the impacts of BB on PM 2.5 in South China was investigated. • Contributions of BB in Southeast Asia to PM 2.5 over South China are quantified. • Dominant factors affecting the transboundary transport are explored. • BB in west Myanmar had a dominant contribution to tropospheric PM 2.5 in South China. [ABSTRACT FROM AUTHOR]

Abstract The Qinghai–Tibet Plateau (QTP) is particularly sensitive to global climate change, especially to elevated temperatures, when compared with other ecosystems. However, few studies use long‐term field measurements to explore the interannual variations in plant biomass under climate fluctuations. Here, we examine the interannual variations of plant biomass within two vegetation types (alpine meadow and alpine shrub) during 2008–2017 and their relationships with climate variables. The following results were obtained. The aboveground biomass (AGB) and belowground biomass (BGB) response differently to climate fluctuations, the AGB in KPM was dominated by mean annual precipitation (MAP), whereas the AGB in PFS was controlled by mean annual air temperature (MAT). However, the BGB of both KPM and PFS was only weakly affected by climate variables, suggesting that the BGB in alpine ecosystems may remain as a stable carbon stock even under future global climate change. Furthermore, the AGB in PFS was significantly higher than KPM, while the BGB and R/S in KPM were significantly higher than PFS, reflecting the KPM be more likely to allocate more photosynthates to roots. Interestingly, the proportion of 0–10 cm root biomass increased in KPM and PFS, whereas the other proportions both decreased, reflecting a shift in biomass toward the surface layer. Our results could provide a new sight for the prediction how alpine ecosystem response to future climate change.

The Yellow Sea (YS) experiences heavy advection fog during boreal summer, which seriously affects marine transport and harbor activities. Using a set of long‐term observations, the present study reveals the interannual variability in the YS fog during its core season (May‐June‐July, MJJ). The spaceborne lidar supports that a station‐based index represents the fog over the northern YS in a seasonal mean sense. The composite soundings according to the YS fog index show that the temperature difference is evident within the boundary layer and becomes indistinguishable in the free atmosphere. This implies that the driver of the MJJ YS fog originates from the bottom boundary of the fog layer. Regression analyses of sea surface temperature (SST) and air‐sea fluxes show that the local SST strongly modulates the northern YS fog at interannual scale. The fog during foggier years features a significant decrease in specific humidity, suggesting that the colder sea surface facilitates fog occurrence through strong turbulent cooling. This study identifies the local SST as a key driver of the interannual variation in the northern YS fog during the core season and provides predictive values by linking the YS fog to the preceding SST. Key Points: The observations of coastal stations can reflect the interannual variability in Yellow Sea (YS) fogThe local sea surface temperature (SST) drives the the interannual variability in YS fogThe April‐May SST helps to predict the YS fog in May‐June‐July [ABSTRACT FROM AUTHOR]

Summertime upwelling off the southern Vietnamese coast is one of the most essential oceanographic features in the South China Sea. Based on analyzing the 38‐year (1982–2019) sea surface temperature (SST) images, locations of summertime Vietnamese upwelling centers are found to be classified into three sub‐regions: the Southern Coastal Upwelling (SCU; south of 12.5°N), the Northern Coastal Upwelling (NCU; north of 12.5°N), and the Offshore Upwelling (OU; east of 110°E). Variations of upwelling intensities in the three sub‐regions are further quantified via an adaptive SST‐based upwelling index, and possible processes relevant to wind field (including wind stress and its curl) and currents are, respectively, proposed. The analyses show that the local along‐shore wind stress, inducing offshore Ekman transport, can produce the coastal upwelling‐favorable condition but is not the only one of main factors in controlling the interannual variability of the coastal upwelling. The enhancement of wind stress curl dipole off the southern Vietnamese coast, which accompanies the scaling up of the double‐gyre structure east of Vietnam and results in the reinforcement and southward shift of eastward‐flowing jet, and the exaggeration of the cyclonic gyre‐associated southward along‐shore current are responsible for the intensification of upwelling in the SCU, but suppress the development of upwelling in the NCU. The well‐developed double‐gyre structure serves as the essential condition for the OU occurrence and the OU is much more sensitive to the change of cyclonic gyre to the north of the jet. Plain Language Summary: Upwelling is one of the most important oceanographic features, and it plays important roles in regulating local and global climates and marine ecosystem. In general, past research has suggested that upwelling off eastern Vietnam in the South China Sea occurs in summer and significantly suffers interannual changes, and wind forcing, along‐shore current, and eastward‐flowing jet off the eastern Vietnam could be the controlling factors. In this study, we explore the Vietnamese upwelling in detail by separating the entire upwelling area into three sub‐regions (the southern Vietnameses coast, the northern Vietnameses coast, and the offshore region) and clarify the roles of controlling factors in each region. Along the Vietnamese coastal regions, the local along‐shore wind stress can produce the coastal upwelling‐favorable condition but is not the main factor. The enhancement of wind stress curl dipole off the southern Vietnamese coast and the southward along‐shore current north of ∼12°N are responsible for the intensification of upwelling in the southern coast, but suppress the development of upwelling in the northern coast. In the offshore region, the well‐developed double of oceanic gyre is the essential condition and the change of cyclonic gyre to the north of the jet plays a more important role. Key Points: The summertime Vietnamese upwelling can be grouped into Northern and Southern Coastal Upwelling regions, and Offshore Upwelling regionEnhanced wind stress curl dipole favors (suppresses) the development of upwelling in the Southern (Northern) Coastal Upwelling regionThe essential condition for the development of Offshore upwelling is the well‐developed oceanic double‐gyre structure [ABSTRACT FROM AUTHOR]

