Author

Sadik Ahmed

Date of Award

9-2010

Degree Type

Thesis

Degree Name

Master of Applied Science (MASc)

Department

Civil Engineering

Supervisor

Paulin Coulibaly

Co-Supervisor

Ioannis Tsanis

Language

English

Abstract

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The objective of this thesis is to investigate the potential of ensemble

meteorological forecasts (15 members for each day) in improving ensemble flow

prediction up to 14 days ahead. Large scale ensemble meteorological forecasts generated

by the National Centers for Environmental Prediction's (NCEP) Global Forecast System

(GFS) are used. The hydrologic model used in watershed analysis of the study area is

Hydrologiska Byrâns Vattenbalan-avdelning (HBV). The study area is located in the

Saguenay-Lac-Saint Jean watershed in northeastern Canada and comprises the Serpent

River and Chute-du-Diable basins and a reservoir in Chute-du-Diable.

The NCEP ensemble meteorological forecast data is initially used as input in the p.p1 {margin: 0.0px 0.0px 0.0px 0.0px; font: 11.5px Times} span.s1 {font: 7.5px Helvetica}

hydrological model HBV to simulate ensemble reservoir inflows and the Serpent River

flows for 5 to 14 days ahead. The ensemble inflow and flow forecasts are compared with

the case where only observed historical data are used. The study results show that there is

a significant improvement in the model forecast performance when NCEP forecast data

are used. The improvement for 5 to 14 day forecasts is revealed by an approximately 20%

decrease in root mean square error (RMSE) for both reservoir inflow and river flow. A

decrease in the Brier score (BS) and rank probability score (RPS) indicates considerable

improvement and an increase in the correlation coefficient (r) and the Nash and Sutcliffe

coefficient (R²) is shown for reservoir inflow and the Serpent River flow respectively,

indicating the advantage of using NCEP data. This improvement is also revealed by the p.p1 {margin: 0.0px 0.0px 0.0px 0.0px; font: 11.5px Times}

visual inspection of scatter plots, hydrographs of ensemble mean and ensemble members.

The hydrologic forecasts are also assessed on a seasonal basis indicating an improvement

in forecasting indicated by a 30% decrease in RMSE during the spring season, and a

decrease in BS and RPS values. For other seasons, specifically autumn and summer, the

use of the ensemble meteorological forecasts do not provide significant improvement

because of the poor skill of predicted precipitation. More accurate predictions of reservoir

inflow and river flow with adequate lead time will assist in improving relevant issues in

water resources management and planning.

McMaster University Library


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