10 Hydrological Impacts of Climate Changes in Romania
311
The results of the studies mentioned above show heterogeneous spatial patterns of
the identified streamflow trends, both at regional and national scales. The magnitude
and statistical significance of the identified trends are sensitive to the period examined. On a global scale, according to [4], 70% of the total of 195 stations analyzed
do not exhibit any statistical trend at the 10% significance level, and the remaining stations had either positive or negative trends in the annual maximum flow (for
observation periods of at least 40 years). During 1948–2004, only about one-third
of the 200 investigated rivers have registered statistically significant trends, 45 with
downward trends and 19 with upward trends [32].
Regionally, some spatial differences can be distinguished. Thus, a streamflow
decrease was generally noticed in regions affected by lower rainfall (e.g., vast areas
in Africa, eastern and southeastern Asia and eastern Australia) [4, 10, 16, 32 etc.].
In other regions, where rainfall and temperatures increased, higher streamflow was
identified, as in some areas of northern Eurasia, Central and Far-East Asia, northern
North America, southern South America [4, 21, 22, 27, 28, 31].
In Europe, a regionally coherent picture of mean annual streamflow tendency was
identified (during 1962–2004), with negative trends in southern and eastern regions,
and generally positive trends elsewhere [63].
Concerning the changes in observed extreme streamflow, the general conclusion
is that in recent decades there are no clear trends in flood discharge at a regional or a
national scale in Europe [64]. In terms of floods, geographically organized patterns
of climate-driven changes in their magnitude and frequency could not be detected,
but an increase in the number of large floods in Europe during 1985–2010 has been
identified [65]. For some small regions, increases in flood peak discharges were
detected, as in some alpine basins [66], in Switzerland [51], northern part of Austria
[33], northeast France [35, 36], as well as in some regions in Germany [37–40], and
northern and western UK [56]. Decreases in peak discharges were noticed in some
areas or at hydrometric stations in the Baltic region [59, 60], in Poland [42], etc.
10.2.2 Future Hydrological Changes
Assessing the potential impacts of climate changes on the hydrological cycle and
water resources in the future has become, together with change detections studies
based on observational data, one of the most important concerns in contemporary
hydrology. This issue has a major interest in developing and implementing appropriate measures to adapt the society to the climate changes related effects. Consequently,
worldwide, a large number of researches has focused on the future projections of the
hydrological impacts of climate changes. The assessments are made by using modelbased simulations, considering different climate scenarios. Depending on the specific
climate scenario and model used, the projections may show different results, with
more or less severe hydrological impacts. Generally, each climate and hydrological
projection is subject to limitations and uncertainties in its ability to model the climate
and the water-related system. Most of the hydrological projection are based on cli-
311
The results of the studies mentioned above show heterogeneous spatial patterns of
the identified streamflow trends, both at regional and national scales. The magnitude
and statistical significance of the identified trends are sensitive to the period examined. On a global scale, according to [4], 70% of the total of 195 stations analyzed
do not exhibit any statistical trend at the 10% significance level, and the remaining stations had either positive or negative trends in the annual maximum flow (for
observation periods of at least 40 years). During 1948–2004, only about one-third
of the 200 investigated rivers have registered statistically significant trends, 45 with
downward trends and 19 with upward trends [32].
Regionally, some spatial differences can be distinguished. Thus, a streamflow
decrease was generally noticed in regions affected by lower rainfall (e.g., vast areas
in Africa, eastern and southeastern Asia and eastern Australia) [4, 10, 16, 32 etc.].
In other regions, where rainfall and temperatures increased, higher streamflow was
identified, as in some areas of northern Eurasia, Central and Far-East Asia, northern
North America, southern South America [4, 21, 22, 27, 28, 31].
In Europe, a regionally coherent picture of mean annual streamflow tendency was
identified (during 1962–2004), with negative trends in southern and eastern regions,
and generally positive trends elsewhere [63].
Concerning the changes in observed extreme streamflow, the general conclusion
is that in recent decades there are no clear trends in flood discharge at a regional or a
national scale in Europe [64]. In terms of floods, geographically organized patterns
of climate-driven changes in their magnitude and frequency could not be detected,
but an increase in the number of large floods in Europe during 1985–2010 has been
identified [65]. For some small regions, increases in flood peak discharges were
detected, as in some alpine basins [66], in Switzerland [51], northern part of Austria
[33], northeast France [35, 36], as well as in some regions in Germany [37–40], and
northern and western UK [56]. Decreases in peak discharges were noticed in some
areas or at hydrometric stations in the Baltic region [59, 60], in Poland [42], etc.
10.2.2 Future Hydrological Changes
Assessing the potential impacts of climate changes on the hydrological cycle and
water resources in the future has become, together with change detections studies
based on observational data, one of the most important concerns in contemporary
hydrology. This issue has a major interest in developing and implementing appropriate measures to adapt the society to the climate changes related effects. Consequently,
worldwide, a large number of researches has focused on the future projections of the
hydrological impacts of climate changes. The assessments are made by using modelbased simulations, considering different climate scenarios. Depending on the specific
climate scenario and model used, the projections may show different results, with
more or less severe hydrological impacts. Generally, each climate and hydrological
projection is subject to limitations and uncertainties in its ability to model the climate
and the water-related system. Most of the hydrological projection are based on cli-