Developing a yearly warning index to assess the climatic impact on the water resources of Taiwan, a complex-terrain island

Changes in the annual supply and demand ratio with respect to the past mean state are quantified and indexed to evaluate the effect of climate change on the water resources in Taiwan, a complex-terrain island. Four sub-regions were divided based on general terrain structures and major river flows. The changes in future temperature, precipitation and river runoff were projected statistically from monthly mean atmosphere–ocean coupling global circulation model (AOGCM) outputs. The results show that water resources will increase over the unpopulated eastern region, but will decrease over other densely populated and densely industrialized regions. Significant yearly variation is another worrisome factor burdening the vulnerable water management system. The developed yearly warning index for assessing the climatic impact on water resources is very useful to the water management agency and has a universal application potential.