Catchment Processes Research Articles

South Africa needs a hydrological soil map: a case study from the upper uMngeni catchment

Accurate hydrological modelling to evaluate the impacts of climate and land use change on water resources is pivotal to sustainable management. Soil information is an important input in hydrological models but is often not available at adequate scale with appropriate attributes for direct parameterisation of the models. In this study, conducted in three quaternary catchments in the midlands of KwaZulu-Natal, three different soil information sets were used to configure SWAT+, a revised version of the Soil and Water Assessment Tool (SWAT). The datasets were: (i) the Land Type database (currently the only soil dataset covering the whole of South Africa), (ii) disaggregation of the Land Type database using digital soil mapping techniques (called DSMART), and (iii) a dataset where DSMART were complemented by field observations and interpretations of the hydropedological behaviour of the soils (DSMART+). Simulated streamflow was compared with measured streamflow at three weirs with long-term measurements, and the impact of the soil datasets on water balance simulations was evaluated. In general, the simulations were acceptable when compared to other studies, but could be improved through calibration and including small reservoirs in the model. The DSMART+ dataset yielded more accurate simulations of streamflow in all three catchments with Nash-Sutcliffe efficiencies increasing by between 9% and 67% when compared to the Land Type dataset. The value of the improved soil maps is, however, highlighted through the enhanced spatial detail of streamflow generation mechanisms and water balance components. The internal catchment processes are represented more accurately, and we argue that South Africa needs a detailed hydrological soil map for effective water resource management.

Evaluating the post-earthquake landslides sediment supply capacity for debris flows

Earthquake-triggered landslides provide sufficient loose material for the formation of subsequent debris flow events in earthquake-affected catchments. The landslides sediment supply capacity (SSC) for debris flows plays an important role in post-earthquake sediment transportation, which is influenced by landslide location during different post-earthquake periods. In this study, the logarithmic slope–area diagram was used to distinguish hillslope and channel processes in catchments affected by the Wenchuan earthquake, adopting a threshold between hillslopes and channels set at 1 km2. In comparison with the existing structural sediment delivery ratio (SDR), it was found that the SSC assessed using the SDR showed a decreasing trend of power exponent as distance increased, effectively eliminating the impact of earthquake-triggered sediment supply. To efficiently assess the SSC of post-earthquake landslides for debris flows, we proposed a novel dimensionless index, namely Mean Landslide Sediment Delivery Ratio (MLSDR), by considering the impact of earthquakes and eliminating the impact of catchment area. It was found that, the SSC of coseismic landslides assessed by the MLSDR in catchments affected by the Wenchuan earthquake could better reflect seismic impact, with higher values concentrated along the seismogenic fault of the earthquake, thereby highlighting the satisfactory applicability of the method in the Wenchuan earthquake-affected area. Moreover, it was found that the proposed index had a reasonable corresponding relationship with debris flow development in Wenchuan earthquake-affected catchments, mainly for values of 0.2 ≤ MLSDRout ≤ 2.25 and 0.3 ≤ MLSDRchannel ≤ 4.5, which could help identify potential debris flow development. The controlling factors of long-term changes in coseismic and post-earthquake SSC in the Wenchuan earthquake-affected region were assessed. It was found that SSC was controlled by earthquakes during first three years and subsequently controlled by precipitation and grain composition. This study will strengthen the understandings of the long-term evolution of post-earthquake debris flow.

