A resampling scheme for regional climate simulations and its performance compared to a dynamical RCM

Summary A new statistical method for regional climate simulations is introduced. Its simulations are constrained only by the parameters of a linear regression line for a characteristic climatological variable. Simulated series are generated by resampling from segments of observation series such that the resulting series comply with the prescribed regression parameters and possess realistic annual cycles and persistence. The resampling guarantees that the simulated series are physically consistent both with respect to the combinations of different meteorological variables and to their spatial distribution at each time step. The resampling approach is evaluated by means of a cross validation experiment for the Elbe river basin: Its simulations are compared both to an observed climatology and to data simulated by a dynamical RCM. This cross validation shows that the approach is able to reproduce the observed climatology with respect to statistics such as long-term means, persistence features (e.g., dry spells) and extreme events. The agreement of its simulations with the observational data is much closer than for the RCM data. Correspondence: B. Orlowsky, Potsdam Institute for Climate Impact Research, P.O. Box 60 12 03, 14412 Potsdam, Germany     

Recent anomalies of mean temperature of 12 consecutive months – Germany, Europe, Northern Hemisphere

Anomalies of mean air temperature of 12 consecutive months were detected recently at a number of spatial scales: from local via national and continental, to hemispheric. At all these spatial scales, pre-2007 records were exceeded by considerable margins. The recent rise in the mean temperature of 12 consecutive months at several scales has remained largely unnoticed, because the 12-month means are seldom analyzed. Broad attention is typically focused on monthly, seasonal and annual temperatures. Analysis of shifted 12-month periods helps spot peculiar 12-month episodes with remarkable temperature anomalies that do not coincide with a calendar year. Introducing 12-month running mean temperatures into the global warming debate can prove useful.     

Simulated global-scale response of the climate system to Dansgaard/Oeschger and Heinrich events

By using an Earth system model of intermediate complexity we have studied the global-scale response of the glacial climate system during marine isotope stage (MIS) 3 to perturbations at high northern latitudes and the tropics. These perturbations include changes in inland-ice volume over North America, in freshwater flux into the northern North Atlantic and in surface temperatures of the tropical Pacific. The global pattern of temperature series resulting from an experiment in which perturbations of inland ice and freshwater budget are imposed at high northern latitudes only, agree with paleoclimatic reconstructions. In particular, a positive correlation of temperature variations near Greenland and variations in all regions of the Northern Hemisphere and some parts of the southern tropics is found. Over the southern oceans a weak negative correlation appears which is strongest at a time lag of approximately 500 years. Further experimentation with prescribed temperature anomalies applied to the tropical Pacific suggests that perturbation of tropical sea-surface temperatures and hence, the tropical water cycle, is unlikely to have triggered Dansgaard/Oeschger (D/O) events. However, together with random freshwater anomalies prescribed at high northern latitudes, tropical perturbations would be able to synchronize the occurrence of D/O events via the mechanism of stochastic resonance.     

Winter storm- and summer thunderstorm-related loss events with regard to climate change in Germany

The development of winter storm- and summer thunderstorm-related loss events within the next decades in Germany was investigated with regard to change in frequency and intensity caused by climate changes. As a first step, observed meteorological data were connected with insurance data on a statistical basis. A regional climate model was then used to estimate future climate development. Using the statistical relations between meteorological and insurance data, the development of climate-driven damages was calculated. Results show that an increase of loss events can be expected within the next decades. These results show loss ratios shifting from higher return periods to smaller ones. In progressive decades, all these loss events become regionally more differentiated.     

Climatological drivers of changes in flood hazard in Germany

Since several destructive floods have occurred in Germany in the last decades, it is of considerable interest and relevance (e.g., when undertaking flood defense design) to take a closer look at the climatic factors driving the changes in flood hazard in Germany. Even if there also exist non-climatic factors controlling the flood hazard, the present paper demonstrates that climate change is one main driver responsible for the increasing number of floods. Increasing trends in temperature have been found to be ubiquitous in Germany, with impact on air humidity and changes in (intense) precipitation. Growing trends in flood prone circulation pattern and heavy precipitation are significant in many regions of Germany over a multi-decade interval and this can be translated into the rise of flood hazard and flood risk.     

Applying Non-Hierarchical Cluster Analysis Algorithms to Climate Classification: Some Problems and their Solution

Summary  Extended non-hierarchical cluster analysis is improved by deriving the initial cluster number and estimating the outliers in the final cluster set. These improvements are tested and compared with an established cluster algorithm using a toy example. Applying the improved cluster analysis to a classification of the European climates shows that the proposed techniques can be of great practical relevance. Received September 3, 1998 Revised July 5, 1999     

A short update on Koeppen climate shifts in Europe between 1901 and 2003

The question is investigated how far global warming in the period 1901–2003 will affect the region of Europe. For this purpose, changes of the climate zones that exist according to Koeppen will be analysed. The trends and outliers in terms of expansion and location of individual climate types are used as statistical indicators of climate change. The most important results of this study are: a) a significant increase of the extension of the climate types BS and Cr; b) a significant decrease of the extension of the climate types Dc and Ec; c) the largest changes are observed within the last two decades. These changes are discussed in relation to the mean conditions of temperature and precipitation. Moreover, significant correlations between the area extensions of climate types and the NAO index could be found.