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Understanding and accurately predicting how the sensitivity of terrestrial vegetation productivity to rising atmospheric CO2 concentration (β) is crucial for assessing carbon sink dynamics. However, the temporal characteristics and driving mechanisms of β remain uncertain. Here, observational and CMIP6 modeling evidence suggest a decreasing trend in β at the Northern Middle and High Latitudes during the historical period of 1982–2015 (−0.082 ± 0.005% 100 ppm−1 year−1). This decreasing trend is projected to persist until the end of the 21st century (−0.082 ± 0.005% 100 ppm−1 year−1 under SSP370 and −0.166 ± 0.006% 100 ppm−1 year−1 under SSP585). The declining β indicates a weakening capacity of vegetation to mitigate warming climates, posing challenges for achieving the temperature goals of the Paris Agreement. The rise in vapor pressure deficit (VPD), that triggers stomata closure and weakens photosynthesis, is considered as the dominated factor contributing to the historical and future decline in β, accounting for 62.3%–75.2% of the effect. Nutrient availability and water availability contribute 15.7%–21.4% and 8.5%–16.3%, respectively. These findings underscore the significant role of VPD in shaping terrestrial carbon sink dynamics, an aspect that is currently insufficiently considered in many climate and ecological models. [ABSTRACT FROM AUTHOR]

• Global sensitivity of water use efficiency to increasing CO 2 present a declining trend. • Increasing vapor pressure deficit is the main cause for the decreasing sensitivity. • CMIP6 models underestimate the decreasing water use efficiency sensitivity. Ecosystem water use efficiency (WUE), which measures the ratio of carbon gain to water loss, is crucial to the global water, energy, and carbon cycles. It is an important metric in understanding how efficiently an ecosystem uses water to assimilate carbon and is affected by various environmental factors, including CO 2 levels. However, the temporal dynamics of CO 2 -induced changes in WUE (CO 2_ WUE) remain uncertain. After isolating CO 2_ WUE from total changes in WUE , we assessed historical changes in global CO 2 _WUE and future projected trends. We found that the increasing atmospheric CO 2 concentration enhanced global WUE by 5.65 ± 1.14 % 100 ppm−1 during 1982–2015. However, CO 2 -driven gains in WUE exhibit a significant declining trend across most of the Earth's land surface during 1982–2015 (−1.38 ± 0.19 % 100 ppm−1 yr−1). This widespread CO 2_ WUE decline is projected to continue throughout the remainder of the 21st century. The decline in CO 2_ WUE implies that the global land surface is likely to witness a higher water cost to maintain the land carbon sink. This finding suggests a heightened difficulty of mitigating global warming and an elevated risk of global water scarcity. The global CO 2_ WUE decline is primarily driven by rising vapor pressure deficit (VPD) reducing photosynthesis and increasing total evaporation. Our findings highlight the key role of VPD in the coupling of global water and carbon cycles and reveal a continuous increase in the water cost of the global land carbon sink. [ABSTRACT FROM AUTHOR]

• Vegetation growth contributes 85.4–90.5% of the increased water consumption. • 94.3–98.8% of global vegetation land are sustainable due to rising precipitation. • Unsustainable regions will continuously expand due to the greening world. The global vegetation cover is increasing and is expected continue increasing till 2100, owing to CO 2 fertilisation and afforestation. This greening phenomenon may create conflicting demands for water between ecosystems, atmosphere, and humans, and has aroused a series of controversies. For exploring the effects of greening phenomenon on terrestrial water availability, we estimated the balance between water supply (precipitation and snowmelt runoff) and water consumption (evaporation, human water use, transpiration, and interception losses) in the global vegetation land based on the outputs of 30 models from the Coupled Model Intercomparison Project Phase 6. Water consumption showed an increasing trend in most regions of global vegetation land for the period 1982–2016 as well as 2040–2100, mainly driven by the increased transpiration and interception losses for vegetation growth (contributing 85.4–90.5%). Although the greening phenomenon widely exacerbates water shortages, 94.3–98.8% of the global vegetation land was still found to be sustainable during 1982–2100, due to the water supply exceeding the total water consumption. More attention should be paid to the unsustainable regions where the total water consumption exceeded the total water supply. Such areas were continuously found to increase from 2.1–5.3% (1982–2016) to 5.4–5.7% (2040–2100) of the global vegetation land. We predict that Oceania, Northern India, the southern coastal regions of North America will be transformed from sustainable regions in 1982–2016 to unsustainable regions in 2040–2100. [ABSTRACT FROM AUTHOR]

