Long-Lead Prediction of the 2015 Fire and Haze Episode in Indonesia

We conducted a case study of National Centers for Environmental Prediction Climate Forecast System version 2 seasonal model forecast performance over Indonesia in predicting the dry conditions in 2015 that led to severe fire, in comparison to the non-El Nino dry season conditions of 2016. Forecasts of the Drought Code (DC) component of Indonesia's Fire Danger Rating System were examined across the entire equatorial Asia region and for the primary burning regions within it. Our results show that early warning lead times of high observed DC in September and October 2015 varied considerably for different regions. High DC over Southern Kalimantan and Southern New Guinea were predicted with 180 day lead times, whereas Southern Sumatra had lead times of up to only 60 days, which we attribute to the absence in the forecasts of an eastward decrease in Indian Ocean sea surface temperatures. This case study provides the starting point for longer-term evaluation of seasonal fire danger rating forecasts over Indonesia. Plain Language Summary During the 2015 El Nino, drier-than-normal conditions led to human-caused fires getting out of control over Indonesia's fire prone regions in Sumatra and Kalimantan, and on the island of New Guinea. Recent analyses have shown that the 2015 CO2-equivalent biomass burning emissions for all of Indonesia were in between the 2013 annual fossil fuel CO2 emissions of Japan and India. Millions of people were exposed to hazardous air quality levels for weeks, and, at its peak, a plume of pollution from the fires stretched halfway around the world at the equator. In this study, we examined how far in advance the dangerously dry conditions could have been anticipated over different fire prone regions. We used forecasts from a coupled atmosphere-ocean model to compute 180-day forecasts of a fire danger indicator used by the Indonesian government. We found that dry conditions could have been anticipated at least 60 days in advance over Sumatra, and at least 180 days in advance over Kalimantan and New Guinea. Our analysis serves as the starting point for the development of early warning systems for fire managers in Indonesia.