Two dynamic global vegetation models (DGVMs), IBIS and LPJ, were used to assess the projected impacts of climate change on forests in terms of the shifts in vegetation types and changes in NPP (net primary productivity) in the mid Brahmaputra, Koshi, and upper Indus river basins. Changes were assessed for the mid-term (2021–2050) and long-term (2071–2100) periods with respect to the baseline (1961–1990) under the RCP4.5 and RCP8.5 scenarios using precipitation and temperature as the key climate variables. The DGVMs were driven by the ensemble mean climate projections from five CMIP5 climate models. While both DGVMs projected vegetation shifts in the forest areas of the basins, there were differences in the area projected to be affected by the shifts. This can be attributed mainly to differences in the representation of land surface processes and in the number of vegetation types (plant functional types) defined and simulated in the two models. There was some agreement in the changes in NPP projected by the two models under the high emission RCP8.5 scenario, but with differences in degree.
Notwithstanding the uncertainties with respect to climate change projections at watershed and sub-basin level, and the variation in impact assessment from the two DGVMs, it is necessary to make some attempt to assess the vulnerability of the forest ecosystems and forest dependent communities and to develop and implement resilience or adaptation measures. In the absence of more DGVMs to enable the results to be refined, assessment of vulnerability and designing of adaptation strategies could be undertaken for all the forested grids shown to be impacted by either the IBIS or the LPJ models.
The report was co-funded by the Royal Norwegian Embassy in Nepal.