12 research outputs found

    Short-term streamflow forecasting using the feature-enhanced regression model

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    Reservoir inflow forecasting is extremely important for the management of a reservoir. In practice, accurate forecasting depends on the feature learning performance. To better address this issue, this paper proposed a feature-enhanced regression model (FER), which combined stack autoencoder (SAE) with long short-term memory (LSTM). This model had two constituents: (1) The SAE was constructed to learn a representation as close as possible to the original inputs. Through deep learning, the enhanced feature could be captured sufficiently. (2) The LSTM was established to simulate the mapping between the enhanced features and the outputs. Under recursive modeling, the patterns of correlation in the short term and dependence in the long term were considered comprehensively. To estimate the performance of the FER model, two historical daily discharge series were investigated, i.e., the Yangtze River in China and the Sava Dolinka River in Slovenia. The proposed model was compared with other machine-learning methods (i.e., the LSTM, SAE-based neural network, and traditional neural network). The results demonstrated that the proposed FER model yields the best forecasting performance in terms of six evaluation criteria. The proposed model integrates the deep learning and recursive modeling, and thus being beneficial to exploring complex features in the reservoir inflow forecasting. Moreover, for smaller catchments with significant torrential characteristics, more data are needed (e.g., at least 20 years) to effectively train the model and to obtain accurate flood-forecasting results

    Influence of hydrometeorological and vegetation conditions on the dynamics of nitrate flushing

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    Procesi kroženja enega najpomembnejŔih elementov, duŔika, so neposredno odvisni od količine padavin in njihove časovne ter prostorske razporeditve, saj voda predstavlja glavni transportni medij in gonilno silo Ŕtevilnih ekosistemskih procesov. Na manj kot 1 km2 velikem gozdnatem porečju v občini Polhov Gradec smo med aprilom 2018 in aprilom 2020 izvajali hkratne meritve padavin, pretokov, vsebnosti vode v tleh in kemizma vodotoka Kuzlovec. Meritve smo izvajali s kratkim časovnim korakom 20 minut. V doktorski disertaciji smo se osredotočili na analizo hidrometeoroloŔkih in sezonskih vplivov na spremembe koncentracij in iznose nitratnega duŔika s porečja. Za oceno vplivov smo uporabili multivariatne statistične analize, za identifikacijo procesov poti stekanja in virov nitratnega duŔika na porečju pa smo uporabili metodo časov zakasnitve na podlagi težiŔč diagramov in hkratne analize časovnih sprememb obravnavanih procesov. Količine iznesenega nitratnega duŔika v času padavinskih dogodkov so se izkazale kot pomemben člen v izračunih masnih bilanc. Z naraŔčanjem intenzitete in količine padavin pa lahko pričakujemo tudi večje spremembe koncentracij med dogodki, medtem ko se je pri količinah iznesenega duŔika poleg količine padavin kot pomemben dejavnik izkazalo trajanje padavin. Trajanje padavin je tudi eden najpomembnejŔih kazalnikov časa pojava težiŔča iznosa nitratnega duŔika in hidrograma. S krajŔimi in intenzivnejŔimi dogodki bi tako lahko pričakovali Ŕe hitrejŔi odziv porečja, kar bi pomenilo večje volumne vode in količine spranega nitratnega duŔika v krajŔem času. Raziskave na naravnih porečjih, ki pokrivajo Ŕirok spekter podnebnih dejavnikov in hidrogeoloŔkih lastnosti porečij, so zato ključnega pomena za oceno vplivov podnebnih sprememb in človekovih dejavnosti na vodni in duŔikov krog. Pri tem bodo ključnega pomena predvsem tehnologije, ki omogočajo meritve s kratkim časovnim korakom in ustrezno točnostjo. Kot se je izkazalo v pričujoči nalogi, lahko na podlagi pogostih meritev kemizma vode bolje sklepamo o prevladujočih procesih padavinskega odtoka in transporta snovi ter izboljŔamo njihovo konceptualno razumevanje.Processes of nitrogen cycling are directly dependent on the amount of precipitation and its temporal and spatial distribution, as water is the main transport medium and the driving force of many ecosystem processes. Between April 2018 and April 2020 we performed simultaneous measurements of precipitation, discharges, soil moisture, and the physico-chemical parameters of the Kuzlovec stream in a forested catchment in Polhov Gradec municipality. The area of the catchment is less than 1 km2. The measurements were performed with a short time step of 20 minutes. In the doctoral dissertation, we focused on the analysis of the hydrometeorological and seasonal effects on changes in concentrations and amounts of exported nitrate nitrogen. Multivariate statistical analyses were used to assess the effects. Moreover, the methodology of centroid time lags was used to identify the processes of runoff formation,. The amounts of nitrate nitrogen exported during the rainfall events proved to be an important element in the calculations of mass balances. If the intensity of precipitation increases, we can expect higher absolute changes of concentrations during events, whereas rainfall duration, besides rainfall amount, proved to be important for the amounts of exported nitrogen. The rainfall duration proved to be one of the most important indicators of the time of occurrence of the centroid of nitrate nitrogen export diagram and of the hydrograph. With shorter and more intense events, we could expect an even faster response of the river catchment, which would mean larger volumes of water and amounts of flushed nitrate nitrogen in a shorter time. Research in a natural river catchment, covering a wide range hydrometeorological factors is therefore crucial for assessing the impacts of climate change and human activities on the water and nitrogen cycle in the future. Technologies that enable measurements with a short time step and appropriate accuracy will be of key importance. As shown in this dissertation, based on high-frequency measurements of water chemistry we can better infer the predominant processes of rainfall-runoff and transport of nutrients and improve their conceptual understanding

