Small Catchment Research Articles

Hydrological Effects of Spatial Harvest Patterns in a Small Catchment Covered by Fast-Growing Plantations in the Neotropics

<em>Eucalyptus</em> forests are expanding worldwide and concerns exist about their impact on water resources. There is a lack of information about the hydrological effects of spatial harvest patterns in terms of their effects on streamflow. In this paper, we examined harvest amount and hillslope position effects on flow indices (Q70; Q50 and Q10) and water yield in a small catchment covered with a fast-growing <em>Eucalyptus</em> plantation. To do that, we used the Gridded Surface Subsurface Hydrologic Analysis (GSSHA), a physical-based distributed hydrological model, to simulate harvesting scenarios with different harvest amounts (30% and 70% of the forest plantation) at two hillslope positions (downslope and upslope). We also verified the influence of the amount of rainfall on peak flows for all scenarios. The results showed that the increase in water yield is positively related to the harvest amount and that, under the same harvest amount, harvests in downslope areas caused a larger increase in water yield than harvests in upslope areas. Downslope harvests led to a greater increase in peak flow under the 30% harvest. For the 70% harvest, no substantial effects of harvest position on peak flow could be detected. Incorporating harvest amounts and spatial patterns in <em>Eucalyptus</em> plantations management practices may be useful to mitigate their effects on water resources, especially in regions where water availability is generally lower.

Watershed urbanization dominated the spatiotemporal pattern of riverine methane emissions: Evidence from montanic streams that drain different landscapes in Southwest China

Methane (CH4) emissions from streams are an important component of the global carbon budget of freshwater ecosystems, but these emissions are highly variable and uncertain at the temporal and spatial scales associated with watershed urbanization. In this study, we conducted investigations of dissolved CH4 concentrations and fluxes and related environmental parameters at high spatiotemporal resolution in three montanic streams that drain different landscapes in Southwest China. We found that the average CH4 concentrations and fluxes in the highly urbanized stream (2049 ± 2164 nmol L−1 and 11.95 ± 11.75 mmol·m−2·d−1) were much higher than those in the suburban stream (1021 ± 1183 nmol L−1 and 3.29 ± 3.66 mmol·m−2·d−1) and were approximately 12.3 and 27.8 times those in the rural stream, respectively. It provides powerful evidence that watershed urbanization strongly enhances riverine CH4 emission potential. Temporal patterns of CH4 concentrations and fluxes and their controls were not consistent among the three streams. Seasonal CH4 concentrations in the urbanized streams had negative exponential relationships with monthly precipitation and demonstrated greater sensitivity to rainfall dilution than to the temperature priming effect. Additionally, the CH4 concentrations in the urban and semiurban streams showed strong, but opposite, longitudinal patterns, which were closely related to urban distribution patterns and the HAILS (human activity intensity of the land surface) within the watersheds. High carbon and nitrogen loads from sewage discharge in urban areas and the spatial arrangement of the sewage drainage contributed to the different spatial patterns of the CH4 emissions in different urbanized streams. Moreover, CH4 concentrations in the rural stream were mainly controlled by pH and inorganic nitrogen (NH4+ and NO3−), while urban and semiurban streams were dominated by total organic carbon and nitrogen. We highlighted that rapid urban expansion in montanic small catchments will substantially enhance riverine CH4 concentrations and fluxes and dominate their spatiotemporal pattern and regulatory mechanisms. Future work should consider the spatiotemporal patterns of such urban-disturbed riverine CH4 emissions and focus on the relationship between urban activities with aquatic carbon emissions.

New remote method to systematically extract bedrock channel width of small catchments across large spatial scales using high‐resolution digital elevation models

