Downscaling ECMWF seasonal precipitation forecasts in Europe using the RCA model

E Díez,B Orfila,M D Frías,J Fernández,A.S Cofiño,J M Gutiérrez

doi:10.1111/j.1600-0870.2011.00523.x

E Díez, B Orfila + Show 4 more

Open Access

https://doi.org/10.1111/j.1600-0870.2011.00523.x

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Abstract

The operational performance and usefulness of regional climate models at seasonal time scales are assessed by downscaling an ensemble of global seasonal forecasts. The Rossby Centre RCA regional model was applied to downscale a five-member ensemble from the ECMWF System3 global model in the European Atlantic domain for the period 1981–2001. One month lead time global and regional precipitation predictions were compared over Europe—and particularly over Spain—focusing the study in SON (autumn) dry events. A robust tercile-based probabilistic validation approach was applied to compare the forecasts from global and regional models, obtaining significant skill in both cases, but over a wider area for the later. Finally, we also analyse the performance of a mixed ensemble combining both forecasts.

Highlights

Seasonal forecasting is nowadays a well-established operational area and different centres around the world run global seasonal forecasting systems (Kirtman and Pirani, 2009), such as the Climate Forecast System from the National Center for Environmental Prediction, NCEP CFS, (Saha et al, 2006), the Australian POAMA (Wang et al, 2001), or the European EURO-SIP multimodel (Palmer et al, 2004; Vitart et al, 2007)
This method is invariant to any increasing transformation of the predictions and/or observations and has been introduced in a previous study to assess the skill of seasonal predictions from DEMETER and System2 over Spain
We present the results of an unprecedented hindcast experiment consisting of dynamically downscaling an ensemble of global seasonal forecasts for autumn (SON) and spring (MAM) from the ECMWF operational model System3 over Europe for a 20-yr period

Summary

Introduction

Seasonal forecasting is nowadays a well-established operational area and different centres around the world run global seasonal forecasting systems (Kirtman and Pirani, 2009), such as the Climate Forecast System from the National Center for Environmental Prediction, NCEP CFS, (Saha et al, 2006), the Australian POAMA (Wang et al, 2001), or the European EURO-SIP multimodel (Palmer et al, 2004; Vitart et al, 2007). The Rossby Centre (RCA) regional model was applied by AEMET to dynamically downscale these global predictions over the Euro–Atlantic region, considering the 12 initializations, month by month, around the year (Orfila et al, 2007) This long period allowed us to perform a robust probabilistic analysis of the results. The main goal of this paper is analysing the performance of a regional climate model (the RCA model) coupled over Europe to the global seasonal predictions of ECMWF System (Section 2) To this aim, a robust probabilistic validation framework is applied to compute the skill and the corresponding statistical significance of the global and regional predictions; the results are compared at a continental and regional (Spain) level (Section 3)

Data and area of study

Validation results

Findings

Conclusions