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The frequency of large-scale anomalous precipitation events over China has increased during 1961–2018. However, it remains challenging to understand the mechanisms associated with these anomalous events showing different spatial patterns. Here, we applied an autoencoder technique to identify large-scale anomalous precipitation events for both observations and model simulations, which were then classified into several patterns through a self-organizing map method. The synoptic behavior and atmospheric circulation background of different anomalous patterns were also analyzed using simultaneous composite analyses. Results show that occurrences of different anomalous precipitation patterns have increased significantly, except those centered in North China, Northeast China, and the Yangtze River basin. The anomalous precipitation patterns manifest various intraseasonal distributions, which are linked to zonal oscillations of the western North Pacific subtropical high (WNPSH) and meridional displacements of East Asia westerly jet (EAJ). Accompanied by the westward movement of WNPSH, anticyclonic systems transport warm moist air from the Indian Ocean and the South China Sea to converge with the cold air caused by anomalous cyclones over the northwest flank of the WNPSH, leading to large-scale anomalous precipitation in these regions. Besides WNPSH, the northward and southward displacements of EAJ also favor the occurrence of anomalous precipitation events in northern and southern China, respectively. Our study also illustrates that the occurrence frequency of anomalous precipitation events is projected to increase remarkably under the Shared Socioeconomic Pathway 5–8.5 (SSP585) scenario by rates of twofold to fourfold. [ABSTRACT FROM AUTHOR]

Drought is one of the most frequent and devastating natural disasters. Based on future climate scenarios and land use/land cover (LULC) patterns, the copula framework was employed to calculate the probabilities of meteorological and hydrological drought risks for the next 30 years (2021–2050) in the Wanquan River Basin, meanwhile, the relationship between hydrological and meteorological droughts was revealed by correlation analysis and cross-wavelet transform (XWT). The results are as follows: (1) In the next 30 years, the risk of intra-seasonal meteorological drought (short-term drought) in the WRB is high at a probability of 40–70%, while the risk of inter-seasonal meteorological drought is relatively small at a probability of close to 30%; (2) compared with meteorological drought, the risk of intra-seasonal hydrological drought is small, but the probability of inter-seasonal hydrological drought (medium- or long-term drought) is 30–50%, and the risk of hydrological drought in the upstream is greater than that in the downstream; (3) the future meteorological and hydrological droughts in the WRB are significantly and positively correlated, and that hydrological drought lags behind meteorological drought. [ABSTRACT FROM AUTHOR]

Precipitation in China is controlled by a combination of multiple weather systems and is susceptible to their spatiotemporal variability under climate warming. Based on the daily precipitation dataset developed by the China Meteorological Administration and ERA5 6-hourly data from 1979 to 2018, we detected tropical cyclones, extratropical cyclones, and fronts affecting mainland China of an altitude less than 1500 m using objective methods and identified their individually associated precipitation. We quantified climatological characteristics of precipitation associated with these three meteorological causes and their proportion of precipitation totals, and evaluated their relative contribution to change in precipitation. Results show that precipitation associated with tropical cyclones (TCP), extratropical cyclones (ETCP), and fronts (FRTP) accounted for 3.0%, 21.2%, and 20.4% of the total precipitation in China, and constituted the largest percentage in August, June, and January, respectively. The total proportion of these three types of precipitation exceeded 50% in more than 55% of China's regions. The high-value regions of corresponding precipitation were directly related to the locations of frequent occurrences of these weather systems. TCP and FRTP increased over the past four decades, while ETCP decreased. The western part of Northeast China and the middle and upper reaches of the Yangtze River show precipitation decreases, 37.8% of which is contributed by ETCP decreases. Precipitation increased in most regions of China during the dry season, 34.1% of which is contributed by FRTP increases. Among them, Northeast (Northwest) China significantly increased it precipitation by 14.4% decade−1 (21.8% decade−1), 33.6% (51.3%) of which is contributed by FRTP increases. [ABSTRACT FROM AUTHOR]

