This paper analyses the bivariate relationship between flood peaks and corresponding flood event volumes modelled by empirical and theoretical copulas in a regional context, with a focus on flood generation processes in general, the regional differentiation of these and the effect of the sample size on reliable discrimination among models. A total of 72 catchments in North-West of Austria are analysed for the period 1976-2007. From the hourly runoff data set, 25 697 flood events were isolated and assigned to one of three flood process types: synoptic floods (including long- and short-rain floods), flash floods or snowmelt floods (both rain-on-snow and snowmelt floods). The first step of the analysis examines whether the empirical peak-volume copulas of different flood process types are regionally statistically distinguishable, separately for each catchment and the role of the sample size on the strength of the statements. The results indicate that the empirical copulas of flash floods tend to be different from those of the synoptic and snowmelt floods. The second step examines how similar are the empirical flood peak-volume copulas between catchments for a given flood type across the region. Empirical copulas of synoptic floods are the least similar between the catchments, however with the decrease of the sample size the difference between the performances of the process types becomes small. The third step examines the goodness-of-fit of different commonly used copula types to the data samples that represent the annual maxima of flood peaks and the respective volumes both regardless of flood generating processes (the traditional engineering approach) and also considering the three process-based classes. Extreme value copulas (Galambos, Gumbel and Hüsler-Reiss) show the best performance both for synoptic and flash floods, while the Frank copula shows the best performance for snowmelt floods. It is concluded that there is merit in treating flood types separately when analysing and estimating flood peak-volume dependence copulas; however, even the enlarged dataset gained by the process-based analysis in this study does not give sufficient information for a reliable model choice for multivariate statistical analysis of flood peaks and volumes.
Recently hydrological mapping have gained renewed interest in connection with climate-change impact studies, determination of water budgets at different temporal and spatial scales and the validation of atmospheric simulation models and hydrological models. Grids maps are often chosen for the representation of the spatial distribution of diverse physiographic and hydrologic information. This study focuses on the spatial estimation of the long-term mean annual actual (ET) and potential (EP) evapotranspiration in mountainous basins in Central Slovakia. Three methods used for EP and ET estimations are compared in a mapping framework: the modified empirical Turc model, the energy based SOLEI model and continuous water balance simulation using WASIM model. The spatial variability and consistency of EP and ET estimated by the different methods is evaluated and the performance of resulting ET grid maps is compared with the observed long-term water balance in three Hron river basins: river Hron to Bystra, Hron to Brezno and Hron to Banska Bystrica profiles. and Mapovanie prvkov hydrologickej bilancie má čoraz väčšie uplatnenie pri modelovaní priestorových zmien jednotlivých hydrologických prvkov, na určenie komponentov hydrologickej bilancie vybraných území, pri overovaní platnosti údajov pre rôzne atmosférické a hydrologické modely, ale aj pri štúdiách spojených s posudzovaním dôsledkov možnej zmeny klímy na hydrologický cyklus. Táto práca je venovaná možnostiam mapovania dlhodobého priemerného ročného aktuálneho (ET) a potenciálneho výparu (EP) s využitím rastrovej (štvorcovej) formy vyjadrenia ich priestorovej variability. Na konštrukciu máp EP a ET boli použité tri rôzne metódy: empirický model Turca, energeticky založený model SOLEI a model hydrologickej bilancie WaSiM. Výsledkom práce bolo zhodnotenie priestorovej variability a vzájomnej konzistencie rôznych metód aplikovaných na mapovanie EP a ET a porovnanie ich presnosti voči meraným dlhodobým prvkom hydrologickej bilancie v troch povodiach - povodí Bystrej, povodí Hrona po profil Brezno a po profil Banská Bystrica.