Assessing recharge process in plain catchments using isotopic and hydrochemical techniques

In order to increase the sustainability and conservation of water resources, a joint approach of isotopic and hydrochemical techniques was attempted to identify and quantify water sources and favourable recharge areas that would explain the integral functioning of a typically plain catchment. Chloride and δ18O and δ2H were measured in rain, groundwater, and pond samples. Chloride mass balance approach was applied to calculate the recharge and mixed water calculation was carried out using conservative tracers. Also, the local meteoric water line was calculated. Depleted isotopic and slightly progressive chloride contents are observed and they are grouped around to the local meteoric water line in the upper part and in the west of the lower catchment. In the East lower area 20% of recharge is calculated; isotopes are more enriched and lower concentration of chloride are observed. Depleted isotopic fingerprint and low salinity concentration for Ballenera pond were identified in a well close to it. This work demonstrates that in very flat zones, small changes in the hydrologic fluxes can impact on the water table of surface waters and groundwaters, leading to establish very local recharge zones that hardly can be recognized in large scale or esatfrequency of measurement, but can quiet easily be identified when chemical conservative tracers and water stable isotopes are used. Also, isotopic data demonstrate the importance of shallow wetlands as certain recharge areas to the regional aquifer, becoming areas of high groundwater vulnerability.

Catchment controls of denitrification and nitrous oxide production rates in headwater remediated agricultural streams

Heavily modified headwater streams and open ditches carry high nitrogen loads from agricultural soils that sustain eutrophication and poor water quality in downstream aquatic ecosystems. To remediate agricultural streams and reduce the export of nitrate (NO3−), phosphorus and suspended sediments, two-stage ditches with constructed floodplains can be implemented as countermeasures. By extending hydrological connectivity between the stream channel and riparian corridor within constructed floodplains, these remediated ditches enhance the removal of NO3− via the microbial denitrification process. Ten remediated ditches were paired with upstream trapezoidal ditches in Sweden across different soils and land uses to measure the capacity for denitrification and nitrous oxide (N2O) production and yields under denitrifying conditions in stream and floodplain sediments. To examine the controls for denitrification, water quality was monitored monthly and flow discharge continuously along reaches. Floodplain sediments accounted for 33 % of total denitrification capacity of remediated ditches, primarily controlled by inundation and stream NO3− concentrations. Despite reductions in flow-weighted NO3− concentrations along reaches, NO3− removal in remediated ditches via denitrification can be masked by inputs of NO3−-rich groundwaters, typical of intensively managed agricultural landscapes. Although N2O production rates were 50 % lower in floodplains compared to the stream, remediated ditches emitted more N2O than conventional trapezoidal ditches. Higher denitrification rates and reductions of N2O proportions were predicted by catchments with loamy soils, higher proportions of agricultural land use and lower floodplain elevations. For realizing enhanced NO3− removal from floodplains and avoiding increased N2O emissions, soil type, land use and the design of floodplains need to be considered when implementing remediated streams. Further, we stress the need for assessing the impact of stream remediation in the context of broader catchment processes, to determine the overall potential for improving water quality.

An environmental magnetic record of Holocene climatic variability from the Chilika Lagoon, Southern Mahanadi Delta, east coast of India

Core sediments from the Chilika Lagoon in the eastern part of the Core Monsoon Zone (CMZ) of India have provided a record of local environmental changes and catchment processes during the past 7800 cal. years B.P. Variations in the rock magnetic parameters (χlf, χhf, χARM and IRM's at varying field strengths) of sediment samples reflect climate-induced changes in the Chilika Lagoon catchment. The down-core variations in the concentration-dependent magnetic parameters indicate an intensified summer monsoon and enhanced terrigenous input to the lagoon during the Early to Mid-Holocene (∼7.8 ka to ∼ 5.5 ka B.P.). In contrast, the Mid- to Late Holocene period witnessed a weaker Indian Summer Monsoon Rainfall (ISMR) and less terrigenous input to the lagoon, with an intermediate phase of strengthened monsoon around 2 to 1 ka B.P. Spectral analysis of sedimentary magnetic susceptibility (χlf) data show significant periodicities (at 95 % significance level) of 2523, 573, 147, 93, 59, and 55 years, which are in agreement with the periodicities shown by other paleoclimatic proxies from the region.

