Unravelling the process controls of the spatial coherence of precipitation

2020 ◽  
Author(s):  
Hannes Müller-Thomy ◽  
Korbinian Breinl ◽  
David Lun ◽  
Günter Blöschl
Keyword(s):  
Spatial Coherence ◽  
Separation Distance ◽  
Time Dependent ◽  
Ungauged Catchments ◽  
Self Organizing Maps ◽  
Mountainous Regions ◽  
Observational Network ◽  
Time Dependencies ◽  
Synthetic Precipitation ◽  
Low Dimensional

<p>Precipitation is a key input variable for precipitation-runoff models. For catchments without precipitation observations generating rainfall fields is a possibility to enable precipitation-runoff simulations. These synthetic precipitation fields have to reproduce the spatial precipitation distribution adequately, especially at large catchment scales. Since the spatial precipitation coherence in ungauged catchments is unknown, it has to be transferred from an existing observational network. Ideally, the meteorological regime of the area of the observational network should be similar to that of the ungauged catchment in terms of the processes and factors controlling the spatial precipitation coherence.</p><p>This study identifies these processes and conceptualises them for rainfall modelling. We analyse precipitation time series of 1200 stations in the Greater Alpine Region (including Austria and Southern Germany, ~300,000 km²). Precipitation data subsets are constructed based on space-dependent (including climate zone, land use, altitude, slope, exposition) and time-dependent factors (seasons, circulation patterns, temperature). The analyses are carried out for different temporal resolutions (1, 12 and 24 hours) to unravel possible time-dependencies. The spatial precipitation coherence is represented by bivariate characteristics (Pearson’s correlation coefficient, continuity ratio, probability of occurrence) as a function of station separation distance. Uncertainty and variability of the spatial coherence are quantified via function spaces. Self-organizing maps are applied to translate the multi- dimensional results into low-dimensional maps.</p><p>In the low lands of the study domain, time-dependent factors are expected to influence the spatial precipitation coherence stronger than space-dependent factors, while in the mountainous regions the space-dependent factors will have a stronger influence due to the air movement being forced by the topography.</p>

scholarly journals Hortonian runoff closure relations for geomorphologic response units: evaluation against field data

2013 ◽  
Vol 17 (7) ◽  
pp. 2981-3004 ◽  
Author(s):  
E. Vannametee ◽  
D. Karssenberg ◽  
M. R. Hendriks ◽  
M. F. P. Bierkens
Keyword(s):  
Scale Effects ◽  
Local Scale ◽  
Runoff Generation ◽  
Catchment Scale ◽  
Ungauged Catchments ◽  
Closure Relation ◽  
Physically Based ◽  
Low Dimensional ◽  
Hortonian Runoff ◽  
Ks Values

Abstract. This paper presents an evaluation of the closure relation for Hortonian runoff, proposed in Vannametee et al. (2012), that incorporates a scaling component to explicitly account for the process heterogeneity and scale effects in runoff generation for the real-world case studies. We applied the closure relation, which was embedded in an event-based lumped rainfall–runoff model, to a 15 km2 catchment in the French Alps. The catchment was disaggregated into a number of landform units, referred to as Geomorphologic Response Units (GRUs), to each of which the closure relation was applied. The scaling component in the closure relation was identified using the empirical relations between rainstorm characteristics, geometry, and local-scale measurable properties of the GRUs. Evaluation of the closure relation performance against the observed discharge shows that the hydrograph and discharge volume were quite satisfactorily simulated even without calibration. Performance of the closure relation can be mainly attributed to the use of scaling component, as it is shown that our closure relation outperforms a benchmark closure relation that lacks this scaling component. The discharge prediction is significantly improved when the closure relation is calibrated against the observed discharge, resulting in local-scale GRU-properties optimal for the predictions. Calibration was done by changing one local-scale observable, i.e. hydraulic conductivity (Ks), using a single pre-factor for the entire catchment. It is shown that the calibrated Ks values are somewhat comparable to the observed Ks values at a local scale in the study catchment. These results suggest that, in the absence of discharge observations, reasonable estimates of catchment-scale runoff responses can possibly be achieved with the observations at the sub-GRU (i.e. plot) scale. Our study provides a platform for the future development of low-dimensional, semi-distributed, physically based discharge models in ungauged catchments.

