3,481 research outputs found
Sub-grid scale representation of vegetation in global land surface schemes: implications for estimation of the terrestrial carbon sink
Terrestrial ecosystem models commonly represent vegetation in terms of
plant functional types (PFTs) and use their vegetation attributes in
calculations of the energy and water balance as well as to investigate the
terrestrial carbon cycle. Sub-grid scale variability of PFTs in these models
is represented using different approaches with the "composite" and
"mosaic" approaches being the two end-members.
The impact of these two approaches on the global carbon
balance has been investigated with the Canadian Terrestrial Ecosystem
Model (CTEM v 1.2) coupled to the Canadian Land Surface Scheme (CLASS
v 3.6). In the composite (single-tile) approach, the vegetation
attributes of different PFTs present in a grid cell are aggregated and
used in calculations to determine the resulting physical environmental
conditions (soil moisture, soil temperature, etc.) that are common to
all PFTs. In the mosaic (multi-tile) approach, energy and water
balance calculations are performed separately for each PFT tile and
each tile's physical land surface environmental conditions evolve
independently. Pre-industrial equilibrium CLASS-CTEM simulations yield
global totals of vegetation biomass, net primary productivity, and
soil carbon that compare reasonably well with observation-based
estimates and differ by less than 5% between the mosaic and
composite configurations. However, on a regional scale the two
approaches can differ by > 30%, especially in areas with
high heterogeneity in land cover. Simulations over the historical
period (1959–2005) show different responses to evolving climate and
carbon dioxide concentrations from the two approaches. The cumulative
global terrestrial carbon sink estimated over the 1959–2005 period
(excluding land use change (LUC) effects) differs by around
5% between the two approaches (96.3 and 101.3 Pg, for the
mosaic and composite approaches, respectively) and compares well with
the observation-based estimate of 82.2 ± 35 Pg C over the same
period. Inclusion of LUC causes the estimates of the terrestrial C
sink to differ by 15.2 Pg C (16%) with values of 95.1 and
79.9 Pg C for the mosaic and composite approaches,
respectively. Spatial differences in simulated vegetation and soil
carbon and the manner in which terrestrial carbon balance evolves in
response to LUC, in the two approaches, yields a substantially
different estimate of the global land carbon sink. These results
demonstrate that the spatial representation of vegetation has an
important impact on the model response to changing climate,
atmospheric CO<sub>2</sub> concentrations, and land cover
The influence of soils on heterotrophic respiration exerts a strong control on net ecosystem productivity in seasonally dry Amazonian forests
Net ecosystem productivity of carbon (NEP) in seasonally dry forests
of the Amazon varies greatly between sites with similar
precipitation patterns. Correctly modeling the NEP seasonality with
terrestrial ecosystem models has proven difficult. Previous
modelling studies have mostly advocated for incorporating processes that
act to reduce water stress on gross primary productivity (GPP)
during the dry season, such as deep soils and roots,
plant-mediated hydraulic redistribution of soil moisture, and
increased dry season leaf litter generation which reduces leaf age
and thus increases photosynthetic capacity. Recent observations,
however, indicate that seasonality in heterotrophic respiration also
contributes to the observed seasonal cycle of NEP. Here, we use the
dynamic vegetation model CLASS-CTEM (Canadian Land
Surface Scheme–Canadian Terrestrial
Ecosystem Model) – without deep soils or roots,
hydraulic redistribution of soil moisture, or increased dry season
litter generation – at two Large-Scale Biosphere–Atmosphere
Experiment (LBA) sites (Tapajós km 83 and Jarú
Reserve). These LBA sites exhibit opposite seasonal NEP cycles
despite reasonably similar meteorological conditions. Our simulations are able
to reproduce the observed NEP seasonality at both sites. Simulated
GPP, heterotrophic respiration, latent and sensible heat fluxes,
litter fall rate, soil moisture and temperature, and basic
vegetation state are also compared with available observation-based
estimates which provide confidence that overall the model behaves
realistically at the two sites.
Our results indicate that
representing the effect of soil moisture on heterotrophic respiration in terms of soil matric potential and constraining
heterotrophic respiration when absolute soil matric potential is both low (wetter soils) and high (drier soils), with optimum conditions in between, allows
%appropriately representing the influence of soil texture and depth,
%through soil moisture, on seasonal patterns of GPP and, especially,
% heterotrophic respiration is important
to correctly simulate NEP
seasonality
Heart Failure in Hispanic Americans: Improving Cultural Awareness
Hispanic Americans are the largest and fastest growing ethnic group in the United States. Hispanic Americans have high rates of heart failure (HF) risk factors, such as hypertension, diabetes mellitus, obesity, obstructive sleep disorders, and dyslipidemia. Certain unique HF risk factors prominent among Hispanic Americans are uncommon in the general population, such as younger onset of valvular disease and Chagas disease. Advanced practice nurses providing care to Hispanic Americans have an ethical obligation to provide culturally competent care and assist these patients in overcoming barriers to health care so that they can effectively manage their HF
Updated fracture incidence rates for the US version of FRAX®
# The Author(s) 2009. This article is published with open access at Springerlink.com Summary On the basis of updated fracture and mortality data, we recommend that the base population values used in the US version of FRAX ® be revised. The impact of suggested changes is likely to be a lowering of 10-year fracture probabilities. Introduction Evaluation of results produced by the US version of FRAX ® indicates that this tool overestimates the likelihood of major osteoporotic fracture. In an attempt to correct this, we updated underlying fracture and mortality rates for the model. Methods We used US hospital discharge data from 2006 t
Developments at the Advanced Design Technologies Testbed
A report presents background and historical information, as of August 1998, on the Advanced Design Technologies Testbed (ADTT) at Ames Research Center. The ADTT is characterized as an activity initiated to facilitate improvements in aerospace design processes; provide a proving ground for product-development methods and computational software and hardware; develop bridging methods, software, and hardware that can facilitate integrated solutions to design problems; and disseminate lessons learned to the aerospace and information technology communities
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