Runoff Contribution Research Articles

Near-daily monitoring of surface temperature and channel width of the six largest Arctic rivers from space using GCOM-C/SGLI

Spatio-temporal changes in water temperature and discharge of the Arctic rivers are important variables to be observed not only for estimating runoff contributions from snow melt, rainfall, and thawing of permafrost over the continents but also for assessing their impacts on the Arctic sea-ice and marine ecosystem. Nevertheless, the number of ground water gauging stations and the frequency of in-situ measurements for temperature and discharge has been decreasing since the 20 Century due to the shrinkage of budgets for maintaining the in-situ stations. In this study, we explored the possibility to perform near-daily monitoring of river surface temperature (RST) and river channel width (RCW) from space using a Japanese satellite-borne optical sensor named SGLI which can observe radiances at the spectral bands from near-ultraviolet to thermal infrared regions at the same spatial resolution of 250-m on a global scale. River surface brightness temperature (RSBT) measured with SGLI TIR band was used as RST without atmospheric correction. RCW was derived as the widths of water pixels identified along river channels using SGLI reflectances at visible to shortwave infrared bands. Analysis results of two-year SGLI data acquired in 2018 and 2019 show that RSBT and RCW can be retrieved successfully from the SGLI observations on a daily basis after applying a spatio-temporal interpolation. The accuracies of the retrieved RSBT evaluated with in-situ water temperatures are about 2.57 K with the interpolation (and 1.84 K without the interpolation but with lower observation frequencies). Retrieved RCWs are correlated well with in-situ river water discharges indicating potentials to assess variations of not only snow melt water but also precipitation within the river basin. Thus, SGLI data can be used to reconstruct not only the river water temperature but also the river water discharges along the continental river channels for assessing heat flux flowing into the Arctic Ocean.

Spatiotemporal Drivers of Hydrochemical Variability in a Tropical Glacierized Watershed in the Andes

AbstractThere is a critical knowledge gap about how glacier retreat in remote and rapidly warming tropical montane watersheds will impact solute export, which has implications for downstream geochemical cycling and ecological function. Because tropical glacierized watersheds are often uniquely characterized by year‐round ablation, upslope vegetation migration, and significant groundwater flow, baseline understanding is needed of how spatiotemporal variables within these watersheds control outlet hydrochemistry. We implemented a recently developed reactive transport watershed model, BioRT‐Flux‐PIHM, for a sub‐humid glacierized watershed in the Ecuadorian Andes with young volcanic soils and fractured bedrock. We found a unique simulated concentration and discharge (C‐Q) pattern that was mostly chemostatic but superimposed by dilution episodes. The chemostatic background was attributed to large simulated contributions of groundwater (subsurface lateral flow) to streamflow, of which a notable fraction (37%) comprised infiltrated ice‐melt. Relatively constant concentrations were further maintained in the model because times and locations of lower mineral surface wetting and dissolution were offset by concentrating effects of greater evapotranspiration. Ice‐melt did not all infiltrate in simulations, especially during large precipitation events, when high surface runoff contributions to discharge triggered dilution episodes. In a model scenario without ice‐melt, major ion concentrations, including Na+, Ca2+, and Mg2+, became more strongly chemostatic and higher, but weathering rates decreased, attenuating export by 23%. We expect this reduction to be exacerbated by higher evapotranspiration and drier conditions with expanded vegetation. This work brings to light the importance of subsurface meltwater flow, ecohydrological variability, and interactions between melt and precipitation for controlling hydrochemical processes in tropical watersheds with rapidly retreating glaciers.