Understanding the impacts of climate extremes on the carbon cycle is important for quantifying the carbon-cycle climate feedback and highly relevant to climate change assessments. Climate extremes and fires can have severe regional effects, but a spatially explicit global impact assessment is still lacking. Here, we directly quantify spatiotemporal contiguous extreme anomalies in four global data sets of gross primary production (GPP) over the last 30 years. We find that positive and negative GPP extremes occurring on 7% of the spatiotemporal domain explain 78% of the global interannual variation in GPP and a significant fraction of variation in the net carbon flux. The largest thousand negative GPP extremes during 1982?2011 (4.3% of the data) account for a decrease in photosynthetic carbon uptake of about 3.5?Pg?C?yr?1, with most events being attributable to water scarcity. The results imply that it is essential to understand the nature and causes of extremes to understand current and future GPP variability.

Agricultural nitrogen (N) non-point source pollution in the North China Plain is a major factor that affects water quality and human health. The characteristics of N leaching under different N application conditions should be further quantified accurately in winter wheat (Triticum aestivum L.) and summer maize (Zea mays L.) rotation farmland in North China, and a basis for reducing the risk and evaluation of N leaching in this area. A three-year field experiment was conducted using an in situ leakage pond method at a typical farmland in Henan in 2017–2020. Crop yield, soil nitrate N residues, and N utilization were also studied during the study period. Five N fertilizer rates were established with 0 (CK), 285 (LN), 465 (MN), 510 (MNO), and 645 (HN) kg N ha−1 for one rotation cycle. MNO was applied with chemical and organic fertilizers. The concentration of nitrate N in the soil leaching solution of CK, LN, MN, MNO, and HN was 0.81-, 1.49-, 3.65-, 5.55-, and 7.57-fold that of the World Health Organization’s standard for underground drinking water. The exponential relationship between the N application rate and leaching was obtained when the annual N input exceeded 300 kg ha−1, and the N leaching rate increased greatly. The leaching rate of nitrate N in the total N was 50.6–82.4% under different treatments of N application. The combination of chemical and organic fertilizers treatment (MNO) reduced the amount of N that was leached in dry years. The nitrate leaching amount of summer maize accounts for 83.0%, 49.4%, and 72.0% of the total nitrate leaching amount of the whole rotation cycles in 2017–2020. LN and MN were recommended as the optimized N application here (285–465 kg N ha−1) with the two-season rotation grain yield of 17.2 ton ha−1 (16.5–17.9 ton ha−1) and nitrate N leaching of 21.6 kg ha−1 (12.6–30.5 kg ha−1).

To investigate the main modes of interannual variation of chlorophyll-a (Chla) with seasonal evolution and its variation cycle in the North Indian Ocean based on satellite-derived products during 1998–2016, a season-reliant empirical orthogonal function (S-EOF) analysis and power spectrum analysis based on Fourier transform are applied in the study. The first three dominate modes reveal distinct Chla variability, as the S-EOF1 features by one dipole pattern have a negative anomaly in the central western Indian Ocean and a positive anomaly off the Java–Sumatra coasts, which is mainly synchronously associated with the climate indices of the positive Indian Ocean dipole (IOD) and eastern Pacific El Nino (EP-El Niño). The S-EOF2 indicates a tripolar structure with positive anomalies located in the central Indian Ocean surrounded by two negative anomalies, which is one year behind a positive IOD and EP-El Niño event. The S-EOF3 exhibits a different dipole distribution, with a positive anomaly in the central west and a negative anomaly in the southeast, synchronized or lagging behind the central Pacific El Nino (CP-El Niño). Moreover, regarding the correlation between the main modes of interannual variation and the IOD and El Nino events, the dynamic parameters (such as SST, SLA, rain, and wind) of the tropical Indo-Pacific Ocean are discussed using time-delay correlation and linear regression analysis to explain the key factors and possible influencing mechanism of the joint seasonal and interannual variations of Chla in the northern Indian Ocean.

Two distinct rainfall stages over the Central Highlands (CH) of Vietnam during the rainy season have been objectively defined using the high‐resolution Vietnam Gridded Precipitation data set for 1983–2010 (28 years): a second rainy stage (SRS) embedded in the conventional rainy season. Surprisingly, the pronounced interannual variation in the SRS onset date has led to three apparent regimes: an early (late) SRS with a 1 month longer (shorter) rainfall period occurring in early July (until mid‐August) and a normal SRS starting in late July. Almost all the early SRS years occur during El Niño developing phases, particularly during the Niño3.4 sea surface temperature (SST) increase from January through December. Water vapor budget analyses reveal that the interannual variation in the divergent water vapor flux is in response to the warmer July tropical Pacific SST anomalies, resulting in rainfall enhancement over the CH and eventually inducing early SRS onset. Plain Language Summary: The Central Highlands (CH) of Vietnam contribute up to 90% of the country's total coffee production and 25% of its total hydropower potential. A second rainy stage (SRS) is observed in late July in this region, which is distinct from the conventional rainy season that occurs in late April–early May. Because the onset of the SRS has a strong impact on coffee yield and hydropower potential in the CH, this study examines the climatology of and interannual variation in the SRS onset date during 1983–2010. An early (late) SRS with a 1 month longer (shorter) rainfall period occurs in early July (until mid‐August). Almost all the early SRS years occur during El Niño developing phases. An association between the early SRS onset years and strengthening of the water vapor flux convergence induced by the warmer July tropical Pacific SST anomalies is discovered. Key Points: A second rainy stage (SRS) is embedded within the conventional rainy seasonEarly (late) SRS with a 1 month longer (shorter) rainfall period occurs in early July (until mid‐August); a normal SRS starts in late JulyAlmost all the early SRS years occur during El Niño developing phases [ABSTRACT FROM AUTHOR]