scholarly journals Dynamic spatio-temporal generation of large-scale synthetic gridded precipitation: with improved spatial coherence of extremes

2019 ◽  
Vol 34 (9) ◽  
pp. 1369-1383 ◽  
Author(s):  
Dirk Diederen ◽  
Ye Liu
Keyword(s):  
Large Scale ◽  
Spatial Coherence ◽  
Original Data ◽  
Return Level ◽  
Data Sets ◽  
Large Set ◽  
Precipitation Data ◽  
Data Set ◽  
Spatio Temporal ◽  
Synthetic Precipitation

Abstract With the ongoing development of distributed hydrological models, flood risk analysis calls for synthetic, gridded precipitation data sets. The availability of large, coherent, gridded re-analysis data sets in combination with the increase in computational power, accommodates the development of new methodology to generate such synthetic data. We tracked moving precipitation fields and classified them using self-organising maps. For each class, we fitted a multivariate mixture model and generated a large set of synthetic, coherent descriptors, which we used to reconstruct moving synthetic precipitation fields. We introduced randomness in the original data set by replacing the observed precipitation fields in the original data set with the synthetic precipitation fields. The output is a continuous, gridded, hourly precipitation data set of a much longer duration, containing physically plausible and spatio-temporally coherent precipitation events. The proposed methodology implicitly provides an important improvement in the spatial coherence of precipitation extremes. We investigate the issue of unrealistic, sudden changes on the grid and demonstrate how a dynamic spatio-temporal generator can provide spatial smoothness in the probability distribution parameters and hence in the return level estimates.

Dynamics of counter-rotating vortex pairs in stratified and sheared environments

1998 ◽  
Vol 361 ◽  
pp. 189-236 ◽  
Author(s):  
J. F. GARTEN ◽  
S. ARENDT ◽  
D. C. FRITTS ◽  
J. WERNE
Keyword(s):  
Spatial Coherence ◽  
Internal Gravity Wave ◽  
Vortex Pair ◽  
Propagation Speed ◽  
Reynolds Numbers ◽  
Separation Distance ◽  
Wave Radiation ◽  
Vertical Propagation ◽  
Vertically Propagating ◽  
Background Shear

The evolution of a vertically propagating vortex pair in stratified and sheared environments is studied with a two-dimensional numerical model. We consider a range of Froude (Fr) and Richardson (Ri) numbers, and a limited number of Reynolds numbers (Re). We find that stratification causes the formation of counter-sign vorticity around each of the original vortices through baroclinic production. At higher Fr, this wake vorticity advects the primary vortices closer together, decreasing their separation distance and increasing their vertical propagation speed, as predicted by Crow (1974) and Scorer & Davenport (1970). For these higher values of Fr, the wake vorticity also participates in an instability of the primary vortex pair, with the direction of propagation of the pair oscillating about the vertical. We term this instability the vortex head instability to distinguish it from the jet instabilities to which the wake itself is also susceptible. At lower Fr, internal gravity wave radiation dominates, and the intensity and spatial coherence of each vortex is rapidly reduced.When a mean horizontal flow having constant shear is present in an unstratified fluid, we find that the vortices eventually rotate about one another with the same rotational sense as the background shear flow, as predicted in Lissaman et al. (1973). When stratification is also present, we find that the distribution of baroclinically generated wake vorticity is asymmetric, which sometimes leads to the emergence of a solitary vortex with the same sign as the background shear vorticity (depending on the values of Fr, Ri, and Re). Our limited survey of parameter space indicates that a solitary vortex emerges more rapidly for smaller values of Ri, smaller values of Fr, and/or larger values of Re.

