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The Loess Plateau is one of the most vulnerable areas in the world as it is extremely susceptible to soil erosion and ecological destruction. Recently, the local government carried out the “Gully Land Consolidation Project” (GLCP) in the Loess Plateau region to increase farmland area, improve rural production and living conditions. Among all the GLCP engineering constructions, slope protection engineering plays an important role in ensuring the safety of the main project, residential lives and properties, although more theoretical and technical research on comprehensive protection of engineering slopes is required. In this study, a field experiment using 12 standard runoff plots (length 4m×width 2m) was performed in Yangjuangou catchment of Yan'an City, to compare and analyze the comprehensive benefit to vegetative growth, soil erosion and engineering benefit from four vegetation styles and three levels of slope gradient (45°, 53°,63°). Results show that under different slope gradient and vegetation styles, significant differences existed in the comprehensive benefit to slopes, as well as the levels of vegetative growth, soil erosion and engineering benefit. The comprehensive benefit of the 53° slope was significantly better than that of 45° and 63° slopes. In addition, the comprehensive benefit of slopes with one or more vegetation styles was better than that of non-vegetation covered slopes. With the increase in slope gradient, the vegetative growth and slope erosion indices of vegetation average height, species richness, vegetation coverage slope, runoff production and sediment yield, showed a remarkable declining trend. Conversely, the engineering benefit index including newly-increased farmland area and excavating earthwork volume, showed an increasing trend. Recently, agricultural geographical engineering (AGE) has become an indispensable method for ecological construction and agricultural development, resulting in an increase in research in the field of geography. These findings not only have theoretical significance and enrich our understanding of the influence of gradient and vegetation styles on excavation slope protection, but also have practical significance and provide a baseline for engineering parameters and suggestions for slope protection engineering strategies.

Maintaining drinking water security is a global issue, and phosphorus is a limiting factor affecting drinking water quality. Hence, this study took Fushi Reservoir as a test area, and set up field runoff observation plots around the reservoir catchment, which is covered by moso bamboo stands. Through field observation, the vertical variation of phosphorus loss in different stands of moso bamboo was initially studied. The results showed that: (1) For the vertical dimensions (atmospheric rainfall, stemflow, throughfall, surface runoff) from high to low, the loss of total phosphorus (TP) increased, and the proportion of dissolved phosphorus increased from 29.29% (atmospheric rainfall) to 62.76% (surface runoff). (2) Different rainfall factors had various impacts on phosphorus loss at the different vertical levels. The accumulation of rainfall had the greatest impact on surface runoff TP loss, with the correlation coefficient reaching 0.994 (P

Runoff coefficient (C) values are tabulated and enshrined in hydrological engineering. These values are considered to be constant although they may not correspond to reality. In the same catchment, they may vary according to intensity, temporal and spatial distribution of precipitation events, humidity conditions, soil and land use. This study aimed to analyze extreme events of precipitation and their corresponding flows to obtain experimental runoff coefficients (C) and compare them with the tabulated values. The study was conducted in five experimental catchments in the state of Sao Paulo, Brazil, with different land uses. The runoff coefficients (C) were obtained from the analysis of hydrograms and using a digital filter, which made it possible to separate the direct runoff from the total flow. We observed a different variation in runoff coefficient values between catchments compared to those obtained from the tables. The runoff coefficients had a high correlation with land use. In catchments with original vegetation cover, such as Cerrado and forest, they varied little among the events analyzed, unlike the catchments where land use is diversified, with predominantly agricultural and urban occupation.

In arid-semiarid regions, understanding the mechanisms by which vegetation change and climate change affect the regional water balance is important for the development of effective measures and for guiding vegetation restoration and adapting to climate change. In this study, we utilize the Budyko equation and dual-source evapotranspiration models to assess the impacts of vegetation change and climate change on the runoff in China's Yellow River Basin (YRB). The aims of the study are as follows: (1) Apply a well-formulated Budyko framework-dual-source evapotranspiration model to explore the eco-hydrological controls of the regional water balance. (2) Precisely assess the contribution of vegetation change, precipitation change, temperature change, wind speed change, the relative humidity change, and radiation change to the decreased runoff. The results indicated that vegetation change was the dominant factor affecting the reduction of runoff in the upper reaches above Lanzhou, Toudaoguai, Longmen, Sanmenxia, and Huayuankou, and the contributions were −80.4%, −58.4%, −52.5%, −46.9%, −39.7%, and −41.6% respectively. In Lanzhou, Taodaoguai, Longmen, and Sanmenxia, the precipitation change was the second affecting factor, and the contributions were −20.8%, −31.6%, −30.0%, and −35.2%, respectively. In Huayuankou and Lijin, the relative humidity change was the second affecting factor, and the contributions were –26.8% and −35.0%, respectively. (3) As the vegetation coverage or the leaf area index (LAI) increased, the runoff decreased linearly.

Direct land-to-atmosphere carbon exchange has been the primary focus in previous studies of peatland disturbance and subsequent restoration. However, loss of carbon via the fluvial pathway is a significant term in peatland carbon budgets and requires consideration to assess the overall impact of restoration measures. This study aimed to determine the effect of peatland land management regime on aquatic carbon concentrations and fluxes in an area within the UK's largest tract of blanket bog, the Flow Country of northern Scotland. Three sub-catchments were selected to represent peatland land management types: non-drained, drained, and restoration (achieved through drain blocking and tree removal). Water samples were collected on a fortnightly basis from September 2008 to August 2010 at six sampling sites, one located upstream and one downstream within each sub-catchment. Concentrations of dissolved organic carbon (DOC) were significantly lower for the upstream non-drained sub-catchment compared to the drained sub-catchments, and there was considerable variation in the speciation of aquatic carbon (DOC, particulate organic carbon (POC), CO2, and CH4) across the monitoring sites, with dissolved gas concentrations inversely correlated with catchment area and thereby contributing considerably more to total aquatic carbon in the smaller headwater catchments. Significantly higher POC concentrations were observed in the restored sub-catchment most affected by tree removal. Aquatic carbon fluxes were highest from the drained catchments and lowest from the non-drained catchments at 23.5 and 7.9 g C m−2 yr−1, respectively, with variability between the upstream and downstream sites within each catchment being very low. It is clear from both the aquatic carbon concentration and flux data that drainage has had a profound impact on the hydrological and biogeochemical functioning of the peatland. In the restoration catchment, carbon export varied considerably, from 21.1 g C m−2 yr−1 at the upper site to 10.0 g C m−2 yr−1 at the lower site, largely due to differences in runoff generation. As a result of this hydrological variability, it is difficult to make definitive conclusions about the impact of restoration on carbon fluxes, and further monitoring is needed to corroborate the longer-term effects.