Effects of single‐ and multi‐site calibration strategies on hydrological model performance and parameter sensitivity of large‐scale semi‐arid and semi‐humid watersheds

AbstractIn large‐scale watersheds, only the calibration of parameters for the outlet may ignore spatial heterogeneity and fail to meet the simulation accuracy of local areas. Based on the runoff observation data of three hydrological stations (Qingyang, Yangjiaping and Zhangjiashan) in the Jinghe River Watershed, single‐ and multi‐site calibration strategies were designed to investigate the performance and applicability of the Soil and Water Assessment Tool (SWAT) in predicting the monthly runoff of nested catchments and evaluate the differences in parameter sensitivity between the upstream and downstream. (i) The two calibration strategies showed little difference in the simulation accuracy of the watershed outlet; the Nash–Sutcliffe efficiency (NSE) and determination coefficient (R2) were approximately 0.8 and 0.6, respectively, and the percentage of bias (PBIAS) was mostly <15%. The single‐site one‐by‐one calibration was significantly better than the multi‐site joint calibration at the interior points of the watershed. Among them, Qingyang decreased most obviously in the joint calibration with Zhangjiashan, with both NSE and R2 < 0.5, whereas Yangjiaping was >0.5 in combination with the other two sites. (ii) The sensitive parameters obtained by the two calibration strategies were different, and different parameters were effective for different‐sized catchments because hydrological processes exhibit astounding variability at all scales. The single‐site one‐by‐one calibration was mainly affected by the hydrological processes of the local catchment, whereas the multi‐site joint calibration was largely constrained by the sensitive parameters of the single‐site calibration. (iii) Parameters at different scales and locations were related to the problem of scaling and regionalization. The multi‐site joint calibration did not significantly improve the model performance of the watershed outlet but increased the capacity for synchronous identification of local sensitive parameters when compared to single‐site calibration. These findings are expected to provide experience for parameter calibration in other similar large‐scale watersheds and to lay a good foundation for the accurate identification of other related hydrological behaviours at watershed scales.

Observing Multisphere Hydrological Changes in the Largest River Basin of the Tibetan Plateau

Abstract Upper Brahmaputra (UB) is the largest (∼240,000 km2) river basin of the Tibetan Plateau, where hydrological processes are highly sensitive to climate change. However, constrained by difficult access and sparse in situ observations, the variations in precipitation, glaciers, frozen ground, and vegetation across the UB basin remain largely unknown, and consequently the impacts of climate change on streamflow cannot be accurately assessed. To fill this gap, this project aims to establish a basinwide, large-scale observational network (that includes hydrometeorology, glacier, frozen ground, and vegetation observations), which helps quantify the UB runoff processes under climate–cryosphere–vegetation changes. At present, a multisphere observational network has been established throughout the catchment: 1) 12 stations with custom-built weighing automatic rain/snow meters and temperature probes to obtain elevation-dependent gradients; 2) 9 stations with soil moisture/temperature observations at four layers (10, 40, 80, 120 cm) covering Alpine meadow, grasslands, shrub, and forest to measure vegetation (biomass and vegetation types) and soil (physical properties) simultaneously; 3) 34 sets of probes to monitor frozen ground temperatures from 4,500 to 5,200 m elevation (100-m intervals), and two observation systems to monitor water and heat transfer processes in frozen ground at Xuegela (5,278 m) and Mayoumula (5,256 m) Mountains, for improved mapping of permafrost and active layer characteristics; 4) 5 sets of altimetry discharge observations along ungauged cross sections to supplement existing operational gauges; 5) high-precision glacier boundary and ice-surface elevation observations at Namunani Mountain with differential GPS, to supplement existing glacier observations for validating satellite imagery. This network provides an excellent opportunity to monitor UB catchment processes in great detail.

