Spatiotemporal assessment of land use/land cover change and associated carbon emissions and uptake in the Mekong River Basin

Land use and land cover (LULC) change caused by human activities is a major source of anthropogenic carbon emissions and a driver of climate change. The Mekong Region is highly dynamic, experiencing extensive LULC change in recent decades. This study provides a spatially and temporally continuous estimate of LULC change for the Mekong River Basin for 2001-2019 using time series analysis of MODIS data coupled with a spatiotemporal carbon bookkeeping model to track carbon losses and recovery. The LULC change product has an overall accuracy of 74.4 +/- 1.9% (82.1 +/- 1.7% after consolidating tree-dominated classes), including an increase of 5.6% after combining with existing MODIS products (referred to as the M-CCDC process). Two of the largest components of LULC change in the region are the establishment of plantations and agricultural expansion, which were estimated to be 33,617 +/- 7342 km(2) and 14,915 +/- 4682 km(2) between 2003 and 2014. We found that 82% of the deforested area was converted to tree plantations. Among all the newly added plantations, 86% replaced natural forests and 12% replaced agricultural land. In addition, existing maps of annual tree canopy cover (TCC) were used to assess forest disturbances that do not result in LULC conversions. The M-CCDC results combined with the forest disturbances derived from TCC maps were coupled to a spatiotemporal carbon bookkeeping model to estimate carbon emissions and uptake. Carbon emissions were 72.9 +/- 6.2 Tg C yr(-1) during 2001-2017; emissions increase to 102.8 +/- 8.6 Tg C yr(-1) if including carbon not yet released to the atmosphere in the form of decomposing slash and wood products. Carbon uptake for the same period was-35.5 +/- 4.9 Tg C yr(-1), with carbon uptake from new plantations offsetting almost half of the emissions from deforestation in this area. Assessment of post-deforestation land use is crucial for quantifying the short-and longer-term carbon consequences of LULC change.