Integrating depression storages and their spatial distribution in watershed-scale hydrologic modeling

Surface depressions are important topographic characteristics for surface runoff initiation, and the spatial distribution of depressions may further affect the timing and quantity of surface runoff reaching channels and outlets. However, many hydrologic models simulate the fill-spill processes for depression-dominated areas in a lumped manner and release outflows from depressions to channels or outlets directly. As a result, the progressive formation of contributing area (CA) and the dynamic runoff contribution process are not well characterized. The objective of this study is to improve depression-oriented hydrologic modeling by incorporating the influence of depression storages and their spatial distribution into the simulation of surface runoff generation and flow routing. To achieve this objective, a modified depression-oriented variable contributing area (MD-VCA) model is developed to simulate the depression-dominated catchment response during rainfall events, which employs a new depressional time-area zone scheme to deal with the spatially distributed depression storages, tracks the intrinsic changing patterns of the connected areas and depression storage, simulates the connected area-based surface runoff generation dynamics, implements a new CA-based surface runoff routing technique, and quantifies the likelihood of occurrence of outlet CA and runoff contributions using the joint probability distribution associated with depression storages and their spatial distribution. The performance of the MD-VCA model was evaluated through the application to a depression-dominated watershed in the Prairie Pothole Region of North Dakota. Simulation results demonstrated that the MD-VCA model was able to simulate the threshold-controlled overland flow dynamics under different rainfall conditions, and it effectively revealed the influences of depression storages and their spatial distribution on surface runoff generation and propagation processes.

Assessment of Riverine Dredging Impact on Flooding in Low-Gradient Coastal Rivers Using a Hybrid 1D/2D Hydrodynamic Model

The current study investigates the effect of large-scale channel modifications via riverine dredging on flood dynamics in low-gradient river systems located in inland-coastal flood transition zones. The study site is the Vermilion River in south Louisiana, US, which is characterized by complex flow regimes, reversal and bi-directional flows, presence of large swamps with significant river-swamp interactions, and large volumes of runoff contributions from lateral tributaries. The study aims to understand the interplay of these factors and how they modulate and get affected by different dredging approaches that vary in spatial extent and the modifications introduced to the channel. The study deploys a hybrid, one-/two-dimensional (1D/2D), hydrodynamic model that simulates flow and stage dynamics in the main river and its major tributaries, as well as the flow exchanges with the interconnected swamp system. Overall, the results show that the dredging activities can significantly alter the flow regime in the watershed and affect flow exchanges between the river and the swamp system. In terms of flooding impact, only dredging approaches that are extensive in spatial extent and modifications to channel longitudinal slope can result in sizeable reductions in flood stages. However, these benefits come at the expense of significant increases in the amplitude and inland propagation of the Gulf tidal wave. On the other hand, less-extensive dredging can still provide moderate and spatially limited flood mitigation; however, they further expose downstream communities to increased levels of flooding, especially during more frequent events. The results reveal that while dredging can increase the hydraulic conveyance of the river system, the large runoff volumes delivered by the urbanized tributaries seem to outweigh the added improvement in the in-channel storage, thus reducing the anticipated flood relief. The results suggest that a watershed-centered approach, instead of a riverine-centered approach is needed for flood management in these systems so that the relative benefits and tradeoffs of different mitigation alternatives can be examined.

Hydrological regime, water availability and land use/land cover change impact on the water balance in a large agriculture basin in the Southern Brazilian Amazon

The Southern Brazilian Amazon, in the North of Mato Grosso state, has experienced significant changes in land use and cover, which can cause major changes in its hydrological regime. Moreover, data availability and technical support are very scarce in the region, which has been causing serious problems and eminent water conflicts. This study assessed the hydrological regime, water availability, and the impact of land use/land cover (LULC) change in a large agriculture river basin in the Southern agricultural frontier of the Brazilian Amazon. The water balance components such as runoff potential, evapotranspiration, lateral flow and groundwater contribution of the Upper Teles Pires basin have been simulated under different LULC scenarios using the Soil and Water Assessment Tool (SWAT). Overall, the SWAT model performed well and was able to reproduce the flow regime adequately for the Upper Teles Pires basin, demonstrating robustness even within a data-sparse basin. The forest conversion to agriculture use has directly impacted the surface runoff and groundwater contribution of the Upper Teles Pires basin from 1986 to 2014, increasing by 30.8% and decreasing by 5.29%, respectively. From 1986 to 2006, a 5% forest change causes a 17% (9.2 mm) change in the runoff, which represented 6.5% of the total runoff in the basin from 1986 to 2006. The information provided in this study would help local authorities and decision-makers to plan water resources strategies in this basin of strategic importance for Brazilian agriculture.