Floods in river deltas are driven by complex interactions between astronomical tides, sea levels, storm surges, wind waves, rainfall‐runoff, and river discharge. Given the anticipated increase in compound flood hazards in river deltas in a warming climate, climate‐informed regional to local extreme water levels (EWLs) is thus critical for decision‐makers to evaluate flood hazards and take adaptation measures. We develop a simple yet computationally efficient stress test framework, which combines historical and projected climatological information and a state‐of‐the‐art hydrodynamic model, to assess future compound coastal‐fluvial flood hazards in river deltas. Our framework is applied in the world's largest single urban area, China's Pearl River Delta (PRD), which is also characterized by densely crossed river network. We find that extreme sea level is the dominant driver causing the compound coastal‐fluvial flood in the PRD over the past 60 years. Meanwhile, there is large spatial heterogeneity of the individual and compound effects of the typhoon intensity, local sea‐level rise, and riverine inflow on coastal‐fluvial floods. In a plausible disruptive scenario (e.g., a 0.50 m sea‐level rise combined with a 9% increase in typhoon intensity in a 2°C warming), the EWL will increase by 0.76 m on average. An additional 1.54 and 0.56 m increase in EWL will occur in the river network and near the river mouth, respectively, if coastal floods coincide with the upstream mean annual flood. Findings from our modeling framework provide important insights to guide adaptation planning in river deltas to withstand future compound floods under climate change. Plain Language Summary: Compound floods pose serious threats to the dense population living in river deltas worldwide. Climate change could increase the compound flood hazards through stronger tropical cyclones, sea level rise, higher extreme precipitation, and river flows. It is urgent to understand how the so‐called grey swan events will evolve under a changing climate in these already flood‐prone areas. Here, grey swan events are high‐consequence events that are beyond people's experience but may be foreseeable and thus can be systematically prepared for. In this study, a storyline‐based framework is proposed to assess the potential grey swan compound floods under a warming climate. We apply this framework to China's Pearl River Delta, the world's largest single urban area. In a plausible disruptive scenario (e.g., a 0.50 m sea‐level rise combined with a 9% increase in typhoon intensity in a 2°C warming), we find that extreme water levels will increase by 0.76 m on average. Our flexible and computationally efficient storyline‐based framework could guide coastal planners to prepare for the grey swan compound flood hazards under climate change. Key Points: A quantitative stress test framework is proposed to assess the compound coastal‐fluvial flood in the river delta at minimal costA state‐of‐the‐art unstructured mesh generation technology is applied to develop an objective and reproducible hydrodynamic modelCompound effects of typhoon intensity, local sea‐level rise, and river inflow on coastal‐fluvial floods are systematically investigated [ABSTRACT FROM AUTHOR]

Vegetation interacts closely with water resources. Conventional field studies of plant–water relations are fundamental for understanding the mechanisms of how plants alter and adapt to environmental changes, while large-scale studies can be more practical for regional land use and water management towards mitigating climate change impacts. In this study, we investigated the changes in the total water storage (TWS), aridity index (AI) and vegetation greenness, productivity, and their interactions in the Pearl River basin since April 2002. Results show an overall increasing trend of vegetation greenness and productivity, especially in the middle reaches where TWS also increased. This region dominated by croplands was identified as the hot spot for changes and interactions between water and vegetation in the basin. Vegetation was more strongly affected by TWS than precipitation (P) at both the annual and monthly scales. Further examination showed that the influence of TWS on vegetation in dry years was stronger than wet years, while the impact of P was stronger in wet years than dry years; moreover, vegetation productivity responded slower but stronger to atmospheric dryness in dry years than wet years. The lag effects resulted in nonlinearity between water and vegetation dynamics. This study implies that vegetation in the basin uses rainwater prior to water storage until the soil becomes dry, and their dynamics indicate that vegetation development is subject to water availability, and that vegetation is not dominant in reducing water availability. [ABSTRACT FROM AUTHOR]

This study identifies the variability of large‐scale atmospheric patterns (LSMPs) and atmospheric moisture circulation patterns associated with the variability of daily precipitation over East China using the self‐organizing maps (SOM) method. The spatiotemporal characteristics of the occurrence and intensity of daily precipitation were linked with the variabilities of LSMPs. Results show that the synoptic moisture transport over East China in both dry season and rainy season can be classified into eight patterns, and the occurrence frequency and primary occurring months of the eight patterns are varied. In the dry season, the wetter pattern (the drier pattern) exhibits a significant decreasing (increasing) trend with a slope of −0.23 (0.63)% year−1 at the confidence level of 0.95 during 1979–2018. The LSMPs corresponding to each atmospheric moisture circulation pattern, including the composite mean values of vertically integrated water vapour transport fields, 500 hPa geopotential height (Z500) anomalies and sea surface temperature anomalies (SSTA) in surrounding oceans, indicate that the primary oceanic moisture source of the dry season is western North Pacific (WNP), while that of the rainy season is WNP and the Indian Ocean. The location and intensity variabilities of subtropical high affect the transport and amount of water vapour along with its western flank to arrive in East China. SSTA has an influential link with the regional circulations and convection activity, and thus plays an important role in affecting water vapour transport. [ABSTRACT FROM AUTHOR]

