## 3 Results
### Interannual Variability in NPP
There have been indications from earlier studies that regional NPP over India is also controlled by remote events such as ENSO. For instance, negative NPP anomaly during El Nino and positive anomaly during La Nino have been shown by recent studies [11,18]. Specifically, it is found that NPP declined during the recent four major ENSO events (1982-1983, 1987-1988, 1997-1998 and 2002-2003) [18]. Further, it has been also shown that NPP in India is inversely correlated to atmospheric CO\({}_{2}\) growth rate anomalies [18]. On a global scale, reduced terrestrial carbon uptake during ENSO leads to larger growth rates of atmospheric CO\({}_{2}\), although terrestrial NPP accounts for only part of the biosphere-atmosphere carbon exchange [8,11]. However, it is not clear if the relationship between global NPP, global atmospheric CO\({}_{2}\), and ENSO would be unchanged when we consider NPP only over India. In Figure 5(a), we show the time series of interannual NPP anomaly (trend and mean removed) and CO\({}_{2}\) growth rate anomaly for 1982-2006. CO\({}_{2}\) growth rate anomaly is calculated as the departure from the averaged CO\({}_{2}\) growth rate which is calculated as the difference in CO\({}_{2}\) between successive years. In contrast to other studies [18], we find that the NPP anomaly is weakly but positively correlated (r = 0.23, R\({}^{2}\) = 0.05) to the CO\({}_{2}\) growth rate anomaly. This suggests that the NPP anomaly over India is not in phase with global NPP anomaly. Figure 5(b) shows that the correlation between NPP anomaly and Nino3-SST anomaly is also weak (r = 0.14, R\({}^{2}\) = 0.02). This result is also in contrast to the recent study [18] which finds declines in NPP during ENSO years (positive Nino3-SST anomaly). The growth in NPP anomaly after the Mount Pinatubo eruption in 1991 (Figure 5) is in agreement with the global study [8]which found that the cooling from the eruption may have promoted plant growth in low latitudes by reducing evapotranspiration and respiration losses. As an alternate to Nino-3 SST index and as in other studies [8,18], we also used the multivariate ENSO index (MEI) as the ENSO index (Figure 5(c)). MEI is the multivariate measure of the ENSO signal as expressed in the first principal component of six observed variables in the tropical Pacific [41]: sea-level pressure, zonal and meridional components of the surface wind, sea surface temperature, surface air temperature, and total cloudiness fraction of the sky. In this case, as well, in contrast to [18], we find the correlation is too low (r = 0.09, R\({}^{2}\) = 0.01). In summary, we do not find a strong correlation between the NPP anomaly over India and the CO\({}_{2}\) growth rate anomaly, nor between the NPP anomaly and ENSO. The cause for the discrepancy between our results and a previous  
Figure 5: Temporal evolutions of interannual NPP anomaly over India and (**a**) CO\({}_{2}\)growth rate anomaly, (**b**) Nino-3 SST anomaly, and (**c**) Multivariate ENSO Index (MEI). The right panels show the corresponding scatter plots. The coefficient of correlation (r) and R\({}^{2}\) values are also shown. study [18] is not clear to us. Further investigation is required to ascertain the existence or lack of correlation between NPP anomalies and remote events.