10 Hydrological Impacts of Climate Changes in Romania
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Fig. 10.13 Mean monthly amount of solid (S) and liquid (R) precipitation (a) and mean monthly
snow depth (b) in Valea Cerbului River catchment for the climatic scenarios B1, A2, A1B
(2001–2065) and the reference period C20 (1961–2000)
decrease of the snow layer depth and duration, directly affecting the streamflow,
because in high mountainous regions, the snowmelt is an important component of
river flow.
For the interval November–February, the projections show a uniform decrease of
snow depth relative to the reference period. From March to May the simulations are
still below the monthly values of the reference period, but for the A2 scenario, the
decrease is lower (Fig. 10.13b). The changes in the snow depth are of approximately
27% at annual level (scenarios average) and up to 68% at the monthly level.
The simulations of the hydrological regime under the emission scenarios indicate
a lower mean annual discharge of −2% up to −6% (depending on the scenario),
but with important monthly and seasonal differences. From January to April, all
the three scenarios indicate increased mean monthly discharges, of 4–22%, with the
maximum difference in January for the B1 scenario (Fig. 10.14). This is the effect
of rising air temperatures, fact that triggers liquid precipitation events, a diminished
snow depth and earlier snowmelt. For May–December the average of the scenarios
estimates lower mean monthly discharges (between −10 and −29%), excepting
several months for the A2 scenario (May–July) and B1 scenario (July), for which the
simulated mean monthly discharges exceed those simulated for the reference period
(with 2–19%) (Fig. 10.14).
The seasonal projected differences are conclusive for the autumn and the winter,
when all three scenarios are consistent with each other and with the changes observed
in the climatic parameters (temperature and precipitation): significant decrease during autumn (−13 to −19%) and slight increase during winter (1–7%).
To analyze the impact of climate changes on the magnitude and frequency of
extreme flows (high and low), we set two thresholds: the discharge with 95%
exceedance probability (Q 95% ) for low flow and the discharge with 5% exceedance
probability (Q 5% ), for high flow.
The results of the simulations show that the Q 5% threshold does not change significantly: the maximum change is predicted by the A2 scenario (8% higher than
337
Fig. 10.13 Mean monthly amount of solid (S) and liquid (R) precipitation (a) and mean monthly
snow depth (b) in Valea Cerbului River catchment for the climatic scenarios B1, A2, A1B
(2001–2065) and the reference period C20 (1961–2000)
decrease of the snow layer depth and duration, directly affecting the streamflow,
because in high mountainous regions, the snowmelt is an important component of
river flow.
For the interval November–February, the projections show a uniform decrease of
snow depth relative to the reference period. From March to May the simulations are
still below the monthly values of the reference period, but for the A2 scenario, the
decrease is lower (Fig. 10.13b). The changes in the snow depth are of approximately
27% at annual level (scenarios average) and up to 68% at the monthly level.
The simulations of the hydrological regime under the emission scenarios indicate
a lower mean annual discharge of −2% up to −6% (depending on the scenario),
but with important monthly and seasonal differences. From January to April, all
the three scenarios indicate increased mean monthly discharges, of 4–22%, with the
maximum difference in January for the B1 scenario (Fig. 10.14). This is the effect
of rising air temperatures, fact that triggers liquid precipitation events, a diminished
snow depth and earlier snowmelt. For May–December the average of the scenarios
estimates lower mean monthly discharges (between −10 and −29%), excepting
several months for the A2 scenario (May–July) and B1 scenario (July), for which the
simulated mean monthly discharges exceed those simulated for the reference period
(with 2–19%) (Fig. 10.14).
The seasonal projected differences are conclusive for the autumn and the winter,
when all three scenarios are consistent with each other and with the changes observed
in the climatic parameters (temperature and precipitation): significant decrease during autumn (−13 to −19%) and slight increase during winter (1–7%).
To analyze the impact of climate changes on the magnitude and frequency of
extreme flows (high and low), we set two thresholds: the discharge with 95%
exceedance probability (Q 95% ) for low flow and the discharge with 5% exceedance
probability (Q 5% ), for high flow.
The results of the simulations show that the Q 5% threshold does not change significantly: the maximum change is predicted by the A2 scenario (8% higher than