Drought is one of the most destructive types of natural disasters, causing great losses of every aspects worldwide. Using a three‐dimensional (longitude, latitude, and time) clustering method based on gridded 3 month standardized precipitation evapotranspiration index data with a resolution of 0.25° collected for East China between 1960 and 2017, we identified and analysed five characteristics of drought events via the Mann–Kendall (MK) test. The results revealed that this method could capture drought events on the basis of their spatiotemporal characteristics. Drought development processes could be visualized via the spatial expansion of drought patches and the transferring path (reconstructed from the centroids of drought patches observed each month). By applying this identification method to the territory of East China, the occurrence of 174 droughts in the last six decades could be determined; furthermore, their objective existence in the spatiotemporal scale was confirmed by comparing the results with historical records and soil moisture data. The increasing moving speed of the centroids and the non‐repetitive rate of the impacted areas suggests that an increasing number of regions have likely been affected over time by large‐scale drought events. The drought patches associated with all of the events identified in the present study tended to move westward in South China and eastward in southwestern China. The remaining four characteristics (i.e., duration, severity, affected area, and intensity), were used to quantify the degree of drought, along with its development, where significant decreasing trends were found among the first three characteristics. In southwestern China, drought events decreased in frequency, but increased spatially, whereas drought events in southeastern China showed an opposite change. Drought events with a small spatial scale occurred more frequently in coastal regions. The majority of drought events mainly occurred in central and North China and moved northward. [ABSTRACT FROM AUTHOR]

Using the observed daily precipitation data across East China, this paper analyzes spatiotemporal changes of annual and seasonal extreme precipitation indices during 1960–2015. Effects of changes in atmospheric circulation on seasonal extremes were also detected by using the singular value decomposition method. Results show that amount of annual, spring and summer extreme precipitation over East China showed a significant increase with a maximum changing rate of 7.2, 3.2 and 5.4 mm decade−1, and the stations with upward tendency mainly located in the southern part of East China. Preceding sea surface temperature of the Indian Ocean and the Equatorial Pacific Ocean shows great influences on spring extreme precipitation over East China through modulating anomalous anticyclones and winds, especially over the downstream of the south of East China. Summer extreme precipitation is statistically significantly correlated with the western North Pacific subtropical high (WPSH) and positive anomalies of 500 hPa geopotential heights. Anomalously strong WPSH combining with two blocking highs in mid-latitude regions tends to trigger more extreme precipitation events in the Yangtze River Basin but less in the Yellow River Basin. [ABSTRACT FROM AUTHOR]

Abstract Under the influences of both anthropogenic activities and natural forces, saltwater intrusion has been a main issue in the Pearl River Estuary (PRE), China, in recent decades. Using long-term observation data for river channel bathymetry, hydrology, hydraulics, and meteorology, the causes and effects of the increasingly severe saltwater intrusion were investigated in this study. The worsening saltwater intrusion is characterized by an increase in salinity, prolonged and seasonally advanced duration with salinity exceeding the national standard, the extension of saltwater intrusion length and the highly stratified salinity, which can be attributed to uneven sand dredging, rising tides and changes of wind directions. Uneven sand dredging indirectly reduced the dilution capacity on the saltwater and made it difficult to discharge the saltwater. Rising tides and northeasterly migration of wind can strengthen the tidal dynamics and push saltwater further upstream. This study aims to draw attention to the issues of saltwater intrusion and offer information for the sustainable utilization of water resources for the estuaries around the world. Graphical abstract Image 1 Highlights • Severe saltwater intrusion has occurred in the Pearl River Estuary (PRE) in China in recent years. • Saltwater intrusion has increased in frequency, duration, and length during the past decade in the PRE. • Uneven sand dredging, rising tides and more frequent northeasterly wind result in severe saltwater intrusion in the PRE. [ABSTRACT FROM AUTHOR]

Crop reference evapotranspiration (ET0), which connects the energy and water balance, is an important indicator used in water resource management and agricultural production. On the basis of daily meteorological data from 479 observation stations, we investigate changes in ET0 and associated climate factors across the main grain‐producing area (MGPA) of China from 1960 to 2015. The Mann–Kendall test and Sen's slope estimator were applied to detect trends in ET0, and regression analyses and composite analyses were used to evaluate the contributions of climatic variables and large‐scale anomalies that may affect ET0. The results of this study show that ET0 in the MGPA decreased (−2.67 mm/decade) during summer throughout the past 56 years, and that this change is largely attributable to decreased sunshine duration and wind speed (WS). Furthermore, decreased WSs in the 850‐hpa geostrophic wind field, are responsible for decreases in ET0 in Northeast China Region (−1.85 mm/decade), which affect ET0 by significantly weakening the observed surface WS. Meanwhile, significant low cloud cover variations accounted for the decrease in ET0 in the Huang‐Huai‐Hai Region (−7.85 mm/decade), Loess Plateau Region (−2.91 mm/decade), Yangtze River Region (−3.96 mm/decade), and Southwest China Region (−2.71 mm/decade). However, decreases in the integrated atmospheric water vapour content (IWVC), which act to weaken the surface relative humidity, are hypothesised to increase ET0 in the South China Region (1.25 mm/decade). Topographic map of China with 479 meteorological stations across main grain‐producing area (MGPA). [ABSTRACT FROM AUTHOR]

