Runoff Regime Research Articles

Long-Term Runoff Variability Analysis of Rivers in the Danube Basin

Abstract The long-term runoff variability is identified to consist of the selected large rivers with long-term data series in the Danube River Basin. The rivers were selected in different regions of the Danube River Basin and have a large basin area (Danube: Bratislava gauge with 131,338 km2; Tisza: Senta with 141,715 km2; and Sava: Sremska Mitrovica with 87,966 km2). We worked with the station Danube: Reni in the delta as well. A spectral analysis was used to identify the long-term variability of three different types of time series: (1) Average annual discharge time series, (2) Minimum annual discharge time series and (3) Maximum annual discharge time series. The results of the study can be used in a long-term forecast of the runoff regime in the future.

Characterizing the spatiotemporal response of runoff to impervious surface dynamics across three highly urbanized cities in southern China from 2000 to 2017

Urbanization affects the regional hydrological cycle, but quantitative assessment of the hydrological regime in regions of high urbanization remains unexplored. This study investigates the response of runoff to impervious surface area (ISA) dynamics across three highly urbanized cities in southern China. The Soil Conservation Service Curve Number hydrologic model is modified by coupling the 1-km high-resolution calibrated precipitation data and 250-m-resolution percentages of remotely sensed land cover. Results demonstrate that runoff metrics increase noticeably during 2000–2017 at the city scale, with larger (smaller) magnitudes observed for high-flow (low-flow) runoff metrics. Runoff trend variations are more pronounced during high-flow seasons and are remarkable over land surfaces. Analyses of linear regression and generalized additive models indicate that ISA changes account for 23–27% of the total variance of increased runoff. The ascending trend of runoff is not affected substantially by the slight decrease in ISA during 2014–2017, which is attributed to the combined influence of land cover changes and climate. At the subwatershed scale, changes in ISA explain 17% of runoff variations. The runoff regime is more (less) responsive at the high (low) ISA percentage, and one threshold indicative of substantial modification to runoff is detected in the ISA percentage. Overall, runoff responses identified in the spatiotemporal analysis underscore the importance of monitoring and assessing the hydrological regime in southern China as urbanization progresses.

Developing Approaches to Analysis of Melt Motion on the Surface of a Fuel Pin

Based on the analysis of experiments carried out on simulators of fuel elements with a cladding of low-melting metals, models of melting and movement of the melt over the surface of fuel elements are proposed. The presented work is a continuation of experimental and theoretical work carried out jointly at the Nuclear Safety Institute, Russian Academy of Sciences, and Kutateladze Institute of Thermophysics, Siberian Branch, Russian Academy of Sciences, to study the features of the movement of a melt over a cylindrical surface that simulates the surface of a fuel element. It analyzes the factors that determine the thermal destruction of fuel elements. One of the important conclusions drawn from the analysis of experimental data was the conclusion about the prevailing film laminar runoff in the heated part of the fuel element simulator. Using this assumption, an analytical model was built that allows predicting the mass of a fuel element carried out of its limits during melting. As a result of calculations using the proposed model, it was shown that, for an accident with the introduction of positive reactivity, when the power increase can reach ten ratings, a modification of the model is necessary to take into account the turbulent runoff regime. For this purpose, a simplified model of the flow of the melt was built. A comparison is made with known techniques and it is shown that the proposed approach makes it possible to describe the turbulent flow regime with satisfactory accuracy. The modified model made it possible to calculate the features of the movement of a stainless steel melt over the surface of a fuel element of a fast neutron (BN) reactor. Information was obtained on the thickness of the melt, its velocity and Reynolds number, depending on the conditions of drainage, and on the mass carried outside the core.