The effects of catchment characteristics and climate variables on water partitioning into evapotranspiration and runoff can be evaluated using the Budyko framework. However, the influence of glaciers on catchment characteristics within the framework has yet been adequately investigated. Here we extend the Budyko framework and apply the elasticity method to examine the effects of glaciers on runoff between 2001 and 2010 in 25 upstream catchments of the Tarim River Basin in western China. The consideration of glacier mass balance and glacier fraction improves the performance of the Budyko framework, especially for the catchments with a high glacier fraction. We found that the catchment characteristic parameter ω was strongly affected by glacier fraction, and it changes from 1.15 to 2.09 when glacier fraction decreases from 0.4191 to 0.0005. This also reflects the change in water–energy partitioning that eventually effects on evapotranspiration and runoff. We further assessed the average runoff responses to changes in precipitation, potential evapotranspiration, glacier mass balance, and glacier fraction in the 25 catchments. Although the runoff appears most sensitive to precipitation in average, its sensitivity to glacier mass balance and glacier area in fact rises from −0.07% to 0.17% and about 0–0.54%, respectively, when the glacier fraction increases from 0.0005 to 0.4191, further demonstrating the increasing influence of glaciers when the fraction becomes larger. After all, the inclusion of glacier factors in the Budyko framework allows us to understand more about the impacts and contributions of glaciers to runoff at a catchment scale.

Most hydrology measurement involving input and output analysis use small catchments because long-term measurement is a feasible proposition. The fundamentals of measurement of streamflow and rainfall on a small catchment are reviewed. The integration of data to go from instantaneous to hourly, daily, monthly or annual data and the gains and losses in information are examined. The issue of extracting information from complex hydrographs is reviewed, and examples are given as to how this might be done. A formal introduction to the concept of the catchment water balance is given. This is used to introduce the methodology of “Zhang Curves” and their transformations to yield approximate measures of percentage runoff and rainfall elasticity.

Murray-Darling Freshwater Research CentreMDFRC item.This paper assesses the capacity of a small (450 m2) constructed wetland in Victoria, Australia, to decrease nutrient loads generated by both background flows and storm events within the period March 1993 to January 1995. Under Australian conditions the effectiveness of wetlands in controlling diffuse pollution is influenced by extreme hydrological events which often carry a large proportion of the annual load from the catchment. The wetland retained a varying proportion of the nitrogen and phosphorus load over a range of hydrological events and seasonal conditions. The wetland also acted as a source of these nutrients on occasions. An annual nutrient budget was calculated for the period February 1994 to January 1995 by measuring all loads between and during storm events entering and leaving the wetland. The wetland ‘retained' 10 kg N yr−1 (23 g N m−2 yr−1) of nitrogen and 1.24 kg P yr−1 (2.80 g P m−2 yr−1) of phosphorus, representing 11 and 17%, respectively of the incoming nutrient loads for the budget period.Storm event size influenced the impact of the wetland on the nutrient loads generated in these events. Increasing event volumes generally resulted in decreased nutrient interception. The results of this study indicate that for significant load reduction to occur the scale of the wetland should be such that there is sufficient residence time to enable wetland processes to operate. Small strategically located wetlands high up in catchments which will have a cumulative impact on runoff generated in large storm events are likely to be more effective in intercepting nutrient loads than larger downstream structures.

Issues related to large uncertainty and parameter equifinality have posed big challenges for hydrological modeling in cold regions where runoff generation processes are particularly complicated. Tracer-aided hydrological models that integrate the transportation and fractionation processes of water stable isotope are increasingly used to constrain parameter uncertainty and refine the parameterizations of specific hydrological processes in cold regions. However, the common unavailability of site sampling of spatially distributed precipitation isotopes hampers the practical applications of tracer-aided models in large-scale catchments. This study, taking the precipitation isotope data (isotopes-incorporated global spectral model – isoGSM) derived from the isotopic general circulation models (iGCMs) as an example, explored its utility in driving a tracer-aided hydrological model in the Yarlung Tsangpo River basin (YTR; around 2×105 km2, with a mean elevation of 4875 m) on the Tibetan Plateau (TP). The isoGSM product was firstly corrected based on the biases between gridded precipitation isotope estimates and the limited site sampling measurements. Model simulations driven by the corrected isoGSM data were then compared with those forced by spatially interpolated precipitation isotopes from site sampling measurements. Our results indicated that (1) spatial precipitation isotopes derived from the isoGSM data helped to reduce modeling uncertainty and improve parameter identifiability in a large mountainous catchment on the TP, compared to a calibration method using discharge and snow cover area fraction without any information on water isotopes; (2) model parameters estimated by the corrected isoGSM data presented higher transferability to nested subbasins and produced higher model performance in the validation period than that estimated by the interpolated precipitation isotope data from site sampling measurements; (3) model calibration forced by the corrected isoGSM data successfully rejected parameter sets that overestimated glacier melt contribution and gave more reliable contributions of runoff components, indicating the corrected isoGSM data served as a better choice to provide informative spatial precipitation isotope than the interpolated data from site sampling measurements at the macro scale. This work suggested plausible utility of combining isoGSM data with measurements, even from a sparse sampling network, in improving hydrological modeling in large high mountain basins.

The magnitude and variation of the sediment loads transported by rivers have important implications for the functioning of river systems and changes in the sediment loads of rivers are driven by numerous factors. In this paper, the key drivers of changes in the sediment loads of the major rivers of China are identified by reviewing recent studies of changes in their sediment loads. Except for the Songhua River, which presents no clear tendency of change in runoff or sediment load, nearly all the major rivers of China are characterized by an apparent decline in annual sediment load. The total annual sediment load of major Chinese rivers transported to the coast decreased from 2.03 billion t/yr during the period 1955–1968 to 0.50 billion t/yr during the period 1997–2010. The primary drivers of changes in the sediment loads of the rivers are dam construction, implementation of soil and water conservation measures, catchment disturbance, agricultural practices, sand mining and climate change. Examples drawn from Chinese rivers are used to demonstrate the importance of these drivers. Construction of a large number of reservoirs in the Yangtze River basin represents the primary driver for the reduced sediment load of the Yangtze River. The implementation of soil and water conservation programmes is one of the key drivers for the sharp decline in the sediment load of the Yellow River. Catchment disturbance explains why the reduction of the sediment load of the Lancang-Mekong River at the Chiang Saen gauging station was much less than that at the Gajiu gauging station upstream. A reduction in sediment load resulting from the expansion of agricultural production may be the main driver for the reduced sediment load of the Huaihe River. The decrease in the sediment load of the Pearl River has been influenced by sand mining activities. Climate change is one of the key drivers responsible for the greatly reduced sediment load of the rivers in the Haihe River Basin.

Headwater streams play a major role for provision of ecosystem services, e.g. drinking water. We investigated a high-altitude headwater catchment of the Kharaa River (including 41 1st-order rivers) to understand the impact of land cover (especially forest cover), environment and human usage on runoff, chemical water quality and macroinvertebrate fauna in a river basin under discontinuous permafrost conditions in an arid, sparsely populated region of Mongolia. To verify our hypotheses that different landuses and environmental impacts in permafrost headwaters influence water quality, we investigated 105 sampling sites, 37 of them at intermittent stream sections without water flow. Discharge was positively impacted by land cover types steppe, grassland and forest and negatively by shrubland, forest burnt by wild fires (indicating a reduction of permafrost) and slope. Water quality was affected by altitude, longitude and latitude, shrub growth and water temperature. Shannon diversity of macroinvertebrates was driven by water temperature, iron content of the water, flow velocity, and subbasin size (adjusted R2 = 0.54). Sample plots clustered in three groups that differed in water chemistry, macroinvertebrate diversity, species composition and bio-indicators. Our study confirms that steppes and grasslands have a higher contribution to runoff than forests, forest cover has a positive impact on water quality, and diversity of macroinvertebrates is higher in sites with less nutrients and pollutants. The excellent ecological status of the upper reaches of the Kharaa is severely threatened by forest fires and human-induced climate change and urgently needs to be conserved.

