Hydrology and Earth System Sciences Discussions

Journal: Hydrology and Earth System Sciences Discussions

Abbreviation

Hydrol. earth syst. sci.

Publisher

Copernicus

ISSN

1812-2116
1812-2108

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Publications 1 - 10 of 23

Anthropogenic and catchment characteristic signatures in the water quality of Swiss rivers: a quantitative assessment
Botter, Martina; Burlando, Paolo; Fatichi, Simone (2018)
Hydrology and Earth System Sciences Discussions
The hydrological and biogeochemical response of rivers carries information about solute sources, pathways, and transformations in the catchment. We investigate long-term water quality data of eleven Swiss catchments with the objective to discern the influence of catchment characteristics and anthropogenic activities on delivery of solutes in stream water. Magnitude, trends and seasonality of water quality samplings of different solutes are evaluated and compared across catchments. Subsequently, the empirical dependence between concentration and discharge is used to classify different solute behaviors. Although the influence of catchment geology, morphology and size is sometime visible on in-stream solute concentrations, anthropogenic impacts are much more evident. Solute variability is generally smaller than discharge variability. The majority of solutes shows dilution with increasing discharge, especially geogenic species, while sediment-related solutes (e.g. Total Phosphorous and Organic Carbon species) show higher concentrations with increasing discharge. Both natural and anthropogenic factors impact the biogeochemical response of streams and, while the majority of solutes show identifiable behaviors in individual catchments, only a minority of behaviors can be generalized across catchments that exhibit different natural, climatic and anthropogenic features.
Studying catchment storm response using event and pre-event water volumes as fractions of precipitation rather than discharge
von Freyberg, Jana; Studer, Bjørn; Rinderer, Michael; et al. (2018)
Hydrology and Earth System Sciences Discussions
Temporal variability of subsurface stormflow formation
Kienzler, Peter; Naef, Felix (2007)
Hydrology and Earth System Sciences Discussions
Subsurface storm flow (SSF) can play a key role for the runoffgeneration at hillslopes.Quantifications of SSF suffer from the limited understanding of how SSF is formedand how it varies in time and space. This study concentrates on the temporal variabil-ity of SSF formation. Controlled sprinkling experiments at three experimental slopes were replicated with varying precipitation intensity and varying antecedent precipita-tion. SSF characteristics were observed with hydrometric measurements and tracerexperiments. SSF response was affected in different ways and to varying degree bychanges of precipitation intensity and antecedent precipitation. The study showed thatthe influence of antecedent soil moisture on SSF response depends on the type of SSF formation. Formation of subsurface stormflow was hardly influenced by the increaseof precipitation intensity. As a consequence, subsurface flow rates were not increasedby higher precipitation intensity. Different soil structures determined runoffformation atdifferent precipitation intensities. Saturation and flow formation occurred at the base ofthe soil, but also within the topsoil during high precipitation intensity. This implies that timing and magnitude of flow response can change substantially at different precipita-tion intensities
Effects of record length and resolution on the derived distribution of annual precipitation
Meier, Claudio I.; Moraga, Jorge Sebastián; Pranzini, Geri; et al. (2015)
Hydrology and Earth System Sciences Discussions
Traditional frequency analysis of annual precipitation requires the fitting of a proba-bility model to yearly precipitation totals. There are three potential problems with thisapproach: a long record (at least 25∼30 years) is required in order to fit the model,years with missing data cannot be used, and the data need to be homogeneous. To overcome these limitations, we test an alternative methodology proposed by Eagleson(1978), based on the derived distribution approach (DDA). This allows for better estimation of the probability density function (pdf) of annual rainfall without requiring longrecords, provided that high-resolution precipitation data are available to derive external storm properties. The DDA combines marginal pdfs for storm depth and inter-arrival time to arrive at an analytical formulation of the distribution of annual precipitation underthe assumption of independence between events. We tested the DDA at two temperate locations in different climates (Concepción, Chile, and Lugano, Switzerland), quantify-ing the effects of record length. Our results show that, as compared to the fitting of anormal or log-normal distribution, the DDA significantly reduces the uncertainty in annual precipitation estimates (especially interannual variability) when only short recordsare available. The DDA also reduces the bias in annual precipitation quantiles withhigh return periods. We also show that using precipitation data aggregated every 24 h,as commonly available at most weather stations, introduces a noticeable bias in the DDA. Our results point to the tangible benefits of installing high-resolution (hourly or less) precipitation gauges at previously ungauged locations. We show that the DDA,in combination with high resolution gauging, provides more accurate and less uncertain estimates of long-term precipitation statistics such as interannual variability andquantiles of annual precipitation with high return periods even for records as short as 5 years.
