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Glacial and proglacial erosion are important sediment sources in river basins. The retreat of many glaciers on the Tibetan Plateau has important implications on the supply of fresh water and sediment dynamics for downstream river basins. Despite the importance of water and sediment dynamics at these catchments, existing quantification of suspended sediment fluxes from glacial catchments on the Tibetan Plateau is limited due to poor accessibility and challenging environments. This study presents the results of in‐situ investigations of water discharge and suspended sediment fluxes from the Mingyong Glacier catchment in Yunnan, Southwest China, between August 2013 and July 2017. The results show that the variation in water discharge and suspended sediment was highly seasonal. The variation of average suspended sediment concentration was large—69 ± 45; 119 ± 104; and 94 ± 97 mg/L in 2013, 2015, and 2016, respectively. We estimate that the sediment yield from the Mingyong catchment was highly variable ranging from 1104 t/km2/year in 2013 to 2281 t/km2/year in 2016, with 65%–78% of the total annual sediment load occurring during the summer (June to August). These annual variations in sediment yield can be attributed largely to precipitation patterns and extreme melting events. This study has provided a benchmark dataset that can be used for further works that investigate the impact of climate change on sediment dynamics in glacierized catchments in the Tibetan Plateau. Subsequently, the study helps us to better understand the increasing sediment supply to the Upper Mekong River from glacierized headwater catchments. [ABSTRACT FROM AUTHOR]

The utilization of regional climate methods (RCMs) to predict future climate is an important study under the changing environment. The primary objective of the paper is to correct the temperature and precipitation simulations for the period of 1980–2005 and 2026–2098 in the Wei River Basin (WRB), to evaluate the performance of RCMs for the period of 1980–2005, and further, to analyze the future changes of projected temperature and precipitation during 2026–2098. In this paper, the linear scaling method was used to correct the temperature simulations. Quantile mapping, local intensity scaling method, and hybrid method were used to correct the precipitation simulations. The future changes of projected temperature and precipitation for the near term (2026–2050), mid-term (2051–2075), and far term (2076–2098), relative to the period of 1980–2005, were investigated under RCP 2.6 and RCP 8.5. Results indicate that (1) the temperature biases were either warm or cold in the spatial scale, and the precipitation wet biases were detected. After correction, HadGEM2-ES driven by RegCM4-4 had the best temperature reproducibility, and NCC-NorESM1-M driven by RegCM4-4 had the best precipitation reproducibility. (2) Under RCP 2.6, the projected annual, winter, and spring temperature showed decreasing trends. The temperature was higher than that for the period of 1980–2005 except for the spring temperature decreases in the Beiluo River Basin. Under RCP 8.5, the temperature showed significantly increasing trends. The temperature for the near term was similar to that of the period of 1980–2005, while the temperature increased significantly for the mid-term and far term. (3) Under RCP 2.6, the precipitation had decreasing trends. Under RCP 8.5, precipitation trends were also spatially distributed. The relative deviation of winter precipitation was the largest. Relative to the period of 1980–2005, the light- and moderate-rain days showed little change for the period of 2026–2098, while the extreme-rain days showed significantly increasing trends. [ABSTRACT FROM AUTHOR]

Monitoring and quantifying suspended sediment concentrations (SSC) in estuaries such as the Pearl River Estuary (PRE) provide crucial information for environmental processes, hydrological infrastructure, and navigation. Traditional SSC mapping based on in situ investigations lacks the spatial coverage necessitated by detailed analysis. In this study, based on in situ spectral data and SSC measurements, we developed models to quantify SSC based on Landsat TM/OLI and Sentinel-2 imagery. The models were then used to map the SSC distribution in the PRE for the period 1986–2020. The results indicated that SSC in the entire PRE displayed an overall decreasing trend over the past 35 years, but an abnormal increase was also observed in shallow waters near Hengmen. Geographically, the concentration along the west coast is higher than on the east coast, and the central part of Lingding Bay underwent a slight increase. The decreased sediment output from the Pearl River Basin is the major cause of the decreasing changes in SSC. However, the natural factors and human activities such as channel dredging and the construction of artificial facilities can also disturb the spatial distribution of SSC. Regions with a significant decrease in SSC should have special concerns about retaining the PRE's health and sustainability. [ABSTRACT FROM AUTHOR]