Groundwater accounts for 30% of the world drinking water resources and is rarely taken into account in climate assessments. Climate change affects groundwater levels and regimes, but there is very little specific research on the future impacts of climate change on groundwater. This study examines data from 15 groundwater wells of various ages for the period from 1965 to 2015. To obtain reliable data, an analysis was made of the groundwater level changes in the upper hydrodynamic zone, which is not disturbed by anthropogenic activity. A statistically significant increase in the average annual groundwater levels in the study area was observed, in agreement with data indicating an increase in groundwater runoff in the winter season for large and medium rivers in the region. To explain the revealed changes in the groundwater levels, an analysis of the characteristic climatic changes (air temperature and amount of precipitation) and the groundwater runoff was performed. In winter, the unfrozen moisture content in the soil has increased; accordingly, groundwater recharge and groundwater levels have increased. Meanwhile, in summer, an increase in evaporation from the drainage basin has occurred as a result of the increasing air temperature. To some extent, this compensates for the changes in the annual runoff and groundwater levels that are hydraulically connected to the rivers.

Export of dissolved organic carbon (DOC) from riparian zones (RZs) is an important component of temperate catchment carbon budgets, but export mechanisms are still poorly understood. Here we show that DOC export is predominantly controlled by the microtopography of the RZ (lateral variability) and by riparian groundwater level dynamics (temporal variability). From February 2017 until July 2019 we studied topography, DOC quality and water fluxes and pathways in the RZ of a small forested catchment and the receiving stream in central Germany. The chemical classification of the riparian groundwater and surface water samples (n=66) by Fourier transform ion cyclotron resonance mass spectrometry revealed a cluster of plant-derived, aromatic and oxygen-rich DOC with high concentrations (DOCI) and a cluster of microbially processed, saturated and heteroatom-enriched DOC with lower concentrations (DOCII). The two DOC clusters were connected to locations with distinctly different values of the high-resolution topographic wetness index (TWIHR; at 1 m resolution) within the study area. Numerical water flow modeling using the integrated surface–subsurface model HydroGeoSphere revealed that surface runoff from high-TWIHR zones associated with the DOCI cluster (DOCI source zones) dominated overall discharge generation and therefore DOC export. Although corresponding to only 15 % of the area in the studied RZ, the DOCI source zones contributed 1.5 times the DOC export of the remaining 85 % of the area associated with DOCII source zones. Accordingly, DOC quality in stream water sampled under five event flow conditions (n=73) was closely reflecting the DOCI quality. Our results suggest that DOC export by surface runoff along dynamically evolving surface flow networks can play a dominant role for DOC exports from RZs with overall low topographic relief and should consequently be considered in catchment-scale DOC export models. We propose that proxies of spatial heterogeneity such as the TWIHR can help to delineate the most active source zones and provide a mechanistic basis for improved model conceptualization of DOC exports.

A multiple scenario-based ensemble prediction (MSEP) method is developed for exploring the impacts of climate and land-use changes on runoff in the Naryn River Basin. MSEP incorporates multiple global climate models, Cellular Automata–Markov and Soil and Water Assessment Tool (SWAT) within a general framework. MSEP can simultaneously analyze the effects of climate and land-use changes on runoff, as well as providing multiple climate and land-use scenarios to reflect the associated uncertainties in runoff simulation and prediction. A total of 96 scenarios are considered to analyze the trend and range of future runoff. Ensemble prediction results reveal that (i) climate change plays a leading role in runoff variation; (ii) compared to the baseline values, peak flow would increase 36.6% and low flow would reduce 36.8% by the 2080s, which would result in flooding and drought risks in the future and (iii) every additional hectare of arable land would increase the water deficit by an average of 10.9 × 103 m3, implying that the arable land should be carefully expanded in the future. Results suggest that, to mitigate the impact of climate change, the rational control of arable land and the active promotion of irrigation efficiency are beneficial for water resources management and ecological environmental recovery.

This study aims to assess simulated surface runoff before and after dam construction in the Mono catchment (West Africa) using two lumped models: GR4J (Rural Engineering with 4 Daily Parameters) and IHACRES (Identification of unit Hydrographs and Component flows from Rainfall, Evapotranspiration and Stream data) over two different periods (1964–1986 and 1988–2010). Daily rainfall, mean temperature, evapotranspiration and discharge in situ data were collected for the period 1964–2010. After the model's initialization, calibration and validation; performances analysis have been carried out using multi-objectives functions developed in R software (version 3.5.3). The results indicate that statistical metrics such as the coefficient of determination (R2), the Kling–Gupta Efficiency (KGE), the Nash–Sutcliffe coefficient (NSE) and the Percent of Bias (PBIAS) provide satisfactory insights over the first period of simulation (1964–1986) and low performances over the second period of simulation (1988–2010). In particular, IHACRES model underestimates extreme high runoff of Mono catchment between 1964 and 1986. Conversely, GR4J model overestimates extreme high runoff and has been found to be better for runoff prediction of the river only between 1964 and 1986. Moreover, the study deduced that the robustness of runoff simulation between 1964 and 1986 is better than between 1988 and 2010. Therefore, the weakness of simulated runoff between 1988 and 2010 was certainly due to dam management in the catchment. The study suggests that land cover changes impacts, soil proprieties and climate may also affect surface runoff in the catchment.

Carbon dioxide (CO2) emissions from aquatic ecosystems are important components of the global carbon cycle, yet the CO2 emissions from coastal reservoirs, especially in developing countries where urbanization and rapid land use change occur, are still poorly understood. In this study, the spatiotemporal variations in CO2 concentrations and fluxes were investigated in Wenwusha Reservoir located in the southeast coast of China. Overall, the mean CO2 concentration and flux across the whole reservoir were 41.85 ± 2.03 µmol/L and 2.87 ± 0.29 mmol/m2/h, respectively, and the reservoir was a consistent net CO2 source over the entire year. The land use types and urbanization levels in the reservoir catchment significantly affected the input of exogenous carbon to water. The mean CO2 flux was much higher from waters adjacent to the urban land (5.05 ± 0.87 mmol/m2/hr) than other land use types. Sites with larger input of exogenous substance via sewage discharge and upstream runoff were often the hotspots of CO2 emission in the reservoir. Our results suggested that urbanization process, agricultural activities, and large input of exogenous carbon could result in large spatial heterogeneity of CO2 emissions and alter the CO2 biogeochemical cycling in coastal reservoirs. Further studies should characterize the diurnal variations, microbial mechanisms, and impact of meteorological conditions on reservoir CO2 emissions to expand our understanding of the carbon cycle in aquatic ecosystems.

