Future climate

 

 

Temperature

 

Global rise of temperature is also affecting the whole investigated alpine region, whereas projected changes are very similar in the whole area. In the model, the yearly mean temperature is rising by approximately 1,5 °C until the period 2026-2055 and by 3,8 °C until the end of the century. Therefore, the changes in the alps are very similar to the projected global changes, but generally at the upper end of the skala. A possible reasons for this is, for instance, the reducing of snowcoverage in spring. After IPCC (AR5 2013), a global rise of temperatures between 1 and 2 °C until the mid and between 1,5 and 4 °C until the end of the century can be expected, depending on the emissions of greenhouse-gases. The region is therefore on the upper end of the projected bandwidth. 
This can be partially explained with the generally bigger temperature changes over land surface than over the oceans, which is included in the global mean temperature and therefore reduces it´s amount. But there are also other important influencing factors, which are investigated at the moment. In the Austrian Report on Climate Change 2014 (APCC 2014), a rise of temperatures about 1,7 °C until the mid of the century is projected, but relative to 1961-1990 whereas in our calculations, 1981-2010 has been used. This reduces the climage change-signal.

 

The simulated trends in temperature are very similar to observation data (Böhm 2012). Due to the non-linearity and internal variability of the climate system, warming trends after the year 2000 have slowed down in contrary to the fast 1980´s and 1990´s. But in general, the trend of rising concentrations of greenhouse-gases and therefore rising temperatures remains.

Rising temperatures are fundamental to all changes in the climate system and have far-reaching effects, for example the increase of mean snowfall height (Böhm 2008, Gobiet et al. 2013) or a prolongation of the vegetation period (Menzel et al. 2006). The well-known GLORIA-Project has been doing research about vegetation changes in alpine environments worldwide for several years (www.gloria.ac.at), for example on the mount schrankogel in the stubaier alps (Grabherr et al. 1994). A longer vegetation period theoretically influences the forest border and leads to condensing of trees and earlier flowers ermin. In the alps, forest border is much more influenced by humans then the climate (Grace et al. 2002). Therefore, temperature changes are not enough for changes. For animals, changes in their habitat don´t necessarily mean worsening. Living conditions could get better, thanks to longer breeding seasons or viewer deaths through hunger in winter (Dunn & Winiler 2010). On the other hand, interactions like plant-pollinator-relationships can be influenced in many ways by climate change (Hegland et al. 2009).

 

Warming temperatures cause a thawing of permafrost in the high alpine. As a result, an increase of rockfall (Gruber et al. 2004) and landslides is possible, in which landslides are strongly dependant on precipitation events. This can influence alpine infrastructure like cableway-pillars, avalanche-protections or streets. The mean yearly number of days where the thermometer exceeds 25 °C (summer days) will increase between 0 and 10 in the northern and alpine region and up to 20 in the southern part until mid of the century. The trend continues: 
Until the end of the century, between 50 and 60 more summerdays per year are expected in the southern areas, for example in the Adige valley and the southern regions of Belluno. The projected changes are already recognizable in observation data.

An increase of summerdays will likely lead to more heat load (Zuvela-Aloise 2013), which will be visible in he region in lower areas. In mid height areas, the touristic infrastructure could face better conditions thanks to warmer and possibly dryer summer-months.

 

 

Precipitation

 

Modelling of precipitation-changes in the next decades have a large uncertainty for some reasons, for example the scarse resolution of the model and the alpine orography. The modelled climate projections indicate trends, but in general all analysis regarding precipitation in the future is uncertain.

The yearly mean precipitation in the model is decreasing in the course of the century. At first just a little until the period 2026-2055, then a bit stronger until 2071-2100. Until the end of the current century, the precipitation could reduce between 160 - 180 mm per year, in which the changes in the southern part of Belluno are the strongest with up to -350 mm. In winter, precipitation could increase, because of more western-influenced weather whereas summer could be dryer because of more high-pressure-weather (Haslinger et al. 2015). The increase of precipitation during winter can compensate the decrease of summer precipitation only for the next decades and also just in some areas in the central alps and northern Tyrol. Therefore, a decrease in the second half of the century is likely. The modelling results are concurring with other investigations for the alps. Rajczak et al. (2013) did also show an increase of winterly precipitation and decrease of summerly precipitation for middle europe, in which the decrease in the south was even stronger. Comparable results also could be found by Smiatek et al. (2009) and Kotlarski et al. (2015).

 

Despite their uncertainties, the future scenarios show what is known from observations, but with some differences: Studys from Haslinger et al. (2012) or Brunetti et al. (2006) about trends in precipitation in the last 200 years show an increase of winterly precipitation north of the alps, but only minor changes  in the south. This increase can be explained with a trend of more western-influence weather. In the summer, the trends are slightly negative, but not significant. Despite that, the observation datasets show a significant trend of a precipitation-decrease south of the alps in autumn because of more frequent high pressure weather, which can not be seen so clearly in the models. Analysis of the climate stations in the region between 1961-2010 showed that in Kufstein a significant trend to more precipitation is visible, whereas the southeast of the study area shows a decreasing trend. In the other stations, no trend in yearly precipitation is recognizable.

 

Changing precipitation sums in the different seasons inevitably also change the water balance in the region. The projected changes will likely have no influence on the yearly drainage flow in the rivers. In summer, a decrease in non-glaciated areas can be expected, whereas in winter and spring an increase because of generally more precipitation and a higher percentage of rain is likely (Blaschke et al. 2011). As mentioned, such statements have larger uncertainties than such about developments in temperature-trends. Furthermore, the expected changes in precipitation are far less then the year-to-year variablity (Schöner et al. 2011).

 

Because of the different climate indizes which are being used in science, it´s not easy to directly compare different studies, but nevertheless it is tried here. Smiatek et al. (2009) did research about changes in the 90% percentile of daily precipitation sums for the end of the century in the central alpine area. The modelling results showed an increase in winter between 15-20% and a decrease in summer of about 10%, which would mean a slight increase in total. A europe-wide study from Nikulin et al. (2011) did show an increase in extreme precipitation until 2100, mainly in winter but also a slight increase in summer. Their investigation also showed, that each model can produce very different results: Different spatial patterns and characteristics in the projected changes have been recognized in all models. 

 

Large precipitation-events naturally also have high uncertainties in the simulations. The study from Beniston et al. (2007) shows the differences between several simulations, where the changes in maximum daily precipitationsums for the period 2071-2100 showed a span between -26% and +22%. It is quite obvious that possibly higher humidity in the atmosphere due to higher temperatures lead to more convective events. Some studies from observation datasets (Lenderink and Meijgaard 2010, Mohr and Kunz 2013) show that there is a correlation. But a stronger increase of temperature in the upper troposphere than near the surface can lead to a more stable stratification (APCC 2013), which counteracts the effect of more humidity. Further studies also indicate, that the connection between higher temperatures and more strong-precipitation-events is only valid for certain regions (Shaw et al. 2011, Haerter & Berg 2009) and that extreme precipitation depends on many other factors (orography, advection, size and movement of the system, etc.), which are not necessarily coupled to temperature. 

All these facts make statements about future precipitation very difficult and have therefore to be classified als very uncertain.

 

 

 

 

 

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