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Observational Uncertainties in Water-Resources Modelling in Central America: Methods for Uncertainty Estimation and Model Evaluation
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
2011 (English)Doctoral thesis, comprehensive summary (Other academic)Alternative title
Observationsosäkerheter i vattenresursmodellering i Centralamerika : Metoder för osäkerhetsuppskattning och modellutvärdering (Swedish)
Abstract [en]

Knowledge about spatial and temporal variability of hydrological processes is central for sustainable water-resources management, and such knowledge is created from observational data. Hydrologic models are necessary for prediction for time periods and areas lacking data, but are affected by observational uncertainties. Methods for estimating and accounting for such uncertainties in water-resources modelling are of high importance, especially in regions such as Central America.

Observational uncertainties were addressed in three ways in this thesis; quality control, quantitative estimation and development of model-evaluation techniques that addressed unquantifiable uncertainties. A first step in any modelling study should be the quality control and concurrent analysis of the representativeness of the observational data. In the characterisation of the precipitation regime in the Choluteca River basin in Honduras, four different quality problems were identified and 22% of the daily data had to be rejected. The monitoring network was found to be insufficient for a comprehensive characterisation of the high spatiotemporal variability of the precipitation regime.

Quantitative estimations of data uncertainties can be made when sufficient information is available. Discharge-data uncertainties were estimated with a fuzzy regression for time-variable rating curves and from official rating curves for 35 stations in Honduras. The uncertainties were largest for low flows, as a result of measurement uncertainties and natural variability.

A method for calibration with flow-duration curves was developed which enabled calibration to the whole flow range, accounting for discharge uncertainty and calibration with non-overlapping time periods for model input and evaluation data. The method compared favourably to traditional calibration in a test using two models applied in basins with different runoff-generation processes. A post-hoc analysis made it possible to identify potential model-structure errors and periods of disinformative data. Flow-duration curves were regionalised and used for calibration of a Central-American water-balance model. The initial model uncertainty for the ungauged basins was reduced by 70%. Non-representative precipitation data were found to be the main obstacle to comprehensive regional water-resources modelling in Central America.

These methods bridged several problems related to observational uncertainties in water-balance modelling. Estimates of prediction uncertainty are an important basis for all types of decisions related to water-resources management.

 

Abstract [sv]

Kännedom om hur hydrologiska processer varierar i tid och rum är grundläggande för hållbar vattenresursförvaltning och skapas utifrån observerade data. Hydrologiska modeller är nödvändiga för att förutsäga vattenbalansen för tidsperioder och områden utan data, men påverkas av observationsosäkerheter. Metoder för att hantera sådana osäkerheter i vattenresursmodellering är av stor betydelse i regioner såsom Centralamerika.

Observationsosäkerheter hanterades på tre olika sätt i denna avhandling; kvalitetskontroll, kvantitativ uppskattning och utveckling av modellutvärderingsmetoder för beaktande av icke kvantifierbara osäkerheter. Ett viktigt första steg är kvalitetskontroll och samtidig analys av datas representativitet. Vid karaktäriseringen av nederbördsregimen i Cholutecaflodens avrinningsområde i Honduras identifierades fyra olika kvalitetsproblem och 22 % av data sorterades bort. Stationsnätet var otillräckligt för en fullödig karaktärisering av nederbördsregimens variationer i tid och rum. Dessa var mycket stora som ett resultat av komplexiteten hos de nederbördsgenererande mekanismerna.

Kvantitativ uppskattning av observerade datas osäkerhet kan göras när tillräcklig information är tillgänglig. Osäkerheter i vattenföringsdata uppskattades dels vid beräkning av vattenföring med en oskarp regression för en tidsvariabel avbördningskurva, dels från en analys av officiella avbördningskurvor från 35 stationer i Honduras. Osäkerheten var i båda fallen högst vid låga flöden som ett resultat av högre mätosäkerheter samt större naturlig variabilitet än vid höga flöden.

En metod för modellkalibrering med varaktighetskurvor utvecklades och gjorde det möjligt att kalibrera för hela flödesintervallet samtidigt, ta hänsyn till osäkerheter i vattenföringsdata samt kalibrera med icke överlappande driv- och utvärderingsdata. Metoden testades med två olika modeller i två avrinningsområden med olika avrinningsbildningsprocesser, och visade goda resultat jämfört med traditionell modellkalibrering. En post hoc-analys gjorde det möjligt att identifiera troliga modellstrukturfel och perioder med disinformativa data. Varaktighetskurvor regionaliserades och användes för kalibrering av en regional vattenbalansmodell för Centralamerika, varvid den initiala modellosäkerheten minskades med 70 %.

