Typical Catchment Research Articles

Historical droughts in Irish catchments 1767–2016

AbstractRecent prolonged dry periods in summer 2018 and spring 2020 have reawakened interest in drought in Ireland, prompting questions regarding historical drought occurrence and potential long‐term risks. Employing 250 years of monthly precipitation and flow reconstructions, we investigate historical drought in Irish catchments evaluating the characteristics (number of events, duration, and deficits) of moderate, severe, and extreme droughts as well as the propagation of meteorological to hydrological drought. Using standardized indices, we identify three distinct catchment types. Cluster 1 catchments, located in the wetter northwest are characterized by small areas, low groundwater storage, and the highest frequency of hydrological drought relative to other catchments. Cluster 3 catchments, located in the drier east and southeast have larger areas, greater groundwater storage, the highest frequency of meteorological drought but the least hydrological droughts. However, once established, droughts in Cluster 3 tend to be more persistent with large accumulated deficits. Cluster 2 catchments, located in the southwest and west, are intermediate to Clusters 1 and 3, with hydrological droughts typically of shorter durations, reduced accumulated deficits but greater mean deficits. The most extreme droughts based on accumulated deficits across all catchments occurred in 1803–1806, 1854–1859, 1933–1935, 1944–1945, 1953–1954, and 1975–1977. Although not as severe, droughts in 1887–1888, 1891–1894, and 1971–1974 also appear as significant extremes. Changes in drought characteristics reveal a complex picture with the direction, magnitude, and significance of trends dependent on the accumulation period used to define drought, the period of record analysed, and the reference period used to standardize indices. Of particular note is a tendency towards shorter, more intense meteorological and hydrological droughts. Our findings offer important insight for drought and water management in Ireland given the paucity of extreme droughts in short observed river flow records.

Nuevas herramientas para mejorar la cobertura de vacunación antigripal en los pacientes con factores de riesgo

BackgroundInfluenza vaccination is one of the main interventions to prevent the flu. This study evaluates the impact of automated letter as a method of capturing patients at risk in influenza vaccination campaigns between 2013–2017. MethodsThis is a descriptive observational study in Sector I Zaragoza. Data analysis with SPSS and Excel. We studied 173,935 patients (> 65 years old or with a risk factor) between 2011 and 2017, comparing the type of catchment used for vaccination. Center 1 uses postal mail compared to Center 2 that uses regular information channels. ResultsSignificant differences were observed, with an increase in vaccination in center 1 compared to center 2 (center 1: 29.59%; center 2: 19.76%, p < 0.001). Significant differences are found when comparing the vaccination rates in center 1 pre-post intervention (p < 0.001). These differences are also significant when analyzing the risk groups: > 65 years, asthmatics, patients with COPD, diabetics and patients with coronary heart disease.78.3% of the center 1's surveys considerate quate the patient catchment via postal mail ConclusionsSending a letter to those patients at risk of severe complications from influenza is an effective measure to increase influenza vaccination in the primary care setting.

Distribution and influencing factors of soil organic carbon in a typical karst catchment undergoing natural restoration

Understanding the distribution patterns and controlling factors of soil organic carbon (SOC) in karst areas is important for soil carbon management. However, due to the wide variety of human activities and karst habitats, the factors influencing SOC in karst areas vary. A typical catchment undergoing natural restoration in the karst region of South China was investigated to determine the distribution and variation of soil properties and SOC stocks (SOCSs) under three types of terrain: a hillslope, a depression and a sinkhole. The factors influencing SOC under the different terrain types were determined by redundancy analysis and multiple linear regression modelling. The results indicated that terrain and hydrological conditions affect the distribution of SOC on the hillslope. The spatial heterogeneity of SOC and dissolved organic carbon (DOC) on the hillslope was high. Terrain type and land use differences significantly affected the SOC and DOC concentrations at the catchment scale. SOC loss was more serious in the depression due to agricultural activities, and SOC accumulation was more obvious on the hillslope due to its relatively long natural restoration period. The average SOCSs of the hillslope were 16.5% and 54.6% larger than those of the depression and sinkhole, respectively, and the average dissolved organic carbon stocks (DOCSs) were 70.6% and 179.7% larger, respectively. In addition, the impacts of environmental factors on SOC and DOC varied among the different terrain types. Soil texture and topography were the main factors controlling the distribution of SOC and DOC on the hillslope and in the whole catchment, and soil texture was the main factor controlling SOC at the catchment scale. In addition, soil loss through sinkholes may be an important carbon sink in karst areas. The results of this study are of great significance for evaluating soil carbon storage and vegetation restoration strategies in karst areas.