DYNAMIC SPIN TRANSPORT IN NONMAGNETIC SEMICONDUCTOR SYSTEMS

2006 ◽  
Vol 20 (08) ◽  
pp. 869-895 ◽  
Author(s):  
CHI-SHUNG TANG
Keyword(s):  
Spin Transport ◽  
Transport Model ◽  
Direct Detection ◽  
Spin Current ◽  
Orbit Interaction ◽  
Time Dependent ◽  
Drift Diffusion Model ◽  
Drift Diffusion ◽  
Dynamic Spin ◽  
Low Dimensional

We present a brief review to our recent study concerning dynamic spin transport induced by AC-biased gate in low-dimensional semiconductor systems, in which dynamic spin-orbit interaction plays a crucial role. We construct a Boltzmann spin-transport model and a spin-drift-diffusion model to describe the time-dependent spin transport starting with the framework of Keldysh formalism. Methods for the generation and direct detection of spin current are proposed without optical and magnetic mediators.

scholarly journals Catchment classification by runoff behaviour with self-organizing maps (SOM)

2011 ◽  
Vol 8 (2) ◽  
pp. 3047-3083 ◽  
Author(s):  
R. Ley ◽  
M. C. Casper ◽  
H. Hellebrand ◽  
R. Merz
Keyword(s):  
Cluster Analysis ◽  
Ungauged Catchments ◽  
Self Organizing Maps ◽  
Response Behaviour ◽  
Flow Duration ◽  
Wide Range ◽  
Spatio Temporal ◽  
Flow Duration Curves ◽  
Climatic Characteristics ◽  
Self Organizing

Abstract. Catchments show a wide range of response behaviour, even if they are adjacent. For many purposes it is necessary to characterise and classify them, e.g. for regionalisation, prediction in ungauged catchments, model parameterisation. In this study, we investigate hydrological similarity of catchments with respect to their response behaviour. We analyse more than 8200 event runoff coefficients (ERCs) and flow duration curves of 53 gauged catchments in Rhineland-Palatinate, Germany, for the period from 1993 to 2008, covering a huge variability of weather and runoff conditions. The spatio-temporal variability of event-runoff coefficients and flow duration curves are assumed to represent how different catchments "transform" rainfall into runoff. From the runoff coefficients and flow duration curves we derive 12 signature indices describing various aspects of catchment response behaviour to characterise each catchment. Hydrological similarity of catchments is defined by high similarities of their indices. We identify, analyse and describe hydrologically similar catchments by cluster analysis using Self-Organizing Maps (SOM). As a result of the cluster analysis we get five clusters of similarly behaving catchments where each cluster represents one differentiated class of catchments. As catchment response behaviour is supposed to be dependent on its physiographic and climatic characteristics, we compare groups of catchments clustered by response behaviour with clusters of catchments based on catchment properties. Results show an overlap of 67% between these two pools of clustered catchments which can be improved using the topologic correctness of SOMs.

scholarly journals Catchment classification by runoff behaviour with self-organizing maps (SOM)

2011 ◽  
Vol 15 (9) ◽  
pp. 2947-2962 ◽  
Author(s):  
R. Ley ◽  
M. C. Casper ◽  
H. Hellebrand ◽  
R. Merz
Keyword(s):  
Cluster Analysis ◽  
Ungauged Catchments ◽  
Self Organizing Maps ◽  
Response Behaviour ◽  
Flow Duration ◽  
Wide Range ◽  
Spatio Temporal ◽  
Flow Duration Curves ◽  
Climatic Characteristics ◽  
Self Organizing

Abstract. Catchments show a wide range of response behaviour, even if they are adjacent. For many purposes it is necessary to characterise and classify them, e.g. for regionalisation, prediction in ungauged catchments, model parameterisation. In this study, we investigate hydrological similarity of catchments with respect to their response behaviour. We analyse more than 8200 event runoff coefficients (ERCs) and flow duration curves of 53 gauged catchments in Rhineland-Palatinate, Germany, for the period from 1993 to 2008, covering a huge variability of weather and runoff conditions. The spatio-temporal variability of event-runoff coefficients and flow duration curves are assumed to represent how different catchments "transform" rainfall into runoff. From the runoff coefficients and flow duration curves we derive 12 signature indices describing various aspects of catchment response behaviour to characterise each catchment. Hydrological similarity of catchments is defined by high similarities of their indices. We identify, analyse and describe hydrologically similar catchments by cluster analysis using Self-Organizing Maps (SOM). As a result of the cluster analysis we get five clusters of similarly behaving catchments where each cluster represents one differentiated class of catchments. As catchment response behaviour is supposed to be dependent on its physiographic and climatic characteristics, we compare groups of catchments clustered by response behaviour with clusters of catchments based on catchment properties. Results show an overlap of 67% between these two pools of clustered catchments which can be improved using the topologic correctness of SOMs.