Professor Kenneth John Gregory (1938–2020): The career, contributions and legacy of an eminent geographer and fluvial geomorphologist

AbstractThis paper provides the editorial to accompany a Special Issue of Earth Surface Processes and Landforms produced to honour the memory of Professor Ken Gregory, a key figure in late 20th‐ and early 21st‐century geography and geomorphology. It provides an overview of Ken Gregory's career in research, teaching, and university administration, and elaborates on his key research contributions and legacy across geography and geomorphology. Ten interrelated research themes are identified where Ken made particular impacts: (1) river catchment processes and process–form relationships; (2) wood in rivers; (3) anthropogenic impacts on rivers and catchments; (4) approaches to river management that better respect natural processes; (5) public perceptions of rivers; (6) quantitative palaeohydrology; (7) chronology of river floods and deposits; (8) key physical geography/geomorphology concepts and their metrics; (9) the nature of the discipline of physical geography; and (10) concepts in physical geography teaching. These themes provide a framework to introduce the papers in this Special Issue. Through his publications, leadership style, personality, and positive influence on the many people with whom he interacted, Ken Gregory has left a legacy that will continue to inspire present and future generations of geographers and geomorphologists.

The imprint of catchment processes on Greenlandic ice cap proglacial lake records: analytical approaches and palaeoenvironmental significance

ABSTRACTLakes fed by Greenlandic mountain glaciers and ice caps (GICs) contain important archives of Arctic palaeoenvironmental change. GIC proglacial lake records have been increasingly used to reconstruct Holocene glacier behaviour, largely focusing on macrostratigraphy. However, despite the wide range of topographic settings and catchment characteristics, there has been little systematic analysis of the ways that catchment conditions are registered in the clastic sediments of GIC lakes. Such signals provide valuable insights into landscape processes and palaeoenvironmental conditions that are not routinely captured in other Quaternary glacial morphosedimentary archives. This review synthesises sedimentological and geochemical evidence from existing Holocene GIC proglacial lake records to establish: how catchment‐wide conditions have been recorded in the lacustrine sequences; and our ability to isolate these signals to enhance palaeoenvironmental reconstruction. Our review shows that with careful sedimentological and targeted (bio)geochemical analyses coupled with a clear process‐based understanding, catchment and in‐lake signals can be effectively identified in the microstratigraphic and mineral grain record. Such signals include wind patterns, mass wasting, precipitation events and seasonal lake ice cover, that can complement broader palaeoclimatic proxy evidence. The approaches collated here, if more widely applied, could considerably enhance environmental reconstructions not only in Greenland, but in glaciated catchments elsewhere.

Sensitivity analysis and optimization of land use/cover and aquifer parameters for improved calibration of hydrological model

Integrated Flood Analysis System (IFAS) model, based on Tank model philosophy, is a widely used flood forecasting model that has the capability to simulate the catchment processes of any river system provided the surface and aquifer parameters of each sub-model are accurately calibrated. In this study, sensitivity analysis and optimization of hydrogeological parameters of Tank model have been performed to identify the key hydrogeological parameters and their significance in simulating the stream flows in the basins of two important rivers of Pakistan – Jhelum River and Chenab Rivers – respectively. IFAS includes a set of four sub-models namely: surface tank model, sub-surface tank model, aquifer tank model and river course model. Each of the sub-models simulates its own flow processes using surface/aquifer parameters. In this study, sensitivity analysis is performed to identify the parameters that significantly affect the model performance to simulate the flows in the river. Linear stochastic metamodels of Jhelum River and Chenab River Basins developed in this study played the role of metamodels or surrogate functions to determine the ranges of parameter values in different flow periods. The outcome demonstrates when the aquifer tank parameters values obtained from metamodels are applied, the simulation results in a nearly accurate calibration, which clearly indicates the efficiency of present methodology and the important role of hydrogeological parameters. Further, the analysis of the variability in the effectiveness of these parameters in different flow periods as well as for different catchments areas depicts spatial-temporal heterogeneous characteristics. This confirms that the analysis should be directed independently for each study basin because the results of sensitivity analysis are not transferable among catchments.