Cascade damming can shape land surfaces; however, little is known about the specific impacts of dam construction on watershed land cover changes. Therefore, we developed a framework in which remote sensing, transition patterns, and landscape metrics were coupled to measure the impact of dam construction on watershed land cover changes and landscape patterns in the Longmen–Su (L–S) Creek, a small headwater watershed in Southeast China. During the transition and post-impact periods of dam construction, the land cover in the L–S Creek watershed underwent dynamic changes within the affected area. Changes in land cover were dominated by a surge in water and buildup and a decrease in woodland and cropland areas; bareland also increased steadily during construction. Woodlands and croplands were mainly flooded into water areas, although some were converted to bareland and built-up areas owing to the combined impact of dam construction and urbanization. By linking land cover changes with landscape patterns, we found that land use changes in water were significantly associated with landscape fragmentation and heterogeneity in the impacted zone. Our research demonstrates how damming can change land cover locally and may provide a basis for sustainable land management within the context of the extensive development of cascade hydropower dams. [ABSTRACT FROM AUTHOR]

Climate change will likely increase the total streamflow in most headwaters on the Tibetan Plateau in the next decades, yet the response of runoff components to climate change and permafrost thaw remain largely uncertain. Here, we investigate the changes in runoff components under a changing climate, based on a high‐resolution cryosphere‐hydrology model (Spatial Processes in Hydrology model, SPHY) and multi‐decadal streamflow observations at the upstream (Jimai) and downstream stations (Maqu and Tangnaihai) in the source‐region of the Yellow River (SYR). We find that rainfall flow dominates the runoff regime in SYR (contributions of 48%–56%), followed by snowmelt flow (contributions of 26%/23% at Maqu/Tangnaihai). Baseflow is more important at Jimai (32%) than at the the downstream stations (21%–23%). Glacier meltwater from the Anyê Maqên and Bayankala Mountains contributes negligibly to the downstream total runoff. With increasing temperature and precipitation, the increase in total runoff is smaller in the warm and wet downstream stations than in the cold and dry upstream station. This is because of a higher increase in evapotranspiration and a larger reduction in snowmelt flow in the downstream region in response to a warming climate. With temperature increase, there is less increase in rainfall flow in the downstream region due to increased water loss through evapotranspiration. Meanwhile, the decline in snowmelt flow is larger further downstream, which can negatively impact the spring irrigation for the whole Yellow River basin that supports the livelihoods of 140 million people. Importantly, we find that baseflow plays an increasingly important role in the permafrost‐dominated upstream region with atmospheric warming and permafrost thaw, accompanied by decreased surface flow. These findings improve our current understanding of how different hydrological processes respond to climate change and provide insights for optimizing hydropower and irrigation systems in the entire Yellow River basin under a rapidly changing climate. [ABSTRACT FROM AUTHOR]

Strong anthropogenic activities and climate change have caused distinct hydrology and sediment dynamics in river systems worldwide. Yet, the integrated picture of sediment discharge changes and quantitative attribution of these changes from a basin‐wide perspective were limitedly understood. In this study, we quantified the variations of sediment discharge and in‐reach sediment budget in the Yellow River basin (YRB) during 1956–2019 and examined the underlying reasons. Both streamflow and sediment load in the YRB have substantially decreased during 1956–2000 except the headwater, and the reduction rate increased along the mainstem. However, the streamflow has significantly increased (p < 0.05) since 2000 due to increased precipitation, and the sediment load at most stations tended to stabilize. The contribution of soil conservation measures (SCMs, including check‐dams, terraces, grass plantation, and afforestation) and reservoirs to sediment load reduction was more than 50% in the headwater and middle reaches and over 90% in the upper and lower reaches. The sediment yield coefficient decreased linearly with reservoir capacity and exponentially with the proportional area of SCMs (p < 0.01). With continuous dam construction, the channel erosion in the headwater decreased to nearly zero, and the sediment deposition in the upper and middle reaches increased linearly with storage capacity of reservoirs. In contrast, the sediment deposition in the lower reaches displayed a linear correlation with the concentration of sediment derived from the middle reaches (p < 0.05). This study provides quantitative results for sediment dynamics of entire river system, which facilitates development of sustainable watershed management strategies. Key Points: We provide an integrated picture of sediment flux change and in‐reach sediment budget from the headwater to the delta in the Yellow RiverSediment load decreased greatly during 1956–2019 with increasing reduction rate along the mainstem, but the rate has declined since 2000Sediment deposition in the upper/middle reaches was controlled by dams but it depended more on sediment concentration in the lower reaches [ABSTRACT FROM AUTHOR]