Hypoxia has been observed worldwide and causes great damage to marine ecosystems. In the northeastern mariculture areas of the Shandong Peninsula, summer oxygen depletion and even hypoxia have been observed in the bottom layer, but the underlying dynamics are still poorly understood. In the current study, the physical controls of variations in bottom layer oxygen concentrations in summer and their interannual variations in the northeastern mariculture areas of the Shandong Peninsula were first investigated using in situ observations collected during 2016–2020. Over the past 5 years, the dissolved oxygen (DO) concentrations of the bottom layer have ranged from 0.8 to 13.0 mg L−1 and exhibited a robust annual cycle, with the lowest value occurring in August. Hypoxia events covering several days were observed intermittently in the summers of 2016 and 2017. Summer oxygen depletion was caused by the combined effects of ocean stratification and enhanced biogeochemical oxygen consumption. At the interannual time scale, stratification and bottom layer DO concentrations showed synchronous variations and both peaked in 2018. The underlying mechanism was related to bottom layer currents, which were created by southerly monsoon winds. Strong/weak southerly surface winds induced a strong/weak bottom shoreward advection of cold, oxygen‐rich water and resulted in strong/weak stratification and high/low DO concentrations. The results provide a good reference for coastal mariculture management in the Shandong Province and enrich our understanding of the global distribution of coastal hypoxia. Plain Language Summary: Dissolved oxygen (DO) is necessary to sustain the life of all fish and invertebrates. When the DO concentration falls below 2.0 mg L−1 (≈61 µmol kg−1), hypoxia causes great damage to marine ecosystems. Low DO concentrations in summer and even hypoxia are observed in the bottom layer of northeastern mariculture areas in the Shandong Peninsula, which is mainly farmed for precious seafood such as sea cucumbers, abalones, and scallops that are less mobile and vulnerable to hypoxia. In the current study, the physical controls of bottom layer oxygen variations in summer and their interannual variations in the northeastern mariculture areas of the Shandong Peninsula were first investigated using in situ observations during 2016–2020. The results indicate that bottom layer oxygen depletion in summer was caused by the combined effects of stratification and biogeochemical oxygen consumption. In addition, stratification and bottom layer DO concentrations showed synchronous interannual variations. The underlying mechanism was related to the bottom layer current, which was created by southerly monsoon winds. The results provide a good reference for coastal mariculture management in the Shandong Province and enrich our understanding of the global distribution of coastal hypoxia. Key Points: Summer low dissolved oxygen and even hypoxia was observed in the bottom layer of northeastern mariculture areas of the Shandong PeninsulaBottom layer oxygen depletion in summer was caused by the combined effects of stratification and biogeochemical oxygen consumptionBottom shoreward advection caused by southerly winds controlled synchronous interannual variations in stratification and the oxygen budget [ABSTRACT FROM AUTHOR]

This study investigates the interannual variability of winter precipitation over the Three River Source (TRS) region in China based on precipitation observations collected at stations in the TRS region and reanalysis datasets for the period of 1980–2015. The results suggest that the TRS winter precipitation has distinct interannual variability with discordant trends in different months, that is, an increasing trend is found in November and February, a decreasing trend is found in other winter months, and interannual variations in precipitation are different in different months. The mechanisms for the interannual variation in monthly precipitation over the TRS region are significantly different in different winter months. The interannual variability of TRS precipitation in November is modulated by an anomalous westerly water vapour transport (WVT) branch. This anomalous WVT branch is related to a North Atlantic‐Europe‐Tibetan Plateau (NA‐E‐TP) wave‐train that originates in the North Atlantic due to the ocean–atmosphere interaction. In December, a circum‐global teleconnection (CGT) wave‐train can induce anomalous westerly WVT in the TRS region, resulting in increased precipitation there. This CGT wave‐train is triggered by warm SST anomalies in the central‐eastern tropical Pacific associated with the El Niño‐Southern Oscillation (ENSO). The interannual variability of TRS precipitation in January and February is affected by southwesterly WVT anomalies over the TRS region, which are associated with a southeastward propagating wave‐train over Eurasia caused by the North Atlantic Oscillation (NAO). In March, the interannual variability of TRS precipitation is modulated by the leading mode of the Eurasian circulation that resembles the Scandinavian (EU1) pattern, which can cause anomalous southwesterly WVT in the TRS region. In winter, the characteristics of sea surface temperature anomalies, weather systems, and atmospheric circulations associated with interannual variations of monthly precipitation in the TRS region are different for individual winter months. [ABSTRACT FROM AUTHOR]