Owing to its combination of superior natural conditions and abundant resources, the Pearl River Delta (PRD), China, is densely populated, with concentrated industry and rapid development. The PRD is also one of the most threatened estuaries in the world, as it has been exposed to an increasing series of crises related to water resources. Water conflict, water pollution, and saltwater intrusion have all increased dramatically in the past few decades, which pose a threat to regional water security and impose constraints on regional development. The goal of this paper is to analyze the causes and impacts of some of the water resource crises faced by estuaries under dramatically changing environments, based on studies in the PRD. The PRD is centered around the Pearl River Estuary (PRE) and is the second most economically active district in China. Rapid economic development and a population boom have resulted in an average annual growth rate of 1.43% in water resource demand, which has further accelerated water pollution by a substantial growth in sewage discharge. Water pollution results in the impairment of the ecological functions of the water, and the standard rate of water function areas in the PRD remains under 50%. Large-scale and uneven sand excavations not only decreased the river discharge from upstream but also allowed more tidal prisms to enter, which triggered severe saltwater intrusion. Meanwhile, sea-level rise and changing wind patterns also contribute to increasingly severe saltwater intrusion, which was characterized by gradual increases in salinity, as well as more prolonged periods of higher salinity that exceeds acceptable thresholds occurring earlier in the year. This study is intended to bring attention to these challenging issues and provide some of the information needed to advance research into sustainability assessment of the water resources. [ABSTRACT FROM AUTHOR]

Extreme precipitation event is rare and mostly occurs on a relatively small local scale, which presents marked uncertainties when analyzing its characteristics. Using daily precipitation data covering 1959-2009 from 62 stations over the Pearl River Basin, the percentile method (PM) and the absolute critical value method (ACVM) are applied to define extreme precipitation thresholds (EPT), and their different impacts on the spatial-temporal distribution of extreme precipitation event were analyzed in this study. The findings of this study show: (1) Using the K-means clustering algorithm in terms of precipitation indices and the topography, longitude and latitude of each station, the whole basin is divided into eight precipitation zones. (2) The extreme indices, including extreme precipitation frequency, extreme precipitation proportion and proportion of extremely n-day precipitation, calculated by PM are markedly higher than those calculated by ACVM during five decades, which is particularly obvious in the low precipitation area such as the west-northern of the basin since more daily precipitation events are treated as extreme precipitation in this region if EPT is defined by PM. (3) The spatial distributions of extreme frequencies respectively calculated by these two methods are quite different across the basin. The spatial distribution of extreme frequencies calculated by ACVM shows a high-value center in the southeast coastal areas and a low-value center in the northwest mountain areas. However, the extreme frequencies calculated by PM distribute evenly over the basin, which is obviously inconsistent with the empirical results, an area with heavy precipitation usually has a high extreme precipitation frequency, and vice versa. [ABSTRACT FROM AUTHOR]

The Budyko-based elasticity method has been widely employed to clarify the driving factors behind runoff changes. However, different formulations of the Budyko framework could produce biases in the elasticity analysis and the assessment errors induced from different formulations of the Budyko framework in the elasticity method remain unclear. Here, we attempt to address this issue by validating the performance of elasticity methods derived from two analytical Budyko equations (Fu's equation and Choudhury's equation), as well as one empirical Budyko equation (Wang-Tang's equation) of the Budyko framework across 22 basins in China. Validations show that the runoff change simulated by the elasticity method derived from the empirical equation has lower errors compared with the two analytical Budyko equations. Results reveal that in the semi-humid environment, the alteration of basin characteristics takes the main responsibility for the runoff change. However, a clear divergence was found in simulated runoff changes among different Budyko-based elasticity methods in humid basins. For parts of the humid basin, the precipitation is the main driver of runoff change from the analytical Budyko-based elasticity methods, while the alteration of basin characteristics is the main derive of the runoff changes according to based on the empirical Budyko-based elasticity method. This difference could be attributed to the variations in the simulated contributions from the alteration of basin characteristics on runoff changes. Generally, our results highlight the importance of validating different Budyko equations when applying the elasticity method to investigate the driver of the runoff changes in humid regions. • Analytical Budyko-based elasticity methods overestimate runoff changes in wet and dry basins compared to empirical solutions. • A divergence was found from the attribution analysis of runoff change among Budyko-based elasticity methods in humid regions. • This divergence could be attributed to the variations in the effects of the basin characteristics on runoff changes. [ABSTRACT FROM AUTHOR]

