Climate change projections of terrestrial primary productivity over the Hindu Kush Himalayan forests

Halima Usman,Thomas A M Pugh,Sofia Baig,Anders Ahlström

doi:10.5194/esd-12-857-2021

Abstract

Abstract. Increasing atmospheric carbon dioxide concentration [CO2] caused by anthropogenic activities has triggered a requirement to predict the future impact of [CO2] on forests. The Hindu Kush Himalayan (HKH) region comprises a vast territory including forests, grasslands, farmlands and wetland ecosystems. In this study, the impacts of climate change and land-use change on forest carbon fluxes and vegetation productivity are assessed for HKH using the Lund–Potsdam–Jena General Ecosystem Simulator (LPJ-GUESS). LPJ-GUESS simulations were driven by an ensemble of three climate models participating in the CMIP5 (Coupled Model Intercomparison Project phase 5) database. The modelled estimates of vegetation carbon (VegC) and terrestrial primary productivity were compared with observation-based estimates. Furthermore, we also explored the net biome productivity (NBP) and its components over HKH for the period 1851–2100 under the future climate scenarios RCP2.6 and RCP8.5. A reduced modelled NBP (reduced C sink) is observed from 1986–2015 primarily due to land-use change. However, an increase in NBP is predicted under RCP2.6 and RCP8.5. The findings of the study have important implications for the management of the HKH region, in addition to informing strategic decision making and land-use planning, and clarifying policy concerns.

Highlights

Anthropogenic activities such as combustion of fossil fuels and land-use changes have led to large rises in atmospheric greenhouse gas (GHG) emissions such as carbon dioxide (CO2) and methane over the last century, with atmospheric CO2 mixing ratios increasing from 277 to 409 ± 0.1 ppm in 2019 since the pre-industrial period, and rising at the mean rate of 2.3 ppm yr−1 from 2010 to 2019 (Friedlingstein et al, 2020)
Simulations forced by three CMIP5 Earth system models (ESMs) of mean vegetation carbon (VegC) from 1986–2015 were compared with the observed GEOCARBON dataset (Fig. 2)
A moderate agreement was found between the GEOCARBON and LPJ-GUESS VegC with a mean r2 value of 0.44

Summary

Introduction

Anthropogenic activities such as combustion of fossil fuels and land-use changes have led to large rises in atmospheric greenhouse gas (GHG) emissions such as carbon dioxide (CO2) and methane over the last century, with atmospheric CO2 mixing ratios increasing from 277 to 409 ± 0.1 ppm in 2019 since the pre-industrial period, and rising at the mean rate of 2.3 ppm yr−1 from 2010 to 2019 (Friedlingstein et al, 2020) This uptake is likely primarily driven by the fertilizing effects of elevated atmospheric CO2 concentrations on plant growth (Sitch et al, 2015) and by the regrowth of forests following past disturbances (Kondo et al, 2018; Pugh et al, 2019). The determination of the effect of global rise in temperature on forests is becoming increasingly im-

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