An ensemble of daily simulated runoff data (1981–2099) under climate change conditions for 93 catchments in Switzerland (Hydro‐CH2018‐Runoff ensemble)

AbstractWe present a new ensemble of daily runoff simulations for meso‐scale catchments in Switzerland for the period 1981–2099: The Hydro‐CH2018‐Runoff ensemble. The ensemble contains runoff simulations for 93 catchments in Switzerland covering a wide range of different catchment characteristics governed by pluvial, nival and glacial runoff regimes. The hydrological modelling system PREVAH was thoroughly calibrated and validated for each catchment. The simulations show satisfactory performance with a median Nash‐Sutcliffe efficiency of 0.82 in the calibration and validation period. The calibrated parameters were then used to simulate runoff under climate change for each of the 93 catchments. These simulations were driven by the high‐resolution new Swiss climate change scenarios (CH2018) consisting of 68 GCM‐RCM combinations covering 3 different emission scenarios: RCP2.6, RCP4.5 and RCP8.5. The simulations show good agreement between simulated and observed runoff regimes in the reference period. The Hydro‐CH2018‐Runoff ensemble is publicly available under http://doi.org/10.5281/zenodo.3937485 (Muelchi, R., Rössler, O., Schwanbeck, J., Weingartner, R., and Martius, O. (2020) Hydro‐CH2018‐Runoff ensemble (version v1). Zenodo) and can be used for further impact studies.

The variation and attribution analysis of the runoff and sediment in the lower reach of the Yellow River during the past 60 years

Abstract The water and sediment regimes of the Yellow River are the basis of decision-making of major projects of the Yellow River. Based on water and sediment data at the Huayuankou station, Gaocun station, Aishan station, and Lijin station in the lower reach of the Yellow River, the Mann–Kendall test, the T-test for differences, wavelet analysis, slope change ratio method and the double cumulative curve method were applied to analyze the runoff and sediment regime alteration. The results show that the water and sediment of the lower Yellow River have a significant downward trend, and the annual sediment decreases significantly compared with the annual runoff. The annual runoff and sediment of the four hydrological stations changed around the 1980s and 1990s, respectively. The water and sediment of hydrological stations have periodic variations on multiple time-scales, but the variation scales are different. Precipitation, human activities and other factors lead to the decreasing trend of water and sediment in the lower Yellow River, and their contribution rates to the change of water and sediment are also different. Precipitation contributed 0.15%–8.71% and 0.06%–22.32% to the reduction of runoff and sediment load at the hydrological stations, while human activities contributed 91.29%–99.85% and 77.68%–102.21% to the reduction of runoff and sediment load, respectively. Human activity is the main factor in runoff and sediment reduction.

Assessing the Impact of Land Use and Climate Change on Surface Runoff Response Using Gridded Observations and SWAT+

The Anthropocene period is characterised by a general demographic shift from rural communities to urban centres that transform the predominantly wild global landscape into mostly cultivated land and cities. In addition to climate change, there are increased uncertainties in the water balance and these feedbacks cannot be modelled accurately due to scarce or incomplete in situ data. In African catchments with limited current and historical climate data, precise modelling of potential runoff regimes is difficult, but a growing number of model applications indicate that useful simulations are feasible. In this study, we used the new generation of soil and water assessment tool (SWAT) dubbed SWAT+ to assess the viability of using high resolution gridded data as an alternative to station observations to investigate surface runoff response to continuous land use change and future climate change. Simultaneously, under two representative concentration pathways (RCP4.5 and RCP8.5), six regional climate models (RCMs) from the Coordinated Regional Climate Downscaling Experiment Program (CORDEX) and their ensemble were evaluated for model skill and systematic biases and the best performing model was selected. The gridded data predicted streamflow accurately with a Nash–Sutcliffe efficiency greater than 0.89 in both calibration and validation phases. The analysis results show that further conversion of grasslands and forests to agriculture and urban areas doubled the runoff depth between 1984 and 2016. Climate projections predict a decline in March–May rainfall and an increase in the October–December season. Mean temperatures are expected to rise by about 1.3–1.5 °C under RCP4.5 and about 2.6–3.5 °C under RCP8.5 by 2100. Compared to the 2010–2016 period, simulated surface runoff response to climate change showed a decline under RCP4.5 and an increase under RCP8.5. In contrast, the combine effects of land use change and climate change simulated a steady increase in surface runoff under both scenarios. This suggests that the land use influence on the surface runoff response is more significant than that of climate change. The study results highlight the reliability of gridded data as an alternative to instrumental measurements in limited or missing data cases. More weight should be given to improving land management practices to counter the imminent increase in the surface runoff to avoid an increase in non-point source pollution, erosion, and flooding in the urban watersheds.