We computed annual precipitation totals for six catchments in the West and High Tatra Mountains (Roháčska, Jalovecká, Žiarska, Račkova, Tichá and Kôprová dolina) for hydrological years 1989-1998 using different interpolation and extrapolation methods. Precipitation estimates for the entire period as well as for particular hydrological years were used to compute evapotranspiration from the hydrological balance equation. The results have shown that although we used all existing precipitation data from the region along with the sophisticated methods to estimate catchment precipitation, yet, the water balance of the mountain catchments was not explained satisfactorily. and V práci sú vypočítané ročné zrážkové úhrny v šiestich povodiach Západných a Vysokých Tatier (Roháčska, Jalovecká, Žiarska, Račkova, Tichá a Kôprová dolina) pomocou rôznych interpolačných a extrapolačných metód pre hydrologické roky 1989 až1998, aj pre priemerné ročné úhrny za celé obdobie. Pre zrážkové úhrny určené rôznymi metódami bol z rovnice hydrologickej bilancie vypočítaný výpar a výsledky boli vyhodnotené opäť pre celé obdobie, aj pre jednotlové hydrologické roky. Získané výsledky ukazujú, že ani pri použití všetkých existujúcich údajov a moderných výpočtových metód existujúca meracia sieť nedáva uspokojivú odpoveď na pochybnosti, ktoré vznikajú pri určení základných prvkov hydrologickej bilancie v jednotlivých horských povodiach.
The objective of this paper is to compare the results of two distributed snow models based on different approach to snow accumulation and melt. Model WaSiM is based on the degree-day approach, while model UEB-EHZ is an energy-based model. Simulations in the mountain catchment of Jalovecký creek in winters 1989-2001 showed that both approaches can produce similar results. Model parametrization is more important than basic approach to snow accumulation and melt. Therefore, model UEB-EHZ which took into acccount influence of forest on radiation reduction and snow drift, performed better for the forest sites. The paper presents also brief overview of snow accumulation and melt modelling including calibration and verification of distributed models. Finally, it shows some outupts which can be provided by distributed snow models. and Príspevok je venovaný porovnaniu dvoch distribuovaných matematických modelov akumulácie a topenia snehu s rôznym prístupom k modelovaniu snehu. V horskom povodí Jaloveckého potoka boli hodnotené výsledky energeticky založeného modelu UEB-EHZ a modelu WaSiM, vychádzajúceho z metódy teplotného indexu pre zimy 1988/89 - 2000/2001. Porovnanie výsledkov oboch modelov ukázalo, že pokiaľ ide o základný prístup k modelovaniu topenia snehu (energetická bilancia alebo teplotný index), nemohli sme v danom povodí určiť, ktorý z nich viedol k lepším výsledkom. Väčší vplyv na simuláciu vodnej hodnoty snehu ako výber základného prístupu k modelovaniu akumulácie a topenia snehu, má parametrizácia konkrétneho modelu. V modeli UEB-EHZ bol napríklad čiastočne zahrnutý vplyv lesa na globálne žiarenie a podmienky ukladania snehu (drift). Preto bolo topenie snehovej pokrývky v lese týmto modelom simulované reálnejšie ako modelom WaSiM. Okrem porovnania výsledkov dvoch základných prístupov k modelovaniu akumulácie a topenia snehu v horskom povodí príspevok ukazuje aj niektoré výstupy, ktoré možno získať pomocou distribuovaného snehového modelu a stručne sa zaoberá diskusiou o kalibrácii a validácii takéhoto modelu.