Spatial variation of event-based suspended sediment dynamics in the middle Yellow River basin, China

Event-based suspended sediment dynamics (ESSD) provides insights into soil erosion and sediment transport and signals of changing environments within catchments, but it is still poorly understood in the middle Yellow River basin (MYRB). This study focuses on the hysteresis relationship between suspended sediment concentration (SSC) and flow discharge (Q), interpreting the ESSD and its spatial variation. The datasets in the 1960s from 73 hydrologic gauging stations were analyzed as the baseline of the MYRB without experiencing significant climate change and human disturbances. The Q-SSC hysteresis loops were first analyzed in terms of their direction and shape, and the Lloyd et al.'s (2016a) hysteresis index (HI) was adopted to quantify the hysteresis characteristics. Two types of catchments have been identified across the MYRB in terms of the dominant hysteresis pattern and the sign of the HI value. The dominant loops of the Type A catchments are clockwise with positive HI values and located in the southernmost rock mountain regions; Type B appears elsewhere, i.e., in the softstone, aeolian, and loess regions, where most of the events present anticlockwise or complex loops with generally negative HI values. The HI follows an upward-concave parabolic curve with either mean annual precipitation (Pm) or vegetation cover (NDVI). Two sets of thresholds are determined as Pm or NDVI increases. At Pm = 670 mm or NDVI = 0.74, a transition from Type B to Type A occurs as the HI value changes from negative to positive because the vegetation cover is too high to change the catchment from non-limited to limited supply. At Pm = 490 mm or NDVI = 0.40, the negative HI value reaches its minimum, suggesting the maximum availability of sediment in Type B due to the change in the dominant factor of soil erosion from precipitation erosivity to erosion resistance of vegetation. This study highlights the overall dynamics of soil erosion and sediment transport in the MYRB, which helps prioritize watershed management measures on the Loess Plateau under a changing environment.

Characterizing the Stormwater Runoff Quality and Evaluating the Performance of Curbside Infiltration Systems to Improve Stormwater Quality of an Urban Catchment

The conveyance of stormwater has become a major concern for urban planners, considering its harmful effects for receiving water bodies, potentially disturbing their ecosystem. Therefore, it is important to characterize the quality of catchment outflows. This information can assist in planning for appropriate mitigation measures to reduce stormwater runoff discharge from the catchment. To achieve this aim, the article reports the field data from a typical urban catchment in Australia. The pollutant concentration from laboratory testing is then compared against national and international reported values. In addition, a stochastic catchment model was prepared using MUSIC. The study in particular reported on the techniques to model distributed curbside leaky wells with appropriate level of aggregation. The model informed regarding the efficacy of distributed curbside leaky well systems to improve the stormwater quality. The results indicated that catchment generated pollutant load, which is typical of Australian residential catchments. The use of distributed storages only marginally improves the quality of catchment outflows. It is because ability of distributed leaky wells depended on the intercepted runoff volume which is dependent on the hydrological storage volume of each device. Therefore, limited storage volume of current systems resulted in higher contributing area to storage ratio. This manifested in marginal intercepted volume, thereby only minimum reduction in pollutant transport from the catchment to outlet. Considering strong correlation between contributing impervious area and runoff pollutant generation, the study raised the concern that in lieu of following the policy of infill development, there can be potential increase in pollutant concentration in runoff outflows from Australian residential catchments. It is recommended to monitor stormwater quality from more residential catchments in their present conditions. This will assist in informed decision-making regarding adopting mitigations measures before considering developments.