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.

Past ‘peak water’ in the North Caucasus: deglaciation drives a reduction in glacial runoff impacting summer river runoff and peak discharges

At the end of the 20th—early twenty-first century, mountain glaciers exhibited the most negative mass balances since the beginning of observations. The hydrological consequence of deglaciation is a rise in glacial runoff until a maximum (‘peak water’) is reached, beyond which runoff decreases as glacier extents are reduced. It is likely that the peak water of glacial runoff has already been passed in the central North Caucasus. River basins with more than 1% glacier cover show consistent decreases in mean monthly discharge in July and August (up to 4–6% per decade during 1945–2018), when glacier meltwater contribution to river runoff is high. Meanwhile, in neighbouring non-glacierised basins, runoff in July and August mostly rose. The runoff in June, when glaciers are typically mostly covered by seasonal snowpack, has increased by 2–9% at most gauges. Hydrological data from the Djankuat alpine research catchment in the central North Caucasus indicate a reduction of glacial runoff contribution in recent decades, as the area reduction of Djankuat glacier and increase in debris cover compensate for the increase in glacier melt. The Djankuat river runoff decreased by 29% in July, 42% in August, and 26% in September in 2007–2020 compared with 1968–1978. The mean annual peak discharge has dropped by 1–5% per decade in the central North Caucasus, and it occurs 1–2 weeks earlier. Possible mechanisms of observed changes are discussed. This study provides the data on climate-related changes in the glacial runoff for a previously not investigated region.

Recent progress on studies on cryospheric hydrological processes changes in China

The significant changes in the cryosphere have produced a series of effects on the cryospheric hydrological processes. This paper comprehensively reviews the recent 20 years, especially the new progress in the research on the changes in cryospheric hydrological processes in China, which mainly include glacial meltwater, snowmelt runoff, and frozen ground hydrology. The main progresses in the study on changes in glacial meltwater manifest as:a comprehensive study on glacial meltwater at different scales was carried out, it was found that the glacial meltwater showed continuously increase, and whether the point of the glacial meltwater have appeared has scientifically identified and some basic understandings has obtained, and the modelling on glacial meltwater process had made significant progress. In the study on snowmelt runoff changes, the snowmelt runoff contribution rate to river runoff in various basins were basically grasped by estimating the snowmelt runoff and found that the snowmelt runoff changes in China vary greatly, and it increased in some basins while decreased in some basins. The changes in the start melting period in China are universal with other basins in the world, and the prominent feature is the advance of the peak value. In the study of frozen ground hydrology, the studies on the relationship between surface water, interflow in active layer soil, supra-permafrost water revealed the coupling mechanism of gravity and thermodynamics in the formation of runoff in permafrost regions. The impacts of permafrost change on surface runoff has already appeared, which mainly appears as increase in the winter (dry season) runoff. It also found that the permafrost degradation has a direct replenishment effect on river runoff, and the amount of recharge may have reached a certain level in some basins.

Accelerated continental‐scale snowmelt and ecohydrological impacts in the four largest Siberian river basins in response to spring warming

