Projected future changes in water availability and dry spells in Japan: Dynamic and thermodynamic climate impacts

Abstract

Changes in water resources due to climate change are anticipated to impact a wide variety of sectors. This study investigated the impact of climate change on water availability and dry spells in Japan using large ensemble regional climate projections derived from the database for Policy Decision making for Future climate change (d4PDF). Self-organizing maps were applied to atmospheric circulation fields to study the linkages between water availability and weather patterns (WPs) during summer in the present and future climate simulations. The climate projections exhibited a reduced water availability defined by precipitation and evapotranspiration in the majority of Japan, consistent with increases in both frequency and duration of dry spells. The impacts of climate change on water availability vary by WP, with a significant increase in dry conditions under WPs with intensified climatological Pacific high over eastern Japan. Our results suggest that future changes in water availability can be attributed to changes in WP-related precipitation/evapotranspiration under warming conditions and in WP frequency in relation to the Pacific high, recognized as thermodynamic and dynamic effects of climate change, respectively. The decompositions of climate change impacts by WP analogs revealed that thermodynamic and dynamic effects account for approximately 80 and 20% of water availability changes, respectively. The yielded results are useful in the consideration of adaptive solutions that will ensure the sustainable use of water resources that balances economic and environmental demands.