Catchment properties controlling suspended sediment transport in wind-water erosion crisscross region

Study regionWuding River catchment, the wind-water erosion crisscross region on the Chinese Loess Plateau. Study focusThe wind-water erosion crisscross region suffers severe soil erosion in the world, and various catchment properties control fluvial processes. This study investigated suspended sediment (SS) transport characteristics in a typical catchment with two geomorphological types (aeolian sand and loess hilly). Lorenz curves and partial least-squares regression were used to quantify the SS transport characteristics and attributions. New hydrological insights for the regionThere were significant differences in the SS transport characteristics between the two geomorphological regions. In the aeolian sand region, the mean annual SS loads were much lower than that in the loess hilly region (P < 0.01) under similar precipitation and runoff conditions. Rivers in this region transported SS all year round. The relatively lower concentration indicated that extreme events did not dominate total SS load. Conversely, SS transport in the loess hilly region was highly concentrated during a few events in rainy season, with the largest 10% of the events transporting exceed 80% of the total SS load. Statistical analysis showed that drainage density, catchment slope, and soil texture were the dominant factors controlling SS load, while the concentration of SS transport events was more related to the perimeter-area fractal. These findings have important implications for fluvial sediment transport in arid and semi-arid environments.

Biodiversity and Sediment Contamination in Wet Stormwater Ponds Depending on Design and Catchment Characteristics

Stormwater ponds are a common way to handle stormwater and are used to retain pollutants through sedimentation. The ponds resemble small natural lakes and will be colonized by flora and fauna. How design with respect to age, ratio between wet volume and reduced catchment area and land use influences the retention and how biodiversity is affected was examined. Age and ratio were determined in 135 and 59 ponds, respectively, and 12 of these ponds were selected for studies of dry weight (DW), organic matter (OM), total phosphorus (TP) and aluminum (Al), zinc (Zn), copper (Cu), chromium (Cr), cadmium (Cd) and lead (Pb) in the sediment. Invertebrate biodiversity was determined by Shannon–Wiener index (H’) and Pielou Evenness (J). DW, OM, TP and metals in the sediment close to the outlet of the ponds were influenced by pond age and the volume/area ratio whereas the sediment in the inlet area was more affected by the catchment type. Biodiversity increased with increasing ratio, while age had no effect on the sediment biodiversity but some effect on the water phase biodiversity. Biodiversity decreased with higher OM and TP and tend to decrease with increasing metal content. Higher volume/area ratio results in less sediment accumulation which improves the biodiversity. More pollutants are accumulating with age, which negatively affects the biodiversity. In conclusion, pond ratio, catchment type and, to some extent, age effect the load of contaminants in the sediment and the pond biodiversity. Proper design and management are recommended as a mitigating measure.

Sampling uncertainty of UK design flood estimation

ABSTRACT The UK standard for estimating flood frequencies is outlined by the flood estimation handbook (FEH) and associated updates. Estimates inevitably come with uncertainty due to sampling error as well as model and measurement error. Using resampling approaches adapted to the FEH methods, this paper quantifies the sampling uncertainty for single site, pooled (ungauged), enhanced single site (gauged pooling) and across catchment types. This study builds upon previous progress regarding easily applicable quantifications of FEH-based uncertainty estimation. Where these previous studies have provided simple analytical expressions for quantifying uncertainty for single site and ungauged design flow estimates, this study provides an easy-to-use method for quantifying uncertainty for enhanced single site estimates.

Comprehensive vertical accuracy analysis of freely available DEMs for different landscape types of the Rur catchment, Germany

This study evaluates the vertical accuracy of nine freely available digital elevation models (DEMs) with a medium spatial resolution for a typical mid-latitude flat to hilly landscape in the Rur catchment in Germany. All datasets were evaluated with two reference datasets, a 1 m DEM and a highly precise set of elevation control points. The accuracy was evaluated with regard to different slopes, landforms and land use. The results reveal in flat areas an average error of 2–4 m which increases about two to three times in undulated terrain. Areas with dense tree cover show a mean error of 6–10 m. The highest accuracies were achieved by the SRTM DEM, followed by other DEMs that mainly implemented SRTM data. TanDEM-X and Copernicus DEM showed ambivalent results showing a higher ratio of existing errors in the elevation product for vegetation and water areas that prevent a higher overall accuracy of these DEMs.