Despite growing research on greenhouse gas (GHG) emissions from inland waters, few systematic efforts have been made to assess the regional‐scale GHG emissions from Asian rivers under increasing anthropogenic stress. We examined factors controlling longitudinal and seasonal variations in the partial pressure of CO2 (pCO2), and CH4 and N2O concentrations in the Ganges, Mekong, and Yellow River by simultaneously measuring gas concentrations and stable C isotopes, and optical properties of dissolved organic matter (DOM) from 2016 to 2019. The levels of pCO2 and CH4 were distinctively higher in polluted tributaries and affected reaches of the Ganges and Mekong than in the Yellow River. The highest levels of N2O were found in the Ganges, followed by the Yellow River and Mekong. Across these basins, dry‐season mean concentrations of CO2, CH4, and N2O were 1.6, 2, and 7 times higher than those measured in the monsoon season, respectively. This seasonality was consistent with that of δ13C‐CO2, while δ13C‐CH4 showed an opposite pattern. GHG concentrations exhibited significant positive relationships with DOM concentrations and optical properties including fluorescence index and protein‐like fluorescence, implying the contribution of anthropogenic, labile DOM to production of GHGs in the polluted reaches. Graphical mixing models of δ13C‐CO2 and δ13C‐CH4 support the stronger impact of wastewater on the Ganges and Mekong than on the Yellow River. The overall results suggest that neglecting localized pollution impacts on GHG emissions from increasingly urbanized river basins can result in a substantial underestimation of global riverine GHG emissions. Plain Language Summary: Rapid urbanization and poor wastewater infrastructure are turning many large rivers in Asia into significant sources of greenhouse gases (GHGs). We examined controlling factors for the concentrations of CO2, CH4, and N2O in the Ganges, Mekong, and Yellow River by simultaneously measuring gas concentrations and stable carbon isotopes, and optical properties of dissolved organic matter (DOM). The concentrations of CO2 and CH4 were distinctively higher in polluted tributaries and affected sections of the Ganges and Mekong than in the Yellow River. N2O concentration was highest in the Ganges, followed by the Yellow River and Mekong. Across these basins, the concentrations of the three gases were generally higher during dry periods than in the monsoon season. GHG concentrations were positively related to DOM optical properties indicating the contribution of easily degradable DOM from pollution sources. The stable carbon isotope ratios of CO2 and CH4 support the stronger impact of wastewater on the Ganges and Mekong than on the Yellow River. The overall results suggest that neglecting local pollution impacts on GHG emissions from increasingly urbanized river basins can result in a substantial underestimation of global riverine GHG emissions. Key Points: High CO2, CH4, and N2O concentrations in urbanized river reaches reflect influences from local tributaries carrying wastewaterSeasonality in stable C isotopes and dissolved organic matter properties corresponds to higher dry‐season greenhouse gas concentrations than in the monsoonStable C isotopes and their relationships with CO2 and CH4 concentrations support localized wastewater effects on urbanized rivers [ABSTRACT FROM AUTHOR]