The change structures of precipitation and precipitation intensity and rainy days are analyzed for the Pearl River Basin (from 1959 to 2009) on the basis of a suite of 24 climatic indices derived from daily precipitation data at 62 meteorological stations with the help of the Mann-Kendall test. Contributions of seasonal precipitation and precipitation intensity class to the annual precipitation are also examined using the inverse distance weighted method. The following four conclusions can be drawn: (1) although the average annual precipitation of the entire basin does not show obvious variation, the number of annual rainy days has decreased significantly in 98.3 % of the stations. These two factors result in an obvious increase in precipitation intensity at 64.5 % of the stations. (2) No clear change trend has been found for seasonal precipitation over the entire area; however, the number of rainy days in each season has decreased significantly. In particular, the number of rainy days in the entire year and in the fall season has decreased in 98.3 and 100 % of the stations, respectively. (3) Although the number of rainy days in drizzle has decreased in 83.9 % of the stations, the number of rainy days where heavy rain and extremely heavy rain occurred increased in nearly 75.8 and 82.3 % of the stations, respectively. (4) The number of rainy days in fall and winter contributes more to the change in the number of annual rainy days than the number of rainy days in spring and summer. Heavy rain and extremely heavy rain contribute more to the change in total annual precipitation than drizzle; however, they contribute less to the change in the number of annual rainy days than drizzle. The findings in this study can provide important information for formulating water resource and eco-environment management strategies in the Pearl River Basin to policymakers and stakeholders. [ABSTRACT FROM AUTHOR]

• A sigmoid CO 2 concentration stress function f (Ca) was proposed to reflect ET response. • A process-based transpiration model was extended with the f (Ca) to model total ET. • The model with CO 2 stress is sound and robust to couple water and carbon processes. • The mechanism of CO 2 effect and advantage of a f (Ca) in ET models were discussed. Evapotranspiration (ET) is one of the most difficult hydrologic variables to estimate. In the context of climate change, the rise of CO 2 emissions may improve photosynthesis but depress transpiration thus increasing plant water use efficiency (WUE). Therefore, it is of great importance and necessity to take elevated atmospheric CO 2 concentration (Ca) as a limiting factor for improved assessment of ET and WUE toward a better ecosystem management. In this study, we developed and incorporated a Ca stress function into a modified process-based transpiration model and extended its application from transpiration to total evapotranspiration simulation. The original simplified process-based model (denoted as BTA by combining developers' last name initials), previously modified version with added soil moisture (BTA-θ) and the extended version in this study with CO 2 concentration (BTA-Ca) were tested for daily ET simulation at the Dinghushan forest ecosystem in south China. The results show that eddy covariance based forest ET was well simulated by the models, while the two modified models outperformed the original one. Despite the limited improvement of accuracy, the BTA-Ca model is more superior and meaningful regarding the physical mechanisms. Moreover, we evaluated the biophysical responses of ET and GPP to the major environmental factors, which shows that ET and GPP responded similarly to environmental changes with close linkages between the two. This study proposed a Ca stress function and provides an effective way of coupling water and carbon exchange processes for ET simulations, which can be applied for forest water budget assessment under climate change. [ABSTRACT FROM AUTHOR]