Icke representativa nederbördsdata identifierades som det största hindret för regional vattenresursmodellering i Centralamerika. De metoder som utvecklades i detta arbete gör det möjligt att överbrygga ett flertal problem orsakade av bristfällig tillgänglighet och kvalitet av data och leder därmed till en förbättrad uppskattning av osäkerheten i vattenbalanssimuleringar. Sådana osäkerhetsskattningar är ett viktigt underlag vid alla typer av förvaltningsbeslut som rör vattenresurser.

 

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis , 2011. , 75 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 833
Keyword [en]
Central America, Discharge, Flow-duration curve, Fuzzy regression, GLUE, Model evaluation, Non-stationarity, Observational uncertainty, Precipitation, Quality control, Rating curve, Regionalisation, Uncertainty estimation, Ungauged basins, Water resources
Keyword [sv]
Avbördningskurva, Centralamerika, GLUE, icke-stationaritet, kvalitetskontroll, modellutvärdering, nederbörd, observationsosäkerheter, avrinningsområden utan vattenfö-ringsdata, oskarp regression, osäkerhetsuppskattning, regionalisering, varaktighetskurva, vattenföring, vattenresurser
National Category
Oceanography, Hydrology, Water Resources
Research subject
Hydrology
Identifiers
URN: urn:nbn:se:uu:diva-152074ISBN: 978-91-554-8090-5OAI: oai:DiVA.org:uu-152074DiVA: diva2:413061
Public defence
2011-06-10, Axel Hambergsalen, Earth Sciences Centre, Villavägen 16, Uppsala, 10:00 (English)
Opponent
Supervisors
Available from: 2011-05-12 Created: 2011-04-23 Last updated: 2011-07-01
List of papers
1. Precipitation data in a mountainous catchment in Honduras: quality assessment and spatiotemporal characteristics
Open this publication in new window or tab >>Precipitation data in a mountainous catchment in Honduras: quality assessment and spatiotemporal characteristics
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2010 (English)In: Journal of Theoretical and Applied Climatology, ISSN 0177-798X, E-ISSN 1434-4483, Vol. 101, no 3-4, 381-396 p.Article in journal (Refereed) Published
Abstract [en]

An accurate description of temporal and spatial precipitation variability in Central America is important for local farming, water supply and flood management. Data quality problems and lack of consistent precipitation data impede hydrometeorological analysis in the 7,500 km(2) Choluteca River basin in central Honduras, encompassing the capital Tegucigalpa. We used precipitation data from 60 daily and 13 monthly stations in 1913-2006 from five local authorities and NOAA's Global Historical Climatology Network. Quality control routines were developed to tackle the specific data quality problems. The quality-controlled data were characterised spatially and temporally, and compared with regional and larger-scale studies. Two gap-filling methods for daily data and three interpolation methods for monthly and mean annual precipitation were compared. The coefficient-of-correlation-weighting method provided the best results for gap-filling and the universal kriging method for spatial interpolation. In-homogeneity in the time series was the main quality problem, and 22% of the daily precipitation data were too poor to be used. Spatial autocorrelation for monthly precipitation was low during the dry season, and correlation increased markedly when data were temporally aggregated from a daily time scale to 4-5 days. The analysis manifested the high spatial and temporal variability caused by the diverse precipitation-generating mechanisms and the need for an improved monitoring network.

National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:uu:diva-135001 (URN)10.1007/s00704-009-0222-x (DOI)000280578900012 ()
Available from: 2010-12-06 Created: 2010-12-03 Last updated: 2013-02-11Bibliographically approved
2. Stage-discharge uncertainty derived with a non-stationary rating curve in the Choluteca River, Honduras
Open this publication in new window or tab >>Stage-discharge uncertainty derived with a non-stationary rating curve in the Choluteca River, Honduras
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2011 (English)In: Hydrological Processes, ISSN 0885-6087, E-ISSN 1099-1085, Vol. 25, no 4, 603-613 p.Article in journal (Refereed) Published
Abstract [en]

Uncertainty in discharge data must be critically assessed before data can be used in, e. g. water resources estimation or hydrological modelling. In the alluvial Choluteca River in Honduras, the river-bed characteristics change over time as fill, scour and other processes occur in the channel, leading to a non-stationary stage-discharge relationship and difficulties in deriving consistent rating curves. Few studies have investigated the uncertainties related to non-stationarity in the stage-discharge relationship. We calculated discharge and the associated uncertainty with a weighted fuzzy regression of rating curves applied within a moving time window, based on estimated uncertainties in the observed rating data. An 18-year-long dataset with unusually frequent ratings (1268 in total) was the basis of this study. A large temporal variability in the stage-discharge relationship was found especially for low flows. The time-variable rating curve resulted in discharge estimate differences of -60 to +90% for low flows and +/- 20% for medium to high flows when compared to a constant rating curve. The final estimated uncertainty in discharge was substantial and the uncertainty limits varied between -43 to +73% of the best discharge estimate.

