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Flood Prediction in data-scarce basins: Maximising the value of limited hydro-meteorological data
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Floods pose a threat to society that can cause large socio-economic damages and loss of life in many parts of the world. Flood-forecasting models are required to provide simulations at temporal resolutions higher than a day in basins with concentration times smaller than 24 h. However, data at such resolutions are commonly limited or not available, especially in developing or low-income countries. This thesis covers issues related to the scarcity and lack of high temporal-resolution hydro-meteorological data and explores methods where the value of existing data is maximised to improve flood prediction.

By varying the starting time of daily records (the day definition), it was shown that this definition had large implications on model calibration and runoff simulation and therefore, should be considered in regionalisation and flood-forecasting applications. A method was developed to treat empirically model-parameter dependencies on the temporal resolution of data. Model parameters seemed to become independent of the temporal resolution of data when the modelling time-step was sufficiently small. Thus, if sub-daily forcing data can be secured, flood forecasting in basins with sub-daily concentration times may be possible using model-parameter values calibrated from time series of daily data. A new calibration method using only a few event hydrographs could improve flood prediction compared to a scenario with no discharge data. Two event hydrographs may be sufficient for calibration, but accuracy and reduction in uncertainty may improve if data on more events can be acquired. Using flood events above a threshold with a high frequency of occurrence for calibration may be as useful for flood prediction as using only extreme events with a low frequency of occurrence. The accuracy of the rainfall forecasts strongly influenced the predictive performance of a flood model calibrated with limited discharge data. Between volume and duration errors of the rainfall forecast, the former had the larger impact on model performance.

The methods previously described proved to be useful for predicting floods and are expected to support flood-risk assessment and decision making during the occurrence of floods in data-scarce regions. Further studies using more models and basins are required to test the generality of these results.

Abstract [sv]

Översvämningar är ett samhällshot och ibland en naturkatastrof med förluster av människoliv och omfattande materiella skador på många ställen i världen. Översvämningsprognoser kräver modellsimuleringar av höga flöden med högre tidsupplösning än dygn i avrinningsområden där svarstiden understiger 24 h. Data med sådan tidsupplösning är ofta begränsade eller obefintliga, i synnerhet i låginkomstländer. Denna avhandling behandlar problem relaterade till brist eller avsaknad av hydrometeorologiska data med hög tidsupplösning och undersöker metoder för att maximera värdet av befintliga data för översvämningsprognoser.

Genom att variera starttiden på dygnsdata (dygnsdefinitionen), visades att definitionen hade stor inverkan på modellkalibrering och avrinningssimulering, och därigenom påverkade regionaliserings- och översvämningsberäkningar. En metod utvecklades för att empiriskt hantera modellparametrars beroende av indatas tidsupplösning. Modellparametrarna verkade vara oberoende av indatas tidsupplösning när modellens beräkningstidssteg var tillräckligt litet. Så om drivdata med inomdygnsupplösning kan säkerställas, är det möjligt att förutsäga översvämningar i områden med små svarstider på grundval av modellparametrar som kalibrerats mot tidsserier av dygnsdata. En ny kalibreringsmetod baserad på endast ett fåtal stora flödestoppar kunde förbättra översvämningsprognoser jämfört med en situation där flödesdata helt saknades. Två flödestoppar kan räcka för kalibrering men noggrannheten förbättras och osäkerheten minskar om fler toppar finns tillgängliga. Användning av flödestoppar över ett tröskelvärde som ofta överskrids kan vara lika användbart för kalibrering som användning av extrema, sällan förekommande högflöden. Precisionen av nederbördsprognoserna påverkade starkt den prediktiva förmågan hos en modell för höga flöden kalibrerad med begränsade mängd vattenföringsdata. I jämförelse mellan felen i volym och varaktighet på regnprognosen, så hade den förra större inverkan på modellens resultat.

De beskrivna metoderna var användbara för högflödesprognoser och kan förväntas understödja bedömningen av översvämningsrisker och hanteringen av översvämningar i områden med begränsade data. Allmängiltigheten av resultaten behöver prövas med andra modeller och för andra avrinningsområden.