• A shifting method combing a segmentation procedure and BaRatin stationary model is developed and work well. • The effect of parameter CROPS and Minseglen on segmentation is evaluated by designing sixteen Experiments. • The stage-discharge relationship in the low flow part is more sensitive to the variation of river topography, more segmentations are needed for an accurate low flow prediction. • The BaRatin model can reduce the use of calibration data by employing stage-discharge function with a precise exponent from the hydraulic knowledge. Streamflow time series data are fundamental to hydrological science and water management applications, which are commonly derived from stage-discharge rating curves. The rating curves are usually nonstationary due to temporal characteristics of stream channel and human activities such as indiscriminate dig of sediment. This implies the need for an efficient method to estimate nonstationary rating curves from an adequate dataset. This study employed a shifting method to estimate the nonstationary rating curves and the associated uncertainties. The method includes two steps: a coupled algorithm PELT&CROPS was first performed to divide the gauging samples into homogeneous families by detecting the multiple change points in a time series of a residual indicator. Then, the rating curves were calibrated with the BaRatin stationary model using these homogeneous gaugings within each stationary period. The method was applied at Shijiao Hydrological Station in China. We found that: (1) Set the lower and upper limit of parameter CROPS (c hangepoints for a r ange o f p enaltie s) to 0 and Inf respectively, the whole range of segmentation can be calculated. (2) Parameter Minseglen (min imum seg ment len gth) is of great significance to the segmentation result. More changepoints will be detected as the value of Minseglen decreasing. An appropriate Minseglen value should be assigned to find the optimal segmentation. (3) The stage-discharge relationship in the low flow part is more sensitive to the variation of river topography. Ten segmentations are needed to produce an accurate discharge for low flow prediction, while two segmentations for calibration can produce an accurate discharge for high flow prediction. (4) Information redundancy exists in the vast amount of gaugings. The BaRatin model can reduce the use of calibration data by employing stage-discharge function with a precise exponent from the hydraulic knowledge at a hydrological station. [ABSTRACT FROM AUTHOR]

Analyzing the spatiotemporal characteristics and causes of landscape pattern changes in watersheds around big cities is essential for understanding the ecological consequence of urbanization and provides a basic reference for the watershed management. This study used a land-use transition matrix and landscape indices to explore the spatiotemporal change of land use and landscape pattern over Liuxihe River basin of Guangzhou in the southeast of China from 1980 to 2015 with multitemporal Landsat satellite data in response to the rapid urbanization process. Primary temporal and spatial influencing factors were first quantitatively identified through grey relation analysis (calculating correlation degree between land use changes and influencing factors) and Geodetector (detecting landscape spatial heterogeneity and its driving factors), respectively. Considerable spatial and temporal differences in land use and landscape pattern changes were observed herein, thus determining the influencing factors of these differences in the Liuxihe River basin. These changes were characterized by a large increase in construction land converted from cropland, particularly in the middle and lower reaches of the basin from 2000 to 2010, causing dramatic fragmentation and homogenization of the landscape pattern there. Meanwhile, the landscape pattern gradually transitioned from an agricultural land use dominant landscape to a construction land use dominant landscape in these regions. Furthermore, the rapid growth of a nonagricultural population and the transformation of industry primarily caused the temporal changes of landscape pattern, and the landscape spatial heterogeneity was mainly caused by the interaction of complicated geomorphology and anthropogenic activities in different spatial locations, particularly after 2000. This study not only provides an improved approach to quantifying the main spatiotemporal influencing factors of landscape pattern changes during different time periods, but also offers a reference for decision-makers to formulate optimal strategies on ecological protection and urban sustainable development of different regions in this study area. [ABSTRACT FROM AUTHOR]

• Coupling WT and ANN can solve the nonstationarity in estuarine salinity forecasting. • WT-ANN models performed better than MLR and ANN models in forecasting salinity. • The MF framework of constructing the WT-ANN models outperformed the DF framework. Accurate and reliable predictions of estuarine salinity can lead to more effective water resource management and can alleviate the adverse impacts of saltwater intrusion. Due to the nonlinear and nonstationary features in time series of estuarine salinity, this study is conducted to develop a hybrid model coupling the techniques of wavelet transform (WT) and artificial neural network (ANN) for forecasting estuarine salinity in the Pearl River Estuary, China. Two wavelet-based forecasting frameworks, the direct forecast (DF) framework (i.e., only explanatory variables are decomposed, leading to direct forecasting of the target variables) and multicomponent forecast (MF) framework (i.e., both explanatory and target variables are decomposed, and each target component is forecasted separately), were used to construct the WT-ANN models. The results reveal the superiority of hybrid WT-ANN models in estuarine salinity forecasting over traditional multiple linear regression (MLR) models and single ANN models, indicated by the Nash–Sutcliffe efficiency (NSE), correlation coefficient (R), root mean square error (RMSE), mean absolute error (MAE) and Kling–Gupta efficiency (KGE). Between the two wavelet-based forecasting paradigms, the MF framework outperformed the DF framework for better capturing the mutual dependence (i.e., mutual information, MI) between input and output variables. Additionally, the superiority of WT-ANN models in comparison with MLR and ANN models is increasingly prominent when the forecast lead time is extended from 1 to 3 days. [ABSTRACT FROM AUTHOR]