Approximately 40% of the Tibetan Plateau (TP) is underlain by continuous permafrost, yet its impact on fluvial water and sediment dynamics remains poorly investigated. Here we show that water and sediment dynamics in the permafrost‐dominated Tuotuohe basin on the TP are driven by air temperature and permafrost thaw, based on 33‐year daily in situ observations (1985–2017). Air temperature regulates the seasonal patterns of discharge and suspended sediment concentration (SSC) by controlling the changes in active contributing drainage area (ACDA, the unfrozen erodible landscape that contributes hydrogeomorphic processes within a catchment) and governing multiple thermal processes such as glacier‐snow melt and permafrost thaw. Rainstorms determine the short‐lived fluvial extreme events by intensifying slope processes and channel erosion and likely also by enhancing thaw slumps. Furthermore, the SSCs at equal levels of discharges are lower in autumn (September–October) than in spring (May–June) and summer (July–August). This reduced sediment availability in autumn can possibly be attributed to the increased supra‐permafrost groundwater runoff and the reduced surface runoff and erosion. Due to rapid climate warming, the ACDA has increased significantly from 1985 to 2017, implying expanding erodible landscapes for hydrogeomorphic processes. As a result, the fluvial water and sediment fluxes have substantially increased. In a warmer and wetter future for the TP, the fluvial sediment fluxes of similar permafrost‐underlain basins will continue to increase with expanding erodible landscapes and intensifying thermal and pluvial‐driven geomorphic processes. Thus, permafrost thaw should be considered as an important driver of past and future water and sediment changes for the TP. Key Points: Climate warming expands the erodible landscape and increases fluvial water and sediment fluxes on the Tibetan PlateauAir temperature regulates seasonal discharge and sediment dynamics by controlling glacier‐snow melt and permafrost processesIncreasing rainstorms results in more frequent fluvial extreme events [ABSTRACT FROM AUTHOR]

Soil erosion modulates the atmospheric CO2 level by affecting the redistribution of young biospheric organic carbon (OCbio) and ancient petrogenic organic carbon (OCpetro) in different order streams. However, the fate of soil organic carbon (SOC) in low‐order stream systems is still uncertain due to the complex influences of terrain, land uses, and anthropogenic disturbances. Here, we used the geochemical properties fingerprinting method and a radiocarbon‐based two‐member mixing model to clarify the source, budgets, and composition of SOC in a low‐order stream catchment in the Yellow River basin. The results showed that the primary source of SOC in the catchment was agricultural activity area, which accounted for 68.5%. After vegetation restoration, the SOC delivery rate and loss rate decreased from 0.38 ± 0.06 to 0.26 ± 0.04 and 0.19 ± 0.06 to 0.14 ± 0.04 t·ha−1·yr−1, respectively. The SOC mobilized by soil erosion in the source area was 1,085.8 ± 170.5 t from 1969 to 2015, and the SOC lost during the transport process was 552.9 ± 170.1 t. The lost carbon was dominated by OCbio, whereas the loss of OCpetro was minimal. Soil erosion can mobilize the OCpetro sequestered in terrestrial ecosystems and deliver it to a river system if it is not intercepted. The oxidation of OCpetro during long‐distance fluvial transport may represent a significant carbon source for atmospheric CO2 on a geological timescale. This study contributes to our understanding of the carbon sink/source issue and quantifies the SOC budgets in stream systems. Plain Language Summary: Understanding how soil erosion affects the redistribution and delivery of soil organic carbon (SOC) is essential for clarifying the source, budgets, and composition of SOC and helps us further understand the terrestrial carbon cycle. This study calculated the source of SOC based on differences in geochemical properties in different source areas. Then, we measured the radiocarbon (14C) content to clarify the composition and fate of SOC during the erosion process. We found that the primary source of SOC in the catchment was the agricultural activity area and that agricultural activities and vegetation restoration were shown to significantly affect SOC redistribution. A large amount of modern organic carbon was lost during the transport process and may become an atmospheric CO2 source over short timescales. Almost all ancient organic carbon is intercepted by the dam at the outlet. If there is no check dam, the remaining ancient organic carbon can be exported to the Yellow River and then oxidized during fluvial transport, leading to an increase in long‐term atmospheric CO2 levels. This research clarifies the influence of soil erosion on SOC redistribution and delivery and quantifies the source, budget, and composition of SOC in the low‐order stream system. Key Points: Agricultural activities and vegetation restoration have impacted the sediment and erosion‐induced redistribution of soil organic carbonA large amount of soil organic carbon was lost during the transport process, and the lost carbon was dominated by biospheric organic carbonThe petrogenic organic carbon exported from the low‐order stream may become a carbon source on a geological timescale [ABSTRACT FROM AUTHOR]

