The sensitivity of landscape evolution models to spatial and temporal rainfall resolution

Abstract. Climate is one of the main drivers for landscape evolution models (LEMs), yet its representation is often basic with values averaged over long time periods and frequently lumped to the same value for the whole basin. Clearly, this hides the heterogeneity of precipitation – but what impact does this averaging have on erosion and deposition, topography, and the final shape of LEM landscapes? This paper presents results from the first systematic investigation into how the spatial and temporal resolution of precipitation affects LEM simulations of sediment yields and patterns of erosion and deposition. This is carried out by assessing the sensitivity of the CAESAR-Lisflood LEM to different spatial and temporal precipitation resolutions – as well as how this interacts with different-size drainage basins over short and long timescales. A range of simulations were carried out, varying rainfall from 0.25 h  ×  5 km to 24 h  ×  Lump resolution over three different-sized basins for 30-year durations. Results showed that there was a sensitivity to temporal and spatial resolution, with the finest leading to > 100 % increases in basin sediment yields. To look at how these interactions manifested over longer timescales, several simulations were carried out to model a 1000-year period. These showed a systematic bias towards greater erosion in uplands and deposition in valley floors with the finest spatial- and temporal-resolution data. Further tests showed that this effect was due solely to the data resolution, not orographic factors. Additional research indicated that these differences in sediment yield could be accounted for by adding a compensation factor to the model sediment transport law. However, this resulted in notable differences in the topographies generated, especially in third-order and higher streams. The implications of these findings are that uncalibrated past and present LEMs using lumped and time-averaged climate inputs may be under-predicting basin sediment yields as well as introducing spatial biases through under-predicting erosion in first-order streams but over-predicting erosion in second- and third-order streams and valley floor areas. Calibrated LEMs may give correct sediment yields, but patterns of erosion and deposition will be different and the calibration may not be correct for changing climates. This may have significant impacts on the modelled basin profile and shape from long-timescale simulations.

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Unravelling daily human mobility motifs

Journal of The Royal Society Interface ◽

10.1098/rsif.2013.0246 ◽

2013 ◽

Vol 10 (84) ◽

pp. 20130246 ◽

Cited By ~ 217

Author(s):

Christian M. Schneider ◽

Vitaly Belik ◽

Thomas Couronné ◽

Zbigniew Smoreda ◽

Marta C. González

Keyword(s):

Time Scales ◽

Human Mobility ◽

Underlying Mechanism ◽

Mobility Patterns ◽

Daily Mobility ◽

Simple Rules ◽

Long Time ◽

Daily Scale ◽

Temporal And Spatial ◽

Spatial Trajectories

Human mobility is differentiated by time scales. While the mechanism for long time scales has been studied, the underlying mechanism on the daily scale is still unrevealed. Here, we uncover the mechanism responsible for the daily mobility patterns by analysing the temporal and spatial trajectories of thousands of persons as individual networks. Using the concept of motifs from network theory, we find only 17 unique networks are present in daily mobility and they follow simple rules. These networks, called here motifs, are sufficient to capture up to 90 per cent of the population in surveys and mobile phone datasets for different countries. Each individual exhibits a characteristic motif, which seems to be stable over several months. Consequently, daily human mobility can be reproduced by an analytically tractable framework for Markov chains by modelling periods of high-frequency trips followed by periods of lower activity as the key ingredient.

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Ice flow models and glacial erosion over multiple glacial–interglacial cycles

Earth Surface Dynamics Discussions ◽

10.5194/esurfd-2-389-2014 ◽

2014 ◽

Vol 2 (1) ◽

pp. 389-428

Author(s):

R. M. Headley ◽

T. A. Ehlers

Keyword(s):

Time Scales ◽

Landscape Evolution ◽

Numerical Models ◽

Higher Order ◽

Glacial Erosion ◽

Distinctive Features ◽

Flow Models ◽

Erosion Rates ◽

Long Time ◽

Order Of Magnitude

Abstract. Mountain topography is constructed through a variety of interacting processes. Over glaciological time scales, even simple representations of glacial-flow physics can reproduce many of the distinctive features formed through glacial erosion. However, detailed comparisons at orogen time and length scales hold potential for quantifying the influence of glacial physics in landscape evolution models. We present a comparison using two different numerical models for glacial flow over single and multiple glaciations, within a modified version of the ICE-Cascade landscape evolution model. This model calculates not only glaciological processes but also hillslope and fluvial erosion and sediment transport, isostasy, and temporally and spatially variable orographic precipitation. We compare the predicted erosion patterns using a modified SIA as well as a nested, 3-D Stokes-flow model calculated using COMSOL Multiphysics. Both glacial-flow models predict different patterns in time-averaged erosion rates. However, these results are sensitive to the climate and the ice temperature. For warmer climates with more sliding, the higher-order model has a larger impact on the erosion rate, with variations of almost an order of magnitude. As the erosion influences the basal topography and the ice deformation affects the ice thickness and extent, the higher-order glacial model can lead to variations in total ice-covered that are greater than 30%, again with larger differences for temperate ice. Over multiple glaciations and long-time scales, these results suggest that consideration of higher-order glacial physics may be necessary, particularly in temperate, mountainous settings.