    Temporal response of urban soil water content in relation to the rainfall and throughfall dynamics in the open and below the trees

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    Rainfall interception process is an important part of the biohydrological cycle, in which vegetation plays an important role by regulating the amount and dynamics of rainfall reaching the ground. In this paper, an event-based analysis is performed to discuss the influence of vegetation on dynamic of temporal response of soil volumetric water content (VWC) in the upper soil layer during rainfall events. More specifically, six events that occurred between 19 November 2021 and 30 June 2022, characterized by different hydro-meteorological and vegetation conditions, are analyzed based on continuous measurements of VWC in the open and below groups of two deciduous (Betula pendula Roth.) and two coniferous trees (Pinus nigra Arnold), as well as rainfall in the open and throughfall on an urban experimental plot in Ljubljana, Slovenia. VWC values at the upper depth (16 cm) were the highest under the birch tree, followed by the location in the open and under the pine tree. However, in the lowest depth (74 cm) VWC values were the lowest under the birch tree. VWC responses to rainfall and throughfall showed seasonal patterns related to the pre-event wetness conditions, with a faster occurrence of maximum VWC values in the leafless period. Additionally, rainfall amount and its dynamics during the event significantly affect the response, as VWC in general reaches its peak after the occurrence of more intense rainfall. Such an event-based analysis, offering an insight into the dynamics of the event development, is crucial and very beneficial for understanding of the biohydrological processes

    HidroloŔki vpogled v nehomogeno kraŔko porečje z analizo dinamičnega sistema

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    The hydrological process heterogeneity in karst catchments makes collecting sufficient information about the karst system properties extremely difficult. Consequently, the parameterization and application of currently available modeling approaches is highly uncertain in karst. We implemented a modified dynamical system approach and explored the possibilities to analyze, simulate and characterize karst springs and sinking streams in the heterogeneous Ljubljanica river catchment in Slovenia. The discharge sensitivity functions were used to simulate the hydrographs and identify the differences in the temporal dynamics of the discharge recession. Most of the derived karst springs and sinking streams discharge sensitivity functions express dual discharge recession behavior most likely controlled by the hydraulic conveyance characteristics of karst underground conduits. The implemented approach offers a high potential for advancement in karst hydrology by using basic discharge data for analyses of karst catchment characteristics and future planning of karst water resource management

    Comparison of different-energy-level abrasion in Los Angeles and micro-Deval apparatuses using mass loss and rounding of sediment particles