Climate change is a global issue and causes great uncertainties in runoff and streamflow projections, especially in high-altitude basins. The quantification of climatic indicators remains a tedious job for the scarcely gauged mountainous basin. This study investigated climate change by incorporating GCM (CCSM4) using the SDSM method for RCPs in the Jhelum river basin. Historical climatic data were coupled with Aphrodite data to cope with the scarcity of weather stations. SDSM was calibrated for the period 1976–2005 and validated for the period 2006–2015 using R2 and RMSE. Future climatic indicators were downscaled and debiased using the MB-BC method. The de-biased downscaled data and MODIS data were used to simulate discharge of Jhelum river basin using SRM. Simulated discharge was compared with measured discharge by using Dv% and NSE. The R2 and RMSE for SDSM range between 0.89–0.95 and 0.8–1.02 for temperature and 0.86–0.96 and 0.57–1.02 for precipitation. Projections depicted a rising trend of 1.5 °C to 3.8 °C in temperature, 2–7% in mean annual precipitation and 3.3–7.4% in discharge for 2100 as compared to the baseline period. Results depicted an increasing trend for climatic indicators and discharge due to climate change for the basin. HIGHLIGHTS Climate change has great impacts on the hydrological cycle of the river basin.; Statistical downscaling is the more efficient technique to project climate change using GCMs.; Hydrology of the mountainous river basin has been severely impacted by temperature rise and glacier/snow melting.; The climatic and hydrologic projections for the mountainous river Jhelum basin were made for two RCPs (RCP-4.5 and RCP-8.5).

A quantitative estimate is given to the hypothesis, explaining the paleogeographic data on the extremely high water abundance in rivers in the Caspian Basin in the period when the Late Khvalynian Transgression was forming, by postglacial permafrost in this basin, which could contribute to a decrease of soil infiltration and evapotranspiration, and an increase of river flow. The estimate was based on numerical experiments with a physical-mathematical ECOMAG model of Volga runoff formation. Two series of experiments were carried out to simulate deep soil freezing all over the territory of the present-day Volga basin. In these experiments, the process of seasonal thawing of frozen soils was described taking into account their thawing during the warm (summer–autumn) season and the formation of annual thawed layer (1); in the cases where there was no seasonal thawing, lower values of soil heat conductance were specified (2). If we assume that the climate conditions in the territory of the present-day Volga basin during the formation of the Late Khvalynian transgression were similar to those we see now, the increase in the water abundance in rivers compared with its present-day level can be partly attributed to the occurrence of postglacial permafrost in this basin. At the same time, the increase in the normal annual runoff due to seasonal thawing of permafrost is about 20% (the runoff coefficient increases from 0.36 to 0.44) and does not agree with the huge inflow (>450 km3/year) estimated by paleogeographic data. Under the current climate conditions, an inflow 85% greater than the estimated value (an increase in the runoff coefficient up to 0.67) can be formed in the absence of seasonal thawing of the frozen catchment, i.e., at air temperature lower than its current value.

Stream morphology is an important indicator for revealing the geomorphological features and evolution of the Yangtze River. Existing studies on the morphology of the Yangtze River focus on planar features. However, the vertical features are also important. Vertical features mainly control the flow ability and erosion intensity. Furthermore, traditional studies often focus on a few stream profiles in the Yangtze River. However, stream profiles are linked together by runoff nodes, thus affecting the geomorphological evolution of the Yangtze River naturally. In this study, a clustering method of stream profiles in the Yangtze River is proposed by plotting all profiles together. Then, a stream evolution index is used to investigate the geomorphological features of the stream profile clusters to reveal the evolution of the Yangtze River. Based on the stream profile clusters, the erosion base of the Yangtze River generally changes from steep to gentle from the upper reaches to the lower reaches, and the evolution degree of the stream changes from low to high. The asymmetric distribution of knickpoints in the Hanshui River Basin supports the view that the boundary of the eastward growth of the Tibetan Plateau has reached the vicinity of the Daba Mountains.

The Asian westerly region is one of the regions sensitive to global hydrological and climatic changes. In this study, the annual runoff for 1796–2016 in the lower reaches of the Heihe River basin w...

The Nu-Salween River (NSR), the longest free-flow river in Southeast Asia, plays an irreplaceable role in social development and ecological protection. The lower NSR region is particularly valuable as it is inhabited by approximately 6.7 million people. The basin has limited hydraulic conservancy infrastructure and insufficient ability to cope with climate change risks. Studying the hydrological characteristics and changes in the basin provides the scientific basis for rational protection and development of the basin. However, owing to the limitation of observation data, previous studies have focused on the local area and neglected the study of the lower reaches, which is not enough to reflect the spatial characteristics of the entire basin. In this study, the ECMWF 5th generation reanalysis data (ERA5) and Multi-Source Weighted-Ensemble Precipitation (MSWEP) were applied to develop a geomorphology-based hydrological model (GBHM) for reconstructing hydrological datasets (i.e. GBHM-ERA5 and GBHM-MSWEP). The reconstructed datasets covering the complete basin were verified against the gauge observation and compared with other commonly used streamflow products, including Global Flood Awareness System v2.1, GloFAS-Reanalysis dataset v3.0, and linear optimal runoff aggregate (LORA). The comparison results revealed that GBHM-ERA5 is significantly better than the other four datasets and provides a good reproduction of the hydrological characteristics and trends of the NSR. Detailed analysis of GBHM-ERA5 revealed that: (1) A multi-year mean surface runoff represented 39% of precipitation over the basin during 1980–2018, which had low surface runoff in the upstream, while areas around the Three Parallel Rivers Area and the estuary had abundant surface runoff. (2) The surface runoff and discharge coefficient of variations in spring were larger than those in other seasons, and the inter-annual variation in the downstream was smaller than that in the upstream and midstream regions. (3) More than 70% of the basin areas showed a decreasing trend in the surface runoff, except for parts of Nagqu, south of Shan State in Myanmar, and Thailand, where surface runoff has an increasing trend. (4) The downstream discharge has dropped significantly at a rate of approximately 680 million cubic metres per year, and the decline rate is greater than that of upstream and midstream, especially in summer. This study provides a data basis for subsequent studies in the NSR basin and further elucidates the impact of climate change on the basin, which is beneficial to river planning and promotes international cooperation on the water- and eco-security of the basin.