We investigate global trends in seasonal water discharge using data from 5668 hydrological stations in catchments whose total drainage area accounts for 2/3 of the Earth's total land area. Homogenization of water discharge, which occurs when the gap in water discharge between dry and flood seasons shrinks significantly, affects catchments occupying 2/5 of the total land area, and is mainly concentrated in Eurasia and North America. By contrast, polarization of water discharge, associated with widening of the gap in water discharge between dry and flood seasons, occurs in catchments covering 1/6 of the land area, most notably in the Amazon Basin and river basins in West Africa. Considering the major climatic and anthropogenic controlling factors, i.e. precipitation (P), evaporation (E), glacial runoff (G), and dam operations (D), the world's river basins are classified as P, DEP, GEP, and EP types. Contributions from each controlling factor to either the homogenization or polarization of the seasonal water discharge for each type of river have been analyzed. We found that homogenization of discharge is dominated by dam operations in GDEP and DEP river basins (contributing 48% and 64%) and by homogenized precipitation in GEP and EP river basins. Evaporation and precipitation are primary factors behind the polarization of discharge, contributing 56% and 41%. This study provides a basis for a possible decision tool for controlling drought/flood disasters and for assessing and preventing ecological damage in endangered regions. Unlabelled Image • Homogenization of water discharge occurred in 2/5 of the total land area. • Polarization of water discharge is found in 1/6 of the World's land. • Homogenized discharge is controlled by dam operation and precipitation change. • Polarized discharge is dominated by changes in precipitation and evaporation. [ABSTRACT FROM AUTHOR]

Large differences in projected future annual precipitation increases in North America exists across 27 CMIP6 models under four emission scenarios. These differences partly arise from weak representations of land-atmosphere interactions. Here we demonstrate an emergent constraint relationship between annual growth rates of future precipitation and growth rates of historical temperature. The original CMIP6 projections show 0.49% (SSP126), 0.98% (SSP245), 1.45% (SSP370) and 1.92% (SSP585) increases in precipitation per decade. Combining observed warming trends, the constrained results show that the best estimates of future precipitation increases are more likely to reach 0.40–0.48%, 0.83–0.93%, 1.29–1.45% and 1.70–1.87% respectively, implying an overestimated future precipitation increases across North America. The constrained results also are narrow the corresponding uncertainties (standard deviations) by 13.8–31.1%. The overestimated precipitation growth rates also reveal an overvalued annual growth rates in temperature (6.0–13.2% or 0.12–0.37°C) and in total evaporation (4.8–14.5%) by the original models' predictions. These findings highlight the important role of temperature for accurate climate predictions, which is important as temperature from current climate models' simulations often still have systematic errors. [ABSTRACT FROM AUTHOR]

• Increasing precipitation is the main reason of land wetting. • Land drying is initially associated with precipitation deficit, and then increasing VPD amplifies the drying. • The estimated VPD contribution in the drying region is nearly 6 times of that of precipitation under high forcing pathways. • Elevated CO 2 concentration partly mitigates land drying by altering vegetation physiology. Increase Vapor Pressure Deficit (VPD) imposes higher atmospheric demand on land evaporation in the warming climate. However, it remains uncertain that how the increasing evaporative stress may enhance the global pattern of land drying. Here, we have used self-calibrating Palmer Drought Severity Index (scPDSI) based on outputs from 20 CMIP6 models to study the contribution of VPD, precipitation and other climatic factors to scPDSI changes globally. Global land drying and wetting are found to be regionally dependent, with statistically significant enhancement of drying and wetting under SSP2-4.5, SSP3-7.0 and SSP5-8.5 pathways (2015–2100) compared to the historical period (1961–2014). Increasing precipitation is the main reason of land wetting, while the land drying is initially associated with precipitation deficit, it is partly dominated by the increasing VPD over 20 ∼ 27% of the global land, where the estimated VPD contribution is nearly 6 times of that of precipitation under high forcing pathways. Elevated CO 2 concentration is suggested to partly mitigate land drying by altering vegetation physiology; however, this mitigation is quantified to be limited. Our findings highlight the key role of VPD in accelerating global pattern of land drying and its increasing dominance in the warming climate. [ABSTRACT FROM AUTHOR]

