Evaluation of the influence of ENSO on tropical vegetation in long time series using a new indicator

Abstract

With the intensification of extreme weather events in recent years, the drought, flood and fire caused by super El Niño - Southern Oscillation (ENSO) led to lot’s of vegetation destruction in multiple tropical regions. However, little is known about the influence of ENSO on tropical vegetation of long time series (especially after 2015) and the influence’s internal mechanism. Based on generating the long-term vegetation data (combined multiple satellite sensors data), a new index (Vegetation - ENSO response index, VERI) was created to evaluate the influence of ENSO on vegetation more accurately and comprehensively, which considering several factors including the correlation between ENSO index and NDVI anomaly, the change amplitude of NDVI in ENSO events and the duration time and lag time of the influence of ENSO on vegetation. The analysis indicated that tropical vegetation exhibited a fluctuating increase state with an overall increasing range of 4.46%, and the greening trends were the most significant and dramatical in the Indian Peninsula (0.0031/y), the coast of the Gulf of Guinea (0.0026/y), and the Amazon River estuary (0.0025/y). ENSO can lead to significant enhancement or degradation of vegetation in at least 10% of tropical regions, especially in East Africa (|VERI| =0.16), Southern Africa (|VERI|=0.18) and Indonesia (|VERI|=0.14). Among them, shrubs are the most widely affected areas (32.08%) due to limited water resources. ENSO's greening effect is mainly accomplished by increasing precipitation (warm/r = 0.166, cold/r = 0.249) and its degradation effect is more closely related to temperature increase (warm/r = −0.374, cold/r = −0.101). The change of VERI in different periods indicated that the ENSO's influence on vegetation has changed after 2000, which meant the improving effect of cold events on tropical vegetation was weakened, while the inhibiting effect was enhanced. These findings can help us better understand and respond to the effects of ENSO on tropical vegetation in the context of global change.