Land use and land cover change-induced changes of sediment connectivity and their effects on sediment yield in a catchment on the Loess Plateau in China

The spatial distribution of landscape pattern in catchments has a great impact on the potential sediment detachment and transport capacity. In this study, a sediment connectivity model was applied to evaluate the effect of the spatial distribution of landscape pattern on the sediment transfer in a typical catchment on the Loess Plateau in China based on land use and topography data in 1964, 2004, and 2018. Thereupon, the impacts of changes in different land use types on sediment connectivity and those of sediment connectivity changes on sediment yield reduction in the catchment were quantified. The results showed that (i) grassland and slope farmland were the main land use types in the catchment, and a decrease of the slope farmland area and an increase of the vegetation coverage occurred from 1964 to 2018; (ii) compared with 1964, most parts of the catchment in 2004 and 2018 had an overall lower connectivity index (IC); (iii) the distribution of sediment connectivity presented obvious spatial variability. The hill slopes and tributary gullies tended to be relatively well connected, and the main gully was highly disconnected. Scenario simulations showed that the potential sediment reduction effect was 20%−45% for vegetation, and <10% for terraces or dam lands in 1964, 2004, and 2018. The effect of impounding sediment by check dams was not included in IC calculation in this study, and it was found that the sediment impounded by these dams accounted for about 16% of sediment discharge reduction during 1995–2004 and 1% during 2005–2018. The IC reduction was responsible for 84% of the decrease of sediment discharge during 1995–2004 and 99% during 2005–2018, reflecting that vegetation restoration and terrace construction on slopes has become the main drivers for reducing IC value and sediment yield.

A Systematic Analysis of the Interaction between Rain-on-Grid-Simulations and Spatial Resolution in 2D Hydrodynamic Modeling

A large number of 2D models were originally developed as 1D models for the calculation of water levels along the main course of a river. Due to their development as 2D distributed models, the majority have added precipitation as a source term. The models can now be used as quasi-2D hydrodynamic rainfall–runoff models (‘HDRRM’). Within the direct rainfall method (‘DRM’), there is an approach, referred to as ‘rain-on-grid’, in which input precipitation is applied to the entire catchment area. The study contains a systematic analysis of the model behavior of HEC-RAS (‘Hydrologic Engineering Center—River Analysis System’) with a special focus on spatial resolution. The rain-on-grid approach is applied in a small, ungauged, low-mountain-range study area (Messbach catchment, 2.13 km2) in Central Germany. Suitable model settings and recommendations on model discretization and parametrization are derived therefrom. The sensitivity analysis focuses on the influence of the mesh resolution’s interaction with the spatial resolution of the underlying terrain model (‘subgrid’). Furthermore, the sensitivity of the parameters interplaying with spatial resolution, like the height of the laminar depth, surface roughness, model specific filter-settings and the precipitation input-data temporal distribution, is analyzed. The results are evaluated against a high-resolution benchmark run, and further criteria, such as 1. Nash–Sutcliffe efficiency, 2. water-surface elevation, 3. flooded area, 4. volume deficit, 5. volume balance and 6. computational time. The investigation showed that, based on the chosen criteria for this size and type of catchment, a mesh resolution between 3 m to 5 m, in combination with a DEM resolution from 0.25 m to 1 m, are recommendable. Furthermore, we show considerable scale effects on flooded areas for coarser meshing, due to low water levels in relation to topographic height.

Linking recent changes in sediment yields and aggregate-associated organic matter sources from a typical catchment of the Loess Plateau, China

The historically environmental information of soil erosion and human activity is thoroughly “recorded” in deposited organic matter (OM) in aggregates within the catchment. Although the changes in sediment-associated organic carbon (OC) concentration and source have great impact on the stability and fate of eroded OM on Earth, the response of OM sources of sediment aggregate fluxes in eroding landscapes to land uses still remain unclear. In this study, we selected three sediment deposit profiles in a typically dam-controlled catchment of the Chinese Loess Plateau to trace the 60-year changes in sediment yields and then explored the historical distributions of aggregate-associated OM sources through using the fallout radioisotope dating (137Cs and 210Pbex) and the isotope mixing model based on aggregate size-specific 13C and 15N isotope signatures. The results showed that the deposition rates of sediment trapped the check dam displayed a decreasing trend with year except for an abrupt increase in 2013 over the past 60 year, ranging from 4.47 × 103 to 89.16 × 103 t km−2 yr−1. The average SOC and TN concentrations in deposit profile showed the following order of macroaggregates (> 0.25 mm, 9.55 g kg−1 for SOC and 0.81 g kg−1 for TN) > microaggregates (0.053–0.25 mm, 4.16 g kg−1 for SOC and 0.42 g kg−1 for TN) > silt-clay (< 0.053 mm, 2.41 g kg−1 for SOC and 0.33 g kg−1 for TN), despite there was a opposite trend of mass fraction in aggregate sizes. The data of 13C and C/N among aggregate sizes indicated that the OM in silt-clay fraction had higher decomposition rate than that of other aggregates. The modeling outputs further showed that cropland was the primary contributing sources to transported OM of aggregate flux, accounting for > 20% of the total. Our results demonstrated the influence of erosion processes and changes in land use on the sediment yield and aggregate-associated OM dynamics in this Loess region.