Impounding alters the carbon transport in rivers. To quantify this effect, we measured CO2 effluxes from a mountainous valley-type reservoir in the upper Mekong River (known as Lancang River in China). CO2 evasion rates from the reservoir surface were 408±337 mg CO2 m -2 d -1 in the dry season and 305±262 mg CO2 m -2 d -1 in the rainy season much lower than those from the riverine channels (1567±2312 mg CO2 m -2 d -1 at the main stem and 905±1536 mg CO2 m -2 d -1 at the tributary). Low effluxes in the pelagic area were caused by low allochthonous organic carbon (OC) inputs and photosynthetic uptake of CO2. A negative relationship between CO2 efflux and water temperature suggested CO2 emissions at the pelagic area were partly offset by photosynthesis in the warmer rainy season. CO2 emissions from the reservoir outlet and littoral area, which were usually considered hotspots of CO2 emissions, had a low contribution to the total emission because of epilimnion water spilling and a small area of the littoral zones. Yet at the river inlets effluxes were much higher in the dry season than in the rainy season because different mixing modes occurred in the two seasons. When the river joined the receiving waterbody in the dry season, warmer and lighter inflow became an overflow and large amounts of CO2 were released to the atmosphere as the overflow contacted the atmosphere directly. Extended water retention time due to water storage might also help mineralization of OC. In the wet season, however, colder, turbid and heavier inflow plunged into the reservoir and was discharged downstream for hydroelectricity, leaving insufficient time for decomposition of OC. Besides, diurnal efflux variability indicated that the effluxes were significantly higher in the nighttime than in the daytime, which increased the estimated annual emission rate by half. [ABSTRACT FROM AUTHOR]

Algal assemblages have been widely used as an ecological indicator of aquatic ecosystem health conditions because of their specific sensitivity to a wide variety of environmental conditions. In turbid rivers, as in other aquatic systems, phytoplankton structure plays an important role in structuring aquatic food webs. Worldwide, phytoplankton is less studied in turbid, large tropical rivers compared to temperate river systems. The present study aimed to describe the phytoplankton diversity and abundance in a turbid tropical river (the Red River, northern part of Vietnam from 20°00 to 25°30 North; from 100°00 to 107°10 East) and to determine the importance of a series of environmental variables in controlling the phytoplankton community composition. Phytoplankton community was composed of 169 phytoplankton taxa from six algal groups including Bacillariophyceae, Chlorophyceae, Cryptophyceae, Euglenophyceae, Dinophyceae and Cyanobacteria. Community composition varied both spatially and with season. Sixteen measurement environmental variables were used as input variables for a three-layer backpropagation neural network that was developed to predict the phytoplankton abundance. Phytoplankton abundance was successfully predicted using the tagsig transfer function and the Levenberg-Marquardt backpropagation algorithm. The network was trained to provide a good overall linear fit to the total data set with a slope (R) and mean square error (MSE) of 0.808 and 0.0107, respectively. The sensitivity analysis and neutral interpretation diagram revealed that total phosphorus (TP), flow discharge, water temperature and P-PO 4 3− were the significant variables. The results showed that the developed ANN model was able to simulate phytoplankton abundance in the Red River. These findings can help for gaining insight into and the relationship between phytoplankton and environmental factors in this complex, turbid, tropical river. [ABSTRACT FROM AUTHOR]