In this present study, Soil and Water Assessment Tool (SWAT) embedded with ArcGIS interface has been used to simulate the surface runoff from the un-gauged sub-catchments in the upper catchment of Subarnarekha basin. Model calibration and validation were performed with the help of Sequential Uncertainty Fitting (SUFI-2) in-built in the SWAT-CUP package (SWAT Calibration Uncertainty Programs). The model was calibrated for a period from 1996 to 2008 with 3 years warm up period (1996-1998) and validated for a period of 5 years from 2009 to 2013. The model evaluation was performed by Nash - Sutcliffe coefficient (NSE), Coefficient of determination (R2) and Percentage Bias (PBIAS). The degree of uncertainty was evaluated by P and R factors. Basing upon the R2, NSE and PBIAS values respectively, of the order of 0.90, 0.90 and -12%, during calibration and 0.85, 0.83 and -15% during validation, substantiate performance of the model. All uncertainties of model parameters have been well taken by the P and R factors respectively, of the order of 0.95 and 0.77 during calibration and 0.82 and 0.87 during validation. The runoff generation from 19 sub-catchments of Adityapur catchment varies from 29.2-44.1% of the annual rainfall and average surface runoff simulated for the entire catchment is 545 mm. As the surface runoff generated in most of the sub-catchments amounts to above 30% of rainfall, it is recommended for adequate number of structural interventions at appropriate locations in the catchment to store the rainfall excess for providing irrigation, recharging groundwater and restricting the sediment and nutrient loss.

The present study aims to investigate the homogeneity of runoff time series and also to review the existence of trends in Tale Zang hydrometric station (the hydrometric station at the inflow into the Dez reservoir) runoff, using 61 years (1956–2016) daily recorded data. The Pettit test, which is a common method in investigating the homogeneity of time series, was used to identify change points. Both Mann-Kendall and auto-correlated Mann-Kendall tests were applied to analyze the existence or non-existence of trends in each annual, seasonal, and monthly time series observed in a runoff. In time series, significant trends at the 95% level of confidence were recognized, upper and lower limit values were presented for Sen's slope and it was tested for the increasing or decreasing trends in nature. Based on the results of this study, the significant change point at the 95% level of confidence was recognized in the annual, spring, summer, autumn, March, May, June, July, August, September, and October data sets in 1997,1997, 1999, 1997, 1999, 1999, 1999, 1997, 2000, 2007 and 2008, respectively. Analyzing the existence of a trend at the 95% level of confidence indicated that in spring, and in March, September, and October, for both Mann-Kendall and auto-correlated Mann-Kendall tests, the trend is significant and additive until the change point.

This paper analyses changes in the calculated values of the specific runoff of unconfined and confined groundwaters to the rivers Pivdennyi Buh (Khmilnyk town) and Zhar (a tributary of the Pivdennyi Buh; Vinnytsia and Khmelnytsky regions) by seasons and long-term stages, for a total of 38 years (1980-2017). Regularities of seasonal changes in groundwater runoff in areas with different relief and average long-term groundwater levels (0.5-1.5; 0.8-2.5 and 2.7-4.5 m) are revealed. These changes have been shown to be closely related to abnormal air temperature fluctuations. There are four stages of successive changes in the regime of groundwater and in the volume of their runoff to rivers: I. 1980-1989 (1990) — traditionally minimal winter and autumn underground runoff, moderate summer and predominant spring runoff, dominance of runoff from the area with high GWT; ІІ. 1990-1998 — growth and advantages of groundwater runoff from the area with low GWT, reduction to the long-term minimum of groundwater runoff in the area with high GWT (0.8-2.5 m); III. From 1999 to 2014 — the predominant dominance of winter runoff over spring, slow growth of groundwater runoff in a limited area of the catchment with levels of 0.8-2.5 m; high-amplitude fluctuations of runoff and GWT with the achievement of long-term maximums in the area with GWT = 2.5-4.0 m; IV. 2015-2019 — the most intense reduction of GWT, and in the upper reaches of small rivers — of underground runoff to rivers.There is a progressive decrease in the specific flow of groundwater to rivers, and consequently of their resources — primarily for the aquifers in the upper reaches of rivers with GWT 0.5-1.5 m with no pressure recharge. Aquifers of ground water fed by confined aquifers (mainly within floodplains and the first low terraces of rivers) in the studied area of the Ukrainian massif of fracture waters have greater stability of the level regime on the background of rising temperatures and decreasing precipitation (recorded by 2020) than shallow water (0.5-2.0 m) without signs of such recharge.

This study examines the skills of the Soil and Water Assessment Tool (SWAT) for simulating the monthly streamflow in five catchments of the Mahaweli River Basin (MRB). Daily rainfall (43 rain gauges), terrain, land use and land cover, soil, and daily streamflow (5 stations) were used to run the SWAT model. The Calibration Uncertainty Procedure (SWAT-CUP) is adopted for model calibration (1998–2006) and validation (2007–2014). The model performance was evaluated using the Nash–Sutcliffe efficiency (NSE), coefficient of determination (R2), percent bias (PBIAS), and deviation of runoff volumes (Dv). The results revealed that SWAT is able to reproduce the observed monthly variation of streamflow in 4 catchments, satisfying the model performance evaluation criteria (R2 = 0.5, NSE = 0.5, and PBIAS = ± 25). However, the model shows overall low performance in the catchment with extensive human intervention. The results further demonstrate that SWAT simulated peak flow events in the four catchments with moderate to a reasonable agreement (− 20

Forest cover influences not only the amount of surface runoff, but also its quality. The concentrations of chemicals in surface runoff differ between forest catchments and non-forest catchments (agricultural areas). The authors investigated the chemical compositions of surface runoff in two small neighboring catchments (forest, non-forest), by analyzing and summarizing data over a period of 26 years from 1986 to 2012. During this period, the stock and absorption area of forest stands increased, air quality improved, the agricultural landscape was partly regenerated, and global climate change became apparent. The authors observed differences in surface runoff between forest- and non-forest catchments. However, these differences were not mainly caused by the influence of the forest cover, but by changes in agricultural land management. Since 2006, agricultural land has been managed without the use of artificial fertilizers, which reduced the contents of pollutants in surface runoff from the non-forest catchment. The existence of the forest as such excludes or noticeably eliminates the use of fertilizers and chemical substances that affect water quality.

Analysis of the state of water resources in Ukraine provides an opportunity to improve the ecological situation on the basis of hydrographic and water management zoning using the latest methodological approaches and technologies for constructing the water balance of the basin areas. The aim of the research is to establish patterns of change in the quality indicators of the country's water resources in the largest basin of the Dnipro River. The study was carried out on the basis of an assessment of indicators for monitoring changes in the quantitative and qualitative indicators of water resources in the Dnipro basin in 2016-2021.A decrease in the Dnipro runoff was recorded: the average long-term natural runoff at the mouth is 53.3 km3, and the actual runoff is about 11 km3 (20%) less than the natural runoff. A decrease in the quantitative indicators of water intake from the Dnipro basin in 7365 million m3, a decrease in the quantity (up to 547.1 million m3) and a deterioration in the quality of return water and the general state of water resources in the basin from the northwest to the southeast. The measurements’ results of the indicators of the waters’ qualitative state in the reservoirs and the main watercourses of the basin at the locations of the monitoring points indicate that the norms are exceeded by a multiplicity of more than 5 times, including in terms of BOD and COD, which reflect the intensity of pollution of water bodies with easily oxidizing and difficult oxidizing organic compounds. The screening of pollutants revealed the content of pesticides, drugs, antidepressants, heavy metals-carcinogens in the Dnipro water, which makes it possible to investigate the problems with water resources, taking into account the specifics of the river basin. Such an assessment shows that climate change and industrial enterprises, as notable anthropogenic component, are significant factors affecting water resources. This indicates the importance of the direction of the policy of state regulation on water monitoring, the introduction of an irrigation and drainage strategy, the construction of centralized water supply and sanitation systems and strict control over the indicators of wastewater discharge.

