Frequency analysis of extreme hydrologic events and water stress in a changing climate

Climate change and its effects and impacts on human societies and environment are now a reality and of major concern to all stakeholders at different levels. It is characterized by the increase in global atmospheric temperature attributed to increase in carbon dioxide concentration caused by both natural factors (e.g. volcanic eruptions) and anthropogenic activities. While there are still more uncertainties that need to be better understood about climate change, it has already been established beyond responsible and reasonable doubt based on recent studies and global observations and measurements. Recent assessments on climate change noted that the warming of the climate system is unequivocal, and it is expected to have profound adverse impacts on food production systems, and also on the hydrology of watersheds. Changes in the hydrologic regime are characterized by the shift in distribution and the disproportionate increase in mean and variance of the hydrologic variables. This means that more intense extreme events are expected to occur more frequently which will be evident in the occurrence of stronger typhoons accompanied by high rainfall and wind speed, severe droughts, and related hydrologic phenomena. Thus climate change impact studies should consider both the impacts on water scarcity or stress as well as on extreme hydrologic events. This study presents an analysis of recurrence intervals of extreme rainfall events in the Philippines under current climate conditions as well as anticipated or future climate scenarios defined in terms of incremental percent increase in precipitation. Frequency analysis of annual maximum rainfall is conducted for selected locations whose future rainfall distributions simulated by a weather data generator. Empirical records of shifts in distribution and their corresponding impacts are also presented. Magnitudes of extreme rainfall events for specified return periods (10-, 20-, 50- and 100-year) were also process-based crop growth and crop yield model were simulated. The impacts of climate change on water availability and water scarcity in the Philippines besides the extreme events are also analyzed based on water withdrawals, consumption, and per capita requirements. The paper also describes some knowledge-based priority adaptation strategies and mitigation measures to address the adverse impacts of changing and variable climate.