Manobavan, Manoharadas (2003) The responses of terrestrial vegetation to El Nino southern oscillation perturbations. (PhD thesis), Kingston University, .
Abstract
The enhanced warming effect possibly due to anthropogenic green house gas emissions has led to the derangement of global climatic mechanisms (especially at the interannual scale). This has led to the disturbances to the equilibrium of the Earth System and the interconnected self-regulatory processes. Terrestrial vegetation takes an active role in the regulation of the equilibrium of the Earth System by the processes of resistance and resilience. Whilst comprehensive and extensive modelling studies that investigate the effects of climatic change in terrestrial systems have been undertaken, few investigations have focused on the change and evolution in these systems from a holistic geophysiological perspective. In the first part of this thesis, econometric time-series modelling techniques were applied to National Oceanographic and Atmospheric Administration Advanced Very High Resolution Radiometer derived Normalized Difference Vegetation Index data sets in order to evaluate the responses of terrestrial South American vegetation to the interannual El Nino Southern Oscillation climatic perturbations. Lags between vegetation response and the El Nino Southern Oscillation perturbations are identified and quantified. The results indicate that the terrestrial vegetation loses its sensitivity to El Nino Southern Oscillation perturbations in the post 1993 period, leading to the hypothesis that the terrestrial system maybe showing a Gaian behaviour that would enable homeostasis in the system of concern. The null hypothesis of this was tested using a stochastic Auto Regressive Integrative Moving Average model, which further strengthens the argument put forward by the hypothesis. Further comprehensive analysis was performed by using the Hybrid version 4.1, a mechanistical model of vegetation dynamics to test the effects of varying changes in the phase and amplitudes of the El Nino Southern Oscillation on terrestrial vegetation. Simulations of different interannual El Nino Southern Oscillation climatic scenarios under varying trends for increases in atmospheric C02 concentrations confirm the possibility of such a homeostatic property in the terrestrial vegetation system within its geophysiologicallimits.
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