As an important soil and water conversation endeavor, the 'Grain for Green' project launched by the Chinese Central Government almost doubled the vegetation cover on the Loess Plateau between 1999 and 2013. The corresponding vegetation restoration considerably diminished slope erosion throughout the Loess Plateau, although erosion in gullies remains poorly understood. In this paper, a composite fingerprinting approach was employed to assess the relative importance of the erosion of gully and slope soils within a typical dam‐controlled catchment of the Loess Plateau. A total of 23 couplets were identified based on the deposited layer thicknesses and extreme rainfall event records along the sediment profile. The results suggest that gullies contributed 71% to the overall sediment proportion, and those sediments had an increased tendency to accumulate during 2010–2016 under the 'Grain for Green' project. The sediment inputs from slope areas were predicted to be 29%. The eroded gullies materials mainly consisted of silt‐sized particles, which dominated the eroded sediment. Silt particles with sizes of 0.02–0.05 mm constituted the main particles in both deposit sediments and gully materials, whereas the slope areas mainly contained particle sizes of <0.01 mm. The check dam proved to be effective at trapping coarse silt with 27–42% of the total sediment content. This study presents reliable information on the importance of gullies as sediment source materials and verifies the applicability of tracing procedures for collecting information on sediment effluxes from both slopes and gullies. [ABSTRACT FROM AUTHOR]

Riverine export of terrestrially derived carbon represents a key component of the global carbon cycle. In this study we quantify the fate of riverine carbon within the Wuding River catchment on the Chinese Loess Plateau. Export of dissolved organic and inorganic carbon (DOC and DIC) exhibited pronounced spatial and temporal variability. While DOC concentration first presented a downward trend along the river course and then increased in the main-stem river, it showed no significant seasonal differences and was not sensitive to flow dynamics. This likely reflects the predominance of groundwater input over the entire year and its highly stable DOC. DIC concentration in the loess subcatchment is significantly higher than that in the sandy subcatchment, due largely to dissolution of carbonates that are abundant in loess. In addition, bulk particulate organic carbon content (POC%) showed strong seasonal variability with low values in the wet season owing to input of deeper soils by gully erosion. The downstream carbon flux was (7.0±1.9) × 1010gCyr-1 and dominated by DIC and POC. Total CO2 emissions from water surface were (3.7±0.6)×1010gCyr-1. Radiocarbon analysis revealed that the degassed CO2 was 810-1890 years old, indicating the release of old carbon previously stored in soil horizons. Riverine carbon export in the Wuding River catchment has been greatly modified by check dams. Our estimate shows that carbon burial through sediment storage was (7.8±4.1)×1010gCyr-1, representing 42% of the total riverine carbon export from terrestrial ecosystems on an annual basis ((18.5±4.5)×1010gCyr-1). Moreover, the riverine carbon export accounted for 16% of the catchment's net ecosystem production (NEP). It appears that a significant fraction of terrestrial NEP in this arid to semiarid catchment is laterally transported from the terrestrial biosphere to the drainage network. [ABSTRACT FROM AUTHOR]