AbstractBedrock river width is an essential geometric parameter relevant to understanding flood hazards and gauging station rating curves, and is critical to stream power incision models and many other landscape evolution models. Obtaining bedrock river width measurements, however, typically requires extensive field campaigns that take place in rugged and steep topography where river access is often physically challenging. Although prior work has turned to measuring channel width from satellite imagery, these data present a snapshot in time, are typically limited to rivers ≥ 10–30 m wide due to the image resolution, and are physically restricted to areas devoid of vegetation. For these reasons, we are generally data limited, and the factors impacting bedrock channel width remain poorly understood. Due to these limitations, researchers often turn to assumptions of width‐scaling relationships with drainage area or discharge to estimate bedrock channel width. Here we present a new method of obtaining bedrock channel width at a desired river discharge through the incorporation of a high‐resolution bare‐earth digital elevation model (DEM) using MATLAB Topotoolbox and the HEC‐RAS river analysis system. We validate this method by comparing modeled results to US Geological Survey (USGS) field measurements at existing gauging stations, as well as field channel measurements. We show that this method can capture general characteristics of discharge rating curves and predict field‐measured channel widths within uncertainty. As high‐resolution DEMs become more available across the United States through the USGS three‐dimensional elevation program (3DEP), the future utility of this method is notable. Through developing and validating a streamlined, open‐source, and freely available workflow of channel width extraction, we hope this method can be applied to future research to improve the quantity of channel width measurements and improve our understanding of bedrock channels.

Small headwater catchments – spatial delimitation and their classification in terms of runoff risks

Příspěvek představuje plošné vymezení malých horních zdrojových povodí do velikosti 5 km2 na území ČR. Cílem bylo nejen představit vymezení těchto povodí, ale také jejich kategorizaci z hlediska charakteristik ovlivňujících formování rychlého odtoku. Rychlý odtok způsobený přívalovými srážkami je dynamický proces epizodního charakteru a zásadní dopad má právě v malých povodích. Vymezení malých zdrojových povodí, kde probíhají výše zmíněné procesy, tak může doplnit standardní hierarchickou klasifikaci povodí v ČR. Tato povodí tvoří 80 % území ČR.

Comparing the Runoff Decompositions of Small Experimental Catchments: End-Member Mixing Analysis (EMMA) vs. Hydrological Modelling

This study is focused on the comparison of streamflow composition simulated with three well-known rainfall–runoff (RR) models (ECOMAG, HBV, SWAT) against hydrograph decomposition evaluated with End-Member Mixing Analysis (EMMA). In situ observations at two small mountain testbed catchments located in the south of Pacific Russia are used. All applied RR models and EMMA analysis demonstrate that two neighboring catchments disagree significantly on the mutual dynamics of the runoff sources. The RR models' benchmark test is based on proximity to EMMA hydrograph composition. Different aggregation intervals (season, month, and pentad) were applied to find a reasonable generalization period ensuring the clarity of results. ECOMAG is most conformable to EMMA outcome; HBV reflects flood events well enough; SWAT exhibits distinctive behavior compared to the other models. It is shown that, along with standard efficiency criteria of simulated and observed runoff proximity, EMMA analysis might provide useful auxiliary information for the validation of modelling results.

Summer-autumn variability of isotopes (2H and 18O) in water at small mountain catchments in South Sikhote-Alin (Pacific Russia)

Summer-autumn variability of isotopes (2H and 18O) in water at small mountain catchments in South Sikhote-Alin (Pacific Russia)

Effects of precipitation changes and land-use alteration on streamflow: A comparative analysis from two adjacent catchments in the Qilian Mountains, arid northwestern China

Comparative analysis of the impacts of precipitation and land use on streamflow from adjacent catchments is critical to exploring pathways toward water security and sustainable development. In this work, two adjacent catchments (the Mayinghe and Xidahe, abbreviated as MYC and XDC, respectively) in northwestern China were selected to compare the impacts of precipitation change and land use alteration on streamflow change during 1956–2019 using field observation streamflow data and satellite data. An opposite trend of streamflow was found for the two catchments from 1956 to 2019: the streamflow decreased significantly in the MYC (-0.63 × 107m3/10a, p < 0.05), while it increased in the XDC (0.71 × 107m3/10a, p < 0.05). Land conversion dominated the streamflow reduction in the MYC, with a contribution of about 68.3%. In the XDC, precipitation was confirmed to be the major factor driving the increase in streamflow. The streamflow for farmland irrigation reached 27.97 × 104 m3/km2 in the MYC, which was the leading factor of streamflow reduction in the basin. The findings obtained from this work can shed light on the quantitative understanding of streamflow changes in small catchments and offer a scientific basis for sustainable water management in other inland river basins.

