Even though existing remote-sensing-based drought indices are widely used in many different types of ecosystems, their utility has not been widely assessed in tropical dry forests (TDFs). The aim of this study is to evaluate the performance of three remote-sensing-based drought indices, the Vegetation Condition Index (VCI), Temperature Condition Index (TCI), and Vegetation Health Index (VHI), for meteorological drought monitoring in TDFs using the moderate-resolution imaging spectroradiometer (MODIS) products. The correlation between the VCI, TCI, and VHI and multiple time scales of the Standardized Precipitation Index (SPI) (1, 3, 6, 9, 12, 15, 18, 21, 24 months) for each month (January to December) and each season (dry season, dry-to-wet season, wet season and wet-to-dry season) were conducted using the Pearson correlation analysis. We also correlated year-to-year changes of satellite-based drought indices with the changes of the in situ annual SPI (A_SPI) which provides annual information on the mean meteorological drought. The analysis reveals that the ability of these remote-sensing-based drought indices for meteorological drought monitoring varies with timing, and the TCI outperforms the VCI and VHI in terms of seasonal and annual scale. These remote-sensing indices performed well in monitoring meteorological drought in the dry season, poorly in the in the dry-to-wet season, and moderately in the wet season. The TCI performed best in monitoring meteorological drought in the wet-to-dry period, followed by VHI, whereas the VCI performed worst. All of these remote-sensing-based drought indices failed to detect drought in May during the green-up period and in September, October, and November when the water content in the root regions was abundant. Our results indicate that the evapotranspiration of TDFs is more sensitive than canopy greenness to detect meteorological drought. Results from this study increase the ability to provide real-time drought monitoring and early warnings of drought in TDFs.

中文翻译：

---

评估各种干旱指数在热带干旱森林中监测气象干旱的效用

尽管现有的基于遥感的干旱指数被广泛用于许多不同类型的生态系统，但它们的效用尚未在热带干旱森林 (TDF) 中得到广泛评估。本研究的目的是评估三个基于遥感的干旱指数，即植被状况指数 (VCI)、温度状况指数 (TCI) 和植被健康指数 (VHI)，用于 TDF 中气象干旱监测的性能。中等分辨率成像光谱仪 (MODIS) 产品。每个月（1月至12月）的VCI、TCI和VHI与标准化降水指数（SPI）的多个时间尺度（1、3、6、9、12、15、18、21、24个月）之间的相关性每个季节（干季、干湿季、湿季和干湿季）均采用 Pearson 相关分析。我们还将卫星干旱指数的逐年变化与原位年度 SPI (A_SPI) 的变化相关联，后者提供了关于平均气象干旱的年度信息。分析表明，这些遥感干旱指数对气象干旱监测的能力随时间而变化，TCI在季节和年度尺度上优于VCI和VHI。这些遥感指标在旱季监测气象干旱方面表现良好，在干湿季表现较差，在雨季表现中等。TCI 在监测干湿期气象干旱方面表现最好，其次是 VHI，而 VCI 表现最差。所有这些基于遥感的干旱指数都未能检测到 5 月份绿化期和 9 月份的干旱，10月、11月根区含水量丰富。我们的结果表明，TDF 的蒸散量比冠层绿度更能检测气象干旱。这项研究的结果提高了在 TDF 中提供实时干旱监测和干旱预警的能力。