Predicting the outcomes of management strategies for controlling invasive river fishes using individual‐based models

Abstract The effects of biological invasions on native biodiversity have resulted in a range of policy and management initiatives to minimize their impacts. Although management options for invasive species include eradication and population control, empirical knowledge is limited on how different management strategies affect invasion outcomes. An individual‐based model (IBM) was developed to predict how different removal (‘culling’) strategies affected the abundance and spatial distribution of a virtual, small‐bodied, r‐selected alien fish (based on bitterling, Rhodeus sericeus) across three types of virtual river catchments (low/intermediate/high branching tributary configurations). It was then applied to nine virtual species of varying life‐history traits (r‐ to K‐selected) and dispersal abilities (slow/intermediate/fast) to identify trade‐offs between the management effort applied in the strategies (as culling rate and the number of patches it was applied to) and their predicted effects. It was also applied to a real‐world example, bitterling in the River Great Ouse, England. The IBM predicted that removal efforts were more effective when applied to recently colonized patches. Increasing the cull rate (proportion of individuals removed per patch), and its spatial extent was effective at controlling the invasive population; when both were relatively high, population eradication was predicted. The characteristics of the nine virtual species were the main source of variation in their predicted abundance and spatial distribution. No species were eradicated at cull rates below 70%. Eradication at higher cull rates depended on dispersal ability; slow dispersers required lower rates than fast dispersers, and the latter rapidly recolonized at low cull rates. The trade‐offs between management effort and the outcomes of the invasion were, generally, optimal when intermediate effort was applied to intermediate numbers of patches. In the Great Ouse, model predictions were that management interventions could restrict bitterling distribution by 2045 to 21% of the catchment (versus 90% occupancy without management). Synthesis and application. This IBM predicted how management efforts can be optimized against invasive fishes, providing a strong complement to risk assessments. We demonstrated that for a range of species' characteristics, culling can control and even eradicate invasive fish, but only if consistent and relatively high effort is applied.

Land Use Change and Farmers’ Sense of Place in Typical Catchment of the Loess Hilly and Gully Region of China

Clarifying the relationship between land use and farmers’ sense of place on a micro scale is significant for enriching the perspective of research on human–environment relationships. Therefore, this paper analyzed land use change and the sense of place of farmers and further explored the interaction between them in the Yangjuangou catchment of Liqu Town in Baota District, Shaanxi Province from 1984 to 2020. The results indicated that: (1) the change in croplands was the most significant, i.e., its share in the total area decreased by 40%, and the decrease in sloping fields was the highest. The average relative altitude of croplands has decreased. The change in ecological land was also more significant, showing an increasing trend. Overall, the exploitation of land resources has declined; (2) the intensity of the sense of place of local farmers fluctuated downwards. The intensity of place attachment and place dependence decreased, and the intensity of the place identity increased; and (3) the decline in the intensity of the place attachment and place dependence promoted the reduction of sloping fields, the growth of ecological land and abandoned fields. By comparison, the increase in ecological land and check dam land promoted an increase in the intensity of place identity for local farmers. This paper suggested that rural areas in the Loess Hilly and Gully Region should strengthen innovation in land use patterns and focus on sustainability of farmers’ livelihoods, in order to promote the harmonious development of human-environmental relations.

