Carbon accumulation of tropical peatlands over millennia: a modeling approach
Sofyan Kurnianto1,2, Matthew Warren3, Julie Talbot1,4, Boone Kaufmann5, Daniel
Murdiyarso2,6, Steve Frolking1
1
Institute for the Study of Earth, Oceans and Space and Department of Earth Sciences,
University of New Hampshire, Morse Hall 8, College Road, Durham NH 03824, USA
2
Center for International Forestry Research, Jalan CIFOR, Situ Gede, Bogor 16115,
Indonesia
3.
USDA Forest Service, Northern Research Station, Durham NH 03824, USA
4
Department of Geography, Université de Montréal, C.P. 6128 Succursale Centre-ville,
Montréal Qc H3C 3J7, Canada.
5
Department of Fisheries and Wildlife, Oregon State University, Corvallis OR 97331
USA.
6
Department of Geophysics and Meteorology, Bogor Agricultural University, Bogor,
16115, Indonesia
Supporting information: Cluster analysis of 20th century rainfall
The HPMTrop model used a probability function for Niño conditions based on a
cluster analysis of the 1900-2010 annual rainfall in three El Niño Southern Oscillation
(ENSO) regimes: El Niño, normal, and La Niña. All years in each regimes were clustered
into four groups, and a mean monthly precipitation was calculated for each of these 12
sets of years. Figures S1 – S3 show the dendrogram resulting from the two-way cluster
analysis in which the X-axis is clustered by monthly rainfall and Y-axis is clustered by
the rainfall inter-annual variability. Monthly precipitation for each of the resulting 12
precipitation classes, P, is also shown in Figure. S4.
In the El Niño precipitation regime, the rainfall clusters P1 and P2 were similar, as
were P3 and P4. P2 and P4 had the minimum and maximum annual rainfall respectively,
but occurred less frequently than P1 and P3 (Fig. S1). About half the years between 1900
– 2010 were in the normal precipitation regime, based on the Southern Oscillation Index
(SOI); the P8 cluster had the lowest rainfall and its pattern was closest to P7. The
dendrogram also shows that the pattern of P5 was very different than P8, in which both
clusters only connected by using the inter-link of clusters P6 and P7 (Fig. S2). In the La
Niña precipitation regime, only three years were aggregated into one cluster, P12, which
had the least annual rainfall of the La Niña class; the other three clusters, P9 – P11, were
relatively similar (Fig. S3).
In terms of monthly precipitation, the La Niña clusters had the least seasonality (Fig.
S4) – monthly rainfall in May to October was still relatively high, at about 150 – 200 cm,
and rainfall < 100 cm occurred in those months with a probability of only 10%. In
contrast, El Niño years had a distinct and relatively long dry season from May to October
– most of the groups had 90% probability of rainfall less than 100 cm during one or more
of those months. In normal years, the rainfall pattern was moderately seasonal, but the
dry season was typically shorter and not as dry as in the El Niño years (Fig. S4).
Supplemental Figure Captions
Fig. S1. The dendrogram of the two-way cluster analysis using the monthly rainfall data
(thickness of horizontal black bars) classified as the El Niño years. Four clusters of
years, separated by horizontal dashed lines, were extracted from this analysis (P1, P2,
P3, and P4). The X-axis and Y-axis represent month and year, respectively, with the
rainfall depth shown for each month.
Fig. S2. Same as Fig. S1 with the rainfall data from normal years. Clusters are P5-P8.
Fig. S3. Same as Fig. S1 with the rainfall data from La Niña years. Clusters are P9-P12.
Fig. S4. Mean monthly precipitation of each group derived by the cluster analysis (see
Figs. S1-S3) for El Niño (top), normal (middle), and La Niña (bottom) conditions.
Values in the legends represent the probability for every rainfall group within the
broad El Niño, normal, and La Niña precipitation regimes.