AbstractRiver runoff from the four largest Siberian river basins (the Ob, Yenisei, Lena, and Kolyma) considerably contributes to freshwater flux into the Arctic Ocean from the Eurasian continent. However, the effects of variation in snow cover fraction on the ecohydrological variations in these basins are not well understood. In this study, we analysed the spatiotemporal variability of the maximum snow cover fraction (SCFmax) in the four Siberian river basins. We compared the SCFmax from 2000 to 2016 with data in terms of monthly temperature and precipitation, night‐time surface temperatures, the terrestrial water storage anomaly (TWSA), the normalised difference vegetation index (NDVI), and river runoff. Our results exhibit a decreasing trend in the April SCFmax values since 2000, largely in response to warming air temperatures in April. We identified snowmelt water as the dominant control on the observed increase in the runoff contribution in May across all four Siberian river basins. In addition, we detected that the interannual river runoff was predominantly controlled by interannual variations in the TWSA. The NDVI in June was strongly controlled by the timing of the snowmelt along with the surface air temperature and TWSA in June. The rate of increase in the freshwater flux from the four Siberian rivers decreased from 2000 to 2016, exhibiting large interannual variations corresponding to interannual variations in the TWSA. However, we identified a clear increase trend in the freshwater flux of ~4 km3/year when analysing the long‐term 39‐year historical record (1978–2016). Our results suggest that continued global warming will accelerate the transition towards the earlier timing of snowmelt and spring freshwater flux into the Arctic Ocean. Our findings also highlight the effects of earlier snowmelt on ecohydrological changes in the Northern Hemisphere.

Importance of snowmelt contribution to seasonal runoff and summer low flows in Czechia

Abstract. The streamflow seasonality in mountain catchments is often influenced by snow. However, a shift from snowfall to rain is expected in the future. Consequently, a decrease in snow storage and earlier snowmelt is predicted, which will cause changes not only in seasonal runoff distribution in snow-dominated catchments, but it may also affect the total annual runoff. The objectives of this study were to quantify (1) how inter-annual variations in snow storages affect spring and summer runoff, including summer low flows, and (2) the importance of snowmelt in generating runoff compared to rainfall. The snow storage, groundwater recharge and streamflow were simulated for 59 mountain catchments in Czechia in the period from 1980 to 2014 using a bucket-type catchment model. The model output was evaluated against observed daily runoff and snow water equivalent. Hypothetical scenarios were performed, which allowed for analysing the effect of inter-annual variations in snow storage on seasonal runoff separately from other components of the water balance. The results showed that 17 %–42 % (26 % on average) of the total runoff in the study catchments originates as snowmelt, despite the fact that only 12 %–37 % (20 % on average) of the precipitation falls as snow. This means that snow is more effective in generating catchment runoff compared to liquid precipitation. This was demonstrated by modelling experiments which showed that total annual runoff and groundwater recharge decrease in the case of a precipitation shift from snow to rain. In general, snow-poor years were clearly characterized by a lower snowmelt runoff contribution compared to snow-rich years in the analysed period. Additionally, snowmelt started earlier in these snow-poor years and caused lower groundwater recharge. This also affected summer baseflow. For most of the catchments, the lowest summer baseflow was reached in years with both relatively low summer precipitation and snow storage. This showed that summer low flows (directly related to baseflow) in our study catchments are not only a function of low precipitation and high evapotranspiration, but they are significantly affected by the previous winter snowpack. This effect might intensify drought periods in the future when generally less snow is expected.

Increasing dependence of lowland populations on mountain water resources

Mountain areas provide disproportionally high runoff in many parts of the world, but their importance for water resources and food production has not been clarified from the viewpoint of the lowland areas downstream. Here we quantify the extent to which lowland inhabitants potentially depend on runoff contributions from mountain areas (39% of the global land mass). We show that ~1.5 billion people (24% of the world’s lowland population) are projected to depend critically on runoff contributions from mountains by the mid-twenty-first century under a ‘middle of the road’ scenario, compared with ~0.2 billion (7%) in the 1960s. This striking rise is mainly due to increased local water consumption in the lowlands, whereas changes in mountain and lowland runoff play only a minor role. We further show that one-third of the global lowland area equipped for irrigation is currently located in regions that both depend heavily on runoff contributions from mountains and make unsustainable use of local blue water resources, a figure that is likely to rise to well over 50% in the coming decades. Our findings imply that mountain areas should receive particular attention in water resources management and underscore the protection they deserve in efforts towards sustainable development.

