Spatiotemporal Variations of Soil Moisture and Groundwater Level in a South Sumatra Peatland, Indonesia During 2015–2018

The peat hydrological unit of the Air Sugihan River – Air Saleh River, South Sumatra, Indonesia, experienced extreme fires during the 2015 El Niño event. Restoration of 2.0 Mha degraded peatlands has been conducted since 2016. This study aims to analyze spatiotemporal variations of soil moisture content and groundwater level in this site from 2015 to 2018. The soil moisture was estimated using a multiple regression analysis method based on the Sentinel-1A and the European Center for Medium-Range Weather Forecast dataset. The groundwater level model was calculated by using linear regression between the estimated soil moisture and water level observed from field measurements. A minimum moisture content of ~0.78 m3m-3 and a minimum groundwater depth of ~0.50 m below the peat surface were estimated to cause smoldering combustion. A sharp decline in the water table depth (around 1.53 m) led to a decrease in moisture content in October 2015. This month, peat fires severely burned both cultivation and protected areas having dense drainage canals and near rivers. Although there was an increasing trend in the groundwater level and moisture content in 2016, between 2017 to 2018 the water table declined to a depth of ~0.7 m with a corresponding moisture content of ~0.25 m3m-3. Such decline may have led to a few peat fires which occurred in the dry season of both 2017 and 2018. We recommended that law enforcement efforts should be conducted to raise the mean annual water table to shallower depths than 0.40 m