Vulnerability assessment of Angat water reservoir to climate change

Global warming due to an anticipated doubling of carbon dioxide concentration in the atmosphere is expected to alter the earth's climate system within the next century. The potential changes in the climate system could affect hydrological cycles and processes. Possible impacts of climate change on water resources should be assessed to evaluate probable adaptation measures. In the Philippines, a preliminary assessment of the vulnerability of water resources to climate change and variability was undertaken. For this particular study, the Angat Reservoir was chosen as the study area. Because of its socioeconomic importance, it is useful to assess its vulnerability to climate change. A rainfall-runoff simulation model, WATBAL, was used to determine the effect of temperature and rainfall changes, based on CO₂ doubling, on inflow to the reservoir. Climate change scenarios developed from results from three general circulation models and incremental changes were used. The results showed that changes in temperature and rainfall could affect runoff either positively or negatively. Using the temperature and rainfall changes from the Geophysical Fluid Dynamics Laboratory model there was a 32% increase in runoff, and with the Canadian Climate Centre Model, there was a 15% decrease in runoff. Under a climate scenario generated by the United Kingdom Meteorological Office model, runoff is estimated to increase by 5%. The use of incremental scenarios revealed the strong sensitivity of runoff to changes in rainfall as compared with changes in temperature.