Trends and Variability of AVHRR-Derived NPP in India

Abstract: In this paper, we estimate the trends and variability in Advanced Very High Resolution Radiometer (AVHRR)-derived terrestrial net primary productivity (NPP) over India for the period 1982–2006. We find an increasing trend of 3.9% per decade (r = 0.78, R² = 0.61) during the analysis period. A multivariate linear regression of NPP with temperature, precipitation, atmospheric CO₂ concentration, soil water and surface solar radiation (r = 0.80, R² = 0.65) indicates that the increasing trend is partly driven by increasing atmospheric CO₂ concentration and the consequent CO₂ fertilization of the ecosystems. However, human interventions may have also played a key role in the NPP increase: non-forest NPP growth is largely driven by increases in irrigated area and fertilizer use, while forest NPP is influenced by plantation and forest conservation programs. A similar multivariate regression of interannual NPP anomalies with temperature, precipitation, soil water, solar radiation and CO₂ anomalies suggests that the interannual variability in NPP is primarily driven by precipitation and temperature variability. Mean seasonal NPP is largest during post-monsoon and lowest during the pre-monsoon period, thereby indicating the importance of soil moisture for vegetation productivity.