Monitoring height changes of drained tropical peatlands in Sumatra using InSAR time series
Zhou, Zhiwei¹; Li, Zhenhong¹; Waldron, Susan¹; Tanaka, Akiko^2
1University of Glasgow, UNITED KINGDOM; ²Geological Survey of Japan, AIST, JAPAN

Globally, the tropical peatlands cover ~ 439,238 km2, which is ~11% of the global peatland area, 57% of the total area in Southeast Asia and this region contributes 68.5 Pg of C, representing 77% of global tropical peatland carbon stores and ~13-15% of the global peat C pool (Page et al., 2010). In this region, Indonesia accounts for the largest share (57.4 Pg or 65%), followed by Malaysia (9.1 Pg or 10%). In the past few decades, because of changes in land-use, drainage has been one of the main driving factors accelerating carbon loss in this region, which results in land subsidence that can be a proxy measure of CO2 emissions to the atmosphere (Hooijer et al., 2012). In this study, small baseline Interferometric Synthetic Aperture Radar (SB InSAR) (Berardino et al., 2002) is employed to investigate the height change of the Jambi peatland in Sumatra. Two adjacent tracks of L-band ALOS PALSAR images acquired during the period from July 2007 to January 2011 are analysed and their agreements in both mean velocity maps and displacement time series provide confidence of these results without the ground data for validation. The InSAR time series results show that: 1) the subsidence rate is up to 5 cm/year in drained plantation areas with a maximum subsidence of 15 cm during the 3-year observation period; 2) different drained areas show different subsidence rates due to drainage ages. Combing these suggest that InSAR time series can be used to monitor long-term peatland height changes, which is useful for C loss estimation.

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Hooijer, A., Page, S., Jauhiainen, J., Lee, W. A., Lu, X. X., Idris, A. & Anshari, G. 2012. Subsidence and carbon loss in drained tropical peatlands. Biogeosciences, 9, 1053-1071.
Page, S., R.Wüst & C.Banks 2010. Past and present carbon accumulation and loss in Southeast Asian peatlands. PAGES news, 18, 25-27.