ALBERT

Description: The effect of plantations on mean annual streamflow is well understood and, there are robust methods available for assessing the impact. Plantations also affect streamflow regime, leading to reductions in low flow and increased number of zero-flow days. Understanding changes in streamflow regime following plantation expansion is important for developing water resources and environmental flow strategy. This study evaluated the impacts of plantations on streamflow regime from 15 catchments in Australia. The selected catchments range in size from 0.6 to 1136 km2 and represent different climatic conditions and management practices. The catchments have at least 20 yr and in most cases 35 yr of continuous daily streamflow data and well documented plantation records. Catchments with perennial streamflow in the pre-treatment periods showed relatively uniform reductions in most flows after plantation expansions, whereas catchments with ephemeral streamflow showed more dramatic reductions in low flows, leading to an increased number of zero-flow days. The Forest Cover Flow Change (FCFC) model was tested using the data from the selected catchments and comparison of predicted and observed flow duration curves showed that 14 of the 15 catchments have coefficients of efficiency greater than 0.8. The results indicate that the model is capable of predicting plantation impacts on streamflow regime.

Description: Terrestrial carbon and water cycles are interactively linked at various spatial and temporal scales. Evapotranspiration (ET) plays a key role in the terrestrial water cycle, altering carbon sequestration of terrestrial ecosystems. The study of ET and its response to climate and vegetation changes is critical in China because water availability is a limiting factor for the functioning of terrestrial ecosystems in vast arid and semiarid regions. To constrain uncertainties in ET estimation, the process-based Boreal Ecosystem Productivity Simulator (BEPS) model was employed in conjunction with a newly developed leaf area index (LAI) data set, MODIS land cover, meteorological, and soil data to simulate daily ET and water yield at a spatial resolution of 500 m over China for the period from 2000 to 2010. The spatial and temporal variations of ET and water yield were analyzed. The influences of climatic factors (temperature and precipitation) and vegetation (land cover types and LAI) on these variations were assessed. Validations against ET measured at five ChinaFLUX sites showed that the BEPS model was able to simulate daily and annual ET well at site scales. Simulated annual ET exhibited a distinguishable southeast to northwest decreasing gradient, corresponding to climate conditions and vegetation types. It increased with the increase of LAI in 74% of China's landmass and was positively correlated with temperature in most areas of southwest, south, east, and central China. The correlation between annual ET and precipitation was positive in the arid and semiarid areas of northwest and north China, but negative in the Tibetan Plateau and humid southeast China. The national annual ET varied from 345.5 mm in 2001 to 387.8 mm in 2005, with an average of 369.8 mm during the study period. The overall rate of increase, 1.7 mm yr−1 (R2 = 0.18, p = 0.19), was mainly driven by the increase of total ET in forests. During 2006–2009, precipitation and LAI decreased widely and consequently caused a detectable decrease in national total ET. Annual ET increased over 62.2% of China's landmass, especially in the cropland areas of the southern Haihe River basin, most of the Huaihe River basin, and the southeastern Yangtze River basin. It decreased in parts of northeast, north, northwest, south China, especially in eastern Qinghai-Tibetan Plateau, the south of Yunnan Province, and Hainan Province. Reduction in precipitation and increase in ET caused vast regions in China, especially the regions south of Yangtze River, to experience significant decreases in water yield, while some sporadically distributed areas experienced increases in water yield. This study shows that the terrestrial water cycles in China's terrestrial ecosystems appear to have been intensified by recent climatic variability and human induced vegetation changes.

Description: The effect of plantations on mean annual streamflow is well understood and there are robust methods available for assessing the impact. Plantations also affect streamflow regime, leading to reductions in low flow and increased number of zero-flow days. Understanding changes in streamflow regime following plantation expansion is important for developing water resources and environmental flow strategy. This study evaluated the impacts of plantation on streamflow regime from 15 catchments in Australia. The selected catchments range in size from 0.6 to 1136 km2 and represent different climatic conditions and management practices. The catchments have at least 20 yr and in most cases 35 yr of continuous daily streamflow data and well documented plantation records. Catchments with perennial streamflow in the pre-treatment periods showed relatively uniform reductions in most flows after plantation expansions, whereas catchments with ephemeral streamflow showed more dramatic reductions in low flows, leading to an increased number of zero-flow days. The Forest Cover Flow Change (FCFC) model was tested using the data from the selected catchments and comparison of predicted and observed flow duration curves showed that 14 of the 15 catchments have coefficient of efficiency greater than 0.8. The results indicate that the model is capable of predicting plantation impacts on streamflow regime.

