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Conditioning ensemble streamflow prediction with the North Atlantic Oscillation improves skill at longer lead times

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posted on 10.08.2021, 15:40 by Seán Donegan, Conor Murphy, Shaun Harrigan, Ciaran Broderick, Dáire Foran Quinn, Saeed Golian, Jeff Knight, Tom Matthews, Christel Prudhomme, Adam Scaife, Nicky Stringer, Robert WilbyRobert Wilby
Skilful hydrological forecasts can benefit decision-making in water resources management and other water-related sectors that require long-term planning. In Ireland, no such service exists to deliver forecasts at the catchment scale. In order to understand the potential for hydrological forecasting in Ireland, we benchmark the skill of Ensemble Streamflow Prediction (ESP) for a diverse sample of 46 catchments using the GR4J hydrological model. Skill is evaluated within a 52-year hindcast study design over lead times of 1 day to 12 months for each of 12 initialisation months, January to December. Our results show that ESP is skilful against a probabilistic climatology benchmark in the majority of catchments up to several months ahead. However, the level of skill was strongly dependent on lead time, initialisation month, and individual catchment location and storage properties. Mean ESP skill was found to decay rapidly as a function of lead time, with continuous ranked probability skill scores (CRPSS) of 0.8 (1 day), 0.32 (2-week), 0.18 (1-month), 0.05 (3-month), and 0.01 (12-month). Forecasts were generally more skilful when initialised in summer than other seasons. A strong correlation (ρ = 0.94) was observed between forecast skill and catchment storage capacity (baseflow index), with the most skilful regions, the Midlands and East, being those where slowly responding, high storage catchments are located. Forecast reliability and discrimination were also assessed with respect to low and high flow events. In addition to our benchmarking experiment, we conditioned ESP with the winter North Atlantic Oscillation (NAO) using adjusted hindcasts from the Met Office’s Global Seasonal Forecasting System version 5. We found gains in winter forecast skill (CRPSS) of 7–18% were possible over lead times of 1 to 3 months, and that improved reliability and discrimination make NAO-conditioned ESP particularly effective at forecasting dry winters, a critical season for water resources management. We conclude that ESP is skilful in a number of different contexts and thus should be operationalised in Ireland given its potential benefits for water managers and other stakeholders.

Funding

Science Foundation Ireland (Grant No. SFI/17/CDA/4783)

History

School

  • Social Sciences and Humanities

Department

  • Geography and Environment

Published in

Hydrology and Earth System Sciences

Volume

25

Pages

4159-4183

Publisher

Copernicus Publications

Version

VoR (Version of Record)

Rights holder

© The Authors

Publisher statement

This is an Open Access Article. It is published by Copernicus under the Creative Commons Attribution 4.0 International Licence (CC BY 4.0). Full details of this licence are available at: https://creativecommons.org/licenses/by/4.0/

Acceptance date

05/06/2021

Publication date

2021-07-22

Copyright date

2021

ISSN

1027-5606

eISSN

1607-7938

Language

en

Depositor

Dr Tom Matthews. Deposit date: 5 June 2021