Climate and land cover change impacts on stormwater runoff in large-scale coastal-urban environments

This study aims to evaluate the individual and synergistic controls of climatic and land cover changes on stormwater runoff regimes, and perform a comparative synthesis of the historical and future runoffs for complex coastal-urban environments. A large-scale (7117km2) mechanistic hydrologic model was developed for Florida Southeast Coasts Basin as the study area using U.S. Environmental Protection Agency (EPA)'s Storm Water Management Model 5.1. The model was calibrated and validated with daily streamflow observations (Nash-Sutcliffe Efficiency=0.74 to 0.92) during 2004-2013 (termed 2010s), computing the corresponding runoff volume as a historical reference. Runoffs for 2050s (2044-2053) and 2080s (2076-2085) were quantified by incorporating climatic projections from 20 General Circulation Models and land cover projections from EPA under the Representative Concentration Pathways (RCP) 4.5 and 8.5 scenarios. We found a predominant climatic control on the potential runoff changes and a high vulnerability in the coastal-urban environments. The concurrent changes in climate and land cover led to synergistic (stronger than the sum of individual effects) nonlinear responses of runoff. The projected changes in climate and land cover together would increase the annual basin runoff volume by 118%, 106%, 86%, and 80% under the 2080s-RCP 4.5, 2050s-RCP 4.5, 2050s-RCP 8.5, and 2080s-RCP 8.5 scenarios, respectively. Greater increases in runoff were noted at and around the urban centers than that at the non-urban areas across the basin. The relative increases in runoff were higher during the dry season and transitional months (October-May) than the wet season (June-September). Our findings would guide stormwater management and ecosystem protection for southeast Florida and coastal built environments across the world.

Spatial-diurnal variability of snow/glacier melt runoff in glacier regime river valley: Central Himalaya, India

Spatial-diurnal variability in the snow/glacier melt isotope signature and their influence on hydrograph separation based on mixing model received less attention. We present isotope data from a high elevation catchment (glacierized area: 286 km2) in the central Himalaya (India) and investigated the spatial-diurnal variability of snow/glacier meltwater along with inferences of groundwater dynamics. Isotope signature variation in streamflow was small during the study period. We applied a two-component mixing model using oxygen-18 and electrical conductivity. Hydrograph separation (snow/glacier meltwater and groundwater) was carried out for Bhagirathi River at three sites i.e., Gaumukh, Bhojbasa, and Gangotri, during the ablation period of 2014 (September). The Bhagirathi River is a major tributary of river Ganga, originate from Gangotri Glacier (~30 km), the largest glacier in central Himalaya. The electrical conductivity of the river is measured in-situ and varies from 10 μS/cm to 100 μS/cm. The river water isotope signature of oxygen was ranged from −15.53‰ to −14.32‰ from Gaumukh to Gangotri, snow samples were ranged from - 17.63‰ to - 15.86‰ collected at Gaumukh. Groundwater samples were varied from −8.53‰ to-7.57‰ from Gaumukh to Gangotri. River water signature is close to snow/glacier melt runoff signature, reveal that the snow/glacier melt runoff contribution is higher in river flow. Average fractions of snow/glacier melt runoff were estimated ~82% to~76%, whereas groundwater was estimated ~18% to ~24%. The results of this study reveal the necessity of a multiple sampling approaches to characterize the snow/glacier melt and the importance of groundwater dynamics in catchments with snow/glacial runoff regime.