Description: In the Northern Hemisphere, atmospheric CO2 concentration declines in spring and summer, and rises in fall and winter. Ground-based and aircraft-based observation records indicate that the amplitude of this seasonal cycle has increased in the past. Will this trend continue in the future? In this paper, we analyzed simulations for historical (1850–2005) and future (RCP8.5, 2006–2100) periods produced by 10 Earth system models participating in the fifth phase of the Coupled Model Intercomparison Project (CMIP5). Our results present a model consensus that the increase of CO2 seasonal amplitude continues throughout the 21st century. Multi-model ensemble relative amplitude of detrended global mean CO2 seasonal cycle increases by 62 ± 19% in 2081–2090, compared to 1961–1970. This amplitude increase corresponds to a 68 ± 25% increase in net biosphere production (NBP). The results show that the increase of NBP amplitude mainly comes from enhanced ecosystem uptake during Northern Hemisphere growing season under future CO2 and temperature conditions. Separate analyses on net primary production (NPP) and respiration reveal that enhanced ecosystem carbon uptake contributes about 75% of the amplitude increase. Stimulated by higher CO2 concentration and high-latitude warming, enhanced NPP likely outcompetes increased respiration at higher temperature, resulting in a higher net uptake during the northern growing season. The zonal distribution and spatial pattern of NBP change suggest that regions north of 45° N dominate the amplitude increase. Models that simulate a stronger carbon uptake also tend to show a larger increase of NBP seasonal amplitude, and the cross-model correlation is significant (R=0.73, p〈 0.05).

Description: Superimposed on the continued increase in the atmospheric CO2 concentration is a prominent seasonal cycle. Ground-based and aircraft-based observation records show that the amplitude of this seasonal cycle has increased. Will this trend continue into future? In this paper, we analyzed simulations for historical (1850–2005) and future (RCP8.5, 2006–2100) periods produced by 10 Earth System Models participating the Fifth Phase of the Coupled Model Intercomparison Project (CMIP5). Our results show a model consensus that the increase of CO2 seasonal amplitude continues throughout the 21st century. The seasonal amplitude of the multi-model global mean detrended CO2 increases from 1.6 ppm during 1961–1970 to 2.7 ppm during 2081–2090, and the mean relative amplitude increases by 62 ± 19%. This increase is dominated by a 68 ± 25% increase from Net Biosphere Production (NBP). We then show the increase of NBP amplitude mainly comes from enhanced ecosystem uptake during Northern Hemisphere growing season under future CO2 and temperature conditions. Separate analyses on net primary production and respiration reveal that enhanced ecosystem carbon uptake contributes to about 75% of the amplitude increase. Stimulated by higher CO2 concentration and high-latitude warming, enhanced net primary production likely outcompetes increased respiration at higher temperature. Zonal distribution and the spatial pattern of NBP change suggest that regions north of 45° N dominate the amplitude increase. We also found that changes of NBP and its seasonal amplitude are significantly (R = 0.73, p 〈 0.05) correlated – models that simulate a stronger carbon uptake tend to show a larger change of NBP seasonal amplitude.

Description: Terrestrial biosphere models (TBMs) have become an integral tool for extrapolating local observations and understanding of land–atmosphere carbon exchange to larger regions. The North American Carbon Program (NACP) Multi-scale synthesis and Terrestrial Model Intercomparison Project (MsTMIP) is a formal model intercomparison and evaluation effort focused on improving the diagnosis and attribution of carbon exchange at regional and global scales. MsTMIP builds upon current and past synthesis activities, and has a unique framework designed to isolate, interpret, and inform understanding of how model structural differences impact estimates of carbon uptake and release. Here we provide an overview of the MsTMIP effort and describe how the MsTMIP experimental design enables the assessment and quantification of TBM structural uncertainty. Model structure refers to the types of processes considered (e.g., nutrient cycling, disturbance, lateral transport of carbon), and how these processes are represented (e.g., photosynthetic formulation, temperature sensitivity, respiration) in the models. By prescribing a common experimental protocol with standard spin-up procedures and driver data sets, we isolate any biases and variability in TBM estimates of regional and global carbon budgets resulting from differences in the models themselves (i.e., model structure) and model-specific parameter values. An initial intercomparison of model structural differences is represented using hierarchical cluster diagrams (a.k.a. dendrograms), which highlight similarities and differences in how models account for carbon cycle, vegetation, energy, and nitrogen cycle dynamics. We show that, despite the standardized protocol used to derive initial conditions, models show a high degree of variation for GPP, total living biomass, and total soil carbon, underscoring the influence of differences in model structure and parameterization on model estimates.