Understanding flood regime changes in Europe: A state of the art assessment
Hall, Julia; Arheimer, Berit; Borga, Marco; et al. (2013)
Hydrology and Earth System Sciences Discussions
Losing streams that are influenced by wastewater treatment plant effluents and combined sewer overflows (CSOs) can be a source of groundwater contamination. Released micropollutants such as pharmaceuticals, endocrine disrupters and other ecotoxicologically relevant substances as well as inorganic wastewater constituents can reach the groundwater, where they may deteriorate groundwater quality. This paper presents a method to quantify exfiltration mass flow rates per stream length unit Mex of wastewater constituents from losing streams by the operation of integral pumping tests (IPTs) up- and downstream of a target section. Due to the large sampled water volume during IPTs the results are more reliable than those from conventional point sampling. We applied the method at a test site in Leipzig (Germany). Wastewater constituents K+ and NO3− showed Mex values of 1241 to 4315 and 749 to 924 mg mstream−1 d−1, respectively, while Cl− (16.8 to 47.3 g mstream−1 d−1) and SO42− (20.3 to 32.2 g mstream−1 d−1) revealed the highest observed Mex values at the test site. The micropollutants caffeine and technical-nonylphenol were dominated by elimination processes in the groundwater between upstream and downstream wells. Additional concentration measurements in the stream and a connected sewer at the test site were performed to identify relevant processes that influence the concentrations at the IPT wells.
Time varying parameter models for catchments with land use change: the importance of model structure
Pathiraja, Sahani; Anghileri, Daniela; Burlando, Paolo; et al. (2017)
Hydrology and Earth System Sciences Discussions
Rapid population and economic growth in South-East-Asia has been accompanied by extensive land use change with consequent impacts on catchment hydrology. Modelling methodologies capable of handling changing land use conditions are therefore becoming ever more important, and are receiving increasing attention from hydrologists. A recently developed Data Assimilation based framework that allows model parameters to vary through time in response to signals of change in observations is considered for a medium sized catchment (2880 km27 ) in Northern Vietnam experiencing substantial but gradual land cover change. We investigate the efficacy of the method as well as the importance of the chosen model structure in ensuring the success of time varying parameter methods. The framework was utilized with two conceptual models (HBV and HyMOD) that gave good quality streamflow predictions during pre-change conditions. Although both time varying parameter models gave improved streamflow predictions under changed conditions compared to the time invariant parameter model, persistent biases for low flows were apparent in the HyMOD case. It was found that HyMOD was not suited to representing the modified baseflow conditions, resulting in extreme and unrealistic time varying parameter estimates. This work shows that the chosen model can be critical for ensuring the time varying parameter framework successfully models streamflow under changed land cover conditions. It also serves as an effective tool for separating the influence of climatic and land use change in retrospective studies where the lack of a paired control catchment precludes such an assessment.
Technical note: An improved discharge sensitivity metric for young water fractions
Gallart, Francesc; von Freyberg, Jana; Valiente, María; et al. (2019)
Hydrology and Earth System Sciences Discussions
Recent virtual and experimental investigations have shown that the young water fraction Fyw (i.e. the proportion of catchment outflow younger than circa 2–3 months) increases with discharge in most catchments. The discharge sensitivity of Fyw has been defined as the rate of increase in Fyw with increasing discharge (Q), and has been estimated by the linear regression slope between Fyw and Q, hereafter called DS(Q). The combined use of both metrics, Fyw and DS(Q), provides a promising method for catchment inter-comparison studies that seek to understand streamflow generation processes. Here we explore the discharge sensitivity of Fyw in the intensively sampled small Mediterranean research catchment Can Vila. Intensive sampling of high flows at Can Vila allows young water fractions to be estimated for the far upper tail of the flow frequency distribution. These young water fractions converge toward 1 at the highest flows, illustrating a conceptual limitation in the linear regression method for estimating DS(Q) as a metric of discharge sensitivity: Fyw cannot grow with discharge indefinitely, since the fraction of young water in discharge can never be larger than 1. Here we propose to quantify discharge sensitivity by the parameter of an exponential-type equation expressing how Fyw varies with discharge. The exponential parameter (Sd) approximates DS(Q) at moderate discharges where Fyw is well below 1; however, the exponential equation and its discharge sensitivity metric better capture the non-linear relationship between Fyw and Q and are robust with respect to changes in the range of sampled discharges, allowing comparisons between catchments with strongly contrasting flow regimes.
Distance in spatial interpolation of daily rain gauge data
Ahrens, Bodo (2005)
Hydrology and Earth System Sciences Discussions