Dynamics of the hydraulic and alluvial regime of the lower reaches of the Amudarya after the commissioning of the Takhiatash and Tuyamuyun hydrosystems

The article presents data on changes in the main hydraulic parameters of the flow in the hydrological sections of the Amudarya river located in the zone of influence of the Takhiatash and Tuyamuyun reservoirs. It has been established that in recent years an acute water shortage has been observed in the lower reaches of the river during the growing season. In dry years for the Amudarya River, the Takhiatash hydroelectric complex becomes the last section, in some periods there are even no sanitary passes through the hydroelectric complex in the prescribed manner, and as a result, a tense situation is created in the Amudarya delta below the Takhiatash hydroelectric complex. Analysis of the hydrological regime of the river showed that in the lower reaches of the Amudarya on the territory of the Kharezm region and Karakalpakstan, the water regime of the river is very different from the domestic one. The low-water period on the river practically begins in September, as there is a large flow of water in September and October. The waters coming from the upper reaches of the river are retained to fill the Tuyamuyun reservoir. At the same time, the end of the low-water period is actually shifted to the beginning of March, since in March, the work of the water accumulated in the reservoir begins and its supply for flushing irrigation begins. The flood waters entering the Tuyamuyun reservoir are either fully accumulated (if the reservoirs are not filled up to the normal retention level of the NRL) or are very strongly transformed (if the reservoir is filled up to the NRL). Analysis of the dynamics of sediment runoff showed that the amplitudes of fluctuations in sediment runoff over periods have a very wide range of changes. In the initial period of operation of the hydroelectric complex, the sediment runoff mode almost repeats the household mode, that is, the largest runoff occurs during the dry season, but with the lowest solid runoff values on average 3 and 8 (at the Samanbai station) times. For 7 years from 1975 to 1981, the annual flow at the Kipchak gauging station amounted to 41.722 thousand tons, that is, 32% of the annual household regime. The largest annual flow at the Kipchak and Samanbai gauging stations took place in the high-water year 1978 and amounted to 66329 and 57971 thousand tons соответственно. The smallest amount of annual runoff at gauging stations was observed in dry 1981 and amounted to 25074 and 3943 thousand tons. The study of the sediment runoff regime of the Amudarya river during the period of joint operation of the Takhiatash and Tyuyamuyun hydrosystems showed that the amount of solid runoff entering the zone of influence of the Takhiatash hydroelectric complex significantly decreased due to a sharp decrease in water discharge under the influence of regulation and low water. At the same time, as the analysis of field studies has shown, despite their relatively small number, accumulation of sediments is observed in the pays of the hydroelectric complex, that is, silting occurs. The amount of sediment siltation in the area of the Takhiatash hydroelectric complex varies depending on the water content of the year and the operating mode of the Takhiatash hydroelectric complex. Analysis of the alluvial regime shows that during the period of operation of the hydroelectric complex, depending on the hydrological regime of the river and the regime of the water level in front of the dam, the clarification of the flow occurs in April, May, June and August. The seasonally average clarification of the flow within the upper pool ranges from 10 to 40%, and in some months, at levels close to the NSP, reaches 90%, that is, the upper pool of the node turns into a kind of settling tank. The composition of suspended sediments of the Amudarya varies both in time and along the length of the river, but particles smaller than 0.25 mm remain predominant. Particles larger than 0.25 mm are found only in the upper areas and in an amount of no more than 3 - 4%. During the flood period, along the entire length of the river, the percentage of fines content increases in comparison with the low-water period.

MONITORING OF FLOODING EVENTS ON THE RIVERS OF THE NORTH-WESTERN CAUCASUS IN 2014-2020

The rivers of the Northwestern Caucasus between Anapa and Tuapse are characterized by a flood runoff regime. Floods leading to material damage occur on the rivers of the region every year. After the 2012 flood, a network of automatic level gauges is developing in the region, recording water levels every 10 minutes. During the expeditions of the SSC RAS in the winter period 2019-2020 the analysis of the installation sites of 69 level gauges was carried out. The features of level gauges influencing the collection of observations are identified: the installation options, floodplain vegetation, the features of the channel, floodplain and river valley. The analysis of the accumulated for 2014–2020 database of level observations on rivers with catchment areas from 1.4 km2 to 1245 km2 was carried out. 34 778 periods of growth, 70 135 periods of stagnation, 39 485 periods of decline and 42 032 gaps were identified. Of these, 3398 flood situations were considered. More than 100 flood events were recorded on 11 level gauges: on the rivers Abin, Shebsh, Psekups, Pshish (3 gauges), Nechepsukho, Dzhubga, Vulan, Pshada and Mezyb. Less than 10 flood situations were recorded on 14 level gauges. To increase the efficiency of the network of automatic level gauges, it is necessary to expand it to the watersheds between rivers Abin and Khable, as well as on Pshish on the northern macroslope and on the watersheds of Pshada, Nechepsukho and Tuapse on the southern macroslope.