Novel variable reconstruction and friction term discretisation schemes for hydrodynamic modelling of overland flow and surface water flooding

Due to the recent advances in computing and data acquisition technologies, numerical models solving the 2D shallow water equations (SWEs) are now widely used in predicting overland flow and surface water flooding process in natural catchments. In catchment-scale flood modelling, in addition to the calculation of convective terms that are usually achieved through solving local Riemann problems to capture transient flow dynamics, correct discretisation of source terms is also essential to handle complex domain topography and ensure accurate and stable numerical solutions. The external forces induced by gravity and bed friction create the key source terms that drive the change of momentum in the SWEs and affect the stability and accuracy of the adopted numerical scheme, especially for applications involving very shallow water depth (e.g. wet and dry fronts, overland flows). Herein, new schemes are introduced to reconstruct the face values of flow variables and a fully implicit algorithm is improved to discretise the stiff friction terms, in the context of developing a Godunov-type finite volume hydrodynamic model for accurate and stable simulation of overland flow and surface water flooding involving very shallow water depth. Five analytical test cases are considered to validate the resulting models and the numerical results are compared with those produed by two alternative numerical schemes. The performance of the models are further demonstrated by reproducing a flood event in the 2500 km2 Eden Catchment, UK.

The vanishing and the establishment of a new ecosystem on an oceanic island – Anthropogenic impacts with no return ticket

A multiproxy approach was applied to a sediment core retrieved from the deep crater Lake Funda, located in the middle of the North Atlantic Ocean on Flores Island, Azores archipelago (Portugal). The purpose of this study was to determine how this ecosystem responded to natural and anthropogenic forces over the last millennium. We distinguished three main phases in lake evolution using multiproxy reconstructions and documentary sources. (A) Climate and lake catchment processes, as well as internal ones, were the main drivers of ecosystem variability before 1335 CE, when human disturbances were absent in the Lake Funda catchment. (B) The second phase is marked by unprecedented changes in all studied proxies between 1335 and 1560 CE, including abrupt changes in the composition and diversity of diatom and chironomid assemblages. Synergistic effects from high climate variability and the onset of human disturbances in the catchment (e.g., introduction of livestock) during the Medieval Climate Anomaly-Little Ice Age transition, led to an increase in lake trophic state from mesotrophic to eutrophic conditions. (C) In the last phase (1560 CE to the present), the eutrophic conditions in Lake Funda were maintained through a positive feedback loop between lake productivity and in-lake phosphorous recycling. Variability within the lake ecosystem was mainly associated with climate variability and internal lake dynamics (e.g., phosphorus remobilization). Our results show that a paleoecological approach is crucial to understanding lake ecological states in the present-day in order to develop locally adapted management and restoration strategies. A long-term perspective enables us to understand the harmful consequences of ongoing climate change and human disturbances on lake ecosystems.

Landslide-Induced Weathering in Tectonically Active Mountains: Evidence From Dissolved Radiogenic Uranium Isotopes

Understanding weathering processes in landslide-dominated catchments is critical for evaluating the role of landslides in chemical weathering and the global carbon cycle. Previous studies have focused on solute concentrations in landslide-impacted landscapes, but have paid less attention to developing isotopic tracers of landslide-induced weathering fluxes. Recent work found that the dissolved radiogenic uranium isotopes in river water are closely related to the denudation rates in catchments draining steep mountains where landslides are thought to be a major erosion mechanism, suggesting the potential of uranium isotopes to trace landslide-induced weathering fluxes. Here we compile the dissolved radiogenic uranium isotopes (234U/238U ratios) in the river water samples from a group of catchments with variable landslide activities in the Minjiang River Basin at the eastern margin of the Tibetan Plateau. We derive three metrics of landslide activity from the analyses of digital topography and an inventory map of the co-seismic landslides triggered by the 2008 Mw7.9 Wenchuan earthquake: the normalized volume of landslides, the mean catchment slope angle, and the fraction of slopes steeper than a threshold angle beyond which slopes are mechanically unstable. The riverine dissolved 234U/238U ratios correlate negatively with the metrics of landslide activity in each catchment, which likely reflect the influence of landslides on the dissolved 234U/238U ratios. Mechanistically, enhanced bedrock landsliding would accelerate the exposure of fresh rock, promoting bedrock weathering and congruent dissolution of 234U and 238U contained in minerals; reduced landslide activities and enhanced regolith weathering would lead to preferential accumulation of 234U against 238U in solutes through alpha-recoil ejection, thus increasing dissolved 234U/238U. Our findings provide field evidence of using the riverine dissolved 234U/238U ratio to trace weathering fluxes driven by landslides, shedding new light on chemical weathering processes in uplifting mountains.