Impacts of small-scale irrigation water use on environmental flow of ungauged rivers in Africa

Failure in Environmental flow in quantity, timing, and quality leads to failure to support ecosystems, human livelihoods, and well-being. Irrigation water use is one of the main actors in impacting the water flow of rivers in quantity and time but was not well investigated in many ungauged catchments under smallholder irrigation systems. This study examined the impact of irrigation water use on environmental flow in Arata's small ungauged catchment. The study estimated the flow in sub-catchment using the area ratio method, the crop irrigation water requirement using F.A.O. cropwat 8.0, and the water balance in the Water Evaluation and Planning System tool and the environmental flow in Tennants, Q95, asnd local area thumb rule. The result showed that the minimum environmental flow of the Arata catchment is 290, 310, and 60 li/sec in the Tennant, Q95, and the local thumb rule. Irrigation consumes only 9% of the water resources of the catchment while 91% is contributed to downstream lake Ziway via Ketar river. January and February have unmet water demand and zero environmental flow. In December Tennant's 10% and Q95 recommended environmental flow had 19% and 24% deficit while the thumb rule environmental flow is 291% more than the minimum requirement. The rest of the months are by far more than the minimum environmental flow requirement. Given the result, meeting the environmental flow of the system throughout the year needs the installation of a water storage facility from upstream to downstream, the introduction of different water-saving irrigation technologies, farmers' capacity building in irrigation water management, and a standardized environmental flow estimation mechanism.

Accuracy of radar-estimated precipitation in a mountain catchment in Slovakia

Abstract Accurate estimation of precipitation in mountain catchments is challenging due to its high spatial variability and lack of measured ground data. Weather radar can help to provide precipitation estimates in such conditions. This study investigates the differences between measured and radar-estimated daily precipitation in the mountain catchment of the Jalovecký Creek (area 22 km2, 6 rain gauges at altitudes 815–1900 m a.s.l.) in years 2017–2020. Despite good correlations between measured and radar-based precipitation at individual sites (correlation coefficients 0.68–0.90), the radar-estimated precipitation was mostly substantially smaller than measured precipitation. The underestimation was smaller at lower altitude (on average by –4% to –17% at 815 m a.s.l.) than at higher altitudes (–35% to –59% at 1400–1900 m a.s.l.). Unlike measured data, the radar-estimated precipitation did not show the differences in precipitation amounts at lower and higher altitudes (altitudinal differences). The differences between the measured and radar-estimated precipitation were not related to synoptic weather situations. The obtained results can be useful in preparation of more accurate precipitation estimates for the small mountain catchments.

Elemental and Cu–Zn isotopic compositions of two bolete mushrooms grown on contrasting substrates

We studied elemental and Cu–Zn isotopic compositions of Boletus edulis and Xerocomus chrysenteron mushroom samples collected from three small catchments underlain by contrasting bedrock (leucogranite, amphibolite, and serpentinite). Elements such as Ag, P, K, Zn, S, Cd, and Rb are significantly enriched in the mushroom's fruiting bodies relative to the substrate. All analyzed elements are distributed unevenly within the fruiting bodies, with the cap and sporophore generally containing higher amounts of trace elements. Overall, the studied samples of the B. edulis more efficiently accumulate nutrients and minerals than the X. chrysenteron samples. Concentration of most trace elements in mushrooms is not site-dependent with the exception of Ca, Rb, Ti, Ba and Sr. Isotopic composition of mushrooms is characterized by higher uptake of heavier isotopes of Zn (Δ66Znstipe-soil = 0.48–0.77‰) for the both species, lighter isotopes of Cu (Δ65Custipe-soil = −0.73 to −1.52‰) for B. edulis, and heavier Cu isotopes (Δ65Custipe-soil = +0.37 to +0.43‰) for X. chrysenteron. The B. edulis samples are characterized by (δ65Custipe > δ65Cucap > δ65Cusporophore) and (δ66Znstipe > δ66Zncap > δ66Znsporophore) within-mushroom isotope distribution schemes, whereas the X. chrysenteron samples display different Cu (δ65Custipe < δ65Cucap > δ65Cusporophore) and Zn (δ66Znstipe > δ66Zncap < δ66Znsporophore) isotope distribution schemes. Changes in fungal isotopic signatures relative to the substrate and within the fruiting body suggest that both fungi species fractionate Cu and Zn isotopes with significantly pronounced differences between the species.