Abstract [es]

Las inundaciones son una amenaza para la sociedad que pueden causar grandes daños socio-económicos y pérdida de vidas humanas en muchos lugares del mundo. En cuencas con tiempo de concentración inferior a 24 h se necesitan modelos que pronostiquen inundaciones con una resolución temporal superior al día. Datos hidro-meteorológicos a esas resoluciones suelen no estar disponibles o no existen, especialmente en países en desarrollo. Esta tesis cubre temas relacionados con la escasez de datos de alta resolución temporal y explora distintos métodos en los que el valor de los datos existentes se maximiza para mejorar la predicción de inundaciones.

Al variar la hora de inicio del día en las observaciones se demostró que la definición del día tuvo un gran impacto en la calibración del modelo y en las simulaciones de caudal, lo cual puede tener un efecto en la regionalización de parámetros hidrológicos. Se desarrolló un método para gestionar empíricamente la dependencia de los parámetros con respecto a la resolución temporal de los datos. Los valores de los parámetros se volvieron independientes de la resolución temporal de los datos cuando el intervalo de tiempo del modelo fue configurado en pasos suficientemente pequeños. Como resultado, si se pudiesen obtener datos de entrada en resoluciones temporales sub-diarias, sería posible hacer pronósticos de inundación en cuencas con tiempo de concentración menor a un día utilizando parámetros calibrados con series de tiempo de datos diarios. Se desarrolló un método de calibración basado en unos cuantos hidrogramas de crecidas para hacer pronósticos de inundaciones más robustos en comparación con el escenario de no tener ninguna observación. Dos hidrogramas de crecidas mostraron ser suficientes para calibrar el modelo, pero las predicciones podrían ser más precisas y con menos incertidumbre si se pudiese disponer de datos de un mayor número de eventos. El uso de crecidas por encima de un umbral con una alta probabilidad de ocurrencia resultó ser igual de útil para la calibración del modelo que el uso de eventos más extremos, que ocurren con menor frecuencia. El rendimiento de un modelo de inundación, previamente calibrado contra un número limitado de crecidas, fue altamente impactado por la precisión de los pronósticos de lluvia. Entre los errores de volumen y duración en los pronósticos de lluvia, el primero tuvo el mayor impacto en los resultados del modelo.

Los métodos descritos en esta tesis demostraron ser útiles para predecir inundaciones y se espera que contribuyan a una mejor evaluación del riesgo de inundaciones en regiones con escasez de datos. Se requieren estudios adicionales que utilicen más modelos y cuencas para probar la generalidad de estos resultados.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2019. , p. 70
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1753
Keywords [en]
Floods, data scarcity, value of information, rainfall-runoff modelling, regionalisation, rainfall-forecasts, event-based calibration, climatological day, discharge day, temporal resolution, modelling time-step.
Keywords [sv]
Databrist, flödestoppsbaserad kalibrering, högflöde, informationsvärde, klimatologiskt dygn, nederbörds-avrinningsmodell, modelltidssteg, regionalisering, regnprognos, tids-upplösning, vattenföringsdygn, översvämning.
Keywords [es]
Inundaciones, falta de datos, valor de información, modelos lluvia escorrentía, regionalización, pronósticos de lluvia, definición del día, resolución temporal, paso de tiempo.
National Category
Other Earth and Related Environmental Sciences
Identifiers
URN: urn:nbn:se:uu:diva-368532ISBN: 978-91-513-0527-1 (print)OAI: oai:DiVA.org:uu-368532DiVA, id: diva2:1268368
Public defence
2019-02-08, Axel Hambergsalen, Villavägen 16, Uppsala, 10:00 (English)
Opponent
Supervisors
Funder
Sida - Swedish International Development Cooperation AgencyAvailable from: 2019-01-14 Created: 2018-12-05 Last updated: 2019-01-21Bibliographically approved
List of papers
1. Definitions of climatological and discharge days: do they matter in hydrological modelling?
Open this publication in new window or tab >>Definitions of climatological and discharge days: do they matter in hydrological modelling?
2018 (English)In: Hydrological Sciences Journal, ISSN 0262-6667, E-ISSN 2150-3435, Vol. 63, no 5, p. 836-844Article in journal (Refereed) Published
Abstract [en]

The performance of hydrological models is affected by uncertainty related to observed climatological and discharge data. Although the latter has been widely investigated, the effects on hydrological models from different starting times of the day have received little interest. In this study, observational data from one tropical basin were used to investigate the effects on a typical bucket-type hydrological model, the HBV, when the definitions of the climatological and discharge days are changed. An optimization procedure based on a genetic algorithm was used to assess the effects on model performance. Nash-Sutcliffe efficiencies varied considerably between day definitions, with the largest dependence on the climatological-day definition. The variation was likely caused by how storm water was assigned to one or two daily rainfall values depending on the definition of the climatological day. Hydrological models are unlikely to predict high flows accurately if rainfall intensities are reduced because of the day definition.

