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The raw water for irrigation must meet the minimum requirements of class IV water quality. This study aims at presenting a water quality assessment of several raw water sources in Bintan Island for irrigation purposes. The methods used are Standardized Precipitation Index, Pollution Index, and Sodium Adsorption Ratio. A climate analysis showed that the potential high risk of the flood was 16 events in 22 years, and severe-to-extreme dry soil moisture and streamflow were 8 to 10 events in 22 years, with durations of every event varying from 1 to 6 months. Severe-to-extreme reduction of reservoir level was five events in 22 years, with a duration of every event varying from 2 to 13 months. The water quality analysis showed that all water sources meet the quality standard to irrigation as a class IV water quality. While based on SAR values, all water sources have excellent categories and good categories, except Dompak pond and Kolong 6 reservoirs that are doubtful categories. The availability of raw water mainly causes the problem of water sources, so better surface water management is necessary for Bintan Island to support food resilience.

Understanding the characteristics of low flows over time is critical to sustainable water resource management in Bintan, a small tropical island in Indonesia. Low flows are driven by precipitation and controlled by the soil and geological parameters of a catchment. A method that integrated the Standardized Precipitation–Evapotranspiration Index (SPEI) and the calculated total runoff (TRO) was developed in order to analyze the change in low-flow intensity over time. This method included steps for the selection of an appropriate SPEI timescale and the development of low-flow intensity classes based on the TRO, and was used to assess the trend in low-flow intensity change in Bintan Island for 1981–2020 and the impact of climate change on low-flow intensity for 2031–2070. The results showed that low-flow intensity in the second half of the 1981–2020 period was 45% less than in the first half, with an estimated increase in low-flow volume of 405 mm (22.4%). The climate-change projection for 2031–2070 indicated an increase in low-flow intensity of 14% compared with 1981–2020, with an estimated 12% decrease in low-flow volume. The integrated method indicated a trend similar to that of a method using only the SPEI, but with better performance in estimating the low-flow volume change, thus providing a better understanding of how the low-flow intensity will change over time.

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