Overflow risk analysis on the Presidente Dutra highway using the quota-volume curve in the Una River Basin in Taubaté, SP, Brazil

Anthropic interventions and vectors of urban occupation have caused changes in the infiltration and runoff regime that can cause or accelerate erosion processes, silting and flooding in river basins. Flooding, as a stochastic phenomenon, can occur at any time and in any place, influenced by climatic factors, physical characteristics of the basin and mainly by human interference in the use and occupation of the land, which affects the type, quality and quantity of vegetation and increases soil impermeability. The aspects of regional urbanization led the State in 2012 to create the Metropolitan Region of Vale do Paraíba and the North Coast (RMVPLN), attracting large real estate investors. In the hydrographic basin of the river Una in the municipality of Taubaté, there has been an increase in flooding episodes and the possibility of worsening due to changes in land use and occupation. In this study, we sought to determine runoff as a function of changes in land use and occupation expressed by the variation in runoff coefficient (C) recommended by the Department of Water and Electricity of the State of São Paulo, (DAEE-SP) for licensing and intervention projects in water resources. The lower limits C = 0.35 and upper C = 0.70 were used admitting variations of 0.05 points in this interval to calculate the water flow (QE) and Intake Volumes (VE) in the basin from an intense precipitation of 100 years of recurrence time, from the use of the UEHARA Method (DAEE, 2006), to the control point located at the intersection of the Una River and the Presidente Eurico Gaspar Dutra Highway (BR 116-SP) and from this the Quota-Volume curve was drawn. The flood shares were obtained by hitting the reserve volumes found on the quota-volume curve.The current runoff coefficient of the basin is C = 0.35, which allows water to pass through the Dutra highway bridge. However, the modification of C = 0.50 due to the advance of urbanization, the level of flooding would reach 557.40 m. That exceeds the level of the lower base of the bridge (556.72 m) and, with C = 0.60, would reach the quota of 558.90 m, which would cover the asphalt surface of the highway. Given the real estate pressures in the metropolitan region, special care is recommended in the conservation, preservation and expansion of native forest vegetation with actions for Payments for Environmental Services (PSAs), de-silting actions of the main gutter and Una's tributaries, to contain the identified advance of urbanization in the basin, as well as the definition and installation of detention and retention basins.

Impact of Climate and Geology on Event Runoff Characteristics at the Regional Scale

The dynamics of flood event characteristics, such as the runoff coefficient and the recession time constant, differ in time and space, due to differences in climate, geology, and runoff generation mechanisms. This study examines the variability of event runoff characteristics and relates them to climatic and hydro-geological characteristics available at the regional scale. The main focus is to examine the role of rainfall patterns (i.e., event precipitation volume, precipitation intensity, and antecedent precipitation) and runoff regime (i.e., initial flow before runoff event and event duration) characteristics on the seasonal dynamics of runoff response. The analysis is performed in four small Austrian catchments representing different hydro-geological settings obtained by field mapping. The results are based on an analysis of 982 runoff events identified from hourly measurements of streamflow and precipitation in the period 2002 to 2013. The results show that larger event runoff coefficients and flow peaks are estimated in catchments with high mean annual precipitation than in drier catchments. In contrast to some previous studies, the results show only poor relation between antecedent precipitation (as an index of catchment wetness) and event runoff response. The initial flow is found to be the main factor influencing the magnitude of runoff coefficient and event peaks in all analyzed catchments and geological settings. The recession time constant tends to be inversely related to the maximum event precipitation intensity, with an exception for one catchment (Wimitzbach), which is characterized by the largest proportion of deep interflow contribution to runoff. The analysis of the runoff response by different event types indicates that runoff coefficients and recession time constants are the largest for snowmelt runoff events.

Warming Climate Is Reducing the Diversity of Dominant Microbes in the Largest High Arctic Lake.

