1,721,148 research outputs found
Fluttuazioni Stocastiche della costante di recessione e struttura probabilistica dei deflussi
No full textCatchment mixing processes and travel time distributions
No full textThis work focuses on the description and the use of the probability density functions (pdfs) of travel, residence and evapotranspiration times, which are comprehensive descriptors of the fate of rainfall water particles traveling through catchments, and provide key information on hydrologic flowpaths, partitioning of precipitation, circulation and turnover of pollutants. Exploiting some analytical solutions to the transport problem derived by Botter et al. (2011), this paper analyzes the features of travel, residence and evapotranspiration time pdfs resulting from different assumptions on the mixing processes occurring during streamflow formation and plant uptake (namely, complete mixing and translatory flow). The ensuing analytical solutions are analyzed through numerical Monte Carlo simulations of a stochastic model of soil moisture and streamflow dynamics. Travel and residence time pdfs are shown to be time-variant as they mirror the variability of the relevant hydrological fluxes. In particular, the temporal fluctuations of the mean residence time are shown to reflect rainfall dynamics, whereas the variability of the mean travel time is chiefly driven by streamflow dynamics, with lower frequency and higher amplitude fluctuations. Dry climates enhance the effect of the type of mixing on catchment transport features (e. g., mean travel times and seasonal dynamics of stream concentrations). The implications for the interpretation of tracer experiments are also discussed, showing through specific examples that models disregarding nonstationarity may significantly misestimate travel time pdfs
Flow regime shifts in the Little Piney Creek (US)
No full textNon-stationarity of climate drivers and soil-use strongly affects the hydrologic cycle, producing significant inter-annual and multi-decadal fluctuations of river flow regimes. Understanding the temporal trajectories of hydrologic regimes is a key issue for the management of freshwater ecosystems and the security of human water uses. Here, long-term changes in the seasonal flow regime of the Little Piney creek (US) are analyzed with the aid of a stochastic mechanistic approach that expresses analytically the streamflow distribution in terms of a few measurable hydroclimatic parameters, providing a basis for assessing the impact of climate and landscape modifications on water resources. Mean rainfall and streamflow rates exhibit a pronounced inter-annual variability across the last century, though in the absence of clear sustained drifts. Long-term modifications of streamflow regimes across different periods of 2 and 8 years are likewise significant. The stochastic model is able to reasonably reproduce the observed 2-years and 8-years regimes in the Little Piney creek, as well as the corresponding inter-annual variations of streamflow probability density. The study evidences that a flow regime shift occurred in the Little Piney creek during the last century, with erratic regimes typical of the 30s/40s that had been progressively replaced by persistent flow regimes featured by more dumped streamflow fluctuations. Causal drivers of regime shift are identified as the increase of the frequency of events (a byproduct of climate variability) and the decrease of recession rates (induced by a decrease of cultivated lands). The approach developed offers an objective basis for the analysis and prediction of the impact of climate/landscape change on water resources
Stochastic recession rates and the probabilistic structure of stream flows
No full textThis paper investigates the impact of interevent variability of streamflow recession
rates on two key streamflow statistics, namely, the equilibrium probability density function
(pdf) and the autocorrelation. The relevance of the problem lies in the need to quantify
and predict streamflow availability, on the basis of measurable rainfall and landscape
attributes, by explicitly incorporating the stochasticity of the underlying climate and
transport processes. Novel expressions for the seasonal pdf and the autocorrelation of the
daily streamflows are derived by incorporating the randomness of the recession rates into a
probabilistic framework where the streamflow fluctuations are explicitly related to the
intermittency of the rainfall forcing. The presence of stochastic recession time constants is
shown to impact only the third‐ and higher‐order moments of the probability density
function of the daily streamflows, without altering the mean and the variance of the pdf.
A remarkable effect is instead produced on the correlation structure, which may exhibit
long‐term persistence even in the presence of a weak randomness of the recession rate.
