Assessments of climate change effects on river flows

Significant variations are foreseen in precipitation and especially temperature values in many regions of the world, with reference to the Fourth Assessment Report (AR4) prepared on the purpose of evaluating the reasons and consequences of the climate change effects in detail within the scope of Intergovernmental Panel on Climate Change (IPCC). It has been considered that, river flows are the primary hydrological processes to be affected from these variations.In the study presented, Tahtali catchment, the foremost fresh water resource of coastal Aegean region which may be affected by the climate change has been examined. Precipitation and temperature variations have been determined according to climate models by using various climate scenarios and selected fourteen models operated under these scenarios specified in the AR4 report. These variations were downscaled to station scale by statistical downscaling model that was developed within the study and thus, variations on local climate were obtained. In addition to used fourteen climate models, a combined climate model, which represents the monthly variations of present day statistics for precipitation and temperature, has been also proposed.The vulnerability of basin to precipitation and temperature variations those of which might be possible in the future periods has also been examined by performing several statistical approaches via transforming the downscaled precipitation and temperature variations of fourteen climate models and combined climate model into runoff by several parametric rainfall-runoff models.In addition to these, Tahtali flows affected by future precipitation and temperature variations were evaluated by several reservoir theories and the performance of the reservoir under the climate change was tested. In implementing these tests, minimum flows method, monthly water budget that gives the ability to perform classical reservoir operation and Gould probability matrix were utilized. Among these methods, the future variations of critical period durations were examined by using the minimum flows method and with the behavior analysis and probability matrix method, the yield-performance relations of the reservoir has been evaluated.When combined climate model results were taken into consideration, decreases of 3% and 13% are foreseen for the optimistic and pessimistic scenarios of precipitation. The increases of 1.5 0C and 2.1 0C are also foreseen for the optimistic and pessimistic scenarios of temperature. The decreases of 9% and 22% are foreseen for the optimistic and pessimistic scenarios of runoff. Under these conditions, it has been also predicted that urban water supply from the reservoir would decrease %11 according to optimistic scenario and %35 according to pessimistic scenario.