ABSTRACT The Loess Plateau ecosystem in China is degraded owing to poor natural conditions and intense human activity. The intensity of soil erosion and deficit of soil moisture are the key factors that influence the ecological restoration and agricultural land productivity in this region. Analysis of the soil moisture dynamic and the relative importance of land use and topography for the spatial variability of soil moisture is the basis for guiding ecosystem restoration and agricultural development. We analysed the spatial variability of soil moisture for five land-use types within 44 sample plots (176 sample points) at the five depths (0-20, 20-40, 40-60, 60-80 and 80-100 cm) in the Anjiagou catchment of the Loess Plateau from April to September 2002. The depth-averaged soil moisture of cropland was the highest among the five land-use types, followed by fallowland, woodland, shrubland and wasteland during high soil-water contents period (from 24 April to 23 June). The time-averaged soil moisture of all the five land-use types first decreased with depth during the wet moisture status and then increased with depth during the dry conditions (from 12 July to 9 August). The time-averaged soil moisture of fallowland, cropland and shrubland was decreased with depth, but both wasteland and woodland was decreased and then increased with depth in the medium moisture status (from 23 August to 18 September). Land use was the key factor that influenced the spatial variability of the time-averaged moisture of the four soil layers (20-40, 40-60, 60-80 and 80-100 cm) during the wet and medium soil-water content condition. Land use had a weak influence on the spatial variability of the time-averaged moisture of all the five soil layers in the dry moisture status. Slope aspect had a significant influence on the time-averaged soil moisture of some soil layers in the wet and medium moisture statuses for wasteland, shrubland, woodland and fallowland. The other four topographic factors (slope profile curvature, slope position, relative elevation and slope gradient) all had weak influence on the time-averaged soil moisture of all the five land use types in the three water statuses. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The sensitivity of runoff to the climate change in the Longitudinal Range-Gorge Region (LRGR) in southwest China was investigated with a case study in the Longchuan Basin of the upper Yangtze River, where the climate change is more complex due to the influences from both global warming and local topography. Non-updating artificial neural networks were calibrated and validated at the baseline condition and were used to predict the response of runoff under 25 hypothetical climate scenarios, which were generated by adjusting the baseline temperature by -1, 0, 1, 2 and 3°C and by scaling rainfall by 0%, ± 10% and ± 20%. The results indicated that runoff is more sensitive to the increase in rainfall. The annual and seasonal runoff changes were determined by the interaction between temperature and rainfall. At seasonal scale, the direction of change in runoff is more determined by temperature in winter and spring; whereas it is more determined by rainfall in summer and autumn. The LRGR in southwest China may experience a higher frequency of floods in the wet season and more serious droughts in the dry season, if a wetter summer and warmer winter is the trend of future climate change, as predicted by many GCMs. [ABSTRACT FROM AUTHOR]

Abstract: Monthly precipitation data covering 1956–2002 at 36 rain stations are analyzed to explore the spatio-temporal variability of the seasonal precipitation in the Dongjiang River basin, south China, using a continuous wavelet transform method, Mann-Kendall trend test, and simple regressive technique. The results indicated that: (1) increasing precipitation is observed in spring and winter; while decreasing precipitation is identified in summer and autumn. The increasing/decreasing precipitation trend mostly occurred near the lower/upper parts of the Dongjiang River basin; (2) the spatial distribution of the precipitation anomaly between 1956–1989 and 1990–2002 is similar to that of precipitation trend; (3) in general, 4 time periods are identified: 1956–1961 and 1975–1985 are featured by increasing areal average annual precipitation; while 1962–1974 and 1986–2002 are characterized by decreasing areal average annual precipitation. The areal average annual maximum precipitation has a decreasing trend; (4) the precipitation changes in the Dongjiang River basin are mainly controlled by the south-east Asian monsoon activities. Intensity of the south-east Asian monsoon carrying excess moisture is the main driving factor for precipitation changes in this study. This result will be greatly helpful for further research on availability and management of the water resources in the Dongjiang River basin, the main focus of an on-going research project. [Copyright &y& Elsevier]

Fecal contamination from sewage and agricultural runoff has been a prevailing problem in coastal watersheds owing to accelerating human stressors and climate change in the Anthropocene. However, the patterns and drivers of fecal indicator bacteria (FIB) exports in typhoon-affected watersheds remain poorly understood. Here, the spatiotemporal variation of FIB and its drivers were systematically investigated in a subtropical coastal watershed, namely the Jiulong River Watershed (JRW), by integrating a decade of monthly in-situ observations and applying them to the Soil and Water Assessment Tool (SWAT) model. The SWAT model was calibrated and validated for streamflow and fecal coliform (FC) simulations with satisfactory performance (Nash-Sutcliffe Efficiency of 0.69 and 0.47, R2 of 0.72 and 0.60 for streamflow and FC in validation period, respectively). Observations of FC in both the North River (220–5580 cfu·100 mL−1) and the West River (3649–46,293 cfu·100 mL−1) of the JRW showed significant declining trends from 2010 to 2020. Source attribution analysis of FC export indicated that livestock manure emissions were the largest contributor (>60%) with urban domestic sewage being the least important contributor (<5%). Furthermore, our observation and modeling results show that FC exports were markedly enhanced during high rainfall events and typhoons, while FC exports decreased during the winter when the climate is dry and cold. The FC loads ranged from 2.6 × 107 to 2.8 × 1010cfu∙L−1∙s−1, with the average loads in agriculture, nature, and urban watershed accounting for 6.3 × 109, 8.3 × 108, and 7.4 × 109cfu∙L−1∙s−1, respectively. Our data support that the FC loads are closely related to anthropogenic indicators and are significantly higher in urban and agricultural watersheds than in natural or pristine watersheds. Future climate change with more frequent rainfall extremes will likely intensify FC exports. Such findings have important implications regarding mitigating FIB pollution for subtropical coastal watersheds under the context of climate change and increasing human impacts. [ABSTRACT FROM AUTHOR]