Keyword
discharge, uncertainty, alluvial river, stage-discharge, rating curve, fuzzy regression
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:uu:diva-148617 (URN)10.1002/hyp.7848 (DOI)000287377200007 ()
Available from: 2011-03-08 Created: 2011-03-08 Last updated: 2013-01-14Bibliographically approved
3. Calibration of hydrologic models using flow-duration curves
Open this publication in new window or tab >>Calibration of hydrologic models using flow-duration curves
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2010 (English)In: Hydrology and Earth System Sciences, ISSN 1027-5606, E-ISSN 1607-7938, no 7, 9467-9522 p.Article in journal (Refereed) Published
Abstract [en]

The degree of belief we have in predictions from hydrologic models depends on how well they can reproduce observations. Calibrations with traditional performance measures such as the Nash-Sutcliffe model efficiency are challenged by problems including: (1) uncertain discharge data, (2) variable importance of the performance with flow magnitudes, (3) influence of unknown input/output errors and (4) inability to evaluate model performance when observation time periods for discharge and model input data do not overlap. A new calibration method using flow-duration curves (FDCs) was developed which addresses these problems. The method focuses on reproducing the observed discharge frequency distribution rather than the exact hydrograph. It consists of applying limits of acceptability for selected evaluation points (EPs) of the observed uncertain FDC in the extended GLUE approach. Two ways of selecting the EPs were tested – based on equal intervals of discharge and of volume of water. The method was tested and compared to a calibration using the traditional model efficiency for the daily four-parameter WASMOD model in the Paso La Ceiba catchment in Honduras and for Dynamic TOPMODEL evaluated at an hourly time scale for the Brue catchment in Great Britain. The volume method of selecting EPs gave the best results in both catchments with better calibrated slow flow, recession and evaporation than the other criteria. Observed and simulated time series of uncertain discharges agreed better for this method both in calibration and prediction in both catchments without resulting in overpredicted simulated uncertainty. An advantage with the method is that the rejection criterion is based on an estimation of the uncertainty in discharge data and that the EPs of the FDC can be chosen to reflect the aims of the modelling application e.g. using more/less EPs at high/low flows. While the new method is less sensitive to epistemic input/output errors than the normal use of limits of acceptability applied directly to the time series of discharge, it still requires a reasonable representation of the distribution of inputs. Additional constraints might therefore be required in catchments subject to snow. The results suggest that the new calibration method can be useful when observation time periods for discharge and model input data do not overlap. The new method could also be suitable for calibration to regional FDCs while taking uncertainties in the hydrological model and data into account.

 

Place, publisher, year, edition, pages
Copernicus Publications, 2010
National Category
Earth and Related Environmental Sciences
Research subject
Hydrology
Identifiers
urn:nbn:se:uu:diva-152070 (URN)10.5194/hessd-7-9467-2010 (DOI)
Available from: 2011-04-23 Created: 2011-04-23 Last updated: 2013-01-09Bibliographically approved
4. On red herrings and real herrings: disinformation and information in hydrological inference
Open this publication in new window or tab >>On red herrings and real herrings: disinformation and information in hydrological inference
2011 (English)In: Hydrological Processes, ISSN 0885-6087, E-ISSN 1099-1085, Vol. 25, no 10, 1676-1680 p.Article in journal (Other academic) Published
National Category
Earth and Related Environmental Sciences
Research subject
Hydrology
Identifiers
urn:nbn:se:uu:diva-152071 (URN)10.1002/hyp.7963 (DOI)
Available from: 2011-04-23 Created: 2011-04-23 Last updated: 2013-01-14Bibliographically approved
5. Regionalisation of a water-balance model for Central America using flow-duration curves
Open this publication in new window or tab >>Regionalisation of a water-balance model for Central America using flow-duration curves
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(English)Manuscript (preprint) (Other academic)
National Category
Oceanography, Hydrology, Water Resources
Research subject
Hydrology
Identifiers
urn:nbn:se:uu:diva-152073 (URN)
Available from: 2011-04-23 Created: 2011-04-23 Last updated: 2013-04-26

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