A more objective assessment of the freshwater scarcity risk at a watershed basis scale contributes to the achievement of the Sustainable Development Goals (SDGs), in which water plays a key role in issues like safe and affordable drinking water, water-related disasters, forest management, biodiversity and ecosystems. Within the SDGs, water scarcity is assessed primarily by using the ratio of withdrawal to availability (WTA). This index has been developed to evaluate the average annual conditions on a broad scale, such as country or large basin. However, there are insufficient cases for assessing specific and detailed risk conditions by using this original WTA concept, due to seasonal and interannual variations of the river discharge and withdrawal volumes. For example, infrastructure (e.g. large dams) and its operation, can drastically change the available water and demand volumes at temporal scales finer than annual. Because recently many daily and monthly records of river discharge and water use have become publicly available, it is possible to conduct water scarcity risk assessments on a monthly basis. By employing these datasets, in this study, we propose to compare volumes of available water and demand by using a Sectoral and Statistical Demand to Availability (SS-DTA) index. The novelty of this index is marked not only by the use of monthly volumes of available and required water but also by how environmental water requirements are included and the statistical relevance of the evaluation. Usually, to determine the available water resources, existing methods deduct from the river discharge the volumes that are required to preserve the surrounding ecosystems. Our proposed method considers the environmental flow requirements as one of the water-demand sectors allowing a simultaneous evaluation of water use that is not possible with existing methods. We applied this method to three representative river basins, two located in Japan (the Tone and the Arakawa River basins) and the Brantas River basin in Indonesia. The results showed the variations of water scarcity risk level through the river operation in each river basin. In the Tone River basin, it was succeeded in a drought year to decrease its risk level from 1 to 0, and to transport sufficient volume of water to the Arakawa River basin through an artificial channel to meet the demands at the same time. In the Brantas River basin, the river operation changed the SS-DTA score from 3 to 2, which means the water scarcity risk level was alleviated, while the main impact of the operation was found in high-water season to decrease the flood risk. Because the number, type, and priority of water demands can be adjusted based on the local situation and all the timeseries data of each demand sector are visualized in parallel, the result includes not only the whole risk level of the river basin but also the practical and specific degree of the risk with demand sector information.

This study identifies a significant positive association between tropical North Atlantic (TNA) sea surface temperature (SST) during preceding spring and the frequency of intense tropical cyclones (TCs) making landfall over mainland China during autumn on interannual time scales. Observational analyses show that a warm SST anomaly in TNA during spring can induce a warm SST anomaly in the western part of the western North Pacific (WNP) in subsequent autumn, through a chain of air‐sea coupled processes such as Rossby‐wave response, wind‐evaporation‐SST feedback, and westward advection of warm surface water. The physical mechanisms are verified using a suite of coupled numerical experiments performed by the state‐of‐the‐art Community Earth System Model. The warm SST anomaly in the western part of WNP is responsible for the genesis and intensification of intense TCs in situ, and the climatologically mean southeasterly steering flow is favourable for the intense TCs to make landfall over mainland China. [ABSTRACT FROM AUTHOR]

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Long-term ecological studies are important for understanding wild populations' dynamics and processes and the actual factors that can determine their decline. Here, we report the results of a 28-years-long (1992–2019) monitoring of three distinct populations of a tortoise, Testudo hermanni , in Central Italy, with an emphasis on their population abundance trends and on the eventual variation in their habitat use across years and among the study areas. Samplings were conducted by Visual Encounter Survey (VES) methodology, and using a suite of statistical analyses including correlations and Generalized Linear Models analyses. Our data showed a statistically significant decline in tortoise sightings through time, and concurrently also a variation in habitat use by tortoises. In all the three study areas, we observed a significant increase of tortoise sighting frequency in the habitat type characterized by high (>taller than 200 cm) shrubby and wooded vegetation. Since our analyses revealed no significant change in the habitat type availability by year in each study area, we suggest that T. hermanni was increasingly selecting closed vegetation spots throughout the years. We hypothesize that this observed trend of shift in habitat selection could be due to lowering their body temperatures to prevent overheating. So, the selection of more covered spots would be a thermal ecology adaptive consequence of the ongoing global warming. [ABSTRACT FROM AUTHOR]

Besides local emissions, biomass burning (BB) emissions in peninsula Southeast Asia (PSEA) and domestic anthropogenic emissions in North China (NC) are also significant black carbon (BC) sources over South China (SC) in spring. Meanwhile, the East Asian summer monsoon (EASM) is established with the wind field reversal, influencing the region‐based contributions to BC over SC. Herein, BC sources for SC were tracked by region and by sector using the Community Earth System Model with a BC‐tagging technique. During the spring of 2000–2014, 27% of BC surface concentration (BCS) and 64% of BC column burden (BCC) over SC stems from nonlocal sources. BC from NC is mainly transported below 850 hPa. It is the dominant nonlocal contribution to BCS (17%) and largely composed of residential and industrial sectors. Nonlocal emissions inside and outside China contribute 28% and 36% to BCC, respectively. Generally transported above 850 hPa, BC from PSEA is the largest nonlocal contributor (20%) to BCC and contributes 80% of BCC in BB sector. Additionally, the interannual variation in EASM onset times bring a maximum of −5% to +7%/−2% to +7% variation in BCC/BCS. The BC outflow/inflow contributed from NC dominates the BC decrease/increase over SC with southerly/northerly wind anomaly induced by early/late EASM onset, yet regional transport from PSEA contributes minor BC changes. The simulated BC is significantly positively correlated with the varying EASM onset times, but not with emissions, indicating the decisive role of meteorology in the interannual variation of BC over SC during springtime. Key Points: Biomass burning from peninsula Southeast Asia dominates the black carbon column burden in biomass burning sector (80%) over South ChinaBC outflow/inflow from North China dominates the BC decrease/increase over South China induced by early/late East Asian summer monsoon onsetVariation in East Asian summer monsoon onset times dominates the interannual variation of BC over South China in spring [ABSTRACT FROM AUTHOR]

