Sensitivity Analysis of Water Resources and of Water Management Works Under Various Hydrologic Scenarios Accounting for Climate Change
Sponsored by the Greek Secretariat for Research and the Ministry of Public Works
Introduction
Regional effects of greenhouse warming on water resources, and more specifically on surface runoff, were
assessed for a mountainous region of central Greece comprising four drainage basins by using a conceptual
model and plausible hypothetical scenarios of temperature and precipitation change. Results showed considerable
sensitivity of runoff characteristics to climate change and indicated certain basin morphoclimatic
characteristics such as snow cover, basin aridity and morphology, runoff coefficients etc., which
modify considerably basin response. The sensitivity of some critical water management issues,
such as reservoir storage and hydroelectric production, to climatic variability and change on a
regional basis was analysed as well. By using a set of plausible hypothetical climatic scenarios to
represent both greenhouse warming and precipitation changes, the sensitivity of the guaranteed annual
fresh water and energy supply levels has been evaluated under conditions of altered runoff for four
connected multipurpose reservoirs in central Greece. It was shown that reservoirs designed and operated
under current climatic conditions are, in general, affected by the climatic changes examined. A
dramatic increase of the risk associated with the annual guaranteed quantity of water supply and
energy production would occur if greenhouse warming was accompanied by a reduction in annual
precipitation. Significant increases of storage volume would then be needed to maintain existing
water and energy yields at tolerable risk levels.
Conclusions
The conclusions drawn from this research are the following:
- Mountainous, seasonally snow-covered Mediterranean basins with effective water retentive mechanisms exhibit under temperature increase serious reduction of mean annual runoff, even more serious reduction of summer runoff and minimum annual runoff along with a significant increase of winter runoff and of maximum annual runoff. In general, reductions are more intense than increases, due to the conducive effect of evapotranspiration. A warmer, humid basin with local characteristics that inhibit water retention exhibits minimal sensitivity of runoff to temperature increase.
- In general, a magnification factor characterises the effects of precipitation change on runoff, and can be thought of as a measure of basin sensitivity to precipitation change. Regarding annual runoff, the magnification factor seems to be independent of temperature and positively associated with basin aridity, whereas on a seasonal basis acidity, whereas on a seasonal basis it depends on the presence of winter snow cover and consequently on temperature increases.
- The already high seasonality of runoff of the Mediterranean type is considerably intensified in basins sensitive to temperature increase, with apparent consequences on reservoir storage capacity.
- Snow is distinguished as the most significant and determining factor of basin response to climatic change. This factor, in turn, depends on the orographic characteristics of the basin besides the general climatic ones. Additional characteristics are shown to be important, for example the coefficient of runoff which, when unusually high, does not permit other hydrological processes, sensitive to climatic change, to be accomplished or even to take place at all.
- A dramatic increase of risk levels of the annual firm water and energy production of the reservoirs examined is exhibited under plausible hypothetical scenarios of climate change. Reservoirs are very, and increasingly, sensitive to precipitation decreases. Downstream reservoirs appear to be more sensitive to precipitation reductions than upstream ones. Risk levels are also affected by temperature increases but the effect is marginal compared to the effect of precipitation reductions.
- Radical increases of reservoir storage volume are required in order to maintain firm water and energy yields at tolerable risk levels. Those volume increases are mainly, and increasingly, affected by precipitation reductions examined. The effect of temperature increase again appears to be marginal as compared with that of precipitation reduction.
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