Performing Hydrological Monitoring at a National Scale by Exploiting Rain-Gauge and Radar Networks: The Italian Case

Hydrological monitoring systems relying on radar data and distributed hydrological models are now feasible at large-scale and represent effective early warning systems for flash floods. Here we describe a system that allows hydrological occurrences in terms of streamflow at a national scale to be monitored. We then evaluate its operational application in Italy, a country characterized by various climatic conditions and topographic features. The proposed system exploits a modified conditional merging (MCM) algorithm to generate rainfall estimates by blending data from national radar and rain-gauge networks. Then, we use the merged rainfall fields as input for the distributed and continuous hydrological model, Continuum, to obtain real-time streamflow predictions. We assess its performance in terms of rainfall estimates from MCM, using cross-validation and comparison with a conditional merging technique at an event-scale. We also assess its performance against rainfall fields from ground-based data at catchment-scale. We further evaluate the performance of the hydrological system in terms of streamflow against observed data (relative error on high flows less than 25% and Nash–Sutcliffe Efficiency greater than 0.5 for 72% and 46% of the calibrated study sections, respectively). These results, therefore, confirm the suitability of such an approach, even at national scale, over a wide range of catchment types, climates, and hydrometeorological regimes, and for operational purposes.

Micropollutants in Urban Stormwater Runoff of Different Land Uses

The main aim of this study was a survey of micropollutants in stormwater runoff of Berlin (Germany) and its dependence on land-use types. In a one-year monitoring program, event mean concentrations were measured for a set of 106 parameters, including 85 organic micropollutants (e.g., flame retardants, phthalates, pesticides/biocides, polycyclic aromatic hydrocarbons (PAH)), heavy metals and standard parameters. Monitoring points were selected in five catchments of different urban land-use types, and at one urban river. We detected 77 of the 106 parameters at least once in stormwater runoff of the investigated catchment types. On average, stormwater runoff contained a mix of 24 µg L−1 organic micropollutants and 1.3 mg L−1 heavy metals. For organic micropollutants, concentrations were highest in all catchments for the plasticizer diisodecyl phthalate. Concentrations of all but five parameters showed significant differences among the five land-use types. While major roads were the dominant source of traffic-related substances such as PAH, each of the other land-use types showed the highest concentrations for some substances (e.g., flame retardants in commercial area, pesticides in catchment dominated by one family homes). Comparison with environmental quality standards (EQS) for surface waters shows that 13 micropollutants in stormwater runoff and 8 micropollutants in the receiving river exceeded German quality standards for receiving surface waters during storm events, highlighting the relevance of stormwater inputs for urban surface waters.

Groundwater inflow in rivers as a controlling factor to surface water nitrate concentrations and impact of groundwater age distribution on response times for remediation strategies

Diffuse groundwater contamination by intense fertilizer use is a widespread problem in most of the agricultural regions in West-Europe and in many other countries worldwide. As a result elevated nitrate concentrations in groundwater are found, and as groundwater is the source of baseflow into rivers and streams, also surface waters show increased nitrate levels. Flanders in the north of Belgium is no exception and despite restrictions on the fertilizer use and remediation practices initiated in the mid-1990s, and still ongoing, in many stream monitoring points, peak concentrations are measured above the 50 mg/l criterium. In many monitoring stations there is apparently a long delay between the start of the restrictions and effect on water quality. Often this delay is related to high concentrations in the groundwater inflow and long residence and travel times of groundwater feeding the streams. To better understand this behavior and estimate response times a tool was developed that incorporates the main water flows in a typical catchment and considers the effects of varying groundwater ages. This tool is conceived as a parsimonious lumped parameter model, simple and easy enough to be used by many people but still capturing the main mechanisms end processes. In this paper the tool is explained and it is applied on two testcases in Flanders to show its performance.