Contemporary landscape transformation in a small Arctic catchment (Bratteggdalen, Svalbard)

Contemporary landscape transformation in a small Arctic catchment (Bratteggdalen, Svalbard)

Landscape spatial configuration influences phosphorus but not nitrate concentrations in agricultural headwater catchments

AbstractLandscape organized (or structured) heterogeneity influences hydrological and biogeochemical patterns across space and time. We developed landscape indices that describe the spatial configuration of nutrient sources and sinks as a function of their hydrological distance to the stream (lateral dimension) or to the outlet (longitudinal dimension) and their intersection with flow‐accumulation areas. Using monthly nitrate, total phosphorus (TP), soluble reactive phosphorus (SRP) and daily discharge (Q) data from 221 rural catchments (1–300 km2) from 2010–2020, we observed higher variability in flow‐weighted mean concentrations in smaller catchments than in larger ones. The variability in landscape configurations also decreased with increasing catchment size. A landscape configuration index, calculated as mean arable land use weighted by spatial data on hydrological distance and flow accumulation, improved prediction of TP and SRP, but not nitrate, compared to the unweighted mean arable land use. We conclude that landscape configuration influences phosphorus transfer more than nitrate transfer, and that flow‐accumulation zones and riparian areas are critical source areas for TP and SRP, respectively. By contrast, landscape spatial configuration in the lateral (upslope–downslope) and longitudinal (upstream–downstream) dimensions did not have an identifiable influence on nutrients temporal dynamics. The indices developed in this study can help design landscapes that minimize diffuse phosphorus losses to streams and show that landscape management is not a first order control for nitrate losses.

Rainfall–streamflow response times for diverse upland UK micro-basins: quantifying hydrographs to identify the nonlinearity of storm response

AbstractWhile it is known that antecedent conditions and rainfall profiles contribute to the nonlinearity of streamflow response and that hydrograph shape can be dependent on the nature of rainfall inputs, how antecedent conditions (with similar rainfall inputs) impact hydrograph shape is less known. Here, a data-based mechanistic (DBM) approach is applied to quantify hydrograph shape, in terms of timing and volume, for the purposes of comparing hydrographs across 17 micro-basins at selected localities in upland UK over a 4-year period. The analysis demonstrates the nonlinearity of storm response for small catchments and revealed that with low antecedent conditions and/or small rainfall inputs there was a high variance in hydrograph shape quantifiers and that these variances decrease (at rates micro-basin dependent) as the micro-basins became wetter or as the storms increased in size, potentially converging to a more stable response.

Relating 137Cs and sediment yield from uncultivated catchments: the role of particle size composition of soil and sediment in calculating soil erosion rates at the catchment scale