Glacier runoff variations since 1955 in the Maipo River basin, in the semiarid Andes of central Chile

Abstract. As glaciers adjust their size in response to climate variations, long-term changes in meltwater production can be expected, affecting the local availability of water resources. We investigate glacier runoff in the period 1955–2016 in the Maipo River basin (4843 km2, 33.0–34.3∘ S, 69.8–70.5∘ W), in the semiarid Andes of Chile. The basin contains more than 800 glaciers, which cover 378 km2 in total (inventoried in 2000). We model the mass balance and runoff contribution of 26 glaciers with the physically oriented and fully distributed TOPKAPI (Topographic Kinematic Approximation and Integration)-ETH glacio-hydrological model and extrapolate the results to the entire basin. TOPKAPI-ETH is run at a daily time step using several glaciological and meteorological datasets, and its results are evaluated against streamflow records, remotely sensed snow cover, and geodetic mass balances for the periods 1955–2000 and 2000–2013. Results show that in 1955–2016 glacier mass balance had a general decreasing trend as a basin average but also had differences between the main sub-catchments. Glacier volume decreased by one-fifth (from 18.6±4.5 to 14.9±2.9 km3). Runoff from the initially glacierized areas was 177±25 mm yr−1 (16±7 % of the total contributions to the basin), but it shows a decreasing sequence of maxima, which can be linked to the interplay between a decrease in precipitation since the 1980s and the reduction of ice melt. Glaciers in the Maipo River basin will continue retreating because they are not in equilibrium with the current climate. In a hypothetical constant climate scenario, glacier volume would reduce to 81±38 % of the year 2000 volume, and glacier runoff would be 78±30 % of the 1955–2016 average. This would considerably decrease the drought mitigation capacity of the basin.

Non-surface mass balance of glaciers in Iceland

AbstractNon-surface mass balance is non-negligible for glaciers in Iceland. Several Icelandic glaciers are in the neo-volcanic zone where a combination of geothermal activity, volcanic eruptions and geothermal heat flux much higher than the global average lead to basal melting close to 150 mm w.e. a−1for the Mýrdalsjökull ice cap and 75 mm w.e. a−1for the largest ice cap, Vatnajökull. Energy dissipation in the flow of water and ice is also rather large for the high-precipitation, temperate glaciers of Iceland resulting in internal and basal melting of 20–150 mm w.e. a−1. The total non-surface melting of glaciers in Iceland in 1995–2019 was 45–375 mm w.e. a−1on average for the main ice caps, and was largest for Mýrdalsjökull, the south side of Vatnajökull and Eyjafjallajökull. Geothermal melting, volcanic eruptions and the energy dissipation in the flow of water and ice, as well as calving, all contribute, and thus these components should be considered in mass-balance studies. For comparison, the average mass balance of glaciers in Iceland since 1995 is −500 to −1500 mm w.e. a−1. The non-surface mass balance corresponds to a total runoff contribution of 2.1 km3a−1of water from Iceland.

Snow and glacier melt runoff simulation under variable altitudes and climate scenarios in Gilgit River Basin, Karakoram region

The snow and glacial resource of the Himalayan region are a major source of fresh water for Indus basin irrigation system on which sustenance of millions of people depends. In the context of recent growth in global warming, it has become inevitable to estimate snow and glacier melt to manage future water resource in this region. In the present study, snow and glacier melt runoff was estimated from various altitudinal ranges and under variable climate scenarios in Gilgit River Basin of Pakistan using an integrated modeling approach. The findings of the study revealed > 80% runoff contribution from 4000 to 5000 m elevation range in the Gilgit Basin. The scenario of temperature increase by 1 °C indicated 9% and 13% rise in annual and summer flows, while 3 °C rise in temperature exhibited an increase of 75% and 95% in annual and summer flows of the Gilgit River. As a result of 10% rise in precipitation, the Gilgit River indicated an increase of 48% in annual and 57% in summer flows. A shift in snow melting period was predicted from April to March due to rising warm temperature. Major contribution in the runoff was estimated from snowmelt followed by glacier melt and rainfall. Overall rising trend in snow cover area was observed in the basin, which support the fact of mass gaining behavior of the Karakoram glaciers. The increased summer flows expected under future climate change in this basin should be managed to fulfill the growing water demands of numerous communities living in the downstream in the future.

