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 byabsorbing 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 ecologicallydistinctzones (EDZs) as a result of the spatial and temporal variation of its climate. TheseEDZs are characterised by different dominant vegetation types and ecosystems with varyingground 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 datahas shown that trends of climate change (i.e., increasing atmospheric temperature andpotential evapotranspiration and decreasing precipitation and soil water availability) of thedifferent climatic zones of Sri Lanka reflect the established global trends. These trends inclimate change are likely to modify the carbon sequestration capacity of different EDZs overtime. Therefore, the objective of this work is to estimate the carbon sequestration and climatechange mitigation capacity of different EDZs of Sri Lanka and its historical variation todetermine the possible impacts of climate change.Simulations from nine dynamic global vegetation models (DGVMs) were used to estimatecarbon balance parameters such as net primary productivity (NPP), heterotrophic respiration(Rh) and net biome productivity (NBP) for eight 1o(latitude)×1o(longitude) grid cellscovering Sri Lanka. Models were run over the period from 1900 to 2009 using the climateforcing data from CRU-NCEP, which were validated using data from the MeteorologyDepartment of Sri Lanka. Carbon balance parameters were calculated for six ecologicallydistinctzones 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 ofthe model outputs was done by comparing simulated NPP with actual NPP for selectedvegetation types. An initial analysis of all nine DGVMs, which included models running atdifferent resolutions (3.75o×2.5o, 2.5°×2.5o and 0.5o×0.5o) showed substantial within-zonevariation and did not clearly distinguish carbon sequestration capacities of different EDZs.This was probably because of spatial averaging of outputs from coarse resolution modelsacross different EDZs. A second analysis with the four finer resolution DGVMs showedsubstantially improved results. Subsequent simulations running the fine resolution modelJULES on a finer grid of 0.5o×0.5o allowed estimation of carbon balance parameters in thirtyfive0.5o×0.5o cells, which substantially-improved the spatial resolution of estimated carbonsequestration capacities of different EDZs of Sri Lanka. Temporal and spatial trends of theestimated carbon balance parameters will be presented along with analyses of theirunderlying causes and climatic drivers.Keywords: Terrestrial carbon balance, Net primary productivity, Climate change, Sri Lanka