Spatial interpolation of rain gauge data is important in forcing of hydrological simula-tions or evaluation of weather predictions, for example. The spatial density of availabledata sites is often changing with time. This paper investigates the application of sta-tistical distance, like one minus common variance of time series, between data sites5instead of geographical distance in interpolation. Here, as a typical representative of in-terpolation methods the inverse distance weighting interpolation is applied and the testdata is daily precipitation observed in Austria. Choosing statistical distance instead ofgeographical distance in interpolation of an actually available coarse observation net-work yields more robust interpolation results at sites of a denser network with actually10lacking observations. The performance enhancement is in or close to mountainousterrain. This has the potential to parsimoniously densify the currently available obser-vation network. Additionally, the success further motivates search for conceptual rain-orography interaction models as components of spatial rain interpolation algorithms inmountainous terrain.
The role of dew and radiation fog inputs in the local water cycling of a temperate grassland in Central Europe
Li, Yafei; Aemisegger, Franziska; Riedl, Andreas; et al. (2020)
Hydrology and Earth System Sciences Discussions
In a warmer climate, non-rainfall water (hereafter NRW) formed from dew and fog potentially plays an increasingly important role in temperate grassland ecosystems under the scarcity of precipitation over prolonged periods. Dew and radiation fog occur in combination during clear and calm nights, and both use ambient water vapor as a source. Research on the combined mechanisms involved in NRW inputs to ecosystems are rare, and the condensation of soil-diffusing vapor, as one of the NRW input pathways for dew formation, has hardly been studied at all. The aim of this paper is thus to investigate the different NRW input pathways into a temperate Swiss grassland at Chamau during prolonged dry periods in summer 2018. We measured the isotopic compositions (δ18O, δ2H, and d = δ2H − 8 · δ18O) of both ambient water vapor and the NRW droplets on leaf surfaces combined with eddy covariance and meteorological measurements during one dew-only and two combined dew and radiation fog events. We employed a simple two end-member mixing model using δ18O and δ2H to split the dew input pathways from different sources. Our results showed a decrease of 0.8–5.5 mmol mol−1 in volumetric water vapor mixing ratio and a decrease of 4.8–16.7 ‰ in ambient water vapor δ2H due to dew formation and radiation fog droplet deposition. A nighttime maximum in ambient water vapor δ18O (−15.5 ‰ to −14.3 ‰) and a 3.4–3.7 ‰ decrease in ambient water vapor d were observed for dew formation in unsaturated conditions. In conditions of slight super-saturation, a stronger decrease of ambient water vapor δ18O (0.3–1.5 ‰) and a minimum of ambient water vapor d (−6.0 ‰ to −4.7 ‰) were observed. The combined foliage NRW and ambient water vapor δ18O and δ2H suggested two different input pathways: (1) condensation of ambient water vapor and (2) of soil-diffusing vapor. The latter contributed 9–42 % to the total foliage NRW. The dew and radiation fog potentially produced 0.06–0.39 mm night−1 NRW gain on foliage, which was comparable with 2.8 mm day−1 daytime evapotranspiration. The ambient water vapor d was correlated and anti-correlated with ambient temperature and ambient relative humidity respectively, suggesting an only minor influence of large-scale air advection and highlighted the dominant role of local moisture as a source for ambient water vapor. Our results thus highlight the importance of NRW inputs to temperate grasslands during prolonged dry periods and reveal the complexity of the local water cycle in such conditions including different pathways of water deposition.
What can we learn from long-term groundwater data to improve climate change impact studies?
Stoll, Sebastian; Hendricks Franssen, Harrie-Jan; Barthel, Roland; et al. (2011)
Hydrology and Earth System Sciences Discussions
Future risks for groundwater resources, due to global change are usually analyzed bydriving hydrological models with the outputs of climate models. However, this modelchain is subject to considerable uncertainties. Given the high uncertainties it is es-sential to identify the processes governing the groundwater dynamics, as these processes are likely to affect groundwater resources in the future, too. Information aboutthe dominant mechanisms can be achieved by the analysis of long-term data, whichare assumed to provide insight in the reaction of groundwater resources to changingconditions (weather, land use, water demand). Referring to this, a dataset of 30 long-term time series of precipitation dominated groundwater systems in northern Switzerland and southern Germany is collected. In order to receive additional informationthe analysis of the data is carried out together with hydrological model simulations.High spatio-temporal correlations, even over large distances could be detected andare assumed to be related to large-scale atmospheric circulation patterns. As a resultit is suggested to prefer innovative weather-type-based downscaling methods to other stochastic downscaling approaches. In addition, with the help of a qualitative proce-dure to distinguish between meteorological and anthropogenic causes it was possibleto identify processes which dominated the groundwater dynamics in the past. It couldbe shown that besides the meteorological conditions, land use changes, pumping ac-tivity and feedback mechanisms governed the groundwater dynamics. Based on these findings, recommendations to improve climate change impact studies are suggested.

Publications 1 - 10 of 23

Journal: Hydrology and Earth System Sciences Discussions

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