• Extreme streamflow and sediment load decreased during 1956–2019, but increased or stabilized since 2000. • Mainstream dams reduced synchronization probability of extreme streamflow and sediment load. • Soil conservation measures reduced extreme streamflow and sediment load in power function. In recent decades, the increasing frequency and magnitude of extreme hydrological events due to climate change and human activities have caused substantial economic losses and damages to human wellbeing. Here, we investigated the spatiotemporal variations of streamflow extremes (QE) and sediment load extremes (SE) in the Yellow River (YR) during 1956–2019. Furthermore, the effects of main human activities and climate change were identified by establishing quantitative relationships between these factors and changing hydrological extremes. Specifically, the QE and SE have decreased significantly (p < 0.05) since 1956 except the headwater (reach above Tangnaihai). However, the QE increased significantly (p < 0.05) during 2000–2019 due to increased extreme precipitation, while the SE tended to stabilize at most stations. Besides, the contribution of QE to annual streamflow declined distinctly in the upper-middle reaches (Lanzhou-Tongguan reach) but increased significantly in the lower reaches (reach below Huayuankou). Likewise, the contribution of SE to annual sediment load increased remarkably in the middle-lower reaches (Huayuankou-Lijin reach). Furthermore, the timing of QE and SE generally tended to disperse from the flood season to the four seasons. While extreme precipitation fundamentally caused the extreme water and sediment discharge, the magnitude and hazard of QE and SE can be strongly regulated by human activities. Particularly, mainstream dams can artificially regulate QE and SE magnitudes and relationships and reduce their synchronization probability, and intra-basin engineering construction and revegetation measures can substantially reduce their possible peaks in a power function form. In addition, changes in the extreme water–sediment relationships indicated that declining erosive power in the middle reaches and decreasing sediment availability in the lower reaches dominated SE reduction. This study provides a scientific basis for flood risk management and water resources development and utilization in large complex river basins. [ABSTRACT FROM AUTHOR]

Abstract: Long monthly streamflow series of three control hydrological stations of the Pearl River basin were analyzed by using the scanning t-test and the scanning F-test. Possible implications of the changing properties of streamflow variations for the water resource management of the Pearl River Delta are also discussed. The results indicated that: 1) more complicated changes were observed in terms of the second center moment when compared to the first original moment. More significant abrupt changes of the second center moment imply more sensitive response of streamflow stability to climate changes and human activities; 2) abrupt behaviors of the first (second) center moment of the streamflow variations tend to be more sensitive to climate changes and/or human activities in the larger river basin when compared to those in the smaller river basin. These phenomena are attributed to buffering functions of more storage space of longer river channel, and more complicated and longer runoff yield and concentration processes in the river basin of larger drainage area; 3) annual minimum streamflow of the Pearl River basin tends to be increasing. This will be helpful for better human mitigation of the salinity intrusion in dry seasons across the Pearl River Delta. Annual maximum streamflow, when compared to annual minimum streamflow, shows larger-magnitude variability reflected by larger standard deviation, implying unfavorable conditions for flood mitigation in the Pearl River Delta. The results of this paper are of scientific and practical merits for water resource management and sound human mitigation to water hazards across the Pearl River Delta, and also are a good case study for similar researches in other river deltas in the world under the changing environment. [ABSTRACT FROM AUTHOR]