Reliability Issue in Projections of the Impacts of Climate Change and Other Changes on Water Resources - page 3

Why do we Believe That Temperature Increase is the Greatest Uncertainty?

The average temperature increase in Serbia in the past 100 years amounts to about 0.6°C (Institute Jaroslav Černi 2013). With all due respect for the correctness of the calculations, climate model outputs (IPPC 2000, 2007), which indicate that temperatures at the end of the 21st century will be 3-4°C higher (the most likely interval), appear to be highly debatable. It is likely that such a temperature increase will result in social changes that are impossible to predict (primarily events precipitated by human response), and that brings into question the adopted initial assumptions concerning social changes and the magnitude of GHG emissions. This is the first reason why temperature increase is deemed to be the greatest uncertainty.

The second reason is related to past temperature peaks on our planet. Figure 3 shows average temperatures in the past 500,000 years (Hansen and Sato 2012, Messinger 2013). It is apparent that the present (Holocene) average temperature is 1°C lower than the highest peaks recorded in the Holsteinian and Eemian. This suggests that our planet might have safety mechanisms against excessive temperature increases, for instance relatively sudden deceleration of thermohaline circulation (large-scale ocean circulation), which could result in more severe winters, particularly in the northern hemisphere.

It is also not impossible for countries across the world to reach an agreement about reducing GHG and other emissions, which they would honor for the most part. At least, we would like to believe in that.

 

Fig03Figure 3: Past temperature changes (Hansen and Sato 2012, Messinger 2013).

 

Concluding Remarks

Observed hydrological changes in Serbia are important. Climate change is only one of the factors that impact water resources. The impact of climate change has been noted at all gauging stations, but its significance varies. In eastern Serbia it is generally dominant, in some parts of the country it is often not of primary concern, and elsewhere it is minor given the magnitude of other impacts (Institute Jaroslav Černi 2013, Nachtnebel 2013).

Even though uncertainty is inherent in any projection, it is quite certain that it grows with the period of time for which the projection is made. Considering all the above, the author believes that all projections that pertain to the distant future (50 or more years) should be deemed purely "academic" and the focus of professional circles and society as a whole should remain on the near future (about the next 30 years), as the average decrease in water resource availability is not only probable but to an important extent measurable. This means that adaptation measures, affordable to the country's economy, are needed across the water sector. 

Priorities also need to be considered, as well as the fact that Serbia can expect a decrease in average water resource availability, at least in the near future, which cannot be disregarded.

It is recommended that one of the future projects that assess the impact of climate change on water resources in the near future (max. increase in average annual temperatures by 1 to 2°C) should include a larger number of national river catchments and seek out climate scenarios and hydrological models that produce average dependencies between river discharges and temperatures at mean annual levels, according to the correlation shown in Figure 2.

 

Acknowledgement

This paper is an outcome of the scientific project "Assessment of Climate Change Impact on Water Resources in Serbia" (TR37005), funded by the Ministry of Education and Science of the Republic of Serbia.