Net Primary Productivity of Urban Ecosystems
In the process of urbanization, land formerly occupied by crops, grasslands or forest becomes permanently paved for buildings, parking lots and transportation. While urban areas have generally a lower photosynthetic capacity than the surrounding rural environments, intensively irrigated and fertilized lawns and trees often counterbalance the decline in net primary productivity (NPP) due to the replacement of vegetated surface with constructed materials.
This study attempts to quantify the NPP of urban areas from MODIS data. Since urban areas are masked out in the MODIS NPP (MOD17) product, the methodology uses MODIS NDVI data (MOD13) and the MOD15 (FPAR/LAI) and MOD17 backup algorithms.
Nighttime citylights from the DMSP/OLS for the years 1992/93 and 2000 and the 1km land cover map derived from the 1992 National Land Cover Data set provide the means to track the type of vegetation replaced by the urban expansion. The effect of urbanization on the regional photosynthetic capacity can be estimated by comparing the urban vegetation NPP with the average NPP of the pre-existing land cover.
Milesi, C., Elvidge, C. D., Nemani, R. R., & Running, S. W. Assessing the impact of urban land development on net primary productivity in the southeastern United States. Remote Sensing of Environment, In press.