PurposeSoil loss is considered one of the most important consequences of land degradation as it affects the production of agricultural and forested areas, and the natural equilibrium of aquatic ecosystems downstream. For these reasons, the availability of tools and techniques able to identify areas at risk of land degradation is essential. Over the last 3–4 decades, theoretical models, based on the use of 137Cs, an anthropogenic radiotracer, proved to be very effective for this purpose. However, these models require specific information on soil and sediment particle size to provide estimates of soil erosion or deposition and this information is summarised by a particle size correction factor ‘P’. Empirical methods of calculation of this factor assume the basic hypothesis that a particle size selectivity takes place in erosion processes and this results in a general enrichment of the fine component in sediments and a corresponding higher radionuclide activity. In this contribution, we demonstrate that this hypothesis is not valid everywhere, and consequently, the P factor cannot be estimated using traditional approaches.Materials and methodsA long-term experiment, conducted in Southern Italy and based on two small experimental catchments (approximately 1.5 ha in size), for which measurements of sediment yield are available for the period 1978–2020, is used in this work. More specifically, 137Cs measurements carried out within the catchments and on a reference area provided the basis to obtain long-term estimates of soil erosion rate in these sites. Combined measurements of 137Cs activity and particle size on both soils and sediments, obtained for 46 events, were also carried out to explore possible particle size effects on the final estimates of soil loss.Results and discussionParticle size analyses of soil and sediments showed that there is evidence of a general enrichment of the eroded soil in the finer size fractions. Conversely, radiometric analyses revealed that 137Cs activity in sediments is generally lower than that in surface soil. These results reflect both the decreasing 137Cs activity associated with depth in undisturbed soils and the higher specific surface area of the deeper horizon in these soils. These findings preclude the application of the available empirical models to calculate P, and suggest the opportunity to use, for long-term estimates of soil erosion, a particle size correction factor P = 1. This assumption and an uncertainty analysis associated with the spatial variability of the 137Cs reference value were incorporated into the Diffusion and Migration Model (DMM) to obtain estimates of soil erosion rates for the study catchments.ConclusionsThe final estimates of soil erosion provided by the DMM showed values very close to the measurements of sediment yield obtained for the two catchments during the study period. The overall results demonstrated that the DMM, if properly calibrated using specific information of particle size and of 137Cs reference value, can be considered a useful tool to individuate areas more prone to risks of land degradation and to identify appropriate strategies able to reduce soil loss in forested sites.

Monitoring COVID-19 spread in selected Prague's schools based on the presence of SARS-CoV-2 RNA in wastewater

The COVID-19 pandemic has demanded a broad range of techniques to better monitor its extent. Owing to its consistency, non-invasiveness, and cost effectiveness, wastewater-based epidemiology has emerged as a relevant approach to monitor the pandemic's course. In this work, we analyzed the extent of the COVID-19 pandemic in five primary schools in Prague, the Czech Republic, and how different preventive measures impact the presence of SARS-CoV-2 RNA copy numbers in wastewaters. Copy numbers were measured by reverse transcription–multiplex quantitative real-time PCR. These copy numbers were compared to the number of infected individuals in each school identified through regular clinical tests. Each school had a different monitoring regime and subsequent application of preventive measures to thwart the spread of COVID-19. The schools that constantly identified and swiftly quarantined infected individuals exhibited persistently low amounts of SARS-CoV-2 RNA copies in their wastewaters. In one school, a consistent monitoring of infected individuals, coupled with a delayed action to quarantine, allowed for the estimation of a linear model to predict the number of infected individuals based on the presence of SARS-CoV-2 RNA in the wastewater. The results show the importance of case detection and quarantining to stop the spread of the pandemic and its impact on the presence of SARS-CoV-2 RNA in wastewaters. This work also shows that wastewater-based epidemiological models can be reliably used even in small water catchments, but difficulties arise to fit models due to the nonconstant input of viral particles into the wastewater systems.

Modelling 2050 Water Retention Scenarios for Irrigated and Non-Irrigated Crops for Adaptation to Climate Change Using the SWAT Model: The Case of the Bystra Catchment, Poland