The zonal shift in the western North Pacific subtropical high (WNPSH) is closely associated with moisture transport in East Asia and is thus an important factor that determines the amount of summer precipitation in the region. Climatologically, the WNPSH retreats eastward from early to late summer. However, there is high variability in the early to late summer shift in the WNPSH from year to year. Thus, the interannual variability in the intraseasonal zonal displacement of WNPSH from early to late summer was examined in this study. The results showed that the intraseasonal shift in the WNPSH from early to late summer was almost unrelated to the El Niño‐Southern Oscillation (ENSO) signal, although previous studies have claimed that ENSO can modulate the variation in the summer mean WNPSH. More specifically, the El Niño or La Niña years were not predictive of how the WNPSH would shift zonally from early to late summer. Otherwise, the zonal displacements of the WNPSH were more of mid‐latitude origin. In the strongly retreating years (SRY), the mid‐latitude wave train was much more significant than that in the weakly retreating years (WRY). The mid‐latitude wave train was reminiscent of the Silk Road teleconnection pattern (SRP). In the SRY, the centres of the wave trains had opposite signs in early and late summer, which resulted in the opposite features of the WNPSH between early and late summer. The consistency of the three reanalysis datasets confirmed the robustness of our results. [ABSTRACT FROM AUTHOR]

The interdecadal changes in the mechanisms accounting for the interannual variation in autumn snow cover over the central eastern Tibetan Plateau (TP) are investigated in this study. An autumn snow index is constructed by area averaging the snow cover over the central eastern TP. The snow index changed from a predominantly negative phase to a positive phase in 1995. Then, the data were divided into two subperiods, 1979–1994 (P1) and 1995–2017 (P2), and the differences in the mechanisms accounting for the variation in autumn snow cover were compared between P1 and P2. An analysis of the local process shows that the autumn snow cover variations over the central eastern TP are caused by snowfall from both autumn and late summer. The autumn snow cover variation over the central eastern TP imposed more significant atmospheric cooling effects during P1 than P2. During P2, except for the local process, the interannual variation in autumn snow cover in the central eastern TP is also affected by atmospheric circulation anomalies originating from the upstream North Atlantic Ocean. During P2, snow‐related North Atlantic sea surface temperature (SST) anomalies (SSTA) can induce a wave train‐like atmospheric pattern that propagates eastward across the Eurasian continent and reaches the TP. Further analysis shows that this wave train‐like atmospheric pattern over the midlatitude Eurasian continent mainly obtains energy from climatological mean flow through baroclinic energy conversion. In contrast, during P1, the North Atlantic SSTA‐related atmospheric circulation pattern tends to propagate northeastward and cannot contribute to the variation in autumn snow cover over the central eastern TP. Key Points: The mechanisms for interannual variations in autumn snow over the central eastern Tibetan Plateau differ before and after 1995An atmospheric wave train pattern contributes to the variation in autumn snow cover over the central eastern TP after the mid‐1990sThe dipole North Atlantic SST anomalies can induce a wave pattern linking the SST‐TP snow relationship after the mid‐1990s [ABSTRACT FROM AUTHOR]

Because of the increase in the nation's need for wind energy, the impacts of climate change on wind energy have been investigated. In addition to long‐term changes, wind energy also shows robust interannual variations, but little effort has been devoted to understanding the underlying mechanisms. In this study, the impact of El Niño on the summer mean wind power density (WPD) over China is investigated. The abilities of five sets of reanalysis data in measuring the interannual variability of the WPD over China are assessed. Encouraging results are seen for all reanalysis datasets, with the MERRA and ERA‐Interim datasets showing the best performance. The relationship between El Niño and the following summer WPD is identified over China. During El Niño decaying year summers, the WPD over south of the Yangtze River valley increases, whereas the WPD over north of the Yangtze River valley decreases. The WPD changes are dominated by an anomalous anticyclone located in the northwestern Pacific. The anticyclone leads to strong southerly winds in southern China and thereby enhances the WPD. In regions north of the Yangtze River valley, the low surface pressure gradient causes a reduction in wind speed and thereby a weak WPD. Because the year‐by‐year variation in El Niño‐Southern Oscillation (ENSO) is highly predictable, our results shed light on the seasonal prediction of wind power over China. [ABSTRACT FROM AUTHOR]

This study identifies a significant positive correlation between the Pacific Meridional Mode (PMM) index and frequency of tropical cyclones (TCs) landfalling in China during peak TC season (June–November) of the period 1977–2018. This interannual association is independent of two types of El Niño–Southern Oscillation. Large‐scale circulation over the western North Pacific (WNP) modulated by PMM can affect TC genesis location/frequency and steering flow that directly determine TC landfalls in China. During the positive PMM phase, anomalous off‐equatorial heating over the eastern North Pacific can induce anomalous low‐level cyclonic circulation and upper‐level anticyclonic circulation over most of the main development region in the WNP, as a Gill‐type Rossby wave response. The resultant larger low‐level relative vorticity and weaker vertical wind shear are conducive to the formation of more TCs over the main development region. The anomalous easterly steering flow in the north flank of the anomalous low‐level cyclonic circulation is favourable for more TCs moving westward/northwestward and making landfall in China. The physical mechanism for the impact of PMM on large‐scale circulation over the WNP is verified by numerical experiments using the Community Atmospheric Model. The PMM index is demonstrated to be a crucial predictor for landfalling TC frequency in China in statistical seasonal prediction models. [ABSTRACT FROM AUTHOR]

