Abstract. The El Niño–Southern Oscillation (ENSO) in 2015 was one
of the strongest observed in almost 20 years and set the stage for a severe
drought and the emergence of widespread fires and related smoke emission
over large parts of Southeast Asia. In the tropical lowlands of Sumatra,
which were heavily affected by the drought and haze, large areas of tropical
rainforest have been converted into oil palm (Elaeis guineensis Jacq.) plantations during the
past decades. In this study, we investigate the impact of drought and smoke
haze on the net ecosystem CO2 exchange, evapotranspiration, yield and
surface energy budget in a commercial oil palm plantation in Jambi province
(Sumatra, Indonesia) by using micrometeorological measurements, the eddy
covariance method, yield data and a multiple linear regression model
(MLRM). With the MLRM we identify the contribution of meteorological and
environmental parameters to the net ecosystem CO2 exchange. During the
initial part of the drought, when incoming shortwave radiation was elevated,
net CO2 uptake increased by 50 % despite a decrease in upper-layer
soil moisture by 35 %, an increase in air temperature by 10 % and a
tripling of atmospheric vapour pressure deficit. Emerging smoke haze
decreased incoming solar radiation by 35 % compared to non-drought
conditions and diffuse radiation almost became the sole shortwave radiation
flux for 2 months, resulting in a strong decrease in net CO2 uptake by
86 %. Haze conditions resulted in a complete pause of oil palm net carbon
accumulation for about 1.5 months and contributed to a decline in oil palm
yield by 35 %. With respect to a projected pronounced drying trend over
the western Pacific during a future El Niño, our model showed that an
increase in drought may stimulate net CO2 uptake, while more severe
smoke haze, in combination with drought, can lead to pronounced losses in
productivity and net CO2 uptake, highlighting the importance of fire
prevention.