Land clearing for cropping and grazing has increased runoff and sediment yield in Central Queensland. The Brigalow Catchment Study (BCS), was established to determine the effect of land clearing on water balance, soils, and productivity, and consisted of three catchments: brigalow forest, cropping, and grazing. Factors responsible for changes in and models for predicting sediment yield have not been assessed. Objectives of this study are to identify climatic, hydrological, and ground cover factors responsible for the increased sediment yield and to assess suitable models for sediment yield prediction. Runoff and sediment yield data from 1988 to 2018 were used to assess the Revised Universal Soil Loss Equation (RUSLE) and the Modified USLE (MUSLE) to predict the sediment yield in brigalow catchments. Common events among the three catchments and events for all catchment pairs were assessed. The sediment yield was approximately 44% higher for cropping and 4% higher for grazing than that from the forested catchment. The runoff amount (Q) and peak runoff rate (Qp) were major variables that could explain most of the increased sediment yield over time. A comparison for each catchment pair showed that sediment yield was 801 kg ha−1 or 37% higher for cropping and 28 kg ha−1 or 2% higher for grazing than for the forested catchment. Regression analysis for three different treatments (seven common events) and for different storm events (15 for forested, 40 for cropping, and 20 for grazing) showed that Q and Qp were best correlated with sediment yield in comparison with variations in ground cover. The high coefficient of determination (R2 > 0.60) provided support for using the MUSLE model, based on both Q and Qp, instead of the RUSLE, and Q and Qp were the most important factors for improving sediment yield predictions from BCS catchments.

The paper concerns the impact of the diverse land use in the Silnica river catchment, within the city of Kielce, on the size and dynamics of concentration and load of transported suspended solids, and the variability of the mineral particles mean grain size, during various flood types. This small river flows through the centre of Kielce, the city of 200,000 population in Poland. In its course, the river flows through areas of various land use. In the upper reaches, the catchment is dominated by forests, in the middle the river flows through a reservoir and the lower – through an urban area. Hydrological measurements and transport of the suspended solids were carried out simultaneously in three hydrometric cross-sections of the Silnica, which close the sub-catchments of the land use as mentioned above. The investigations were carried out during floods of various origins: induced by snowmelt, torrential rainfall and frontal rainfall. The analysis indicates that the two rainfall-induced flood types, characteristic for the summer season, show high runoff dynamics. In contrast, snowmelt-induced floods show high concentration and load of the transported suspended solids. In the section of the watercourse flowing through the city, there is an abrupt increase in runoff and suspended solids concentration. Thus, there may be periodic threats to fish and invertebrates, leading to a reduction in the population of living organisms.

Simulation and forecasting of runoff play an important role in the early warning and prevention of drought and flood disasters. To improve the accuracy of spring runoff simulations, it is important to identify spring runoff production patterns under the combined effect of snow and frozen soil. Based on the theory of the hydrological cycle, three important parameters, which include surface and subsurface runoff, precipitation and temperature, were selected for this study. The trend analysis, statistical analysis and Eckhardt's recursive numerical filtering method were used to qualitatively identify the production patterns of spring runoff, the start and end dates and stage periods of the production patterns. Based on the qualitative identification results, the contribution of each production runoff to the total annual runoff and the total annual spring runoff is quantitatively assessed. The results of the study show that the spring runoff production patterns in the Second Songhua River Basin can be divided into snowmelt runoff, frozen soil conditions of snowmelt–rainfall runoff and rainfall runoff under frozen soil conditions; the snowmelt production is from 21 March, the frozen soil conditions production is from 21 April and the frozen soil ablation ended on 15 June; the shortest phases of each production pattern last 28, 20 and 18 days and the longest last 31, 26 and 24 days. This research provides the basis for improving the principles of production runoff calculation in spring runoff simulation methods. HIGHLIGHTS Determine the main water source of spring runoff in cold regions.; Classify the runoff generation patterns of spring runoff based on the characteristics of runoff generation mechanism in high-latitude mid-temperate regions.; Identify the duration of the runoff according to the characteristics of each runoff pattern.

It is no doubt that the reliable runoff simulation for proper water resources management is essential. In the past, the runoff was generally modeled from hydrologic models that analyze the rainfall-runoff relationship of the basin. However, since techniques have developed rapidly, it has been attempted to apply especially deep-learning technique for hydrological studies as an alternative to the hydrologic model. The objective of the study is to examine whether the deep-learning technique can completely replace the hydrologic model and show how to improve the performance of runoff simulation using deep-learning technique. The runoff in the Hyeongsan River basin, South Korea from 2013 to 2020 were simulated using two models, 1) Long Short-Term Memory model that is a deep learning technique widely used in the hydrological study and 2) TANK model, and then we compared the runoff modeling results from both models. The results suggested that it is hard to completely replace the hydrological model with the deep-learning technique due to its simulating behavior and discussed how to improve the reliability of runoff simulation results. Also, a method to improve the efficiency of runoff simulation through a hybrid model which is a combination of two approaches, deep-learning technique and hydrologic model was presented.

Very large and comprehensive datasets are increasingly used in the field of hydrology. Large-sample studies provide insights into the hydrological cycle that might not be available with small-scale studies. LamaH-CE (LArge-SaMple DAta for Hydrology and Environmental Sciences for Central Europe, LamaH for short; the geographical extension “-CE” is omitted in the text and the dataset) is a new dataset for large-sample studies and comparative hydrology in Central Europe. It covers the entire upper Danube to the state border of Austria–Slovakia, as well as all other Austrian catchments including their foreign upstream areas. LamaH covers an area of about 170 000 km2 in nine countries, ranging from lowland regions characterized by a continental climate to high alpine zones dominated by snow and ice. Consequently, a wide diversity of properties is present in the individual catchments. We represent this variability in 859 gauged catchments with over 60 catchment attributes, covering topography, climatology, hydrology, land cover, vegetation, soil and geological properties. LamaH further contains a collection of runoff time series as well as meteorological time series. These time series are provided with a daily and hourly resolution. All meteorological and the majority of runoff time series cover a span of over 35 years, which enables long-term analyses with a high temporal resolution. The runoff time series are classified by over 20 attributes including information about human impacts and indicators for data quality and completeness. The structure of LamaH is based on the well-known CAMELS (Catchment Attributes and MEteorology for Large-sample Studies) datasets. In contrast, however, LamaH does not only consider independent basins, covering the full upstream area. Intermediate catchments are covered as well, which allows together with novel attributes the considering of the hydrological network and river topology in applications. We not only describe the basic datasets used and methodology of data preparation but also focus on possible limitations and uncertainties. LamaH contains additionally results of a conceptual hydrological baseline model for checking plausibility of the inputs as well as benchmarking. Potential applications of LamaH are outlined as well, since it is intended to serve as a uniform data basis for further research. LamaH is available at https://doi.org/10.5281/zenodo.4525244 (Klingler et al., 2021).