Place, publisher, year, edition, pages
Taylor & Francis, 2018
Keywords
climatological day, discharge day, rainfall-runoff model, daily resolution, regionalization, floods
National Category
Oceanography, Hydrology and Water Resources
Identifiers
urn:nbn:se:uu:diva-353191 (URN)10.1080/02626667.2018.1451646 (DOI)000430212100010 ()
Available from: 2018-06-12 Created: 2018-06-12 Last updated: 2018-12-05Bibliographically approved
2. Sub-daily runoff predictions using parameters calibrated on the basis of data with a daily temporal resolution
Open this publication in new window or tab >>Sub-daily runoff predictions using parameters calibrated on the basis of data with a daily temporal resolution
Show others...
2017 (English)In: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 550, p. 399-411Article in journal (Refereed) Published
Abstract [en]

Concentration times in small and medium-sized basins (similar to 10-1000 km(2)) are commonly less than 24 h. Flood-forecasting models are thus required to provide simulations at high temporal resolutions (1 h-6 h), although time-series of input and runoff data with sufficient lengths are often only available at the daily temporal resolution, especially in developing countries. This has led to study the relationships of estimated parameter values at the temporal resolutions where they are needed from the temporal resolutions where they are available. This study presents a methodology to treat empirically model parameter dependencies on the temporal resolution of data in two small basins using a bucket-type hydrological model, HBV-light, and the generalised likelihood uncertainty estimation approach for selecting its parameters. To avoid artefacts due to the numerical resolution or numerical method of the differential equations within the model, the model was consistently run using modelling time steps of one-hour regardless of the temporal resolution of the rainfall-runoff data. The distribution of the parameters calibrated at several temporal resolutions in the two basins did not show model parameter dependencies on the temporal resolution of data and the direct transferability of calibrated parameter sets (e.g., daily) for runoff simulations at other temporal resolutions for which they were not calibrated (e.g., 3 h or 6 h) resulted in a moderate (if any) decrease in model performance, in terms of Nash-Sutcliffe and volume-error efficiencies. The results of this study indicate that if sub-daily forcing data can be secured, flood forecasting in basins with sub-daily concentration times may be possible with model-parameter values calibrated from long time series of daily data. Further studies using more models and basins are required to test the generality of these results.

Keywords
Rainfall-runoff modelling, Parameter transferability, Temporal resolution, Modelling time-step, Flood forecasting
National Category
Oceanography, Hydrology and Water Resources
Identifiers
urn:nbn:se:uu:diva-330029 (URN)10.1016/j.jhydrol.2017.05.012 (DOI)000404816000032 ()
Funder
Sida - Swedish International Development Cooperation Agency
Available from: 2017-09-29 Created: 2017-09-29 Last updated: 2018-12-05
3. Robustness of Flood-Model Calibration using Single and Multiple Events
Open this publication in new window or tab >>Robustness of Flood-Model Calibration using Single and Multiple Events
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2018 (English)In: Hydrological Sciences Journal, ISSN 0262-6667, E-ISSN 2150-3435Article in journal (Refereed) Submitted
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:uu:diva-368457 (URN)
Funder
Sida - Swedish International Development Cooperation Agency
Available from: 2018-12-04 Created: 2018-12-04 Last updated: 2018-12-05
4. Flood prediction using uncertain rainfall forecasts and parameters calibrated on limited discharge data.
Open this publication in new window or tab >>Flood prediction using uncertain rainfall forecasts and parameters calibrated on limited discharge data.
Show others...
(English)Manuscript (preprint) (Other academic)
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:uu:diva-368458 (URN)
Funder
Sida - Swedish International Development Cooperation Agency
Available from: 2018-12-04 Created: 2018-12-04 Last updated: 2018-12-18

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Reynolds Puga, José Eduardo

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