The response and sensitivity of global vegetation to water stress: A comparison of different satellite-based NDVI products

Normalized Difference Vegetation Index (NDVI) is an effective proxy for vegetation activity and terrestrial productivity, and the widely used global NDVI products include the third generation Global Inventory Modelling and Mapping Studies Advanced Very High-Resolution Radiometer NDVI (NDVI3g), Satellite Pour l’Observation de la Terre VEGETATION NDVI (NDVIsp) and Terra Moderate Resolution Imaging Spectroradiometer NDVI (NDVItr). Here, for the first time, we investigated the differences between the three NDVIs in response and sensitivity to water stress represented by root zone soil moisture, vapor pressure deficit, self-calibrating Palmer Drought Severity Index and Standardized Precipitation Evapotranspiration Index across climate zones, humidity gradients, vegetation types and tree cover gradients. Over the temperate and arid climates region, the three NDVIs show higher consistent response fractions (CRFs) to water stress in the water-limited regions, with their sensitivity being in the order of NDVI3g < NDVIsp < NDVItr. The three NDVIs tend to exhibit inconsistent responses to water stress in the areas with higher humidity and tree cover, and their sensitivities to water stress fall as humidity and tree cover increase. In addition, the three NDVIs display higher CRFs and sensitivities to water stress over the non-forested areas. Our results also show that, in the cold climates region, the three NDVIs respond in the opposite way to water stress as that in water-limited areas, and NDVI3g has higher sensitivity to water stress than NDVIsp and NDVItr. This study highlights the differences between three NDVIs products for qualifying and quantifying their response and sensitivity to water stress.