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The Spread of Pollutants from Harbour Sludge Depots

Water Science & Technology ◽

10.2166/wst.1984.0096 ◽

1984 ◽

Vol 16 (3-4) ◽

pp. 623-633

Author(s):

M Loxham ◽

F Weststrate

Keyword(s):

Time Scales ◽

Molecular Diffusion ◽

Near Field ◽

Parameter Analysis ◽

Migration Patterns ◽

Long Time ◽

Dilution Effects ◽

Short Time ◽

Harbour Sludge

It is generally agreed that both the landfill option, or the civil techniques option for the final disposal of contaminated harbour sludge involves the isolation of the sludge from the environment. For short time scales, engineered barriers such as a bentonite screen, plastic sheets, pumping strategies etc. can be used. However for long time scales the effectiveness of such measures cannot be counted upon. It is thus necessary to be able to predict the long term environmenttal spread of contaminants from a mature landfill. A model is presented that considers diffusion and adsorption in the landfill site and convection and adsorption in the underlaying aquifer. From a parameter analysis starting form practical values it is shown that the adsorption behaviour and the molecular diffusion coefficient of the sludge, are the key parameters involved in the near field. The dilution effects of the far field migration patterns are also illustrated.

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Seasonal Estimates and Uncertainties of Snow Accumulation from CloudSat Precipitation Retrievals

Atmosphere ◽

10.3390/atmos12030363 ◽

2021 ◽

Vol 12 (3) ◽

pp. 363

Author(s):

George Duffy ◽

Fraser King ◽

Ralf Bennartz ◽

Christopher G. Fletcher

Keyword(s):

Time Scales ◽

Snow Water Equivalent ◽

Spatial Scales ◽

Snow Accumulation ◽

High Latitudes ◽

Percentage Points ◽

Snow Water ◽

Time Periods ◽

Predicted Values ◽

Good Agreement

CloudSat is often the only measurement of snowfall rate available at high latitudes, making it a valuable tool for understanding snow climatology. The capability of CloudSat to provide information on seasonal and subseasonal time scales, however, has yet to be explored. In this study, we use subsampled reanalysis estimates to predict the uncertainties of CloudSat snow water equivalent (SWE) accumulation measurements at various space and time resolutions. An idealized/simulated subsampling model predicts that CloudSat may provide seasonal SWE estimates with median percent errors below 50% at spatial scales as small as 2° × 2°. By converting these predictions to percent differences, we can evaluate CloudSat snowfall accumulations against a blend of gridded SWE measurements during frozen time periods. Our predictions are in good agreement with results. The 25th, 50th, and 75th percentiles of the percent differences between the two measurements all match predicted values within eight percentage points. We interpret these results to suggest that CloudSat snowfall estimates are in sufficient agreement with other, thoroughly vetted, gridded SWE products. This implies that CloudSat may provide useful estimates of snow accumulation over remote regions within seasonal time scales.

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Hydrological response to different time scales of climatological drought: an evaluation of the Standardized Precipitation Index in a mountainous Mediterranean basin

Hydrology and Earth System Sciences ◽

10.5194/hess-9-523-2005 ◽

2005 ◽

Vol 9 (5) ◽

pp. 523-533 ◽

Cited By ~ 156

Author(s):

S. M. Vicente-Serrano ◽

J. I. López-Moreno

Keyword(s):

Time Scales ◽

Hydrological Cycle ◽

Standardized Precipitation Index ◽

Precipitation Index ◽

Drought Indices ◽

Long Time ◽

The Standardized Precipitation Index ◽

Hydrological Droughts ◽

Different Time Scales

Abstract. At present, the Standardized Precipitation Index (SPI) is the most widely used drought index to provide good estimations about the intensity, magnitude and spatial extent of droughts. The main advantage of the SPI in comparison with other indices is the fact that the SPI enables both determination of drought conditions at different time scales and monitoring of different drought types. It is widely accepted that SPI time scales affect different sub-systems in the hydrological cycle due to the fact that the response of the different water usable sources to precipitation shortages can be very different. The long time scales of SPI are related to hydrological droughts (river flows and reservoir storages). Nevertheless, few analyses empirically verify these statements or the usefulness of the SPI time scales to monitor drought. In this paper, the SPI at different time scales is compared with surface hydrological variables in a big closed basin located in the central Spanish Pyrenees. We provide evidence about the way in which the longer (>12 months) SPI time scales may not be useful for drought quantification in this area. In general, the surface flows respond to short SPI time scales whereas the reservoir storages respond to longer time scales (7–10 months). Nevertheless, important seasonal differences can be identified in the SPI-usable water sources relationships. This suggests that it is necessary to test the drought indices and time scales in relation to their usefulness for monitoring different drought types under different environmental conditions and water demand situations.

