Oil Palm Yield Over is Negatively Associated with Increased Rainfall Up to Six Months Before Harvest, and Highly Influenced by Site-Level Variation

Abstract

1. CONTEXT: Oil palm is a globally important crop that is rapidly expanding to meet global demands. Palm oil yield is sensitive to rainfall variation, largely because major phenological growth periods of oil palm are affected by water availability. As a result, fluctuation in rainfall, including that associated with El Niño Southern Oscillation (ENSO), is considered to be a key factor influencing yield variability in oil palm. 2. OBJECTIVE: We aimed to investigate the time delays and effects of rainfall variation and extreme rainfall events on palm oil yield brought about by ENSO-related events.3. METHODS: We conducted lag correlation analyses on long-term rainfall and yield data, collected from a site in Riau, Indonesia from 2013-2017, inclusive of an ENSO-related drought (2014-2015) to determine the effects of key rainfall periods on yield. These results were compared to oil palm fruit development stages identified from previous studies as being sensitive to rainfall variation. Simple linear regressions were also used to assess the effects of key rainfall periods on yield.4. RESULTS AND CONCLUSIONS: Lag correlations calculated between monthly rainfall and yield, as well as extreme rainfall events and yield, identified two to five months before harvest as the time period during which rainfall had the greatest effects on yield. Our study also indicated that rainfall, especially extreme rainfall in the months immediately before harvest, negatively impacted palm oil yield. Lag correlations were highly variable across all plots, including those experiencing similar rainfall conditions, indicating that site-specific variation has a marked influence on the effects of rainfall variation on yield. 5. SIGNIFICANCE: We call for more work to explore how small-scale variation might impact the effects of rainfall on palm oil yield, as well as more work to identify possible management approaches to reduce the impacts of long-term changes in precipitation.

Keywords: El Niño Southern Oscillation, oil palm, Elaeis guineensis, extreme rainfall events, lag correlation analysis, Climate change