scholarly journals Document Clustering using Self-Organizing Maps

MENDEL ◽  
2017 ◽  
Vol 23 (1) ◽  
pp. 111-118
Author(s):  
Muhammad Rafi ◽  
Muhammad Waqar ◽  
Hareem Ajaz ◽  
Umar Ayub ◽  
Muhammad Danish
Keyword(s):  
Document Clustering ◽  
Feature Space ◽  
Good Method ◽  
Self Organization ◽  
Self Organizing Maps ◽  
Document Collections ◽  
Document Collection ◽  
Common Technique ◽  
Low Dimensional ◽  
Self Organizing

Cluster analysis of textual documents is a common technique for better ltering, navigation, under-standing and comprehension of the large document collection. Document clustering is an autonomous methodthat separate out large heterogeneous document collection into smaller more homogeneous sub-collections calledclusters. Self-organizing maps (SOM) is a type of arti cial neural network (ANN) that can be used to performautonomous self-organization of high dimension feature space into low-dimensional projections called maps. Itis considered a good method to perform clustering as both requires unsupervised processing. In this paper, weproposed a SOM using multi-layer, multi-feature to cluster documents. The paper implements a SOM usingfour layers containing lexical terms, phrases and sequences in bottom layers respectively and combining all atthe top layers. The documents are processed to extract these features to feed the SOM. The internal weightsand interconnections between these layers features(neurons) automatically settle through iterations with a smalllearning rate to discover the actual clusters. We have performed extensive set of experiments on standard textmining datasets like: NEWS20, Reuters and WebKB with evaluation measures F-Measure and Purity. Theevaluation gives encouraging results and outperforms some of the existing approaches. We conclude that SOMwith multi-features (lexical terms, phrases and sequences) and multi-layers can be very e ective in producinghigh quality clusters on large document collections.

scholarly journals Using damage reports to assess different versions of a hydrological early warning system

2014 ◽  
Vol 11 (4) ◽  
pp. 4365-4401 ◽  
Author(s):  
D. Defrance ◽  
P. Javelle ◽  
D. Organde ◽  
S. Ecrepont ◽  
V. Andréassian ◽  
...  
Keyword(s):  
Warning System ◽  
Flood Damage ◽  
Hydrological Models ◽  
Ungauged Catchments ◽  
Mountainous Regions ◽  
Critical Success ◽  
Flood Warning ◽  
Forecasting System ◽  
Short Time ◽  
Critical Success Index

Abstract. In Europe, flash floods affect mainly the Mediterranean and mountainous regions, even if other regions also occasionally suffer from them. The catchments involved are usually small and ungauged, with short time of concentration. Forecasting this type of event remains difficult using hydrological models, and assessing the models is even more problematic. Typically, assessment is limited to gauged catchments that have relatively different geomorphological characteristics. The aim of this article is to present a method for assessing the models on real ungauged catchments through the use of damage reports and a multi-threshold approach, with assessment criteria that are based on a contingency table of the Critical Success Index type. The main conclusion, as demonstrated by Irstea's "Adaptation d'Information géographique pour l'Alerte en crue" for "Geographic information adaptation for flood warning" (AIGA) flood forecasting system and by the new version of AIGA for high-altitude catchments, is that while assessing hydrological models on gauged catchments is necessary, it is never sufficient and must be supplemented by assessments on ungauged catchments. This underlines the utility of building flood damage databases that are as exhaustive as possible. Such databases can be a valuable addition to more standard, often limited sources of data, especially for mountainous regions.

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