Controls on decadal, annual, and seasonal concentration‐discharge relationships in the Sleepers River Research Watershed, Vermont, northeastern United States

AbstractPast studies on concentration‐discharge (C‐Q) relationships have focused on short‐term or low‐temporal resolution data. While advancing understanding of catchment processes, these studies provided limited insight on catchment response over time or to climate change. Using 15 solutes from 1992 to 2015 at Sleepers River Research Watershed, Vermont, we compared C‐Q relationships over decades, years, and seasons to elucidate controls on stream chemical variation. We applied end‐member mixing analysis (EMMA) to identify solute sources and flow path routing. EMMA identified three end‐members: near‐surface runoff (NSR), riparian groundwater, and hillslope hollow groundwater. Shifting mixing proportions of these end‐members accounted for the temporal variability of conservative (no chemical reaction en route from source to stream) solutes in streamflow. For example, an increase in NSR fraction, typical of high flow, caused flushing (increased concentrations) of NO3−, DOC, Al, and Fe, which were greatest in NSR, dilution of specific conductance and base cation, SO42−, Si, Sr, Ba, and Mn concentrations, which were greatest in the two groundwater end‐members. This behaviour is reflected in the b‐coefficient of the C‐Q relation (C = aQb), which indicates the strength of dilution (b < −0.1) and flushing (b > 0.1) effects. For conservative solutes, the b‐coefficient decreased significantly (p < 0.01) with an increase in the groundwater to NSR concentration ratio. Solutes that are conservative and have relatively constant concentrations in end‐members over time showed consistent annual C‐Q patterns over years and decades. Furthermore, the strength of dilution or flushing was stronger during the snowmelt period, when the NSR fraction peaked, than during the dormant and growing seasons. With shorter snowmelt periods and snow to rain shifts, the flushing or dilution power of snowmelt runoff will weaken and alter catchment response to climate change. These insights provide more tools for the interpretation of catchment processes and responses to climate change.

Functional Multi‐Scale Integration of Agricultural Nitrogen‐Budgets Into Catchment Water Quality Modeling

AbstractDiffuse Nitrogen pollution from agriculture maintains high pressures on groundwater and aquatic ecosystems. Further mitigation requires targeted measures that reconcile agricultural interests in environmental protection. However, the agriculture‐related processes of catchment N modeling remain poorly defined due to discipline‐specific data and knowledge gaps. Using field‐experimental data, crop N uptake responses to fertilizer management were parsimoniously conceptualized and integrated into a catchment diffuse‐N model. The improved catchment modeling further facilitated integration with agricultural budget‐based assessments. The integrated analysis in a mesoscale catchment disentangled contrasting agri‐environment functional mechanisms in typically flashy chemodynamic and transport‐limited chemostatic export regimes. Moreover, the former was actively responsive to interannual climatic variability and agricultural practices; the latter exhibited drought‐induced enhancement of N enrichment, which could likely be mitigated through reduced fertilization. This interdisciplinary integration of data and methods provided an insightful evidence base for multi‐sector targeted measures, especially under cumulative impacts of changing climate and fertilizer‐use intensities.

