Capacity for Carbon Sequestration and Climate Change Mitigation in Different Ecologically-Distinct Zones of Sri Lanka

Abstract

Vegetation has the capacity to mitigate greenhouse gas (GHG) induced climate change by
absorbing and sequestering carbon dioxide, the principal GHG, in plant biomass. Sri Lanka,
an island located in the humid tropical South Asia, has a considerable range of ecologicallydistinct
zones (EDZs) as a result of the spatial and temporal variation of its climate. These
EDZs are characterised by different dominant vegetation types and ecosystems with varying
ground cover. Hence, the carbon sequestration capacity which determines the strength of the
„land carbon sink‟ is likely to vary in the different EDZs. Analysis of long-term climatic data
has shown that trends of climate change (i.e., increasing atmospheric temperature and
potential evapotranspiration and decreasing precipitation and soil water availability) of the
different climatic zones of Sri Lanka reflect the established global trends. These trends in
climate change are likely to modify the carbon sequestration capacity of different EDZs over
time. Therefore, the objective of this work is to estimate the carbon sequestration and climate
change mitigation capacity of different EDZs of Sri Lanka and its historical variation to
determine the possible impacts of climate change.

Simulations from nine dynamic global vegetation models (DGVMs) were used to estimate
carbon balance parameters such as net primary productivity (NPP), heterotrophic respiration
(Rh) and net biome productivity (NBP) for eight 1o(latitude)×1o(longitude) grid cells
covering Sri Lanka. Models were run over the period from 1900 to 2009 using the climate
forcing data from CRU-NCEP, which were validated using data from the Meteorology
Department of Sri Lanka. Carbon balance parameters were calculated for six ecologicallydistinct
zones of Sri Lanka (i.e., south-west, central highlands, eastern coastal plain, northwest,
north-east and north) that were defined based on 1o×1o grid cells. A validation check of
the model outputs was done by comparing simulated NPP with actual NPP for selected
vegetation types. An initial analysis of all nine DGVMs, which included models running at
different resolutions (3.75o×2.5o, 2.5°×2.5o and 0.5o×0.5o) showed substantial within-zone
variation and did not clearly distinguish carbon sequestration capacities of different EDZs.
This was probably because of spatial averaging of outputs from coarse resolution models
across different EDZs. A second analysis with the four finer resolution DGVMs showed
substantially improved results. Subsequent simulations running the fine resolution model
JULES on a finer grid of 0.5o×0.5o allowed estimation of carbon balance parameters in thirtyfive
0.5o×0.5o cells, which substantially-improved the spatial resolution of estimated carbon
sequestration capacities of different EDZs of Sri Lanka. Temporal and spatial trends of the
estimated carbon balance parameters will be presented along with analyses of their
underlying causes and climatic drivers.

Keywords: Terrestrial carbon balance, Net primary productivity, Climate change, Sri Lanka