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The roles of NDVI and Land Surface Temperature when using the Vegetation Health Index over dry regions
Global and Planetary Change ( IF 3.9 ) Pub Date : 2020-07-01 , DOI: 10.1016/j.gloplacha.2020.103198
Virgílio A. Bento , Célia M. Gouveia , Carlos C. DaCamara , Renata Libonati , Isabel F. Trigo

Abstract Dry lands are expected to cover about half of the terrestrial surface in the near future due to climate change. Drought events, which are recurrent over dry lands, are also projected to increase in both frequency and severity. There is a strong need to better monitor droughts over dry regions, and satellite-based indicators such as the Vegetation Health Index (VHI) have been operationally used worldwide in the last two decades. VHI is traditionally defined as the simple average of two components, the Temperature Condition Index (TCI) and the Vegetation Condition Index (VCI) respectively derived from information on the thermal and visible bands. However, the weights of VCI and TCI depend on landcover because of the different contributions of moisture and temperature to the vegetation cycle. By systematically comparing VHI with the Standardised Precipitation-Evapotranspiration Index (SPEI), a multi-scalar drought index, we demonstrate that is possible to disentangle the role played by VCI and TCI on vegetation health. Here we propose a methodology that allows estimating optimal weights for the two components of VHI and we show that VHI is persistently dominated by VCI over dry lands. Results obtained indicate that severe drought episodes over dry lands are better identified when using the proposed methodology. This may be an asset for operational monitoring, paving the way to more efficient social and political responses aiming to mitigate drought impacts. This work is also expected to contribute to the development of optimal sets of VCI and TCI weights that take into consideration expected changes in the land surface based on information from future climate scenarios.

中文翻译:

在干旱地区使用植被健康指数时 NDVI 和地表温度的作用

摘要 由于气候变化,预计在不久的将来,旱地将覆盖大约一半的陆地表面。干旱事件在旱地反复发生,预计其频率和严重程度也会增加。迫切需要更好地监测干旱地区的干旱,并且在过去的二十年中,植被健康指数 (VHI) 等卫星指标已在全球范围内投入使用。VHI 传统上被定义为两个分量的简单平均值,温度条件指数 (TCI) 和植被条件指数 (VCI) 分别来自热波段和可见光波段的信息。然而,由于水分和温度对植被循环的贡献不同,VCI 和 TCI 的权重取决于土地覆盖。通过系统地比较 VHI 与标准化降水蒸发蒸腾指数 (SPEI)(一种多标量干旱指数),我们证明有可能解开 VCI 和 TCI 对植被健康的作用。在这里,我们提出了一种方法,可以估计 VHI 的两个组成部分的最佳权重,并且我们表明 VHI 在旱地上始终由 VCI 主导。获得的结果表明,当使用建议的方法时,可以更好地识别旱地的严重干旱事件。这可能是业务监测的一项资产,为旨在减轻干旱影响的更有效的社会和政治反应铺平道路。
更新日期:2020-07-01
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