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Regional, seasonal and predictor-optimized downscaling to provide groups of local scale scenarios in the complex structured terrain of Austria

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Abstract:

The aim of this study is to derive local scale climate change scenarios for temperature and precipitation at approximately thirty stations in Austria and to discuss the scenarios' dependency on combinations of large scale fields used as predictors in empirical downscaling. We distinguish between the seasons and different climatic provinces in Austria. To accomplish this task we utilize large scale, monthly NCEP/NCAR reanalysis data and station data provided by the Austrian weather service for the second half of the 20th century. These datasets are analyzed by means of Empirical Orthogonal Functions (EOF) and combined via transfer functions derived by Canonical Correlation Analysis (CCA). The performance of the transfer functions is validated in several validation experiments and used to determine a group of best performing large scale predictors. These predictors are extracted from the IS92a 'greenhouse gas only' (GHG) and IS92a 'greenhouse gas plus aerosols' (GHG+ars) scenarios, performed with the ECHAM4/OPYC3 climate model for the first half of the 21st century and projected onto the local scale by the transfer functions. We discuss the local scale impact of different predictors. In order to assess the bulk properties of these ensembles, those variables which generate the wettest/driest or coolest/warmest changes are further discussed. All changes mentioned below refer to scenarios for the first half of the 21st century compared to observations recorded during the second half of the 20th century. Findings depend on seasons, regions and the scenario actually used. In the case of temperature and the IS92a GHG scenario an overall increase of about 1° to more than 3°C is found. The temperature increase introduced by the IS92a GHG+ars scenario shows around 0.8°C lower values. Differences between the warm and cool realizations are in the same range. In the case of precipitation the performance of the empirical models is substantially lower. For the IS92a GHG differences between wet and dry realizations are in some cases large and do not even allow to define the sign of change. The range of the IS92a GHG+ars ensemble is smaller and indicates moderate seasonal precipitation reductions. Possible reasons that may cause different local scale responses are discussed and an approach of how to deal with them, based on BUSUIOC and VON STROCH, (1996), is proposed.

German
Ziel dieser Studie ist es Klimäanderungsszenarien für Temperatur und Niederschlag an rund 30 Stationen in Österreich abzuleiten sowie die Abhängigkeit dieser Szenarien von verschiedenen Kombinationen großräumiger Prädiktorfelder zu diskutieren. Dabei wird zwischen den Saisonen und verschiedenen Klimaregionen unterschieden. Die Studie beruht auf den NCEP/NCAR Reanalysedaten sowie auf Beobachtungen des österreichischen Wetterdienstes, die auf Monatsbasis für die zweite Hälfte des 20. Jh vorliegen. Diese Datensätze werden mit der Methode der Empirischen Orthogonalfunktionen (EOF) analysiert und mit Hilfe der Kanonischen Korrelationsanalyse (CCA) werden zwischen ihnen Transferfunktionen abgeleitet. Die Leistung der Transferfunktionen wird in verschiedenen Validierungsexperimenten bestimmt und dazu verwendet, Kombinationen von großräumigen Feldern zu detektieren, die die beste Leistung zeigen. Diese Prädiktorfelder werden dann aus dem IS92a ,greenhouse gas only' (GHG) und dem IS92a ,greenhouse gas plus aerosols' (GHG+ars) Szenario, die mit dem ECHAM4/OPYC3 Klimamodell für die erste Hälfte des 21. Jh am Deutschen Klimarechenzentrum berechnet worden sind, extrahiert und mit den Transferfunktionen auf die lokale Skala projiziert. Um die unterschiedlichen Auswirkungen der Prädiktorkombinationen auf die lokalskaligen Szenarien zu beschreiben werden jene Kombinationen diskutiert, die auf die feuchtesten/trockensten bzw. kühlsten/wärmsten Szenarien führen. Mögliche Ursachen für die unterschiedlichen lokalskaligen Szenarien werden diskutiert und basierend auf BUSUIOC and VON STROCH, (1996) wird ein Weg vorgeschlagen sie zu behandeln.

Document Type: Research Article

DOI: https://doi.org/10.1127/0941-2948/2005/0014-0031

Publication date: 2005-02-01

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  • Meteorologische Zeitschrift (originally founded in 1866) is the joint periodical of the meteorological societies of Austria, Germany and Switzerland. It accepts high-quality peer-reviewed manuscripts on all aspects of observational, theoretical and computational research out of the entire field of meteorology, including climatology. Meteorologische Zeitschrift represents a natural forum for the meteorological community of Central Europe and worldwide.
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