Aims Litterfall is a key parameter in forest biogeochemical cycle and fire risk prediction. However, considerable uncertainty remains regarding the litterfall variations with forest ages. Quantifying the interannual variation of forest litterfall is crucial for reducing uncertainties in large-scale litterfall prediction. Methods Based on the available dataset (N = 318) with continuous multi-year (≥2 years) measurements of litterfall in Chinese planted and secondary forests, coefficient of variation (CV), variation percent (V P), and the ratio of next-year litterfall to current-year litterfall were used as the indexes to quantify the interannual variability in litterfall. Important Findings The interannual variations of litterfall showed a declining trend with increasing age from 1 to 90 years. The litterfall variations were the largest in 1–10 years (mean CV = 23.51% and mean V P = −28.59% to 20.89%), which were mainly from tree growth (mean ratio of next-year to current-year = 1.20). In 11–40 years, the interannual variations of litterfall gradually decreased but still varied widely, mean CV was ~18% and mean V P ranged from −17.69% to 21.19%. In 41–90 years, the interannual variations minimized to 8.98% in mean CV and ~8% in mean V P. As a result, forest litterfall remained relatively low and constant when stand age was larger than 40 years. This result was different from the previous assumptions that forest litterfall reached relatively stable when stand age was larger than 30, 20 or even 15 years. Our findings can improve the knowledge about forest litter ecology and provide the groundwork for carbon budget and biogeochemical cycle models at a large scale. [ABSTRACT FROM AUTHOR]

Sex ratios are commonly skewed and variable in wild populations, but few studies track temporal trends in this demographic parameter. We examined variation in the operational sex ratio at two protected and declining breeding colonies of Magellanic Penguins (Spheniscus magellanicus) in Chubut, Argentina. Penguins from the two colonies, separated by 105 km, migrate north in the non‐breeding season and have overlapping distributions at sea. Conditions during the non‐breeding season can impact long‐term trends in operational sex ratio (i.e., through sex‐specific survival) and interannual variation in operational sex ratio (i.e., through sex‐specific breeding decisions). We found an increasingly male‐biased operational sex ratio at the two disparate colonies of Magellanic Penguins, which may contribute to continued population decline. We also found that the two colonies showed synchronous interannual variation in operational sex ratio, driven by variation in the number of females present each year. This pattern may be linked to sex‐specific overwintering effects that cause females to skip breeding, i.e., to remain at sea rather than returning to the colony to breed, more often than males. Contrary to our predictions, colony‐wide reproductive success was not lower in years with a more male‐biased operational sex ratio. We did find that males showed more evidence of fighting and were less likely to pair when the operational sex ratio was more male biased. Our results highlight an indirect mechanism through which variation in the operational sex ratio can influence populations, through a higher incidence of fighting among the less abundant sex. Because biased sex ratios can reduce the size of the breeding population and influence rates of conflict, tracking operational sex ratio is critical for conservation. [ABSTRACT FROM AUTHOR]

• The annual ET in a natural oak forest in central China did not exhibit an obvious trend over the six years with a larger interannual variation (IAV). • Environmental factors had a greater impact on the IAV of annual ET than the biological factors, with reference crop evapotranspiration (ET 0) exerting the most significant influence on ET. • The IAV of monthly ET was primarily controlled by precipitation during the early growing season, but it changed to be controlled by radiation and temperature (i.e., atmospheric evaporation demand) during the mid-growing season. Investigating the interannual variation (IAV) of evapotranspiration (ET) is important for understanding the water cycle in forest ecosystems. However, there has been little research on interannual variability of ET in warm-temperate forests under a changing environment. In this study, 6-year eddy covariance data (2017–2022) in a warm-temperate natural oak forest in central China were used to examine the IAV of ET and its driving factors. The mean and standard deviation of annual ET from 2017 to 2022 were 610 and 122.8 mm (with a coefficient of variation (CV) of 20 %), respectively. The annual ET did not exhibit an obvious trend over the six years with a larger IAV. Environmental factors had a greater impact on the IAV of annual ET compared to the biological factors, with reference crop evapotranspiration (ET 0) exerting the most significant influence on ET. The IAV of monthly ET was primarily controlled by precipitation during the early growing season, but it changed to be controlled by radiation and temperature (i.e., atmospheric evaporation demand) during the mid-growing season. We concluded that atmospheric evaporation demand rather than water supply dominated the IAV of annual ET in the warm-temperate natural oak forest in central China, and occasional seasonal drought only affected the ET in a short time-scale (no more than three years). There is a need to measure three components of ET (transpiration, canopy interception evaporation and soil evaporation) in order to better understand the IAV of ET and the underlying biophysical control mechanisms. [ABSTRACT FROM AUTHOR]

The surface energy balance algorithm for land (SEBAL) is a commonly used method for estimating evapotranspiration (ET) at a regional scale; however, the cloudy and rainy characteristics of subtropical monsoon regions pose a greater challenge for estimating paddy field ET based on remote sensing technology. To this end, a typical subtropical climate region in southern China (Ganfu Plain irrigation system) was selected as the study area. Subsequently, we evaluated the applicability of the SEBAL model for estimating the ET of paddy fields at the daily scale; derived the interannual variation (2000–2017) characteristics of early, middle, and late rice ET; and finally analyzed the spatial distribution patterns of rice in different hydrological years. The results demonstrated that: (1) the SEBAL model estimated ET accurately on a daily scale, with R2, NSE, and RMSE values of 0.85, 0.81, and 0.84 mm/day, respectively; (2) the ET of paddy fields in the irrigated area was higher in July and August and the interannual trend of ET of early rice was not obvious, with a declining trend observed in middle rice and late rice from 2000 to 2009, which was followed by an increasing trend from 2009 to 2017; and (3) variations in the spatial distribution of ET were significant for early and late rice at different precipitation levels and less obvious for middle rice in wet years but significant in dry years. Overall, this study verified the applicability of the SEBAL model for estimating ET in paddy fields in subtropical regions and provided a basis and reference for the rational allocation of water resources at a regional scale.