Temperatures in the Arctic are expected to increase dramatically over the next century, and transform high latitude watersheds. However, little is known about how microbial communities and their underlying metabolic processes will be affected by these environmental changes in freshwater sedimentary systems. To address this knowledge gap, we analyzed sediments from Lake Hazen, NU Canada. Here, we exploit the spatial heterogeneity created by varying runoff regimes across the watershed of this uniquely large high-latitude lake to test how a transition from low to high runoff, used as one proxy for climate change, affects the community structure and functional potential of dominant microbes. Based on metagenomic analyses of lake sediments along these spatial gradients, we show that increasing runoff leads to a decrease in taxonomic and functional diversity of sediment microbes. Our findings are likely to apply to other, smaller, glacierized watersheds typical of polar or high latitude ecosystems; we can predict that such changes will have far reaching consequences on these ecosystems by affecting nutrient biogeochemical cycling, the direction and magnitude of which are yet to be determined.

Influence of the Vilyui hydropower plant on the regime of the Vilyui river

Based on the analysis and comparison of the Vilyui river regime in the natural and regulated state, the article reveals the features of changes in the annual distribution of runoff, level and ice regimes and the regime of solid runoff. To assess the consequences of the impact of large hydroelectric power stations in the Far North, comprehensive studies of the Vilyui river basin were conducted. Vilyui hydroelectric station is the first hydroelectric power station in the permafrost zone. The reservoir is completely located within the Republic of Sakha (Yakutia). Despite the low level of development of water resources in the Far East, the prospects for the construction of traditional hydropower plants remain. The hydropower potential of the republic is estimated at 283 billion kWh, which is 66 % of the total hydropower potential of the Far East region. The construction and operation of hydropower plants on rivers leads to fundamental changes in the natural conditions of the river. The results of the study show that flow regulation by large reservoirs is the main factor of anthropogenic disturbances in the flow volume and water regime of the Arctic rivers. To date, the diverse effects of river regime changes after the construction of a hydroelectric power station on the territory of permafrost are not fully considered in either design or prospective planned developments. The importance of accounting and studying the consequences of flow regulation can be judged by the complex economic problems that arose after the construction of hydropower facilities in the European part of Russia. In this regard, a comprehensive study of changes in environmental conditions in the territory of permafrost distribution after regulation of river flow by large reservoirs is one of the most important tasks.

Analysis of coastal-plain fluvial architecture and high-frequency stacking patterns in the Upper Cretaceous Masuk Formation, Utah, U.S.A.: Climate-driven cyclicity?

ABSTRACTMost sequence stratigraphic models are based on the premise that relative changes in sea level (RSL) control stacking patterns in continental-margin settings. An alternative hypothesis, however, is that upstream factors, notably variations in relative water discharge (RQW) or the ratio of water to sediment discharge can influence or control stratal stacking patterns in fluvial systems. Sequence boundaries of RQW-driven systems differ from those driven by base-level fluctuations in that: 1) the depth of incision increases updip, and 2) rates of erosion are spatially uniform, leading to the formation of widespread, planar sequence boundaries. This paper presents an architectural and stratigraphic analysis of the well-exposed Masuk Formation of the Henry Mountains Syncline in southern Utah, an Upper Cretaceous coastal-plain fluvial succession that is interpreted to have been influenced significantly by RQW. Six lithofacies are recognized, three (Facies 1–3) recording floodbasin, mire, and (in one short interval) estuarine environments, and three (Facies 4–6) record different kinds of channel fills on a coastal alluvial plain. Seven major composite channel bodies (Facies 4–6), separated by intervals of non-channel deposits (Facies 1–3), are recognized in the stratigraphic interval. Composite channel bodies display planar, sheet-like geometry and are laterally continuous to a significantly greater extent (> 10 km) than would be expected from purely autogenic channel-belt construction. Together, these intervals record a series of high-frequency sequences, formed along the western margin of the Western Interior Seaway. In each individual sequence is a repetitive facies succession from a basal chaotic sandstone with admixed mudrock and sandstone transitioning upward to a more organized cross-bedded and stratified sandstone. This is interpreted to record cyclical changes from a peaked (flashy) discharge regime to a more normal runoff regime. Paleoflow data indicate a dominance of transverse (eastward-directed) dispersal early in the accumulation of the Masuk Formation, shifting to a pattern of greater axial (northward) dispersal over time. The RQW signal is strong in the lower part of the formation, decreasing upward. This suggests that the relatively short-headed streams draining from the rising Sevier fold–thrust belt were strongly influenced by climatic cyclicity, whereas more distally sourced systems were not. This study provides new insights into the architecture and stacking patterns of coastal-plain fluvial successions, emphasizing the plausible role that climate can play in shaping alluvial architecture in the rock record.

