Spatial Patterns of NDVI Variation over Indonesia and Their Relationship to ENSO Warm Events during the Period 1982–2006

Abstract

The present study is based on the assumption that vegetation in Indonesia is significantly affected by climate anomalies that are related to El Niñ o-Southern Oscillation (ENSO) warm phases (El Niñ o) during the past decades. The analysis builds upon a monthly time series from the normalized difference vegetation index (NDVI) gridded data from the Advanced Very High Resolution Radiometer (AVHRR) and two ENSO proxies, namely, sea surface temperature anomalies (SSTa) and Southern Oscillation index (SOI), and aims at the analysis of the spatially explicit dimension of ENSO impact on vegetation on the Indonesian archipelago. A time series correlation analysis between NDVI anomalies and ENSO proxies for the most recent ENSO warm events showed that, in general, anomalies in vegetation productivity over Indonesia can be related to an anomalous increase of SST in the eastern equatorial Pacific and to decreases in SOI, respectively. The net effect of these variations is a significant decrease in NDVI values throughout the affected areas during the ENSO warm phases. The 1982/83 ENSO warm episode was rather short but-in terms of ENSO indices-the most extreme one within the study period. The 1997/98 El Niñ o lasted longer but was weaker. Both events had significant impact on vegetation in terms of negative NDVI anomalies. Compared to these two major warm events, the other investigated events (1987/88, 1991/92, 1994/95, and 2002/03) had no significant effect on vegetation in the investigated region. The land cover-type specific sensitivity of vegetation to ENSO anomalies revealed thresholds of vegetation response to ENSO warm events. The results for the 1997/98 ENSO warm event confirm the hypothesis that the vulnerability of vegetated tropical land surfaces to drought conditions is considerably affected by land use intensity. In particular, it could be shown that natural forest areas are more resistant to drought stress than degraded forest areas or cropland. Comparing the spatially explicit patterns of El Niñ o-related vegetation variation during the major El Niñ o phases, the spatial distribution of affected areas reveals distinct core regions of ENSO drought impact on vegetation for Indonesia that coincide with forest conversion and agricultural intensification hot spots.

Response of CO<sub>2</sub> and H<sub>2</sub>O fluxes in a mountainous tropical rainforest in equatorial Indonesia to El Niño events

“…Also, in lowland parts of Sulawesi, characterized by higher temperatures and lower precipitation, the vegetation response to ENSO events is likely to be different and more pronounced (Erasmi et al, 2009).…”

“…Even though remote-sensing analyses have shown that the site is representative of the region (Ibrom et al, 2007;Propastin et al, 2012), the response to ENSO might differ in the region due to differences in altitude and land use (Erasmi et al, 2009). In general, anthropogenic deforestation has removed most parts of lowland forests so that the remaining forest cover consists mostly of mountainous forests.…”

“…Both phenomena, El Niño and La Niña, lead to essential changes in pressure distribution and atmospheric circulation and, as a result, to anomalous changes in precipitation amount, solar radiation, and temperature fields, both in the regions of sea surface temperature anomalies and in a wide range of remote areas through the mechanism of atmospheric bridges (Wang, 2002;Graf and Zanchettin, 2012;Yuan and Yan, 2013). Typically, in Indonesia El Niño results in dryer conditions and La Niña results in wetter conditions, potentially impacting the land vegetation (Erasmi et al, 2009). ENSO events are irregular, characterized by different intensities and, are usually observed at intervals of 2-7 years.…”

“…To describe the possible effects of ENSO events on the CO 2 and H 2 O exchange between the land surface and the atmosphere, many studies for different western Pacific regions were carried out during recent decades (Feely et al, 1999;Malhi et al, 1999;Rayner and Law, 1999;Aiba and Kitayama, 2002;Hirano et al, 2007;Erasmi et al, 2009;Gerold and Leemhuis, 2010). They are mainly based on the results of modeling experiments and remote-sensing data (Rayner and Law, 1999).…”

Utilization of Near Real-Time Noaa-Avhrr Satellite Output for El Niño Induced Drought Analysis in Indonesia (Case Study: El Niño 2015 Induced Drought in South Sulawesi)

“…Climate variability in Indonesia is strongly influenced by the global climate phenomenon such as El Niño Southern Oscillation or ENSO (Ropelewski and Halpert 1987;Chang et al, 2004;Qian et al 2010). Warm phase of ENSO, known as El Niño, generally affect decreases rainfall and lead to drought in most parts of Indonesia (Harger 1995;D'Arrigo and Wilson 2008;Erasmi et al 2009;Setiawan 2011;Setiawan 2014).…”