Use of NDVI and Land Surface Temperature for Drought Assessment: Merits and Limitations

TLDR

Spaceborne-derived relationships between land surface temperature (LST) and NDVI underpin many water‑ and climate‑related applications, such as drought monitoring, and typically rely on a negative LST–NDVI slope identified in site‑ and time‑specific studies. The study examines whether the LST–NDVI relationship holds across diverse moisture and climatic/radiation regimes in North America during the summer growing season. The authors used 21 years of AVHRR‑derived LST and NDVI data to assess the relationship across latitudes up to 60°N. The LST–NDVI correlation is negative when water limits vegetation (low latitudes, midseason) but positive when energy limits growth (higher latitudes, early season); solar radiation dominates at season start and end, while air temperature drives midsummer correlations, indicating that empirical LST–NDVI relationships should be applied cautiously and only where negative correlations exist, i.e., when water is the limiting factor.

Abstract

Abstract A large number of water- and climate-related applications, such as drought monitoring, are based on spaceborne-derived relationships between land surface temperature (LST) and the normalized difference vegetation index (NDVI). The majority of these applications rely on the existence of a negative slope between the two variables, as identified in site- and time-specific studies. The current paper investigates the generality of the LST–NDVI relationship over a wide range of moisture and climatic/radiation regimes encountered over the North American continent (up to 60°N) during the summer growing season (April–September). Information on LST and NDVI was obtained from long-term (21 years) datasets acquired with the Advanced Very High Resolution Radiometer (AVHRR). It was found that when water is the limiting factor for vegetation growth (the typical situation for low latitudes of the study area and during the midseason), the LST–NDVI correlation is negative. However, when energy is the limiting factor for vegetation growth (in higher latitudes and elevations, especially at the beginning of the growing season), a positive correlation exists between LST and NDVI. Multiple regression analysis revealed that during the beginning and the end of the growing season, solar radiation is the predominant factor driving the correlation between LST and NDVI, whereas other biophysical variables play a lesser role. Air temperature is the primary factor in midsummer. It is concluded that there is a need to use empirical LST–NDVI relationships with caution and to restrict their application to drought monitoring to areas and periods where negative correlations are observed, namely, to conditions when water—not energy—is the primary factor limiting vegetation growth.