[Display omitted] • Mild impact of climate extremes on vegetation was found for Hu Line transect in China. • Latitudinal and altitudinal patterns of vegetation responses to climate were analyzed. • Non-woody plants in the mid-to-high latitudes were more sensitive to climate extremes. • Productivity above 45°N increased with drought severity due to favorable environment. • Policy making suggestions were proposed with emphasis on the identified hotspots. Climate projections infer increasing frequency of extreme events in the future which would alter terrestrial hydrologic functioning and ecosystem services. Understanding the responses of vegetation to extreme events can provide prerequisite knowledge to mitigate climate change impacts. The relationships between climate extremes and vegetation phenology and productivity were examined for a transect along the Hu Line across China during 1988–2014. Results show that high frequency and severity of droughts existed in the mid-latitude regions where happened to be mostly occupied by grassland and cropland with relatively low productivity compared to trees. Prolonged growing seasons (4.3 days/decade) resulted mostly from advanced green-up were observed over the transect. No strong impact of extreme droughts on vegetation was observed for any plant functional types, due to the timing of drought occurrences primarily in pre- and post-growing seasons while water supply was likely not so limited during growth indicated by a drought index. Non-woody plants in the mid-to-high latitudes (37-54°N) were identified more sensitive to climate extremes than woody plants in the low latitudes. Meanwhile, grassland in the relatively low-elevation areas (<1000 m.a.s.l) was more responsive than that in the high-elevation areas. Productivity above 45°N increased with drought severity attributable to an intensified favorable environment during frequent and mild droughts with warmer temperature and increased solar radiation. The results may suggest the generally relative stability of the ecosystems along the Hu Line, however, with further deteriorating climate, the stable relationships between climate and ecosystems may be shifted, likely starting from low-elevation grassland. [ABSTRACT FROM AUTHOR]

Microbial source tracking (MST) technology represents an innovative approach employed to trace fecal contamination in environmental water systems. The performance of primers may be affected by amplification techniques, target primer categories, and regional differences. To investigate the influence of these factors on primer recognition performance, a meta-analysis was conducted on the application of MST in water environments using three databases: Web of Science, Scopus, and PubMed (n = 2291). After data screening, 46 studies were included in the final analysis. The investigation encompassed Polymerase Chain Reaction (PCR)/quantitative PCR (qPCR) methodologies, dye-based (SYBR)/probe-based (TaqMan) techniques, and geographical differences of a human host-specific (HF183) primer and other 21 additional primers. The results indicated that the primers analyzed were capable of differentiating host specificity to a certain degree. Nonetheless, by comparing sensitivity and specificity outcomes, it was observed that virus-based primers exhibited superior specificity and recognition capacity, as well as a stronger correlation with human pathogenicity in water environments compared to bacteria-based primers. This finding highlights an important direction for future advancements. Moreover, within the same category, qPCR did not demonstrate significant benefits over conventional PCR amplification methods. In comparing dye-based and probe-based techniques, it was revealed that the probe-based method's advantage lay primarily in specificity, which may be associated with the increased propensity of dye-based methods to produce false positives. Furthermore, the heterogeneity of the HF183 primer was not detected in China, Canada, and Singapore respectively, indicating a low likelihood of regional differences. The variation among the 21 other primers may be attributable to regional differences, sample sources, detection techniques, or alternative factors. Finally, we identified that economic factors, climatic conditions, and geographical distribution significantly influence primer performance. [Display omitted] • Meta-analysis for primers and impact factors to their recognition performance. • Viruses-based primers showed a better specificity and recognition ability. • Regional differences of HF183 was not observed in China, Canada, and Singapore. • The influence factors from sample to environment of 21 primers had been listed. • Meta-analysis of economy, climate, and geographic zone on the primers. [ABSTRACT FROM AUTHOR]

• WUE trends were determined by the WUE magnitude, followed by atmospheric CO2 concentration and N deposition. • Individualized effects of five driving factors on WUE were quantified through machine learning. • Precipitation was found to shape most of the spatial patterns of WUE. • WUE was increased by increased atmospheric CO 2 concentration, but WUE growth rate declined with increased CO 2 growth rate. • WUE and N deposition exhibited positive or negative correlations depending on the different nutrient constraints on vegetation. The responses of ecosystem water use efficiency (WUE) to environmental perturbations are non-linearly dependent on how strongly coupled are water and carbon cycling. Here, we evaluate the structure of these non-linearities using two high-fidelity explainable machine learning (XML) models to disentangle the confounding effects of the air temperature (Ta), precipitation (PR), downward shortwave radiation (SR), atmospheric CO 2 concentration (Ca), and nitrogen deposition (Ndep) on WUE. The findings suggest that mean annual PR plays a dominant role in shaping the spatial pattern of WUE. Spatially, WUE responded positively to PR and Ca but negatively to Ta and SR , while Ndep had little impact on WUE. For temporal trends, the spatial pattern of the mean annual WUE determined the spatial pattern of the WUE trend. Furthermore, the spatial patterns of the Ndep and Ca trends also contributed substantially to the spatial pattern of the WUE trend. Notably, the WUE and Ca trends exhibited negative correlations, while the WUE and Ndep trends showed positive or negative correlations depending on the different nutrient constraints on vegetation. The WUE growth rate responded negatively to SR in both spatial patterns and temporal trends. Additionally, using the trend of 0.077 K yr−1 and 0 mm yr−1 as the threshold, the trends of Ta and PR shifted from positive to negative relationships on WUE growth. Our results help identify key sensitivities and thresholds in WUE to environmental controls over space and time. [ABSTRACT FROM AUTHOR]

