## 3 Results
### Development of GPP over the Netherlands in 2008  
Based on the stored vegetation products in the dynamic WMS, an analysis was made of the spatio-temporal development of GPP over the Netherlands in 2008 (Figure 3). The analysis clearly shows the phenology of the vegetation with low productivity at the end of the winter in February (GPP \(<\) 2 gC\(\cdot\)m\({}^{\text{-2}}\cdot\)day\({}^{\text{-1}}\)) and increasing productivity at the start of the growing season in March and April. Differences between biomes over the season are observed with especially relatively high productivity values for the large-scale nature reserve the Veluwe in the centre of the Netherlands (e.g., dates 240608 and 200908 in Figure 3). In addition, the late arable crops in the Flevopolder along the IJsselmeer can clearly be observed (red/orange colors due to bare soil) from the vegetation productivity map of the 5 th of May (Figure 3). Maximum productivity occurs at the end of June after which the productivity is reducing again till winter levels at the end of October. Within Figure 3 several disturbance can be observed on the spatial distribution of vegetation productivity. First of all, cloud coverage reduces for some dates the productivity estimation over the complete surface area of the Netherlands. This can either be a large continuous area (e.g., date 230308 in Figure 3) or smaller scattered areas (e.g., date 250808 in Figure 3) depending on the cloud coverage at the time of acquisition of the MODIS image. In addition, the effect of a relatively low number of  
Figure 2: User interface of the dynamic WMS for spatio-temporal development of vegetation productivity over the Netherlands. Vegetation productivity is expressed as GPP in gC m\({}^{\text{-2}}\) day\({}^{\text{-1}}\). meteorological stations on the quality of spatial interpolation can be observed in the productivity map for March 23. This results in some sharp linear boundaries between vegetation productivity classes which in reality probably will not be present. Within a vegetation map for a specific day, there is a considerable difference in the spatial distribution of GPP for different biomes. Figure 4 shows the distribution of all calculated GPP values per biome over the Netherlands for June 24 which is around maximum productivity. The graph shows a clear differentiation between biomes which for a large part is driven by the defined potential LUE per biome (Table 1). The variability around the maximum GPP value per biome (Figure 4) is caused by spatial variation in meteorological parameters and FPAR. The temporal development of GPP over the year also shows clear differences between biome types (Figure 5). Deciduous needle forest has a relatively higher productivity compared to shrubland and grassland. The influence of FPAR on the estimated GPP can clearly be observed by the difference for the biomes grassland and shrubland (Figure 5) in start of growing season (respectively, March and April) and the timing of maximum productivity (respectively, May and July). The relatively late development of vegetation productivity for shrubland is caused by the delayed phenology of the heath land vegetation which is the main vegetation type present in the shrubland biome. Figure 3: Monthly development of GPP (gC m\({}^{-2}\) day\({}^{-1}\)) over the Netherlands for the year 2008. The numbers above the maps refer to the date (ddmmyy) for which the map was produced. Figure 5 shows that although there is a clear trend in development of GPP, also a considerable scatter around this trend is present. This scatter is mainly caused by day-to-day variations in weather resulting in considerable variation in PAR. During the growing season the influence of S\({}_{\rm Tmin}\) will be limited while the S\({}_{\rm VPD}\) will influence the productivity during dryer periods. Due to a long period of clouded conditions at time of overflight of the MODIS sensor in the month of August only a limited number of observations was available for this month (Figure 5).