The paper presents the estimated changes in the soil water content, the total runoff, the sediment yield and the actual evapotranspiration for the small Bystra catchment in the east of Poland. The findings are based on the results of three simulations covering the years of 2041–2050. The simulations were based on a calibrated and validated SWAT model (2010–2017). The first variant covers just the climate change and the existing structure of soil cultivation for the three regional climate models supported by the EC-EARTH global climate model in the emission scenarios RCP4.5 and RCP8.5. Variants two and three are based on the first variant in terms of the changing climate. The second variant, however, involves placing a pond in each farm in the catchment, while the third variant involves designing huge reservoirs as a result of land consolidation. Variants two and three occur in five adaptation scenarios each. The first adaptation scenario (V2.1 and V3.1) involves only increasing the number of ponds on the farm or increasing the number of reservoirs for non-irrigated arable land crops, i.e., WWHT (winter cereals), BARL (spring cereals), CANP (rapeseed) and CRDY (other crops). The second adaptation scenario (V2.2 and V3.2) involves growing vegetables without irrigation (instead of cereals). The third adaptation scenario (V2.3 and V3.3) involves growing vegetables with irrigation (instead of cereals). The fourth adaptation scenario (V2.4 and V3.4) involves partial cultivation of vegetables and cereals. The fifth adaptation scenario (V2.5 and V3.5) involves partial cultivation of orchards and cereals. The adaptation scenarios of the irrigation of vegetables from deep water-bearing layers (second variant) or reservoirs (third variant) contribute to the increase in water content in the soil, especially in summer, in comparison with the adaptation scenarios for vegetable cultivation without irrigation. What is more, the actual evapotranspiration was higher in the adaptation scenarios involving irrigation than in scenarios without irrigation. It is known that the changes in water content in soil and the intensification of water erosion are gravely affected by modifications in crops and soil cultivation. A change from cereal cultivation to irrigated vegetable cultivation or orchards increased the water content in the soil in most climatic projections. However, the increase in the number of ponds in the second variant had little impact on the soil water content, actual evapotranspiration and overall runoff, while the erosion loss decreased. With the lower precipitation levels in the years 2041–2050 relative to 2010–2017, as presented in the emissive scenario RCP 4.5, the soil water content decreases by up to 14% for most variants. Total runoff for most variants will also be lower by 4–35%. The percentage change in sediment yield will fluctuate between −86% and 116%. On the other hand, the actual evapotranspiration for most variants will be higher. With higher precipitation levels in the years 2041–2050 relative to 2010–2017, as presented in the emissive scenario RCP 8.5, the soil water content changes slightly from −7% to +3%. Total runoff for most variants will also be higher by as much as 43%. Sediment yield for most scenarios may increase by 226%. The actual evapotranspiration for most variants will also be higher. Irrigation variants tend to increase soil available water while increasing evapotranspiration and total outflow in the catchment as compared to non-irrigated LULC. The largest increase in the soil water content is observed in most irrigation variants for RCP 4.5 (annual average 316–319 mm) (V2.3-V2.5, V3.2, and V3.3) and RCP 8.5 (annual average 326–327 mm) (V2.3-V2.5 and V3.3) as compared to V1 (BaU) (315 mm–RCP 4.5 and 324 mm–RCP 8.5) for the years 2041–2050. On the other hand, the lowest increase in soil water content is observed in the V3.5 variant, with an annual average of 292 mm for RCP 4.5 and an annual average of 311 mm for RCP 8.5. Thus, for future climate change scenarios, irrigation with water reservoirs (ponds and storage reservoirs) should be considered. The study proves the rationale behind building ponds in small catchments in order to increase water resources in a landscape and also to counteract adverse effects of climate changes, i.e., sediment outflow and surface water erosion.

Concentrations and Stoichiometric Characteristics of C, N, and P in Purple Soil of Agricultural Land in the Three Gorges Reservoir Region, China

Soil stoichiometry is an essential tool for understanding soil nutrient balance and cycling. Previous studies have recognized that some relationships were observed between particle size and carbon and nitrogen parameters. This study attempted to evaluate nutrient element concentrations and their stoichiometric ratios of surface soil (0–10 cm) under different land use types (forest, sloping arable land, paddy fields, and orchards). and different particle sizes (&lt;32 µm, &lt;63 µm, and &lt;125 µm) from a small typical hilly catchment (0.35 km2) in the Three Gorges Reservoir Region of China. The contents of soil organic carbon (SOC), total nitrogen (TN). and total phosphorus (TP) were measured, and the ratios of C:N, C:P, N:P were calculated. The results indicated that land use type and soil particle size have diverse impacts on the studied indexes (SOC, TN, TP, C:N, C:P, and N:P). Six indexes were significantly affected by land use type (p &lt; 0.01), while only C:N ratio was statistically influenced by soil particle size (p &lt; 0.05). Furthermore, several significant differences of studied parameters of four land use types grouped within three particle sizes were found. The concentrations of SOC (12.34~13.46 g kg−1), TN (1.27~1.59 g kg−1), and TP (0.71~0.92 g kg−1) in the study site were lower than the national average values of China. Moreover, the productivity in the study area was mainly limited by TN concentration. Additionally, the concentration of TP decreased obviously with the increase in particle size. Furthermore, various coupling relationships were validated by linear and nonlinear fitting among different indexes. At the small catchment scale, take forest as a reference, human activities have significant impact on C-N-P stoichiometry (p &lt; 0.05). Especially, tillage may reduce SOC and TN contents, leading to a decline in soil quality. Overall, our findings can provide a basis for rational utilization and sustainable development of land resources.