• Actinobacterial diversity and copy number were closely related to methanogenic potential. • Propionibacterium was the biggest contributor to methanogenic potential. • Actinobacteria indirectly affect methanogenic potential by controlling negative cohesion. Microorganisms are the core drivers of coal biogeochemistry and are closely related to biological coalbed methane. However, the Actinobacterial taxa in coals and their roles in the context of biological coalbed methane remain poorly understood. In this study, 16S rRNA gene sequencing and quantitative PCR were used to analyze the Actinobacterial taxa and abundance in coals from different regions of China. The results indicated that Proteobacteria was the predominant bacterial phylum, and Actinobacteria accounted for only 1.64 % of the coal bacterial communities. However, Actinobacteria was the largest contributor to methanogenic potential, followed by Firmicutes and Cyanobacteria. The Shannon diversity, structure and absolute abundance of Actinobacteria were closely related to methanogenic potential. In addition, widely detected genera included Propionibacterium , Corynebacterium , Brevibacterium , Arthrobacter , Micrococcus , Phycicoccus and Brachybacterium , all of which belong to the order Actinomycetales. Among them, Propionibacterium was the most important genus contributing to the methanogenic potential, followed by Corynebacterium and Phycicoccus. In the microbial co-occurrence network, actinobacterial-related nodes and links accounted for 18.29 % and 33.16 % of the total nodes and links, respectively, and actinobacterial OTUs belonging to the genera Propionibacterium , Corynebacterium , Arthrobacter , Dietzia , Phycicoccus , Rhodococcus and Micrococcus were identified as connectors. Furthermore, partial least squares path modeling indicated that Actinobacteria can affect methanogenic potential indirectly by controlling community negative cohesion. In summary, Actinobacteria appear to play important roles in maintaining the microbial co-occurrence network and regulating coal biological methanogenic potential, which is help to understand the coal microbial ecology and geochemical processes. [ABSTRACT FROM AUTHOR]

Compound Drought and Saltwater intrusion Events (CDSEs) refer to hydrologic drought and saltwater intrusion occurring simultaneously or consecutively in estuaries, and exacerbate the negative impacts resulting from an individual extreme event. CDSEs have been drawing increasing attention due to their potential adverse impacts on water resources, crop production, and food security. A new Standardized compound Drought and Saltwater intrusion Index (SDSI) was developed in this study to systematically detect changes in the severity of CDSEs in six estuaries (Little Back, Ebro, Rhine, Orange, Pearl River and Murray). The results illustrated that (1) compared to the Standardized Runoff Index (SRI), SDSI effectively characterizes and quantifies the occurrences and severity of CDSEs in major river estuaries worldwide. (2) Temporally, the SDSI trend varied across estuaries. Specifically, a decreasing trend was observed in the Little Back, Ebro, and Orange estuaries, with corresponding Zs values of -2.43, -3.63, and -3.23. (3) Spatially, moderate CDSEs occurred more frequently among different estuaries, and their frequency, duration and severity varied in different estuaries. Notably, Ebro, Rhine and Murray River estuaries had the highest probability of CDSEs, nearing 60%. Among them, the Murray Estuary had the longest average duration, spanning 7.68 months, and the highest severity was 5.94. (4) According to the contributions analysis, saltwater intrusion plays a dominant role in influencing SDSI severity, accounting for a substantial percentage (54%-95.30%) compared to runoff. Notably, the Orange Estuary experienced the greatest impact from saltwater intrusion (81.54%-95.30%), while the Murray Estuary had relatively equal contributions from hydrological drought and saltwater intrusion., Competing Interests: Declaration of competing interest The authors declare no conflict of interest., (Copyright © 2023 Elsevier Ltd. All rights reserved.)