WATER BALANCE CHARACTERISTICS OF KEI KECIL ISLAND, SOUTHEAST MALUKU: AN INITIAL APPROACH TO GROUNDWATER MANAGEMENT ON A SMALL CARBONATE ISLAND

Abstract

Small carbonate islands commonly depend on groundwater as their primary freshwater resource, making an understanding of water availability essential for sustainable groundwater management. This study characterises the water balance of Kei Kecil Island, Southeast Maluku, Indonesia, as an initial step toward understanding groundwater availability in a small carbonate-island environment. The study used precipitation, evapotranspiration, and available water capacity (AWC) data. Precipitation and evapotranspiration data for 2000–2025 were processed spatially and temporally to derive monthly and annual characteristics within the Kei Kecil Island boundary. AWC data for the upper 0–30 cm soil layer were used to support the interpretation of near-surface water storage. The water balance was determined from the difference between precipitation and evapotranspiration and was subsequently evaluated at monthly and annual scales. The results show a mean annual precipitation of 2,409.94 mm/year and mean annual evapotranspiration of 1,488.95 mm/year, resulting in a positive annual water balance of 920.99 mm/year. The AWC ranged from 4.95 to 63.75 mm, with a mean of 35.60 mm, indicating spatial variation in the upper soil layer's capacity to retain water. The positive water balance shows that precipitation provides an important water input to Kei Kecil Island's hydrological system after accounting for evapotranspiration losses. However, the calculated water surplus cannot be directly considered equivalent to groundwater recharge because excess water may be partitioned into infiltration, runoff, soil-water storage, and groundwater discharge. The findings provide a preliminary hydrological framework that complements existing information on the freshwater groundwater system and supports using water balance characterisation as an initial approach to groundwater management on small carbonate islands.