A regional analysis of soil temperature (ST) is essential for improving our understanding of the soil thermal regime and its link with the atmosphere. This study attempts to assess trends in the Poyang Lake Basin (PLB) ST magnitude during 1960–2016 from station observations at multiple depths. The Mann–Kendall, Thiel-Sen, linear regression, and probability density statistics (PDF) are used for ST trend assessment with a significance level of 95%. The ST seasonal variability shows minimum values in winter (8℃) and maximum in the summer season (32 ℃). On an interannual scale, spring and winter seasons exhibited a significant increase in both land surface temperature (LST) (0.4℃, 0.4℃) and ST (0.3 °C, 0.15℃) magnitude than summer (LST − 0.1℃, ST 0.2℃) and autumn seasons (LST 0.3℃, ST 0.2℃). The northern basin exhibited a significant increase in LST, and ST magnitude, especially during the cold seasons (spring, winter) than the warm seasons. The maximum and minimum temperature trend and their diurnal difference infer an increase in the minimum temperature, especially during the summer, autumn, and winter seasons. The PDF further inferred that extreme cold events' frequency decreased, and a significant increase in extreme warm events is obvious in the recent decade. The increasing trend in soil temperature magnitude is more in the northern basin than the high-altitude southern basin. Large-scale global warming and regional water and energy cycle changes can be the leading factors of such a warming trend. [ABSTRACT FROM AUTHOR]

• Empirical formulae for estimating normal-/back- flow discharge at distributary ends. • Function charts for rapid identification of three back-flow forms in distributaries. • Contributions of driving factors to flow discharge change at distributary ends. Unusual back-flow events occurred in 2015 and 2017 at the near-mainstream ends of the three distributaries of the Jingjiang Reach, middle Yangtze River, China. It is presently challenging to precisely quantify back-flow discharges at river distributary ends where normal-flow discharges are measured chronically. This problem is more complicated at the ends of the three Jingjiang distributaries, each of which is more than 100 km long, and thus favors the generation of different back-flow forms. We use empirical formulae based on the Saint-Venant Equation and the Fall Index Method to quantify impacts on flow discharges at the two ends of each distributary of three key hydrodynamic variables: (1) water discharge at Zhicheng hydrological station, (2) total discharge from the four southwest tributary rivers, and (3) water levels at the two ends of the distributaries. We use the variable control approach to identify the contribution ratios of natural and human driving factors to flow discharges at the two ends of the distributaries during five historical stages. The empirical formulae provide reasonable results, with high values of correlation coefficients (R 2 = 0.84 ∼ 0.98) obtained, demonstrating that the total water discharge from the four southwest tributary rivers is negligible. These formulae perform well in reproducing observed flow discharges at the two ends of the distributaries, especially the maximum discharges and cumulative volumes for normal-flow and back-flow events. Three charts are devised for different flow conditions at the two ends, from which back-flow events can be rapidly identified. Before impoundment of the Three Gorges Dam (TGD), riverbed adjustment caused by the lower Jingjiang Cutoff Projects and the Gezhou Dam contributed the most to flow discharge changes (≥50 %) at the near-mainstream ends of the distributaries. Afterwards, precipitation dominated (>60 %). In the future, back-flow events are expected only to occur at Mituosi (i.e., Taipingkou) and Nanxian hydrological stations, for which optimal reservoir operation and water resource utilization could remedy the back-flow crisis. Use of climate models and more advanced technologies such as remote sensing and GIS are recommended to enhance the reliability of predictions. [ABSTRACT FROM AUTHOR]

• The influence of human activities on river bed scour is discussed. • The influences of human activities on bifurcation relationship of branch and morphology of bar are revealed. • The relationship between the Yangtze River and major rivers in the world is compared and analyzed. Reservoirs and river management projects have operational impacts on the runoff, sediments, and morphologies of tidal reaches. Therefore, it is of great significance to analyze the influence of human activities on the hydrology and geomorphology of the tidal reaches of the Yangtze River (YR). We measured topographic and water–sediment flux over the past 40 and 60 years, respectively, to determine changes in the characteristics of riverbed lowering or deposition, shoal areas, and diversion ratio of branch channel (DRBC), along with the dynamics and driving mechanisms. The results indicated that cumulative scouring of the tidal reaches occurred from 1981 to 2021 (time-averaged annual riverbed lowering depth = 4.35 cm), which was mainly controlled by reductions in sediment influxes, followed by sand mining and waterway dredging. Riverbed lowering or deposition in the tidal reaches were characterized by deep channel lowering and shoal deposition from 1981 to 2001. From 2001 to 2021, lowering of both deep channel and shoal occurred, with the riverbed lowering volume of the low-flow channel accounting for 79.3 % of the total riverbed lowering volume. The shoal areas exhibited an increasing trend from 1981 to 2001, but reduced by 2.35 % in the 2001–2021 period mainly due to the operation of Three Gorges Reservoir (TGR). Moreover, the implementation of waterway improvement projects slightly increased the shoal areas since 2016. Particularly, the DRBC accounted for 15–50 % of the increase in bifurcation ratio during the 1962–1981 periods. Reductions in sediment influxes and unbalanced riverbed lowering caused by adjustments of flow processes increased the DRBC from 1981 until prior to the implementation of the river and waterway improvement projects. After the implementation, further increases in the DRBC were effectively inhibited or the ratio was decreased. In the near future, the amounts of sediment influxes in the YR Basin will remain low or even further decrease, leading to sustained or intensified scouring of the tidal reaches, and the impacts of shrinking shoal and scouring of branch channels should be focused upon. Overall, the findings of this study provide an in-depth understanding of the impacts of human activities on the riverbed morphologies of tidal reaches. [ABSTRACT FROM AUTHOR]