The emphasis of the present study is on trends and abrupt change points for the runoff and sediment load in a major river basin and anthropogenic factors that influence these trends. The methods ad...

The results of a comprehensive agroecological assessment of the main watercourses of the Zuya river basin are presented. Studies were conducted in 2017–2020 and included: conducting a visual survey, measuring water consumption, assessing the qualitative characteristics of runoff, including phytotesting and determining its suitability for irrigation purposes. It was determined that the main pollutants of the watercourses were sulphates, phosphates, heavy metals. The assessment of salt composition of water resources has shown that they are mostly suitable for irrigation without restriction. However, according to the results of phytotesting, an inhibitory effect was recorded, which indicates a possible decrease in the yield of crops sensitive to water-contained pollutants. The water balance calculations showed the presence of a shortage of water resources in the Zuya river basin. The environmental situation on the surveyed water bodies was identified as unfavorable. The set of priority environmental measures includes: the creation of a permanent monitoring network, the arrangement of settlements with water disposal systems, the inventory of small water storage facilities and the implementation of the required repair and operational work on them, and the optimization of the number of water users.

Global warming influencing regional climate is playing a significant role in triggering recurrent drought. The current study demonstrates a PCA (Principal Component Analysis) driven watershed prioritization in a part of Koel river basin by runoff computation during monsoon season along with assessment of Vegetation Health Index (VHI) derived from MODIS satellite data during the period from 2000 to 2017. Koel river catchment area of 7,261 sq km was divided into 82 sub-watersheds based on drainage networks derived from a Survey of India (SOI) topographical map at scale 1: 50,000. High resolution satellite image of Sentinel-2 was used to prepare a land use land cover map. Soil conservation service curve number method (SCS CN) was used to estimate runoff. The result obtained from runoff estimation of 82 sub watersheds shows high runoff (50 to 60% of rainfall) with 290,000 m3 total runoff volume in the upper and middle parts of the catchment dominated by agricultural/fallow and barren lands, whereas low runoff was estimated (20 to 30%) with 29,467 m3 in the lower catchments where a large area is covered with forests. The value of satellite based VHI ranges between 23 to 53 with major parts of the area exhibiting values less than 30, reflecting poor vegetation health. Most of the sub-watersheds in parts of Ranchi, Lohardaga, Gumla and Khunti districts experienced high total runoff, with poor vegetation health index reflecting more proneness to drought. Watershed prioritization was done based on correlation among four parameters viz., rainfall, drought zones, direct runoff and total runoff through PCA. Strong correlation between total runoff volume and drought areas was used for watershed prioritization, which indicated 42 sub-watersheds (4,703 sq km) in the upper catchment required high prioritization. The outcomes of the study would help proper planning of water resources and soil moisture management to overcome the recurrent drought conditions at watershed level.

Catchment urbanization is widely recognised as a primary driver of stream degradation by increasing stormwater runoff, which causes major changes to key ecosystem processes. Reinstating the “natural” hydrogeomorphic conditions is central in designing successful, self-sustaining restoration actions; however, addressing urban stream degradation by re-establishing the hydrogeomorphic conditions remains a challenge, and comparatively limited measurable progress has been observed, particularly in achieving ecological objectives. This review articulates that stream restoration goals might be better achieved when management measures take a broader approach that considers anticipated hydraulic condition effects that liaise relationships between flow and ecology. The study argues that fluvial systems are characterised by complex and dynamic ecosystem processes primarily governed by the hydraulic conditions (e.g., velocity, depth, shear stress); thus, as the practice of addressing urban stream restoration becomes increasingly common, it is critical to explore and understand the anticipated response of the hydraulic conditions. It describes how hydraulic regime consideration provides further opportunity for a holistic approach to urban stream management given their capacity to account for multiple ecological and geomorphic objectives. This review suggests that developing suitable flow–biota–ecosystem processes nexus is critical to addressing urban stream degradation, and hydraulic consideration in restoration actions provides an important step towards that. It discusses opportunities to evolve management actions to achieve restoration goals by highlighting how the management of the two key levers (addressing altered flow regime and morphology) to improve the hydraulic conditions can help to address the urban stream disturbance.

The irrigation water quality is crucial to ecosystems services, soils preservation, and crops’ development. Paddy-rice culture is highly implemented in the lower Tejo river basin and its tributaries (Almansor and Sorraia) alluviums, using irrigation waters with diverse types (ditches, water supply system, water reservoir, water canal, and rivers runoff) and irrigation abilities (C1S1–C4S4 by Wilcox classification). The factorial analysis Principal Components Analysis was used as a multivariate statistical method to understand the relations between water quality variables and their location in the irrigated area. The location of the higher irrigation water mineralization is in the Southern section of Lezirias area, where paddy-rice crops’ implementation prevails. As paddy-rice is considered a salts sensitive crop along with the considerable salinity supply through irrigation, sustainability and crop continuity concerns start to arise. The preservation of natural resources is mandatory to maintain agriculture practices in this highly productive but highly sensitive region. Increasing salinity in soils can force to adaptation measures, namely the blending of irrigation waters or the shift for more salinity tolerant cultures.

The study was conducted to understand the influence of interactions of atmospheric deposition with different land use surfaces and change in water chemistry of river Ganga through changes in runoff water quality. Four different land use surfaces in the catchment of the river Ganga, namely cemented, open fallow land, woodland and grassland were selected for data comparison. The results indicated that although some woody perennials showed throughfall enrichment in response to atmospheric deposition, catchment vegetation invariably reduced the runoff flushing of heavy metals and nutrient ions to the Ganga river. Grassland absorbed the metals 1.5–2.2 times more effectively than other land use surfaces and the same was observed 2.0–2.5 times more effective for nutrients. In the present study, DOC input through runoff varied with site and land use ‘type’, for metal and nutrient ions. The trend of DOC was almost opposite as it was for metals and nutrients with respect to site and land use pattern. The lowest DOC was recorded at Rajghat downstream site for cemented land use (1.900 mg/L) in the first runoff. The concentration of DOC increased in rest of the runoff. This has relevance as far as carbon capture, storage, and transport to riverine systems is concerned. It is suggested that extensive plantation in the river catchment would be an effective approach for reducing runoff fluxes of toxic metals and nutrient ions to the Ganga river coming from atmospheric sources. It will slow down the process of eutrophication and direct contamination with toxic metals. This management process will be highly effective for the sustainability of the dying river Ganga.

The Kud’ma River, a tributary of the Cheboksary Reservoir, has been studied to evaluate the contributions of the surface and subsurface runoff components and perched groundwater runoff to the diffuse export of mineral nitrogen and phosphorus from river catchment areas in the northern part of the forest-steppe zone in the Volga basin. The role of water balance elements in the removal of nutrients has been shown to vary considerably both from season to season and in the long-term aspect. The proportions of the atmospheric and landscape components in the balance have been determined. The nutrient runoff has been shown to increase considerably in the recent years because of the greater role of new hydroclimatic conditions, especially, an increase in the runoff of infiltration origin (groundwater and perched water). Promising lines of further studies of nutrient removal from river catchments are proposed.