Research on Parameter Regionalization of Distributed Hydrological Model Based on Machine Learning

In the past decade, more than 300 people have died per year on average due to mountain torrents in China. Mountain torrents mostly occur in ungauged small and medium-sized catchments, so it is difficult to maintain high accuracy of flood prediction. In order to solve the problem of the low accuracy of flood simulation in the ungauged areas, this paper studies the influence of different methods on the parameter regionalization of distributed hydrological model parameters in hilly areas of Hunan Province. According to the terrain, landform, soil and land use characteristics of each catchment, we use Shortest Distance, Attribute Similarity, Support Vector Regression, Generative Adversarial Networks, Classification and Regression Tree and Random Forest methods to create parameter regionalization schemes. In total, 426 floods of 25 catchments are selected to calibrate the model parameters, and 136 floods of 8 catchments are used for verification. The results showed that the average values of the Nash–Sutcliffe coefficients of each scheme were 0.58, 0.64, 0.60, 0.66, 0.61 and 0.68, and the worst values were 0.27, 0.31, 0.25, 0.43, 0.35 and 0.59. The random forest model is the most stable solution and significantly outperforms other methods. Using the random forest model to regionalize parameters can improve the accuracy of flood simulation in ungauged areas, which is of great significance for flash flood forecasting and early warning.

Li isotopic seasonality in a small catchment at the northeastern Tibetan Plateau: Roles of hydrology and temperature dependency

Silicate weathering is critical to sustain our habitable planet. Lithium (Li) isotopes enable us to investigate the nature of silicate weathering. A number of riverine Li isotope (δ7Lirw) investigations have been made from polar to equatorial terrains, but there remains no consensus about the controlling mechanisms of both weathering and δ7Lirw. Here we investigated δ7Lirw response to climate by collecting weekly river water samples in a small catchment (the Buha River within the Lake Qinghai basin) on the northeastern Tibetan Plateau, with stable tectonic, lithology, and topography. In the hydrology year of 2007 of the Buha River, we find that during the dry seasons, δ7Lirw ratios show temperature dependency typically, when the groundwater fed the river. During the monsoon seasons, δ7Lirw were obviously lower than the temperature dependency predicted values, when abundant rock dissolved and thereby fresh Li release into rivers. We propose that the hydrology and temperature dependency together play important roles in regulating δ7Lirw ratios in such an alpine small catchment. The mechanism is that long residence time facilitates the equilibrium chemical and Li isotopic fractionation during the dry seasons, so a temperature dependency of δ7Lirw is achieved. In contrast, rapid erosion and weathering contribution of fresh rock-like δ7Li to river water would significantly decrease δ7Lirw ratios during the monsoon seasons. This hypothesis can better interpret previously reported data of seasonal δ7Lirw variation, as a superposition between temperature dependency and hydrology regulation on silicates weathering in the small catchments besides tectonics.

Trend Analysis of Selected Hydroclimatic Variables for the Hornad Catchment (Slovakia)

This study examines the trends in air temperature, precipitation and flow rates over a 50-year observation period (1961–2010) and compares two periods, 1961–1985 and 1986–2010. The research was carried out in terms of annual and monthly values. The research area is the Hornad River in Slovakia. The main aim of the study was to examine the evolution of precipitation, air temperature and flows in the Hornad River catchment area, as well as to identify the regions (sub-catchments) most vulnerable to climate change. Increasing trends in air temperature in the years 1961–2010 were found to be statistically significant (the Sen’s slope was between 0.0197 and 0.0239). On the other hand, a statistically significant downward trend in flows was recorded only at the Stratená station (a small mountain catchment, where the Sen’s slope was −0.0063). The remaining upward and downward trends were not statistically significant. Greater differences in the course of the trends were recorded on a monthly basis in individual multi-years. Increasing trends in air temperature were statistically significant from May to August in the period 1961–2010. No trends in precipitation were recorded in the period 1961–2010, and only an upward trend in precipitation was recorded in June from 1986–2010.