East Asian summer rainfall is affected by both the continental northern East Asian low (NEAL) and the western North Pacific subtropical high (WNPSH) in the lower troposphere. This study investigates the joint effect of the two circulation factors on East Asian summer rainfall. It is found that the rainfall in East Asia behaves differently in the years with in-phase and out-of-phase variation between the NEAL and WNPSH. When the NEAL and WNPSH vary in phase, i.e. when they are both stronger, the rainfall anomaly shows a dipole pattern in East Asia and displays opposite changes between north and south of 30°N. When the two circulation factors vary out of phase, the rainfall anomaly is concentrated in the Yangtze River valley.

The wind field plays a decisive role in haze generation and dissipation processes over the Beijing–Tianjin–Hebei (BTH) region. Although geographically the BTH region is under the influence of the East Asian winter monsoon (EAWM), this study finds that common indices of the EAWM cannot adequately describe the actual wind speed changes in the BTH region. Thus, observational data are used to analyze the interannual variations of the winter wind field over the BTH region. The results show that the average winter wind speed is 2.0 m s−1, with a slight rate of decline of 0.01 m s−1 yr−1. In most cases, strong-wind years correspond to negative sea surface temperature (SST) anomalies over the tropical Pacific, whereas weak-wind years correspond to positive SST anomalies. Moreover, correlation and composite analyses show that the interannual variability is affected by multiple factors, including the following: (1) the pressure gradient in the high and middle latitudes of the Northern Hemisphere, as in strong-wind years the pressure gradient helps cold air move from high latitudes to middle latitudes; (2) the skin temperature in Eurasia, as low skin temperature in Eurasia in strong-wind years is conducive to the accumulation of cold air; and (3) the SST of the tropical Pacific east of the Philippines, as in strong-wind years the high temperature of this area affects the BTH region through anticyclonic activity and associated tropical circulation systems.

Under the background of global warming, the interannual variation trend of coastalupwelling has become a research hotspot of global climate change in recent years. Based on thedata of temperature, chlorophyll concentration and wind field from 2002 to 2016, marine catches inGuangdong Province from 2010 to 2018, this paper studies the interannual variation trend ofintensity and center of upwelling along the east coast of Guangdong Province, and discusses therelationship between upwelling intensity and wind speed, marine catches and upwelling intensity.The results show that in the past 15 years, the intensity of upwelling in the east coast ofGuangdong Province is generally strengthened; the center of upwelling is at 23.6°~23.7°N in allprobability, and there is a trend of northward movement.The coastal wind plays an important rolein the interannual variation of upwelling; excluding the damage of fishing structure and otherfactors, the correlation between marine catches and upwelling in Guangdong Province is very high,and the correlation coefficient reaches to -0.81.

Runoff series is the basic data for the planning, design and operation management inhydraulic engineering. As the largest tributary of the Yangtze River, the Hanjiang River is thewater source area of middle route of the South-to-North Water Diversion Project and Hanjiang-to-Weihe River Water Diversion Project in Shaanxi province. Therefore, it has great significance tostudy the runoff evolution rule in Hanjiang River Basin for ensuring the water resources securityand improving the carrying capacity of regional water resources. Based on the 48-year measureddaily runoff series of the hydrological stations of Yangxian, Huangjiagang and Huangzhuang in themain stream of the Hanjiang River, this paper comprehensively analyzes the spatial-temporalevolution trend, year of abrupt change, periodic variation, interannual variation and annualdistribution of runoff in Hanjiang River Basin via multi methods and multi dimensions. The resultsshow that the runoff consistency was broken as follows: ① The annual runoff from the upper,middle and lower reaches of the Hanjiang River decreased with the trend of -312 million m3/(10a),-1 478 million m3/(10a) and -593 million m3/(10a) respectively, and the downward trend continuedstrongly, but the monthly runoff of lower reaches of the Hanjang River was increased significantlyin January and February; ② The abrupt change of the Hanjiang River occurred in 1985 and 1990, andthe inter-annual variation characteristic values and the annual distribution characteristicindexes of these stations decreased slightly after the abrupt change; ③ The runoff series of theHanjiang River had three types of periodic changes: 40~48 a, 11a and 4~7 a; ④ The inter-annualrunoff variation coefficient of the Hanjiang River was between 0.28 and 0.46, and the extremeratio was between 2.72 and 7.73; ⑤ The maximum monthly average runoff of the three stations wasin July or September, and the minimum monthly average runoff was in December or February, and theannual distribution of runoff was concentrated in July to October, accounting for more than 50% ofthe annual runoff. This study has guiding significance for the future planning, design, operationmanagement, and water resources allocation of hydraulic engineering in the Hanjiang River Basin.At the same time, it can provide a research idea for analyzing the spatial-temporal evolution ruleof runoff in other river basins.

Based on the historical data of meteorological disasters in East China during 2004–2015, the overall characteristics, interannual variations and the hazards of meteorological disasters in different provinces of East China were analyzed. The results indicated that flood disaster (including landslide and mud-rock flow) induced by rainstorms had caused the largest affected area and total failure area of crops, and also caused the largest number of affected people and collapsed houses. Strong convection weather (including gale, hail, thunder and lightning) disaster resulted in the largest number of deaths and typhoon disaster caused the greatest direct economic losses. There were significant decreasing trends in the affected area and the total failure area of crops, and the number of affected people and deaths during 2004–2015, while the direct economic loss caused by meteorological disasters showed no significant trend in East China. The hazards of meteorological disasters had obvious regional differences. In the northern part of East China, the hazards of drought and strong convection weather disasters were higher, but in the southern part, there were higher hazards of flood disaster. In the eastern coastal areas of East China, the hazards of typhoon disaster were higher. Hazard analysis of meteorological disasters has important significances for disaster prevention and mitigation, risk management and crisis response.

