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In the circumpolar north (45–90°N), permafrost plays an important role in vegetation and carbon (C) dynamics. Permafrost thawing has been accelerated by the warming climate and exerts a positive feedback to climate through increasing soil C release to the atmosphere. To evaluate the influence of permafrost on C dynamics, changes in soil temperature profiles should be considered in global C models. This study incorporates a sophisticated soil thermal model (STM) into a dynamic global vegetation model (LPJ-DGVM) to improve simulations of changes in soil temperature profiles from the ground surface to 3 m depth, and its impacts on C pools and fluxes during the 20th and 21st centuries. With cooler simulated soil temperatures during the summer, LPJ-STM estimates ~ 0.4 Pg C yr − 1 lower present-day heterotrophic respiration but ~ 0.5 Pg C yr − 1 higher net primary production than the original LPJ model resulting in an additional 0.8 to 1.0 Pg C yr − 1 being sequestered in circumpolar ecosystems. Under a suite of projected warming scenarios, we show that the increasing active layer thickness results in the mobilization of permafrost C, which contributes to a more rapid increase in heterotrophic respiration in LPJ-STM compared to the stand-alone LPJ model. Except under the extreme warming conditions, increases in plant production due to warming and rising CO 2 , overwhelm the e nhanced ecosystem respiration so that both boreal forest and arctic tundra ecosystems remain a net C sink over the 21st century. This study highlights the importance of considering changes in the soil thermal regime when quantifying the C budget in the circumpolar north. [ABSTRACT FROM AUTHOR]

Abstract: Adequate quantification of evapotranspiration (ET) is crucial to assess how climate change and land cover change (LCC) interact with the hydrological cycle of terrestrial ecosystems. The Mongolian Plateau plays a unique role in the global climate system due to its ecological vulnerability, high sensitivity to climate change and disturbances, and limited water resources. Here, we used a version of the Terrestrial Ecosystem Model that has been modified to use Penman–Monteith (PM) based algorithms to calculate ET. Comparison of site-level ET estimates from the modified model with ET measured at eddy covariance (EC) sites showed better agreement than ET estimates from the MODIS ET product, which overestimates ET during the winter months. The modified model was then used to simulate ET during the 21st century under six climate change scenarios by excluding/including climate-induced LCC. We found that regional annual ET varies from 188 to 286mmyr−1 across all scenarios, and that it increases between 0.11mmyr−2 and 0.55mmyr−2 during the 21st century. A spatial gradient of ET that increases from the southwest to the northeast is consistent in all scenarios. Regional ET in grasslands, boreal forests and semi-desert/deserts ranges from 242 to 374mmyr−1, 213 to 278mmyr−1 and 100 to 199mmyr−1, respectively; and the degree of the ET increase follows the order of grassland, semi-desert/desert, and boreal forest. Across the plateau, climate-induced LCC does not lead to a substantial change (<5%) in ET relative to a static land cover, suggesting that climate change is more important than LCC in determining regional ET. Furthermore, the differences between precipitation and ET suggest that the available water for human use (water availability) on the plateau will not change significantly during the 21st century. However, more water is available and less area is threatened by water shortage in the Business-As-Usual emission scenarios relative to level-one stabilization emission scenarios. [Copyright &y& Elsevier]