Terrestrial net primary productivity dynamics under climatic variability and urban expansion in western Himalaya

The western Himalaya is one of the most climate-sensitive and ecologically vulnerable ecosystems of the world. In the recent past, the region has undergone rapid alterations owing to climate change and paced urbanization. These alterations have significantly impacted Terrestrial Net Primary Productivity (TNPP) of the region. The present study takes the emerging urbanizing centers: Pithoragarh (Uttarakhand) and Dharamsala (Himachal Pradesh), situated in Indian western Himalaya to estimate TNPP dynamics of various land use classes. The study demonstrates usage of Enhanced Spatial and Temporal Adaptive Reflectance Fusion Model (ESTARFM) for predicting a high spatio-temporal Normalised Difference Vegetation Index (NDVI) imagery obtained by fusing spatial details of Landsat NDVI and temporal details of Moderate Resolution Imaging Spectroradiometer (MODIS) NDVI images. The predicted NDVI showed a good agreement with actual Landsat NDVI (R²=0.64 and 0.89; RMSE: 0.09 and 0.04; p < 0.01 for Dharamsala and Pithoragarh, respectively), therefore was reliable for TNPP estimations. This was assimilated in Carnegie Ames Stanford Approach (CASA) model for TNPP estimation for the years 2001 to 2019. The preliminary results show a net loss in TNPP in both of the urbanizing centers. During the study period 2001-2019, TNPP fluctuated annually and showed a decreasing trend of 1475.77 g C m^-2 year^-1 and 790.84 g C m^-2 year^-1 in Dharamsala and Pithoragarh, respectively. Among the forest vegetation classes, Oak the most dominant forest class experienced the highest decline in TNPP accounting for 67.55% and 34.04% of net TNPP loss in Dharamsala and Pithoragarh, respectively. The urban expansion contributed to 14.77% (Dharamsala) and 9.77% (Pithoragarh) decline of net TNPP loss. The results provide a better understanding of spatio-temporal dynamics of TNPP consequent to climatic variability and urbanization and provide a theoretical reference for future urban planning.