Combining FDR and ERT for monitoring soil moisture and temperature patterns in undulating terrain in south-eastern Norway

The occurrence of freeze–thaw cycles modifies water infiltration processes and surface runoff generation. Related processes are complex and are not yet fully investigated at field scale. While local weather conditions and soil management practices are the most important factors in both runoff generation and surface erosion processes, local terrain heterogeneities may significantly influence soil erosion processes in catchments with undulating terrain.This paper presents a field-based investigation of spatial and temporal heterogeneities in subsurface soil moisture and soil temperature associated with freezing, thawing, and snowmelt infiltration. The field setup consists of a combination of traditional point measurements performed with frequency domain reflectometry (FDR) and electrical resistivity tomography (ERT). The transect was approximately 70 m long and spanned an entire depression with a north-facing slope (average slope of 11.5%) and a south-facing slope (average slope of 9.7%). The whole depression was entirely covered with stubble.Observed resistivity patterns correspond well to the measured soil moisture patterns. During the observation period, the north facing slope froze earlier and deeper compared with the south facing slope. Freeze–thaw cycles were less pronounced in the north-facing slope than in the south-facing slope. There were also differences in soil temperature and soil moisture patterns between lower and upper parts of the monitored depression. These indicate that initiation and development of runoff related processes, and consequently soil erosion, in regions with freeze–thaw cycles may differ significantly depending on local terrain characteristics. Consequently, it indicates that spatial terrain heterogeneities, especially slope aspects, may be important when studying soil erosion processes, water flow and nutrient leaching in lowlands where patchy snowpacks and dynamic freeze–thaw cycles are predominating.

Understanding climate-induced changes of snow hydrological processes in the Kaidu River Basin through the CemaNeige-GR6J model

Snow-affected mountainous areas are highly vulnerable to climate changes in arid and semi-arid regions. Previous studies have put more emphasis on runoff, however, research about snow hydrological processes is still insufficient. Based on the optimization of calibration strategies, this study aims to provide a more realistic simulation of snow hydrology by coupling both a lumped rainfall-runoff model (GR6J) and a semi-distributed snow model (CemaNeige). Compared with calibration using only runoff, the multi-objective calibration with both runoff and snow not only significantly improved the KGE (Kling-Gupta efficiency) of snow from 0.34/0.47 to 0.67/0.69 during the calibration/validation period, but also slightly improved the KGE of runoff from 0.84/0.75 to 0.86/0.78, respectively. Additionally, we also found that the calibration using only runoff may underestimate snow cover (41%) and overestimate snowpack (20%), while there is little discrepancy in snowmelt and runoff. Snowmelt runoff is 57.7 mm accounting for 26% of the annual runoff. In the historical period (1980–2011), the runoff varied with a positive trend of 2.15 mm year−1 (p < 0.1), while its tendency became negative in the future. A 15% to 30% decline in runoff was projected for SSP370 (SSP3-RCP7) and SSP585 (SSP5-RCP8.5) in the 2085s (2070–2100) compared with that in the 1985s (1970–2000). Through further study on seasonal variations, we found that the future runoff decline is probably due to mild rise in rain not enough to alleviate the larger AE (actual evaporation), and for the runoff and AE we also found the variations in summer dominated the annual changes. In response to global warming, SCED (snow cover end date) advances while SCOD (snow cover onset date) recedes in all four scenarios as the year increases. Generally, coupling different hydrological models and multi-objective calibration strategies is vital for understanding the hydrological processes in snow-affected catchments.

Investigation of subsurface connectivity and subsurface stormflow in low mountain ranges—Findings from the two research catchments Obere Brachtpe and Bohlmicke (Germany)