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Nonlinearities of heart rate variability in animal models of impaired cardiac control: contribution of different time scales

Journal of Applied Physiology ◽

10.1152/japplphysiol.00059.2017 ◽

2017 ◽

Vol 123 (2) ◽

pp. 344-351 ◽

Cited By ~ 14

Author(s):

Luiz Eduardo Virgilio Silva ◽

Renata Maria Lataro ◽

Jaci Airton Castania ◽

Carlos Alberto Aguiar Silva ◽

Helio Cesar Salgado ◽

...

Keyword(s):

Nonlinear Dynamics ◽

Heart Rate ◽

Heart Rate Variability ◽

Time Scales ◽

Multiscale Entropy ◽

Time Frequency ◽

Cardiac Control ◽

Long Time ◽

Nonlinear Features ◽

Short Time

Heart rate variability (HRV) has been extensively explored by traditional linear approaches (e.g., spectral analysis); however, several studies have pointed to the presence of nonlinear features in HRV, suggesting that linear tools might fail to account for the complexity of the HRV dynamics. Even though the prevalent notion is that HRV is nonlinear, the actual presence of nonlinear features is rarely verified. In this study, the presence of nonlinear dynamics was checked as a function of time scales in three experimental models of rats with different impairment of the cardiac control: namely, rats with heart failure (HF), spontaneously hypertensive rats (SHRs), and sinoaortic denervated (SAD) rats. Multiscale entropy (MSE) and refined MSE (RMSE) were chosen as the discriminating statistic for the surrogate test utilized to detect nonlinearity. Nonlinear dynamics is less present in HF animals at both short and long time scales compared with controls. A similar finding was found in SHR only at short time scales. SAD increased the presence of nonlinear dynamics exclusively at short time scales. Those findings suggest that a working baroreflex contributes to linearize HRV and to reduce the likelihood to observe nonlinear components of the cardiac control at short time scales. In addition, an increased sympathetic modulation seems to be a source of nonlinear dynamics at long time scales. Testing nonlinear dynamics as a function of the time scales can provide a characterization of the cardiac control complementary to more traditional markers in time, frequency, and information domains. NEW & NOTEWORTHY Although heart rate variability (HRV) dynamics is widely assumed to be nonlinear, nonlinearity tests are rarely used to check this hypothesis. By adopting multiscale entropy (MSE) and refined MSE (RMSE) as the discriminating statistic for the nonlinearity test, we show that nonlinear dynamics varies with time scale and the type of cardiac dysfunction. Moreover, as complexity metrics and nonlinearities provide complementary information, we strongly recommend using the test for nonlinearity as an additional index to characterize HRV.

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Relationship between temporal and spatial averages in grid turbulence

Journal of Fluid Mechanics ◽

10.1017/jfm.2013.351 ◽

2013 ◽

Vol 730 ◽

pp. 593-606 ◽

Cited By ~ 9

Author(s):

L. Djenidi ◽

S. F. Tardu ◽

R. A. Antonia

Keyword(s):

Strong Support ◽

Statistical Properties ◽

Grid Turbulence ◽

Mean Flow ◽

Lateral Direction ◽

Ergodic Hypothesis ◽

Long Time ◽

The Mean ◽

Temporal And Spatial ◽

Boltzmann Method

AbstractA long-time direct numerical simulation (DNS) based on the lattice Boltzmann method is carried out for grid turbulence with the view to compare spatially averaged statistical properties in planes perpendicular to the mean flow with their temporal counterparts. The results show that the two averages become equal a short distance downstream of the grid. This equality indicates that the flow has become homogeneous in a plane perpendicular to the mean flow. This is an important result, since it confirms that hot-wire measurements are appropriate for testing theoretical results based on spatially averaged statistics. It is equally important in the context of DNS of grid turbulence, since it justifies the use of spatial averaging along a lateral direction and over several realizations for determining various statistical properties. Finally, the very good agreement between temporal and spatial averages validates the comparison between temporal (experiments) and spatial (DNS) statistical properties. The results are also interesting because, since the flow is stationary in time and spatially homogeneous along lateral directions, the equality between the two types of averaging provides strong support for the ergodic hypothesis in grid turbulence in planes perpendicular to the mean flow.

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