Ecological restoration is not sufficient for reconciling the trade-off between soil retention and water yield: A contrasting study from catchment governance perspective

Ecological restoration program (ERP) is widely recognized as an effective measure to combat land degradation and improve environmental quality. However, inappropriate ERPs lead to trade-offs between soil retention and water yield as well as conflicts of soil and water resources between the midstream and the downstream of catchment. This study aims to assess the efficiency of ERPs in soil erosion control and identify the trade-offs between soil retention and water yield through the lens of runoff and sediment regimes in contrasting catchments of the Loess Plateau (LP) and the Karst Plateau (KP). Although favorable climate and rapid vegetation restoration substantially reduced water erosion in both these areas, the hydrological responses were not the same because of climate differences. In the arid LP, water and energy variables correlated closely with vegetation cover. Excessive afforestation programs in drylands increased vegetation transpiration and soil evaporation, further exhausting soil water resources, and eventually causing water yield reduction. However, soil and water conservation programs (SWCPs) in the humid KP reduced sediment yield substantially, and the runoff remained stable. Significant runoff reduction in the midstream of the Yellow River aggravated water scarcity and threatened the downstream water demand. Meanwhile, sediment load decline in the LP and the KP impacted sediment deposition in the downstream and estuary formation. From the perspective of integrated catchment governance, human interventions including ERP and SWCP should be more sustainable and consider not only the target process at the local scale (intracoupling effect), but also unprecedented non-target process at the regional scale (telecoupling effect). In addition, it should allow for the supply-demand balance of competing soil and water resources to achieve the coordinated development of resources, environment, and production.

Evidence of Hydrological Intensification and Regime Change From Northern Alaskan Watershed Runoff

AbstractSnowmelt‐dominated runoff regimes have defined northern Alaskan rivers. Discharge records from three watersheds within the National Petroleum Reserve in Alaska (NPR‐A) span 19 years and capture three notable periods of changing runoff. In the first, 2001–2008, mean annual runoff (MAR) averaged 90 mm, characterized by sharp snowmelt runoff and summer drought. Over the next 7 years, larger MAR averaged 120 mm driven by high and early snowmelt runoff. The most recent 4 years, 2016–2019, had even higher MAR of 163 mm with high and sustained late summer flows. Hydrograph analysis suggests a shift toward rainfall‐dominated runoff in the most recent period compared to snowmelt‐dominated hydrographs in the previous two. Declining sea ice appears closely linked to increasing late summer precipitation and a shift toward rainfall runoff. Future development in the NPR‐A will require continued hydrological monitoring and planning to mitigate flood and erosion hazards, permafrost degradation, and ecosystem impairment.

Deposition- and transport-dominated erosion regime effects on the loss of dissolved and sediment-bound organic carbon: Evaluation in a cultivated soil with laboratory rainfall simulations

