## 3 Results
### Seasonal Variability in NPP  
The NPP time series for four seasons corresponding to southwest summer monsoon (June-August), northeast winter monsoon (December to February), spring or pre-monsoon (March-May) and autumn or post-monsoon (September to November) is shown in Figure 6 (top left), and the mean seasonal cycle of NPP and key climate variables are shown in Figure 6 (top right).  
We see that the maximum NPP is observed during the post-monsoon period (SON) rather than during summer monsoon season (JJA). NPP reaches minimum value in pre-monsoon period (MAM). The discussion of interannual variations in the previous section would suggest a maximum NPP in JJA when the precipitation reaches the maximum (Figure 6). However, since temperature (which has a negative correlation with NPP) is also high during this period, it is likely to reduce the NPP during JJA. We find that the soil water content is a maximum during SON (Figure 6) which is closely associated with the maximum NPP observed during SON.  
Figure 6: Temporal evolutions of domain-averaged seasonal mean NPP for pre-monsoon (MAM), southwest summer monsoon (JJA), post-monsoon (SON) and northeast winter monsoon (DJF) seasons (**top left**), mean seasonal cycle of NPP, surface temperature, precipitation, solar radiation and soil moisture (**top right**), and the multivariate NPP estimated using precipitation and temperature as independent variables (blue), soil water and surface solar radiation as independent variables (green), precipitation, temperature and soil water as independent variables (black) and precipitation, temperature, soil water and solar radiation as independent variables (orange; **bottom**). The correlation coefficient (r) between seasonal NPP anomaly and independent variables are shown in the top right panel. R\({}^{2}\) values for the regression between seasonal cycle of NPP and the various multivariate NPP are shown in bottom panel.  
We performed both single variable and multivariate regression analysis (Equation (1)) on the mean seasonal cycle over the period 1982-2006. The correlation coefficients are shown in Table 1 and the averaged seasonal cycle of NPP and the multivariate-generated seasonal cycles are shown in Figure 6 (bottom). We have used only 23 years for the regression analysis because of the uncertainty in soil moisture data for the years 1996 and 1997. We find that the correlation between observed mean seasonal cycle of NPP and the soil water is 0.95 (R\({}^{2}\) = 0.90), thereby indicating a strong control of soil water on the seasonal cycle of NPP. The correlation is relatively lower with the seasonal cycle of precipitation (r = 0.52, R\({}^{2}\) = 0.27), temperature (r = 0.01, R\({}^{2}\) = 0.0) and solar radiation (r = -0.63, R\({}^{2}\) = 0.40). Further, correlation with multivariate seasonal NPP is only 0.65 (R\({}^{2}\) = 0.42) when the independent variables are temperature and precipitation but very large (r = 0.95 to 0.98, R\({}^{2}\) = 0.91 to 0.96) when soil water is one of the independent variables for the multivariate regression (Figure 6, Table 1). This suggests that the seasonal cycle of NPP is primarily driven by soil water.