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    During the routing of coarse particles in sedimentary environments, the particles are subjected to abrasion, leading to mass loss and changes in the particlesā€™ morphology. The particles become more spherical, rounded, and smooth. Here, particlesā€™ (quarried dolomite) morphological evolution of three shape aspects (form, roundness, and texture) and the mass decreases obtained in two sets of experiments in two different setups are presented. Abrasion experiments were carried out in cycles. Between cycles, morphological parameters and mass losses were tracked. Abrasion was investigated with consideration of the energy and power the apparatuses used that the material was subjected to, in contrast to the often-used estimated travel distances or duration of the abrasion. The goal was to examine if the two setups can be comparable and inter-transferrable, also to other similar abrasion setups. The experimental equipment, a micro-Deval apparatus and a Los Angeles machine, are standardised and widely used. The applied tests were modified. Morphological/shape parameters were determined using dynamic image analysis. The results of the tests show the influence of machine power (energy introduction rate) on mass loss and morphological change. Los Angeles (high-energy) abrasion resulted in higher mass loss values than micro-Deval (low-energy) abrasion. The mass loss results can be brought to comparable values by a newly introduced mass- and powerdependent coefficient. Low-energy abrasion resulted in faster rounding than high-energy abrasion, whereas form stayed nearly the same. In contrast, form changed rapidly during high-energy abrasion

    Investigating the interplay of the hydrometeorological and seasonal forest vegetation role in regulating the nitrate flushing in a small torrential catchment

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    Forest vegetation is a very topical research subject as part of nature-based solutions for flood protection, soil erosion, water quality improvement, etc. However, limited capabilities of such measures are rarely investigated. Therefore, in this paper, study on the interplay of the hydrometeorological and seasonal forest vegetation role in regulating the nitrateā€‘nitrogen (NO3_3-N) flushing from a forested, torrential catchment is presented. For the 43 identified rainfall events it was found that there are no statistically significant seasonal differences in NO3_3-N concentrationshowever, during baseflow conditions such differences were noted. The rainfall events were described by 17 hydro-meteorological and vegetation variables to investigate similarities between the events from the NO3_3-N export point of view using clustering methods. Additionally, the relationship between explanatory and dependent variables, i.e. NO3_3-N concentration and export variables, was modelled. In the models, the first four principal components were used as explanatory variables after the reduction of the initial number of variables. It was found that phenological phases as indicators of the forest vegetation seasonal activity are generally not able to considerably influence the NO3_3-N concentration and flushing dynamics. The results indicate that during baseflow conditions, the influence of the forest vegetation in the torrential catchment becomes predominant. During rainfall events, the role of vegetation is blurred and might be generally considered as insignificant. The characteristics of rainfall events apparently exceed the limits of a forest\u27s ability to control NO3_3-N flushing. Given the pronounced impact of rainfall intensity on NO3_3-N flushing, the challenge for the future will be to mitigate the potential negative effects of climate change related impacts, especially through measures able to reduce the intensity of rainfall-runoff formation. The seasonal role of vegetation in diminishing the intensity of nutrient flushing in natural torrential catchments might be relatively constrained and probably also overwhelmed by the hydrometeorological conditions

    Investigation of low- and high-flow characteristics of karst catchments under climate change

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    It is not clear how projected climate change will impact the hydrological functioning of complex catchments that have significant karst characteristics. Therefore, in this paper we focused on the investigation of the low- and high-flow characteristics of the karst Ljubljanica River catchment. One smaller (51 km2^2) and one larger (1135 km2^2) catchment were selected in order to investigate the projected climate change impact on the hydrological conditions. For the investigation of the hydrological situation in the future, we used a lumped conceptual hydrological model. The model was calibrated using past measured daily data. Using the calibrated model, we investigated the impact of five different climate models outputs for the moderately optimistic scenario (RCP4.5). We investigated the situation in next 30-years periods: 2011-2040, 2041-2070, and 2071-2100. Several low and high-flow indices were calculated and compared. The results indicate that a summer precipitation decrease (i.e., 2011-2070) could lead to lower low-flow values for the investigated areas, which could increase the vulnerability of karst areas. Thus, additional focus should be given to water resource management in karst areas. On the other hand, mean flow could increase in the future. The same also applies for the high-flows where flood frequency analysis results indicate that a climate adaptation factor could be used for the hydrotechnical engineering design. However, differences among investigated models are large and show large variability among investigated cases