Background Sub-lakes are important for the maintenance of the ecosystem integrity of Lake Poyang, and zooplankton play an important role in its substance and energy flow. Methods A seasonal investigation of zooplankton was conducted in spring (April), summer (July), autumn (October) and winter (January of the following year) from 2012 to 2016 in a sub-lake of Lake Poyang. The aim of the present study was to understand the seasonal dynamics and interannual variation of zooplankton communities and their relationship to environmental factors. Results A total of 115 species were identified in all samples in the four years, which comprised of 87 Rotifera, 13 Cladocera and 15 Copepoda. Rotifera was the dominant group in terms of quantity, and its species richness and abundance were significantly higher when compared to Cladocera and Copepoda (P

Present study analyzes spatial patterns and factors of interannual variations of 10–20-day and 30–60-day intraseasonal oscillation (ISO) intensity during boreal summer over tropical western North Pacific (WNP). The three leading modes of 10–20-day ISO intensity variation feature a southeast–northwest distribution, a southeast–northwest contrasting pattern, and large loading over the subtropics, respectively. The two leading modes of 30–60-day ISO intensity variation show a west–east distribution and a west–east dipole pattern, respectively. Three types of sea surface temperature (SST) influences are identified on the ISO intensity variation. One is a direct influence of El Niño–Southern Oscillation (ENSO) on seasonal mean background over tropical WNP via a Rossby wave type response. This type of influence is prominent on the leading mode of 10–20-day ISO intensity and the eastern portion of the second mode of both 10–20-day and 30–60-day ISO intensity. Second is an indirect influence of ENSO on seasonal mean background over subtropical WNP and the Maritime Continent through anomalous Walker circulation. This type of influence includes the western portion of the second mode of both 10–20-day and 30–60-day ISO intensity. Third is an influence of regional SST anomalies. Opposite SST anomalies in the North Indian Ocean and tropical North Pacific work together to modulate seasonal mean background over tropical WNP. This type of influence is prominent on the leading mode of 30–60-day ISO intensity. In addition, internal atmospheric process may play a role in 10–20-day ISO intensity change over subtropical WNP. [ABSTRACT FROM AUTHOR]

Based on the regional climate model RegCM4.5 driven by National Centers for Environmental Prediction (NCEP) reanalysis, the influence of cumulus convection schemes (CCSs) on the winter North Pacific storm track (WNPST) is investigated. It is found that the climatology, interannual variation, spatial modes and characteristic indices of the WNPST are extremely sensitive to the choice of CCS. Among the selected CCSs, WNPST climatology and interannual variation in the Kuo scheme are better than in other CCSs, with a smaller root mean square error. The WNPST spatial modes and strength indices in the Kuo and Grell schemes are more consistent with NCEP reanalysis. The Kuo scheme has a stronger ability to simulate the WNPST latitude index and the interannual variation of winter characteristic indices. In addition, we attempt to reveal the possible reasons for the different performances of CCSs from the viewpoint of baroclinic energy conversion (BCEC). It is found that the energy conversion from the mean available potential energy to the eddy available potential energy (BCEC1) has no significant difference among the Kuo, Grell and Emanuel schemes, while energy conversion from the eddy available potential energy to eddy kinetic energy (BCEC2) in the Kuo scheme is obviously better than other CCSs, which means that the differences in BCEC2 among these CCSs may be one of the key reasons affecting the simulation results of the WNPST. [ABSTRACT FROM AUTHOR]

The persistence and distribution of species under changing climates can be affected by both direct effects of the environment and indirect effects via biotic interactions. However, the relative importance of direct and indirect climate effects on recruitment stages is poorly understood. We conducted a manipulative experiment to test the multiway interaction of direct and competition-mediated effects of climate change on vegetation dynamics. Following stand-replacing fire in California mixed-conifer forest, we seeded two conifer species, Pinus ponderosa and Abies concolor, in two consecutive years, one relatively normal and the other with an unusually wet and snowy winter followed by a hot summer. We additionally manipulated snow amount and competitive environment for both years. We found the effects of the snowpack treatment were contingent upon other abiotic factors (year of seeding) and biotic factors (shrub competition). Under ambient snowpack, shrubs reduced recruitment of P. ponderosa seedlings, but this negative effect disappeared with reduced snowpack. Additionally, the effects of shrubs on seedlings differed between cohorts and by life stage. In a warmer future, decreased snowpack may increase seedling emergence, but hotter and drier summers will decrease seedling survival; the effects of shrubs on conifers may become less negative as temperatures increase. [ABSTRACT FROM AUTHOR]

The long-term variability of chlorophyll a (Chl-a) was analyzed during a 12- year period (2002 - 2014) in the Bransfield Strait, Antarctica, to assess the interannual variability of the Chl-a and its main regulating environmental variables. We found that Chl-a was significantly correlated with the El Nino Southern Oscillation (ENSO) phase (r = -0.65), sea surface temperature (SST) (r = 0.70), and wind speed (r = 0.72), and changes in these factors preceded the Chl-a change by 0 - 4 months. High phytoplankton blooms (indicated by Chl-a levels) tended to coincide with higher SSTs, and lagged with wind speed variation during La Nina periods. This suggests that atmospheric teleconnections with ENSO-related processes, SST, and wind speed could have a direct impact on phytoplankton biomass in the Bransfield Strait in short-term (< 4 months) scales. Furthermore, our simple multivariable regression analysis showed the prominent possibility of usina the three variables to prediet Chl- a in the Bransfield Strait region. Overall, this study will help us to understand how atmospheric and oceanic fluctuations could affect phytoplankton dynamics in the Southern Ocean. [ABSTRACT FROM AUTHOR]