Response of vegetation to El Niño-Southern Oscillation (ENSO) via compound dry and hot events in southern Africa

Abstract

El Niño-Southern Oscillation (ENSO) events are well-known to be related to dry and hot extremes and have considerable impacts on the terrestrial ecosystem in southern Africa. However, the impact pathway from ENSO to vegetation (i.e., relationship among ENSO, climate anomalies, and vegetation) is still unclear in southern Africa. In this study, we investigated the impact of ENSO on vegetation (represented by the Normalized Difference Vegetation Index, NDVI) through its impacts on compound dry and hot extremes in austral summers (December-January-February, DJF) from 1982 to 2015 in southern Africa. The Standardized Precipitation Index (SPI) and Standardized Temperature Index (STI) are used as dry and hot indicators, respectively. The response of NDVI to ENSO during DJF is assessed based on correlation analysis and negative correlation coefficients are present for 87.3% of southern Africa. In addition, the response of NDVI anomaly (NDVIA) to both dry and hot conditions are also investigated, which shows positive NDVIA-SPI correlations and negative NDVIA-STI correlations for 83.2% and 76.5% of the area, respectively. The area percentage with significant impacts of ENSO on concurrent dry and hot events is estimated as 45.29%. Finally, we also evaluated lag effects between vegetation and dry/hot conditions and between dry/hot conditions and ENSO. Vegetation changes from September to December 2015 illustrate the connection among ENSO, compound dry and hot events, and vegetation decline in southern Africa. This study can aid our understanding of ENSO induced climate extremes and their impacts on vegetation in southern Africa. • Quantify ENSO's impacts on vegetation in southern Africa. • Investigate impact pathway from ENSO to vegetation in southern Africa. • Evaluate vegetation response to compound dry and hot events with lag effects.