In this paper a comparison of methods for estimating rainfall-runoff model parameters in ungauged basins based on geographical location are presented. As a pilot basin the Hron River basin in Slovakia with an available daily flow, precipitation and air temperature time series needed for calibration to obtain model parameter values in subcatchments was selected. The rainfall-runoff model was calibrated using a daily time step at 23 subcatchments. The Nearest Neighbour, Lumped Basin and Best Similarity Index methods were used to transfer the model parameters from the gauged to ''ungauged'' subcatchments. Finally, the effectiveness of the estimation method for ungauged basins was tested by comparing the model simulations to observed hydrographs and computing the Nash-Sutcliffe optimization criterion. The results were finally compared, and the best method was recommended for practical application by estimating of the rainfallrunoff model parameters in an ungauged catchment in this region. and V štúdii sú prezentované výsledky nepriamych metód odhadu parametrov zrážkovo-odtokového modelu na povodiach bez priamych hydrologických pozorovaní, ktoré sú založené na geografickej polohe povodí. Povodie Hrona bolo vybrané ako pilotný región s 23 čiastkovými povodiami, ktoré mali dostupné časové rady pozorovaní priemerných denných prietokov, zrážok a teploty vzduchu, potrebné na kalibráciu modelu. Zrážkovo-odtokový model bol v týchto podpovodiach nakalibrovaný na údajoch s denným časovým krokom. Následne boli použité na regionalizáciu parametrov modelu metódy Nearest Neighbour (Metóda najbližšieho suseda), Lumped Basin (Metóda sústredeného povodia) a Best Similarity Index methods (Metóda najlepšej podobnosti). Kvalita regionalizačných metód sa overovala pomocou optimalizačného kritéria Nash-Sutcliffe. Najlepšie výsledky boli dosiahnuté Metódou najlepšej podobnosti, ktorá môže byť v praxi odporúčaná na odhad parametrov zrážkovo-odtokového modelu na testovanom povodí.
In this paper hydrological scenarios of changes in the long-term mean annual and the mean monthly runoff due to the climate change in the upper part of the Hron River basin were evaluated. The Hron river basin was selected as a representative mountainous basin in Central Slovakia. An empirical raster-based and a conceptual hydrological balance model were used for modelling changes in runoff with an annual and monthly time step. Both models were calibrated using data from a standard period 1951-1980, which is considered to be representative for the distribution of runoff in unchanged conditions. Four different climate change scenarios were used in the study. Two scenarios were downscaled from the outputs of the CCCM and GISS Global Circulation Models (GCMs), the others represent analogies with warmer climatic periods in the past. The runoff change scenarios developed for the upper Hron River basin for future time horizons 2010, 2030 and 2075 show the decrease in the long-term mean annual runoff and changes in the runoff distribution within the year. and V článku sú odvodené scenáre zmien dlhodobých priemerných ročných a priemerných mesačných prietokov, vyjadrujúce možný vplyv zmeny klímy na odtok v budúcnosti na povodí horného Hrona. Na modelovanie dlhodobých priemerných ročných prietokov bol použitý rastrovo-orientovaný empirický model hydrologickej bilancie, na modelovanie priemerných mesačných prietokov bol použitý koncepčný hydrologický bilančný model so sústredenými parametrami. Obidva modely boli kalibrované na údajoch z obdobia 1951-1980, ktoré sme považovali za reprezentatívne obdobie pre nezmenené podmienky hydrologického režimu. Ako scenáre zmeny klímy boli použité scenáre CCCM a GISS, regionalizované z najnovších výstupov globálnych cirkulačných modelov atmosféry, a scenáre SD a WP, vyvinuté v rámci Národného klimatického programu SR na základe analógie s teplými obdobiami v minulosti u nás. Scenáre zmeny odtoku, odvodené pre časové horizonty 2010, 2030 a 2075 ukazujú možný pokles dlhodobých priemerných ročných prietokov, ako aj zmenu priemerných mesačných prietokov na povodí horného Hrona v budúcnosti.
This study is focused on the snowmelt runoff simulations for the upper Hron basin using dte degree-day approach of the SRM model. Our effort was directed at the determination and selection of input data and model parameters using GIS tools. The aim of this paper was to simulate the snowmelt runoff using only regularly measured data, without their special pre-processing. Comparison between measured and computed runoff indicates that the SRM model could be used for the snowmelt runoff simulation for the upper Hron basin. Results for the smaller upper Telgart subbasin were not so acceptable, because of lack of representative input data, which is essential for the determination of the snow depletion curve. and Práca je venovaná simulácii odtoku zo snehu pre povodie horného Hrona s využitím modelu odtoku zo snehu - SRM. Hlavným cieľom práce bolo posúdiť a otestovať možnosti výberu a určenia vstupných údajov a kalibrácie parametrov do modelu SRM s využitím dát pravidelne meraných v sieti meteorologických staníc. Z výsledkov vyplýva, že SRM veľmi dobre simuluje prietok pre povodie horného Hrona ako celku. Simulácia pre povodie horného Hrona rozdeleného na dve výškové zóny, a najmä pre čiastkové povodie Hrona po Telgárt, nedosiahla akceptovateľné výsledky. Tento fakt spôsobili najmä nedostatečné vstupné údaje. Kritickým sa ukázali najmä vstupné informácie o priestorovom rozložení snehovej pokrývky.