Description: Terrestrial carbon and water cycles are interactively linked at various spatial and temporal scales. Evapotranspiration (ET) plays a key role in the terrestrial water cycle and altering carbon sequestration of terrestrial ecosystems. The study of ET and its response to climate and vegetation changes is critical in China since water availability is a limiting factor for the functioning of terrestrial ecosystems in vast arid and semiarid regions. In this study, the process-based Boreal Ecosystem Productivity Simulator (BEPS) model was employed in conjunction with a newly developed leaf area index (LAI) dataset and other spatial data to simulate daily ET and water yield at a spatial resolution of 500 m over China for the period from 2000 to 2010. The spatial and temporal variations of ET and water yield and influences of temperature, precipitation, land cover types, and LAI on ET were analyzed. The validations with ET measured at 5 typical ChinaFLUX sites and inferred using statistical hydrological data in 10 basins showed that the BEPS model was able to simulate daily and annual ET well at site and basin scales. Simulated annual ET exhibited a distinguishable southeast to northwest decreasing gradient, corresponding to climate conditions and vegetation types. It increased with the increase of LAI in 74% of China's landmass and was positively correlated with temperature in most areas of southwest, south, east, and central China and with precipitation in the arid and semiarid areas of northwest and north China. In the Tibet Plateau and humid southeast China, the increase in precipitation might cause ET to decrease. The national mean annual ET varied from 345.5 mm yr−1 in 2001 to 387.8 mm yr−1 in 2005, with an average of 369.8 mm yr−1 during the study period. The overall increase rate of 1.7 mm yr−2 (r = 0.43 p = 0.19) was mainly driven by the increase of total ET in forests. During the period from 2006 to 2009, precipitation and LAI decreased widely and consequently caused a detectable decrease of national total ET. The temporal patterns of ET varied spatially during the 11 yr study period, increasing in 62.2% of China's landmass, especially in the cropland areas of southern Haihe river basin, most of the Huaihe river basin, and southeastern Yangtze river basin. Decreases of annual ET mainly occurred in parts of northeast, north, northwest, south China, especially in eastern Qinghai-Tibet plateau, the south part of Yunnan province, and Hainan province. Vast regions in China, especially the regions south of Yangtze river, experienced significant decreases in water yield caused by the reduction of precipitation and increase of ET while some areas sporadically distributed in northeast, east, northwest, central, and south China experienced increases in water yield. This study shows that recent climatic variability and human activity induced vegetations changes have intensified the terrestrial water cycles in China's terrestrial ecosystems, which is worthy of further thorough investigation.

Description: Both historical and idealized climate model experiments are performed with a variety of Earth system models of intermediate complexity (EMICs) as part of a community contribution to the Intergovernmental Panel on Climate Change Fifth Assessment Report. Historical simulations start at 850 CE and continue through to 2005. The standard simulations include changes in forcing from solar luminosity, Earth's orbital configuration, CO2, additional greenhouse gases, land use, and sulphate and volcanic aerosols. In spite of very different modelled pre-industrial global surface air temperatures, overall 20th century trends in surface air temperature and carbon uptake are reasonably well simulated when compared to observed trends. Land carbon fluxes show much more variation between models than ocean carbon fluxes, and recent land fluxes appear to be slightly underestimated. It is possible that recent modelled climate trends or climate–carbon feedbacks are overestimated resulting in too much land carbon loss or that carbon uptake due to CO2 and/or nitrogen fertilization is underestimated. Several one thousand year long, idealized, 2 × and 4 × CO2 experiments are used to quantify standard model characteristics, including transient and equilibrium climate sensitivities, and climate–carbon feedbacks. The values from EMICs generally fall within the range given by general circulation models. Seven additional historical simulations, each including a single specified forcing, are used to assess the contributions of different climate forcings to the overall climate and carbon cycle response. The response of surface air temperature is the linear sum of the individual forcings, while the carbon cycle response shows a non-linear interaction between land-use change and CO2 forcings for some models. Finally, the preindustrial portions of the last millennium simulations are used to assess historical model carbon-climate feedbacks. Given the specified forcing, there is a tendency for the EMICs to underestimate the drop in surface air temperature and CO2 between the Medieval Climate Anomaly and the Little Ice Age estimated from palaeoclimate reconstructions. This in turn could be a result of unforced variability within the climate system, uncertainty in the reconstructions of temperature and CO2, errors in the reconstructions of forcing used to drive the models, or the incomplete representation of certain processes within the models. Given the forcing datasets used in this study, the models calculate significant land-use emissions over the pre-industrial period. This implies that land-use emissions might need to be taken into account, when making estimates of climate–carbon feedbacks from palaeoclimate reconstructions.