    Efficient calibration of a conceptual hydrological model based on the enhanced Gaussā€“Levenbergā€“Marquardt procedure

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    Various models were developed in the past to simulate different hydrological processes. However, discrepancies between simulated and observed values are still significant and pose a challenge to many researchers. Models contain many parameters that cannot be directly measured. The values of most of these parameters are determined in the calibration process conditioning the efficiency of such models. This paper introduces the use of the enhanced Gaussā€“Levenbergā€“Marquardt (GLM) procedure in combination with the singular value decomposition (SVD) and Tikhonov regularization to improve the process of hydrological model calibration. The procedure is tested on a freely available hydrological model using a synthetic dataset. Based on several efficiency measures, the GLM procedure, in combination with SVD and Tikhonov regularization, was found to provide efficient model history matching and almost perfect parameter calibration. Moreover, by comparing the results of the proposed procedure with the results of global evolutionary calibration procedures, it was found that the only calibration using the combined GLM procedure gave a perfect fit in low flows. Last but not least, the noise in the calculation results with the combined GLM method was practically the same in either the calibration or validation procedure, suggesting that only computational noise remained in the results

    Lag times as indicators of hydrological mechanisms responsible for NO3_3-N flushing in a forested headwater catchment

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    Understanding the temporal variability of the nutrient transport from catchments is essential for planning nutrient loss reduction measures related to land use and climate change. Moreover, observations and analysis of nutrient dynamics in streams draining undisturbed catchments are known to represent a reference point by which human-influenced catchments can be compared. In this paper, temporal dynamics of nitrate-nitrogen (NO3_3-N) flux are investigated on an event basis by analysing observed lag times between data series. More specifically, we studied lag times between the centres of mass of six hydrological and biogeochemical variables, namely discharge, soil moisture at three depths, NO3_3-N flux, and the precipitation hyetograph centre of mass. Data obtained by high-frequency measurements (20 min time step) from 29 events were analysed. Linear regression and multiple linear regression (MLR) were used to identify relationships between lag times of the above-mentioned processes. We found that discharge lag time (LAGQ_Q) and NO3_3-N flux lag time (LAGN_N) are highly correlated indicating similar temporal response to rainfall. Moreover, relatively high correlation between LAGN_N and soil moisture lag times was also detected. The MLR model showed that the most descriptive variable for both LAGN_N and LAGQ_Q is amount of precipitation. For LAGN_N, the change of the soil moisture in the upper two layers was also significant, suggesting that the lag times indicate the primarily role of the forest soils as the main source of the NO3_3-N flux, whereas the precipitation amount and the runoff formation through the forest soils are the main controlling mechanisms

    Data on 33 years of erroneous usage of rainfall erosivity equations

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    This paper describes the data gathered for a paper published in Earth-Science Reviews (DOI: 10.1016/j.earscirev.2023.104339) to address the problem of studies using incorrect equations to calculate rainfall erosivity (R factor), which can lead to issues related to land degradation, soil productivity loss, and biodiversity loss. The aim was to locate articles containing the incorrect equations and create a relational database that could be used to perform an in-depth analysis of the errors. Because the search target is an equation, it is impossible to directly query any literature database for the articles that contain the incorrect R equations. Therefore, a manual search of multiple databases was conducted. Subsequently, the literature search was broadened to identify the origin of the misuse of the R equations, and SQL (Structured Query Language) queries were formulated to understand why the errors continued to persist for a minimum of 33 years. The resulting entity-relationship-based Microsoft Access database was determined to be a valuable tool for performing in-depth analysis. It can be used to add incorrect studies and perform further analysis. It is suggested that further research should be conducted to determine the extent of the impact of these errors on soil erosion, ecosystems, and the environment
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