A typology of Corsican headwater catchments based on multivariate analysis of morphometric characteristics

This article is a study of headwater catchments and streams that aims at a first morphological typology of such catchments for Corsica island. Such typology offers a base for various studies or assessments regarding, for instance, water management, geological hazards assessments or faunal and/or floral species conservation. Corsica island comprises 120 peaks over 2000 m above sea-level. Herein, the characteristics and developments of 83 Corsican headwater catchments found above 1200 m above sea-level are evaluated using a digital elevation model, a principal component analysis and a hierarchical cluster analysis based on 14 morphometric parameters. It appears that 65.31% of the data’s total variance is clarified by the first three principal components. On the first principal component maximum elevation, mean elevation, mean slope and Melton ratio are found opposed to area and perimeter. Moreover, a latitudinal gradient on the first principal component is confirmed by the supplementary variable latitude’s coordinate. On the second principal component the form factor is opposed to the Lemniscate ratio. The most representative catchment points are best highlighted in terms of the catchments of the seven main streams. The cluster analysis allows to divide the catchments into four groups or types, unequivocally reflecting the first principal component and emphasising the comparable results for the two analyses. These four types of catchments are numerically characterised by four main parameters, which are area, Melton ratio, mean elevation and mean slope. A first morphological typology for Corsican headwater catchments is proposed in accordance to both principal components and cluster analyses.

Evaluating Baseflow Simulation in the National Water Model: A Case Study in the Northern High Plains Region, USA

AbstractThe National Water Model (NWM) is a high‐resolution hydrological model capable of providing streamflow forecast at 2.7 million reaches across the conterminous United States (U.S.). It utilizes a conceptual (not physically explicit) module for estimating groundwater discharge (baseflow) to streams, and the baseflow module only allows for one‐way flux from the aquifer to the streams, with no interflow between surficial or groundwater catchments. This study evaluated the ability of the NWM to simulate baseflow in different geologic conditions with a case study in the Northern High Plains region. The study also evaluated two alternative formulations for the baseflow module in the NWM with the goal of improving simulated baseflow accuracy. The NWM simulated baseflow more accurately in a clayey catchment than in a sandy catchment. The model, however, over simulated baseflow during storm runoff events and under simulated during low flow events in both catchments. Analysis of groundwater recharge simulation showed that the NWM over simulated groundwater recharge for both catchment types, and reducing groundwater recharge using U.S. Geological Survey Baseflow Indexes improved the model performance for baseflow simulation, especially in the sandy catchment. Evaluation of the alteranative formulations showed that a modified Rorabaugh‐Rutledge formulation was able to improve the baseflow simulation with RMSE of 7.98 m3/s and R2 of 0.41 and also improved the timing of peak flows.

Implications of event-based loss model structure on simulating large floods

Event-based rainfall-runoff models used for design flood estimation and operational flood forecasting commonly represent losses (the amount of rainfall which does not appear as runoff) using lumped, parsimonious models. In gauged catchments, these loss values are typically estimated by calibrating models to observed flood events. Studies which compare loss models tend to focus on which model best reproduces observed events, however, flood modelling often requires estimating events larger than those used for calibration. It is thus of interest to examine how loss models perform over a range of flood magnitudes, particularly larger floods. Here, we evaluate the efficacy of different loss models by exploring the dependence between event magnitude and model performance. We assess four loss models commonly used in flood modelling: Initial Loss Continuing Loss (ILCL), Initial Loss Proportional Loss (ILPL), Soil Conservation Service Curve Number (SCSCN) and Probability Distributed Model (PDM).The four loss models were incorporated into a lumped rainfall runoff model that was calibrated to observed storm events for 35 small, rural Australian catchments using a total of 876 unique storm events. In calibration, ILPL was found to best reproduce observed hydrographs, however the difference in performance between the four different models in terms of NSE was small. Dependence between event magnitude and model performance was explored by re-simulating observed events with the loss model parameters fixed to represent typical catchment conditions. These typical parameters were estimated from the median of the observed parameter ranges in each catchment with the largest five events excluded so that the impact of extrapolating model parameters to events larger than which they were calibrated could be explored. When these typical parameters were applied to large flood events the ILCL model displayed minimal dependence between model performance and event magnitude. In contrast, ILPL, SCSCN and PDM all clearly displayed an underprediction bias which increased with increasing event size. We explain this behaviour through the loss model structure of ILCL where ongoing loss (the loss which occurs after runoff begins) is constant and independent of rainfall fvmagnitude. In contrast, the three remaining models represent ongoing loss as a proportion of rainfall. As the difference in magnitude between small and large floods increases with climate change, extrapolation of flood models is likely to become a more pertinent issue in the future. We conclude that loss models which are independent of event magnitude are better suited to flood modelling applications where extrapolation is required.