Publisher's note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. Correction to: Long-term changes in observed soil temperature over Poyang Lake Basin, China, during 1960-2016 Dan Lou SP 2 sp - Xiao Shi SP 1,3 sp - Waheed Ullah SP 4 sp - Dawei Shi SP 5 sp - Chao Li SP 6 sp - Yuanfang Chai SP 7 sp - Xu Jinping SP 8 sp - Hao Zhou SP 9 sp 1 China Meteorological Administration Transportation Meteorology Key Laboratory, Nanjing 210008, China 2 Glarun Technology Co., ltd., Nanjing 211100, China 3 Jiangsu Meteorological Bureau, Meteorological Services Center, Nanjing, China 4 Defense and Security, Rabdan Academy, Abu Dhabi 114646, United Arab Emirates 5 Lianyungang Meteorological Bureau, Lianyungang 222000, China 6 Jiangsu Meteorological Observatory, Nanjing 210008, China 7 Department of Earth Sciences, V.U. University Amsterdam, Amsterdam, Netherlands 8 Anji Meteorological Bureau, Anji 313300, China 9 Peixian Meteorological Bureau, Xuzhou 221000, China The original article has been corrected. [Extracted from the article]

Dam operation profoundly modifies downstream flow-sediment regimes, resulting in a variety of geomorphologic responses, without uniform laws. The Jingjiang reach of the middle Yangtze River has undergone significant adjustment mode alterations, with intensive channel erosion and major adjustment area changing from the bankfull channel to the medium flow channel at the time boundary of the Three Gorges Dam (TGD) impoundment. While these changes have received some attention, little work has been undertaken to reveal the reason. In this study, based on 172 cross sections measured in the post-flood period from 2003 to 2015, different river patterns, longitude and reach-averaged channel dimensions were assessed to reflect the channel adjustment characteristics of the Jingjiang reach. An index has been proposed to measure the cumulative water transport capacity of each discharge interval and to assess the relationship with reach-scale medium flow channel dimensions. The results indicate that the channel adjustment changes are directly driven by the alterations of flow duration and sediment transport capacity. With the deficiency of floods, medium flow channels respond quite well to small and medium discharges of under approximately 16,500 m 3 /s. A discharge of 16,500 m 3 /s which can be regarded as a critical threshold, corresponds to the average top levels of braided and meandering channel bars, which are of morphological significance in constraining the passing flow in the medium flow channel. Small and medium discharges under the critical threshold associate with relatively larger reductions in sediment loads and hold increased geomorphic impacts (Q m JP), eventually resulting in adjustment mode alterations. The results present herein for the Jingjiang reach of the Yangtze River can provide a better understanding of dam operation and the corresponding impacts on downstream channel morphology. [ABSTRACT FROM AUTHOR]

The machine learning algorithms application in atmospheric sciences along the Earth System Models has the potential of improving prediction, forecast, and reconstruction of missing data. In the current study, a combination of two machine learning techniques namely K-means, and decision tree (C4.5) algorithms, are used to separate observed precipitation into clusters and classified the associated large-scale circulation indices. Observed precipitation from the Chinese Meteorological Agency (CMA) during 1961–2016 for 83 stations in the Poyang Lake basin (PLB) is used. The results from K-Means clusters show two precipitation clusters splitting the PLB precipitation into a northern and southern cluster, with a silhouette coefficient ~0.5. The PLB precipitation leading cluster (C1) contains 48 stations accounting for 58% of the regional station density, while Cluster 2 (C2) covers 35, accounting for 42% of the stations. The interannual variability in precipitation exhibited significant differences for both clusters. The decision tree (C4.5) is employed to explore the large-scale atmospheric indices from National Climate Center (NCC) associated with each cluster during the preceding spring season as a predictor. The C1 precipitation was linked with the location and intensity of subtropical ridgeline position over Northern Africa, whereas the C2 precipitation was suggested to be associated with the Atlantic-European Polar Vortex Area Index. The precipitation anomalies further validated the results of both algorithms. The findings are in accordance with previous studies conducted globally and hence recommend the applications of machine learning techniques in atmospheric science on a sub-regional and sub-seasonal scale. Future studies should explore the dynamics of the K-Means, and C4.5 derived indicators for a better assessment on a regional scale. This research based on machine learning methods may bring a new solution to climate forecast. [ABSTRACT FROM AUTHOR]