Dynamics of ENSO drought events on Sabah rainforests observed by NOAA AVHRR

Drought, associated with the El Niño Southern Oscillation (ENSO), can have considerable impact on tropical rainforests. Concern over drought, particularly given the possibility of an increase in its occurrence and intensity, has fostered a desire for an increased understanding of drought events and their impact to inform the development of a drought monitoring system. This paper investigates the use of National Oceanic and Atmospheric Administration (NOAA) Advanced Very High Resolution Radiometer (AVHRR) data in a drought monitoring system for the rainforests of Sabah, Borneo. These rainforests are dynamic with respect to their coupling with ENSO processes and in their biophysical properties, and such dynamism may have implications for how NOAA AVHRR data may be used. In particular, this paper explores the transferability of relationships between a drought indicator (rainfall) and the response of the rainforest, as measured by four NOAA AVHRR variables (middle infrared reflectance; VI3; Ts/VI3 and Ts/NDVI), under particular site conditions. It was found that both spatial variability in forest biophysical properties and geographical variability in drought impact had implications for the transferability of relationships developed under local conditions across Sabah rainforests within a drought monitoring system. Suggestions are presented for how NOAA AVHRR data could be used, with a new drought monitoring index – the Ts/VI3 – recommended.