Abstract A higher drought risk in Java Island is generally known than the other regions in Indonesia. Tracking soil moisture can be an alternative way to monitor drought rather than precipitation-based drought indices. The objective of this study was to assess root-zone water storage (defined by root-zone soil moisture contents) based on a linked approach between the generalized complementary relationship (GCR) and a single bucket model in Java Island. Since it does not require precipitation for estimating actual evapotranspiration (ETa), the GCR allowed implementation of a simple single bucket model. The ETa and root-zone soil moisture estimated in this study were compared against the Global Land Evaporation Amsterdam Model (GLEAM) and the root-zone water storage additionally compared with the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA5 reanalysis data products. Overall, the GCR ETa estimates were higher than those from GLEAM, and similar patterns of the root-zone water storage were found in the comparisons of both GLEAM and ERA5. The comparative evaluation suggests a further study on the adjustment of Priestley-Taylor coefficient value in Java for better application of the GCR. The soil moisture estimated by the single bucket model and the root-zone soil moisture products of GLEAM were highly correlated (0.8 or greater Pearson correlation coefficients). Low root-zone water storage and high ETa rates were found in eastern Java relative to the other areas, indicating high water shortage risks in dry season. This study found that El Nino clearly contributed to the variability of the root-zone water storage in Java especially in wet seasons (December to February). It is also suggested that the proposed approach can be useful to operationally provide soil water availability in Java from readily available meteorological observations.

中文翻译：

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使用基于广义互补原理的多阶段方法进行操作土壤水分建模

摘要 爪哇岛的干旱风险普遍高于印度尼西亚其他地区。跟踪土壤水分可以是监测干旱而不是基于降水的干旱指数的替代方法。本研究的目的是根据爪哇岛的广义互补关系 (GCR) 和单桶模型之间的关联方法评估根区储水量（由根区土壤水分含量定义）。由于它不需要降水来估算实际蒸散量 (ETa)，因此 GCR 允许实施简单的单桶模型。本研究中估计的 ETa 和根区土壤水分与全球土地蒸发阿姆斯特丹模型 (GLEAM) 进行比较，根区蓄水量与欧洲中期天气预报中心 (ECMWF) ERA5 再分析数据产品进行了比较. 总体而言，GCR ETa 估计值高于 GLEAM 的估计值，并且在 GLEAM 和 ERA5 的比较中发现了类似的根区储水模式。比较评估建议进一步研究在 Java 中调整 Priestley-Taylor 系数值以更好地应用 GCR。单桶模型估计的土壤水分与 GLEAM 的根区土壤水分产品高度相关（0.8 或更大的 Pearson 相关系数）。相对于其他地区，爪哇东部的根区储水量低，ETa 率高，表明旱季缺水风险高。该研究发现，厄尔尼诺现象明显导致爪哇根区储水量的变化，尤其是在雨季（12 月至 2 月）。还建议所提出的方法可用于从现成的气象观测中提供爪哇土壤水分的可利用性。