Assessment of future water availability and seasonal patterns of dry seasons under climate change in Cidanau Watershed Banten Province, Indonesia

Cidanau Watershed, Banten Province, Indonesia, features a natural wetland (caldera) surrounded by mountains. The SWAT was employed to assess future hydrological changes in water availability and seasonal patterns of dry seasons in Cidanau watershed. The dry season was determined when the rate of cumulative evapotranspiration was higher than the rate of cumulative rainfall. Using 2002 – 2021 data as a baseline, future projections were evaluated for 2030 s, 2050 s, 2070 s, 2090 s. The SWAT model has been edited with wetland input parameters and calibrated with river channel and watershed parameters. 1) The SWAT model performance marginally improved after incorporating wetland input and river channel parameters in parameterization process; 2) Projected increase in mean Tmin & Tmax range from 0.5°C to 2.9°C, while mean annual rainfall is expected to decrease by −7 %– –10.3 % compare to the baseline periods; 3) As the result, the annual water yield is projected to decline by –11 % – –26 %, with the rainy season experiencing the most significant reduction; 4) The length of dry seasons is projected to increase, further impacting water availability; 5) Additionally, the frequency of extended dry seasons is expected to increase under future climate scenarios. This study highlights the anticipated decline in water availability and shifting dry season pattern, supporting decision-maker in developing adaptive and mitigation strategies for future climate challenges. • The SWAT model performance marginally improved after incorporating wetland input and adding river channel parameters. • T min & T max are projected to increase, while rainfall is projected to decrease, leading to a reduction in water yield. • The Transition of dry and wet season is facing unstable under climate change. • The possibilities of occurrences of extended dry seasons are expected to increase and occur further longer • The changing water yield is affected by rainy season precipitation and its duration