The predictability of river runoff is determined by the maximum lead time of satisfactory forecasts of water discharge obtained by the hydrograph extrapolation method. This indicator characterizes the smoothness of changes in water discharge over time and determines a possibility of using the Hydrometcentre of Russia’s automated system for preparation and daily streamflow forecasting all year long. The dependency between the predictability of river runoff and the main factors of its formation and regime is investigated. In total 18 regions within the territory of Russia are identified; for each of them a dependence between the streamflow predictability indicator and the area and average slope of the catchment is obtained. These regions cover 79% of the entire country. Calculated regional dependencies made it possible to estimate threshold values of the area and average slope of the catchment beyond which satisfactory forecasts are possible with a sufficiently long lead time (8–10 days), or only with a short lead time (1–2 days), or are impossible at all. Keywords: streamflow predictability, hydrograph extrapolation method, maximum forecast lead time, morphometric characteristics of catchment, calculated regional dependencies

Water resources in the Yongding River basin (YRB) are one of the important fundamental conditions in supporting regional water conservation and ecological development. However, the historical changes in water resources under recent human activities remain unknown due to very limited observation data. In this study, terrestrial water storage anomalies (TWSA) as well as multiple precipitation and actual evapotranspiration products from satellites were collected, and the accuracy of the data was verified by observed data or pairwise comparisons. The TWSA during 1980-2016 was reconstructed by using the water balance method, and the reconstructed TWSA was verified using GRACE-observed TWSA, the average depth to groundwater in the Beijing Plain from historical document records and the observed runoff from Guanting Reservoir. The reconstructed TWSA data indicated that the significant decrease occurred during 2000–2016 and the average rate of decreasing trend was -11 mm/year, which may have been caused by a decrease in groundwater storage due to agricultural development. However, the reconstructed TWSA decreased slightly during 1980-1999. The establishment of the water storage deficit index (WSDI) showed that there was no drought or mild drought during 1980-1999; however, the water resource shortage during 2000-2016 was more serious due to groundwater storage decreases caused by agricultural development. The WSDI was verified by using the commonly used self-calibrated Palmer drought severity index. The findings are valuable for sustainable water resource management in the YRB.

Floods are very common in eastern India during southwest monsoon season. It brings a lot of misery to the people of this region. Every year eastern Indian states namely West Bengal, Odisha and Bihar witness such types of flood during monsoon period. Major river basins in eastern India are Ganga river basin in Bihar and West Bengal area, Odisha has three river basins namely Mahanadi, Subarnarekha, Brahmani and Baitarani [Fig. 1(a)]. As majority of tributary rivers of Ganga passing through Bihar and West Bengal; these two states are more prone to massive flood during monsoon season. The abnormal occurrence of rainfall generally causes floods. It occurs when surface runoff exceeds the capacity of natural drainage. The heavy rainfall is frequently occurring event over the area during South-West Monsoon (SWM) every year. The geographical location of the area, orography and its interaction with the basic monsoon flow is considered as one of prime factors of these heavy rainfall activities. Synoptically, the latitudinal oscillation of eastern end of the Monsoon Trough and the synoptic disturbances formed or passing over the eastern India region and / or its neighbourhood that brings moisture laden Easterly or South-Easterly winds over the area are the main causes responsible for heavy rainfall in this area.

Morphologic parameters of a watershed could help in segregating critical sub-watersheds for taking up conservation practices and mitigation interventions. Determination of critical watersheds or prioritization of sub-watersheds is inevitable for efficient and sustainable watershed management programs and allocation of its natural resources. The traditional methods of determination of morphologic parameters are time consuming, expensive and requires huge labor. However, the process becomes easier, cheaper and faster with the advent of Geographical Information System (GIS) and remote sensing technologies. In the present study, a combined approach of using toposheet, remotely sensed digital elevation model and morphometric ArcGIS toolbox has been adopted to determine morphometric parameters in Dudhnai river basin, a sub-basin of river Brahmaputra which is prone to both erosion and sedimentation. Seven sub-watersheds of Dudhnai have been prioritized by using the morphometric parameters and ranked them according to its vulnerability to soil erosion. The results of bifurcation ratio, drainage density, drainage intensity and constant of channel maintenance showed that Dudhnai watershed is a well-dissected watershed with less risk to flooding and soil erosion. However, significantly high values of infiltration number and ruggedness number obtained are indicative of very low infiltration which may result in high surface runoff and soil erosion. The study also revealed that channel erosion is stronger than sheet erosion in the basin. The prioritization of the sub-watersheds implied that Chil sub-watershed is the most susceptible sub-watershed that needs greater attention for soil and water conservation measures. The results of the present study could aid various stakeholders who are involved in the watershed development and management programs.

Permafrost is an important component in hydrological processes because changes in runoff over the Arctic drainage basin cannot be well explained by changes in precipitation-related variables. However, current understanding of the influences of permafrost on hydrological dynamics is insufficient. This study investigated historical variations in permafrost conditions and their potential hydrologic effects over the Russian Arctic drainage basin. The results show that soil temperature (at 0.40 m below surface) has increased about 1.4 °C over the Ob, 1.5 °C over the Yenisei, and 1.8 °C over the Lena River basin from 1936 through 2013, possibly resulted in a significant thawing of permafrost. Rapid active layer changes have occurred since the 1970s. The volume of the active layer increased by 28, 142, and 228 km3 over the Ob, Yenisei, and Lena basins, respectively, since the 1970s. Melting ground ice caused by deepening active layer may be a limited contribution to annual runoff. Runoff during freeze season (October–April) showed significant positive correlations (p 0.05) in the Ob basin. These results imply that, in basins with high permafrost coverage, a deeper active layer increased soil water storage capacity and perhaps contribute to an increase in winter runoff.

The trends in river runoff during the winter lower water period in the Ural River basin have been analyzed in this work. The long-term dynamics of the runoff parameters has been studied. Concurrently, consideration has been given to the phases with a different river water content. It was found that the water regime of the rivers in the study basin is characterized by a stable trend of a decreasing share of the spring runoff and an increasing share of the winter runoff. The growth of the share of winter runoff is caused by an increase in the frequency and duration of positive temperature anomalies and the share of basic (underground) river feeding. Comparison of the annual runoff and 30-day values of the minimum runoff in the winter period illustrates a certain interdependence in the changes of their values. In spite of the general trend of the increasing winter low water discharges, certain differences have been revealed for the rivers of the basin studied due to the heterogeneous conditions under which the runoff is formed. The regional features of the formation of the winter low water runoff confirm the different dates for occurrence of the maximum (complete) depletion of the river runoff. The significant increase in the water content of the rivers in winter affects the decrease in the variability of daily discharges, which is consistent with the previously established trend of decreasing interannual variability of the river runoff in the basin of the Ural River. The increase in the winter low water runoff is of great practical importance, because the runoff value for a given period is the limiting factor that determines the guaranteed and sustainable water consumption. Accordingly, the current trends in the change in the water regime of the rivers of the Urals basin must be taken into consideration when determining the regulations and norms for the use of water resources in the steppe zone.