Multi-Objective Approach for Determining Optimal Sustainable Urban Drainage Systems Combination at City Scale. The Case of San Luis Potosí (México)

A method for determining the optimal Sustainable Urban Drainage Systems (SUDs) combination at city scale is presented in this paper. A comprehensive set of SUDs categories comprising infrastructures aimed at either detaining and locally reusing or infiltrating precipitation are considered. A volumetric water balance is proposed for modelling hydrological processes in urban catchments. A multi-criteria approach combining a cost function and aims for both recharging aquifers and limiting runoff contribution to water courses is proposed to find the optimal SUDs combination. The water balance was run with each possible SUDs combination and the optimal set of SUDs was found. The method was applied to the Metropolitan Area of San Luis Potosí (Mexico). The optimal solutions in this case clearly promoted surface runoff detention and reuse over porous pavements and green roofs but they were sensitive to the considered costs. The SUD requirements to potential new urban developments for each catchment to comply with the original hydrological aims were also studied. The method requires customizing the cost function and using representative climatic data.

Allocating biocide sources and flow paths to surface waters using passive samplers and flood wave chemographs

Biocide emissions have been shown to pose a comparable risk to aquatic life as pesticides in urbanized catchments. Sources of biocides have been reported to be steady flows from wastewater treatment plants as well as direct building wash off during rain events. A simple methodology to separate wastewater from surface runoff contribution during flood waves had been missing until now. This study introduces an elegant passive sampler method used to derive source allocation during flood waves based on the recalcitrant wastewater tracer carbamazepine. Field calibration of sampling rates during low- and high-flow with continuous autosampler monitoring indicated that uptake rates of polar compounds in caged POCIS are very close in both hydrological situations, allowing for a direct comparison. The passive sampler regressions showed that on a regional level carbendazim originated essentially from wastewater flows, while surface runoff contributed 31% and 74% respectively to terbutryn and diuron mass flows during flood-waves. A local autosampler campaign on a 38 km2 catchment using the same wastewater marker approach found increasing surface runoff allocations with event flow in the order terbutryn < carbendazim < diuron in accordance with results from a nearby combined sewer overflow. Both source allocation methods can be used to establish pertinent regional and local biocide mitigation plans. The passive sampler approach is by far the more cost efficient method.

Nitrate and biochemical oxygen demand change in a typical Midwest stream in the past two decades

Abstract Nitrate and organic contamination from Midwest rivers, including the White River at Muncie, IN, has been an on-going concern and contributes to the hypoxic zone in the Gulf. Despite rich data, recent water quality changes have rarely been investigated. This study employed 16 years of continuous monitoring data, including biochemical oxygen demand (BOD), dissolved oxygen (DO), and nitrate–nitrite as nitrogen (NN) from five sites near Muncie, and analyzed the water quality trend and pollution sources. A novel approach, Weighted Regression on Time, Discharge and Seasons (WRTDS) that allows for the representation of long-term water quality patterns by considering seasonal variance and discharge-related effects over time, is adopted. Flow-normalized BOD and NN concentration and flux both increased, and DO concentration and flux decreased. However, the changes vary among sites. Muncie wastewater treatment plant and combined sewage outflows (CSOs) contribute remarkably to NN pollution during low-flow seasons. Urban and agricultural runoff, and CSOs impact BOD levels. Agricultural runoff contribution to BOD is increasing in recent years. Seasonal patterns of nitrate and BOD in the river are also analyzed. The results are helpful for watershed managers to re-think conservation practices and have indications to water quality management beyond the study area.