A relevant case study is then discussed to show that incorporating the stochasticity of
the recession time constant leads to an improvement of the model ability to capture the
behavior of the equilibrium streamflow pdf and of the underlying correlation function
Contrasting signatures of distinct human water uses in regulated flow regimes
Full text linkIn the last century, about 50,000 dams have been constructed all around the world, and regulated rivers are now pervasive throughout the Earth’s landscapes. Damming has produced global-scale alterations of the hydrologic cycle, inducing severe consequences on the ecological and morphological equilibrium of streams. However, a recognizable link between specific uses of reservoirs and their impact on flow regimes has not been disclosed yet. Here, extensive hydrological data are integrated with a physically-based model to investigate hydrological alterations downstream of 47 isolated dams in the Central Eastern U.S. Our results reveal a strong connection between the anthropogenic use and the hydrological impact of dams. Flood control reduces the temporal variability and spatial heterogeneity of river flows proportionally to the specific capacity allocated to mitigate floods (i.e., capacity scaled to the average inflow). Conversely, water supply increases the relative variability and regional heterogeneity of streamflows proportionally to the relative amount of withdrawn inflow. Accordingly, downstream of our multipurpose reservoirs the impact of regulation on streamflow variability is smoothed due to the compensating effect of flood control and water supply. Nevertheless, reservoirs with high storage capacity and overlapping uses produce regulated hydrographs that increase their unpredictability for larger aggregation periods and, thus, resemble an autocorrelated red noise. These findings suggest that the increase of freshwater demand could redefine the cumulative effects of dams at regional scale, reshaping the trajectories of eco-morphological alteration of dammed rivers
Physics-based hydrological modeling of the joint variations of stream network length and catchment discharge
Full text linkImpacts of surface runoff generation processes on stream network dynamics: insights from physics-based modelling
Full text linkModeling of thermal runoff response from an asphalt-paved plot in the framework of the mass response functions
No full textDuring hot summer months, impervious surfaces within urban areas may store
significant amounts of thermal energy, which may be rapidly transferred to stream waters
during runoff events. Modeling of heat release from impervious areas to stream waters
thus represents a first, necessary step to quantify possible negative impacts of increased
stream water temperature on nearby aquatic ecosystems. In this paper, a stochastic
Lagrangian approach is developed to simulate heat transfer from an impermeable surface
to runoff. The approach is based on the framework of the mass response functions
(MRFs), which was originally developed for modeling nonpoint source pollutant transport
in watersheds. The MRF approach has been adapted to describe heat transfer from
impervious surfaces to runoff by coupling a heat balance at the asphalt/water interface and
a one-dimensional heat diffusion equation within the asphalt. The model incorporates a
simplified, physically based description of all the heat fluxes possibly affecting the
ensuing thermal response of impervious areas (e.g., solar radiation and evaporation). The
model was applied to an asphalt-paved plot of 90 m2 where it was able to accurately
reproduce the temperature variation of the asphalt surface and runoff during an artificially
produced rainfall event. Model prediction uncertainty introduced by the estimate of some
key parameters involved in the heat balance is analyzed by sensitivity analysis and by
checking a posteriori the consistency of the estimated heat fluxes through an overall heat
conservation equation. The effect of the heat diffusivity on the surface temperature
response to rainfall input was also examined, showing that the effect could be significant
depending on vertical temperature distributions of the plot
Looking below the ground: analyzing the processes that drive spatiotemporal variation of wet channels in dynamic river networks using a physics-based hydrological model
No full textNonpoint source transport models from empiricism to coherent theoretical frameworks
No full textBasin-scale transport of reactive solute species is studied through a class of stochastic models, termed mass response functions, which incorporate simplified concepts of chemical, physical or biological nonequilibrium kinetics into the theory of the hydrologic response. Here we examine the development of the field since its inception dealing with empirical approaches, a subject to which Giuseppe Bendoricchio actively contributed, and conclude that a coherent theoretical framework nowexists that allows to address large-scale transport problems for catchment studies where geomorphological and hydrological complexity is not simply ignored
- …