In a previous study, the topsoil and root zone ASCAT satellite soil moisture data were implemented into three multi-objective calibration approaches of the TUW hydrological model in 209 Austrian catchments. This paper examines the model parametrization in those catchments, which in the validation of the dual-layer conceptual semi-distributed model showed improvement in the runoff simulation efficiency compared to the single objective runoff calibration. The runoff simulation efficiency of the three multi-objective approaches was separately considered. Inferences about the specific location and the physiographic properties of the catchments where the inclusion of ASCAT data proved beneficial were made. Improvements were primarily observed in the watersheds with lower slopes (median of the catchment slope less than 15 per cent) and a higher proportion of farming land use (median of the proportion of agricultural land above 20 per cent), as well as in catchments where the runoff is not significantly influenced by snowmelt and glacier runoff. Changes in the mean and variability of the field capacity parameter FC of the soil moisture regime were analysed. The values of FC decreased by 20 per cent on average. Consequently, the catchments’ water balance closure generally improved by the increase in catchment evapotranspiration during the validation period. Improvements in model efficiency could be attributed to better runoff simulation in the spring and autumn month. The findings refine recommendations regarding when hydrological modelling could consider satellite soil moisture data added to runoff signatures in calibration useful.
Substantial evidence shows that the frequency of hydrological extremes has been changing and is likely to continue to change in the near future. Non-stationary models for flood frequency analyses are one method of accounting for these changes in estimating design values. The objective of the present study is to compare four models in terms of goodness of fit, their uncertainties, the parameter estimation methods and the implications for estimating flood quantiles. Stationary and non-stationary models using the GEV distribution were considered, with parameters dependent on time and on annual precipitation. Furthermore, in order to study the influence of the parameter estimation approach on the results, the maximum likelihood (MLE) and Bayesian Monte Carlo Markov chain (MCMC) methods were compared. The methods were tested for two gauging stations in Slovenia that exhibit significantly increasing trends in annual maximum (AM) discharge series. The comparison of the models suggests that the stationary model tends to underestimate flood quantiles relative to the non-stationary models in recent years. The model with annual precipitation as a covariate exhibits the best goodness-of-fit performance. For a 10% increase in annual precipitation, the 10-year flood increases by 8%. Use of the model for design purposes requires scenarios of future annual precipitation. It is argued that these may be obtained more reliably than scenarios of extreme event precipitation which makes the proposed model more practically useful than alternative models.
Direct interpolation of daily runoff observations to ungauged sites is an alternative to hydrological model regionalisation. Such estimation is particularly important in small headwater basins characterized by sparse hydrological and climate observations, but often large spatial variability. The main objective of this study is to evaluate predictive accuracy of top-kriging interpolation driven by different number of stations (i.e. station densities) in an input dataset. The idea is to interpolate daily runoff for different station densities in Austria and to evaluate the minimum number of stations needed for accurate runoff predictions. Top-kriging efficiency is tested for ten different random samples in ten different stations densities. The predictive accuracy is evaluated by ordinary cross-validation and full-sample crossvalidations. The methodology is tested by using 555 gauges with daily observations in the period 1987-1997. The results of the cross-validation indicate that, in Austria, top-kriging interpolation is superior to hydrological model regionalisation if station density exceeds approximately 2 stations per 1000 km2 (175 stations in Austria). The average median of Nash-Sutcliffe cross-validation efficiency is larger than 0.7 for densities above 2.4 stations/1000 km2 . For such densities, the variability of runoff efficiency is very small over ten random samples. Lower runoff efficiency is found for low station densities (less than 1 station/1000 km2 ) and in some smaller headwater basins.