Flood vulnerability assessment of the upper Cross River basin using morphometric analysis

Cross River, which originates from Cameroon, flows through several communities in Nigeria. The population upsurge and settlements near the river channel, however, portends the possibility of natural hazards such as floods. Floods within the upper Cross River basin (UCRB) have resulted in the loss of lives and property. The importance of flood studies, therefore, cannot be overemphasized. This study evaluated the influence of sub-basins on the flooding of the main channel in the UCRB using morphometric analysis. The UCRB was delineated into sub-basins using Shuttle Radar Topographic Mission Digital Elevation Model. The drainage network and morphometric parameters were extracted using QSWAT installed as a plugin in QGIS. Based on the compound factors computed from morphometric parameters that directly impact runoff, the UCRB was categorized into three flood vulnerability zones namely: high vulnerability (10.93–13.10), moderate vulnerability (8.75–10.92), and low vulnerability (6.57–8.74). The analysis revealed that sub-basins 18, 10, 8, 17, 1, 6, 15, and 13 have greater potentials to attain peak discharge in a short period, therefore, the instantaneous high runoff contribution of their tributaries to Cross River. The results of this study provide useful information for the effective mitigation and management of the flood vulnerabilities of the UCRB.

Changing runoff due to temperature and precipitation variations in the dammed Jinsha River

Impacts of climatic variations and human activities on water discharge in the lower streams of dammed rivers have been widely studied due to the rich water resources and hydropower potential. However, the effects of climate variations in upper streams on the whole river system are always ignored. Therefore, integrated methods of hydrological modelling and numerical analysis were employed to identify runoff characteristics in response to climatic variations in conjunction with hydroelectric exploitation in the Jinsha River in the “Asian Water Tower” region. While there was no significant rise in annual precipitation for most areas from 1970 to 2017, highly significant upward trends in temperature were observed in areas along the mainstream. Snowmelt periods varied between upper and middle streams due to constantly varying geographic conditions. Peaking runoff of 56.67 m3 s−1, 1350.12 m3 s−1, 175.63 m3 s−1, 2343.89 m3 s−1, 1855.02 m3 s−1, 3285.61 m3 s−1, and 10,922.65 m3 s−1 occurred during July in Tuotuohe, Qingshuihe_Jinsha, Qingshuihe_Yalong, Batang, Kangding, Xianggelila, and Yibin, respectively, along the Jinsha River. During snowmelt periods, runoff in the upper stream was greatly influenced by temperature changes. However, during recent periods, runoff in the middle stream has also become sensitive to rising temperatures, as indicated by change points. The contribution of runoff from upper streams to the outlet increased from 10.57% (naturalised river period) to 13.01% (individual reservoir period), followed by a further increase of 13.37% (cascade reservoirs period). Seasonal differences were observed up to the middle streams, where more runoff occurred at the outlet during flood seasons due to hydroelectric exploitation after 1999. Annually, runoff contribution in different areas increased in response to climatic variations during 1999–2017. This study highlights the vulnerability of runoff variations in upper streams to climate change. Watershed management rather than river regulation alone is needed, which could help water resources management for the entire river system.

An Estimated Contribution of Glacier Runoff to Mongolia's Upper Khovd River Basin in the Altai Mountains

In the semiarid climate of northwestern Mongolia, glaciers are critical contributors to water resources, particularly during the dry summer months. Nevertheless, our knowledge of the contribution of glacier runoff in the Upper Khovd River Basin (UKRB) is limited. This study investigates the impact of glacier recession on the UKRB's hydrology in western Mongolia's Altai Mountains. The analysis included glaciological method measurements, satellite-derived glacier extent records, and a simple ice ablation model. Our modeling used a mass balance gradient of 0.50 meters water equivalent 100 m–1 for the years 2000, 2010, and 2016 and included a sensitivity analysis that applied lower and upper mass balance gradient values and ±200 m around the equilibrium line altitude (ELA). The glacier contribution to the UKRB's water resources decreased from almost 8% in 2000 to 6.7% in 2016. Hypsometries revealed that glacier areas decreased at all elevations, indicating that only small accumulation zones exist. Therefore, applying a modeled increased ELA better represents glacier contribution to total runoff, at 18.7% in 2000 and 15.4% in 2016. The decreasing glacier runoff contribution indicates that the UKRB glaciers have passed the tipping point of an increased contribution that first follows enhanced melting. The continued glacier recession and uncertain water availability represent challenges for water resource management and future human–water relations in the Mongolian Altai.