Erosion-induced soil carbon loss has been identified as a critical process in the global carbon (C) cycle. Surface coverage substantially alters the soil erosion process and the effects of net loss or deposition on soil organic C (SOC). However, information on SOC loss induced by soil erosion at the process level is limited. The aim of this study was to investigate how runoff and erosion regimes affect dissolved and sediment-bound organic C (DOC and SBOC) loss. Thus, six simulated rainfall events were conducted on two laboratory plots (9.75 m × 1.83 m) with different surface coverages (17–83%) and coverage distributions (upslope vs. downslope) using polypropylene geotextiles. The results showed that the variability in the process of runoff and sediment yield existed as a result of altered surface coverage over the erosion zone (SSerosion zone) and covered zone (SScovered zone) on the slope. Thus, the erosion regimes can be identified as deposition- and transport-dominated processes, which were the main soil erosion subprocesses. The surface coverage located downslope (SCtop-bottom slope) can more efficiently reduce runoff (21.9–85.7%) and sediment (67.6–98.3%) than the SCbottom-top slope (runoff: 20.1–83.0%; sediment: 35.0–93.3%), which has the surface coverage located upslope. DOC (8.0–11.3 mg L−1) and SBOC (0.3–0.5 mg g−1) in the deposition-dominated process on the SCtop-bottom slope were higher than in the transport-dominated process on the SCbottom-top slope (DOC: 6.8–10.2 mg L−1; SBOC: 0.2–0.3 mg g−1). The loading of DOC and SBOC was largely dependent on runoff and sediment yield, and DOC load contributed 83.9–89.7% of the SOC loss. Overall, laboratory results highlighted the soil C loss at different hydrological and erosion regimes (deposition- vs. transport-dominated process). This study provides important information that can be used to facilitate further implementations such as watershed modeling of soil C dynamics and the corresponding decision-making processes.

Which Aspects of Hydrological Regime in Mid-Latitude Montane Basins Are Affected by Climate Change?

This study analyzed the long-term alterations in runoff regime, seasonality and variability in headwater montane basins in Central Europe in response to the manifestations of climate change. We tested the common hypotheses on climate change effects on surface runoff dynamics in the Central Europe region, assuming that (i) recent climate warming will result in shifts in the seasonality of runoff, (ii) the runoff balance will remain without significant changes and (iii) that higher variability in runoff can be expected. The analyses were done on eight montane catchments in four mid-latitude mountain ranges in Central Europe, based on the uninterrupted time series of daily discharge observations from 1952 to 2018. We used 33 indicators of hydrologic alteration (IHA), 34 indicators of environmental flow components, the baseflow index, the calculation of surplus and deficit volumes and the frequency of peak and low flows. Homogeneity testing using Buishand, Pettitt and SNHT tests was applied to test the response of the hydrological alteration indicators to climate warming. We have proved the significant shifts in runoff seasonality, coinciding with the timing of the air temperature rise, marked by earlier snowmelt, followed by a decline in spring flows and a prolonged period of low flows. There was detected a rise in the baseflow index across the mountain ranges. Unlike the common hypotheses, the expected rise of runoff variability and frequency of peak flows was not demonstrated. However, we have identified a significant change of the flood hydrographs, tending to steeper shape with shorter recessing limbs as a sign of rising inner dynamics of flood events in montane catchments.

Hydrological Drought Risk Assessment Using a Multidimensional Copula Function Approach in Arid Inland Basins, China

The aim of this research was to use the standardized runoff index (SRI) with a three-month timescale (SRI-3) to analyze hydrological drought risk in two arid river basins characterized by different runoff regimes, Northwest China. Based on SRI-3, hydrological drought levels for different events were defined through run theory. The hydrological drought risk in the two study basins was then comprehensively assessed using a multidimensional copula function that considered the multivariable joint probability of hydrological drought duration, severity, intensity and peak. Results indicate that: (1) the risk of hydrological drought in the two basins between 1961–2018 periodically changed. There was a slight increase in risk within the Yarkant River Basin, while there was a clear decrease in risk within the Kaidu River Basin. The magnitude of drought in the two basins was relatively low; both basins were dominated by mild to moderate hydrological droughts; (2) the drought probabilities of the Yarkant River Basin and Kaidu River Basin from 1961 to 2018 exhibited a falling-rising-falling pattern and a rising-falling trend through time, respectively. These trends were correlated with changes in precipitation and the area of glacial ice, which presumably influenced the amount and source of runoff in the two basins. Hydrological drought risk in the Yarkant River Basin was higher than in the Kaidu River Basin; and (3) the return period of mild, moderate, severe and extreme drought events was 2 yrs, 8 yrs, 20 yrs, and 60 yrs in the Yarkant River Basin, respectively, and 2 yrs, 8 yrs, 23 yrs and 74 yrs in the Kaidu River Basin, respectively.