AbstractThe two small research catchments Obere Brachtpe (2.6 km2; 50.989986, 7.752013) and Bohlmicke (1 km2, 51.079319, 7.892988) are located in the Rhenish Massif, a low mountain range in Germany. Land use in both catchments is dominated by pasture land, spruce stands and mixed forests. Mean annual temperature is 9.1°C, and mean annual total precipitation is 1250 mm, with 15%–20% of the annual precipitation falling as snow. The geology is characterized by sandy silty clay shale from the Lower and Middle Devonian. Loamy Cambisols derived from periglacial slope deposits, complemented by Leptosols and Stagnosols, are the most prominent soils in the catchments. Long‐term hydrological datasets of precipitation, throughfall, discharge, groundwater levels and soil moisture (at different soil depths) in a high temporal and spatial resolution are available for further scientific analysis. Both catchments were monitored within the time period 1999 and 2009, in order to understand how the antecedent soil moisture, stratified soils (periglacial cover beds) and topography (slope form) impacted the subsurface connectivity, and the subsurface stormflow generation ‐ a dominant runoff generation process in humid mountainous catchments. Detailed physically based investigations on runoff processes were carried out, and the obtained results helped to better understand subsurface stormflow generation and subsurface connectivity dynamics. The process knowledge gained, which was presented at several conferences, as well as publications, was the basis for the discussion of open questions within the scientific network ‘Subsurface Stormflow ‐ A well‐recognized, but still challenging process in Catchment Hydrology’ (2016–2021), and the research unit ‘Fast and invisible: conquering subsurface stormflow through an interdisciplinary multisite approach’ (2022–2025), both financed by the German Research Foundation (DFG).

The DESC catchments: Long‐term monitoring of inland Precambrian shield catchment streamflow and water chemistry in Central Ontario, Canada

AbstractSince the early 1970s, the Dorset Environmental Science Centre (DESC) research catchments have been home to long‐term monitoring and study of terrestrial headwater catchment processes, their linkages to inland aquatic ecosystems and the influence of both natural variation and human activities. Located on the Precambrian Shield in central Ontario, Canada, covered by mixed Great Lakes‐St. Lawrence forest, the 29 catchments, defined by inflows and outflows to eight lakes, have been monitored for streamflow, meteorology and water chemistry, with long‐term datasets spanning from 1976 to the present. These datasets have provided insights into cold region hydrologic processes such as runoff generation, wetland and groundwater–surface water interactions, snow and ice processes, and catchment linkages to lake nutrient budgets and ecology. The datasets have supported catchment transit time estimates, hydrological modelling and cold region intercomparison studies. Starting with early research efforts driven by concerns over impacts from cottage development and acid deposition on soils, rivers and lakes, the DESC catchment datasets have supported study of impacts of stressors of forest harvesting, calcium depletion, road salt application and climate change. Ongoing monitoring of streamflow, meteorology and water chemistry in the DESC catchments continues to offer unique opportunities for investigation of critical zone processes in Precambrian shield catchments, their model representation and anthropogenic impacts.

Impacts of Soil Information on Process-Based Hydrological Modelling in the Upper Goukou Catchment, South Africa

Although soils form an integral part of landscape hydrological processes, the importance of soil information in hydrological modelling is often neglected. This study investigated the impact of soil information on streamflow modelling accuracy and hydrological process representation. Two different levels of soil information were compared to long-term streamflow in the upper Goukou catchment (230 km2), South Africa, over a period of 23 years using the Soil Water Assessment Tool (SWAT+). The land-type soil map (LTSM) dataset was less detailed and derived from the best, readily available soil dataset for South Africa currently. The hydrological soil map (HSM) dataset was more detailed and was created using infield hydropedological soil observations combined with digital soil-mapping techniques. Monthly streamflow simulation was similar for both soil datasets, with Nash–Sutcliffe efficiency and Kling–Gupta efficiency values of 0.57 and 0.59 (HSM) and 0.56 and 0.60 (LTSM), respectively. It is, however, important to assess through which hydrological processes were these streamflow values generated as well as their spatial distribution within the catchment. Upon further assessment, the representation of hydrological processes within the catchment differed greatly between the two datasets, with the HSM more accurately representing the internal hydrological processes, as it was based on infield observations. It was concluded that hydropedological information could be of great value in effective catchment management strategies since it improves representation of internal catchment processes.