Climate Change and Energy Systems |
Author: TemaNord 2011This report summarises results from the recently completed research project Climate and Energy Systems (CES), which delivered a new assessment of the future development of renewable energy resources in the Nordic and Baltic Regions. The project focused on climate impacts within the energy sector, addressing both the positive aspects as well as the increased risks associated with expected climate change up to the mid-21st century. Main results produced by CES working groups are briefly summarised in this chapter. Statistical analysis of hydrological and meteorological time series The research group focusing on statistical analyses of hydrological and meteorological time series within the CES project made use of data from the Nordic stream-flow database, which consists of 160 series of daily discharge data from Denmark, Finland, Iceland, Norway and Sweden, to analyse long-term trends at individual stations within the Nordic region. Long-term trends in regional series have also been analysed based on precipitation, temperature and discharge records available in the individual countries. The regional series analyses undertaken all point towards a positive anomaly in annual temperature in recent years, relative to the reference period 19611990. Results for precipitation and runoff are much more variable, both between countries and between regions in individual countries. An increase in annual precipitation occurred in Denmark, Norway and southern Iceland and annual runoff increased up to the year 2000 in these same areas and as well as in northern Sweden. Seasonal analysis of runoff anomalies for the Baltic countries indicates a marked increase in winter runoff throughout the region, and a decrease in summer runoff. A strong negative trend in the timing of spring snowmelt (i.e. earlier snowmelt) is found for many of the stations in the Nordic Region. Analysis of the occurrence of peak flow events exceeding the mean annual maximum flood suggests a pattern of spatial variability, with some stations (for example, in western Norway and in Denmark) exhibiting an increase in the total number of events, and other stations (in Sweden, Finland and parts of Denmark) exhibiting a decrease. For the Baltic re- 12 Climate Change and Energy Systems gion, the analysis of the timing of the spring flood maximum discharge suggests an earlier spring flood due to an earlier spring snowmelt. Climate scenarios for the Nordic and Baltic region Regional climate models (RCMs) were used in CES to produce highresolution (25x25 km) climate scenarios for the Nordic and Baltic region. From an ensemble consisting of 15 RCM climate change simulations, three were selected for use in targeted studies within CES, with focus on the period 20212050. Some of the working groups in CES have used scenarios for the entire 21st century in their modelling studies. All three models project a summer temperature increase of at most 2°C over most of the region for the period 20212050, in comparison with the control period 19611990. Increases in winter temperatures will be more variable and most pronounced (up to 4°C) in the eastern and northern areas. In particular, there is a strong response to the general warming over the northernmost oceans where feedback mechanisms associated with retreating sea-ice come into play. The largest precipitation increase will generally be seen in winter. In summer, there is a larger uncertainty and the possibility that precipitation will decrease in southern parts of the region cannot be excluded, although several regional simulations indicate that summertime precipitation could increase over the Baltic Sea. Wind speed changes are generally small with the exception of areas that will see a reduction in sea-ice cover, where wind speed is projected to increase. The analysed RCM scenarios sample only a part of the full uncertainty range for the future climate. This is true both for the 15 selected scenarios and even more so for a subset of 3 scenarios used in most of the impact studies within the project. In order to characterize the full spread in a better way probabilistic climate change signals were calculated based on a larger ensemble of general circulation models (GCMs). It was found that the selected RCM-scenarios in general fit well within the distributions inferred from the wider range of GCM climate scenarios. However, for some variables, regions and seasons there are deviations where the RCM scenarios deviates from the general picture. The results clearly indicate that one should be careful with drawing far-reaching conclusions based on individual model simulations. CES climate modelers have also downscaled results from global climate models to higher resolution (13 km), producing spatially more detailed scenarios than the standard 25 km simulations. The largest differences are seen in mountainous areas, but coastal effects also come into play. Biases are observed in those high-resolution model outputs, when compared with observations, calling for the development and application of bias correction techniques. Climate Change and Energy Systems 13 Additional work done by the climate modeling group involved examination of the inter-annual variability of future climate, studies of the migration of climatic zones, assessment of 21st century precipitation trends in selected regions, studies of the characteristics of North Atlantic Cyclones, studies of storm statistics and future changes in surface geostrophic wind speeds, solar radiation projections and the possible future change in climate extremes in the CES area of interest, as determined by a range of General Circulation Models (GCMs).