Description: Both historical and idealized climate model experiments are performed with a variety of Earth System Models of Intermediate Complexity (EMICs) as part of a community contribution to the Intergovernmental Panel on Climate Change Fifth Assessment Report. Historical simulations start at 850 CE and continue through to 2005. The standard simulations include changes in forcing from solar luminosity, Earth's orbital configuration, CO2, additional greenhouse gases, land-use, and sulphate and volcanic aerosols. In spite of very different modelled pre-industrial global surface air temperatures, overall 20th century trends in surface air temperature and carbon uptake are reasonably well simulated when compared to observed trends. Land carbon fluxes show much more variation between models than ocean carbon fluxes, and recent land fluxes seem to be underestimated. It is possible that recent modelled climate trends or climate-carbon feedbacks are overestimated resulting in too much land carbon loss or that carbon uptake due to CO2 and/or nitrogen fertilization is underestimated. Several one thousand year long, idealized, 2x and 4x CO2 experiments are used to quantify standard model characteristics, including transient and equilibrium climate sensitivities, and climate-carbon feedbacks. The values from EMICs generally fall within the range given by General Circulation Models. Seven additional historical simulations, each including a single specified forcing, are used to assess the contributions of different climate forcings to the overall climate and carbon cycle response. The response of surface air temperature is the linear sum of the individual forcings, while the carbon cycle response shows considerable synergy between land-use change and CO2 forcings for some models. Finally, the preindustrial portions of the last millennium simulations are used to assess historical model carbon-climate feedbacks. Given the specified forcing, there is a tendency for the EMICs to underestimate the drop in surface air temperature and CO2 between the Medieval Climate Anomaly and the Little Ice Age estimated from paleoclimate reconstructions. This in turn could be a result of errors in the reconstructions of volcanic and/or solar radiative forcing used to drive the models or the incomplete representation of certain processes or variability within the models. Given the datasets used in this study, the models calculate significant land-use emissions over the pre-industrial. This implies that land-use emissions might need to be taken into account, when making estimates of climate-carbon feedbacks from paleoclimate reconstructions.

Description: Terrestrial biosphere models (TBMs) have become an integral tool for extrapolating local observations and understanding of land-atmosphere carbon exchange to larger regions. The North American Carbon Program (NACP) Multi-scale synthesis and Terrestrial Model Intercomparison Project (MsTMIP) is a formal model intercomparison and evaluation effort focused on improving the diagnosis and attribution of carbon exchange at regional and global scales. MsTMIP builds upon current and past synthesis activities, and has a unique framework designed to isolate, interpret, and inform understanding of how model structural differences impact estimates of carbon uptake and release. Here we provide an overview of the MsTMIP effort and describe how the MsTMIP experimental design enables the assessment and quantification of TBM structural uncertainty. Model structure refers to the types of processes considered (e.g. nutrient cycling, disturbance, lateral transport of carbon), and how these processes are represented (e.g. photosynthetic formulation, temperature sensitivity, respiration) in the models. By prescribing a common experimental protocol with standard spin-up procedures and driver data sets, we isolate any biases and variability in TBM estimates of regional and global carbon budgets resulting from differences in the models themselves (i.e. model structure) and model-specific parameter values. An initial intercomparison of model structural differences is represented using hierarchical cluster diagrams (a.k.a. dendrograms), which highlight similarities and differences in how models account for carbon cycle, vegetation, energy, and nitrogen cycle dynamics. We show that, despite the standardized protocol used to derive initial conditions, models show a high degree of variation for GPP, total living biomass, and total soil carbon, underscoring the influence of differences in model structure and parameterization on model estimates.