1,209 research outputs found
The influence of vegetation on the ITCZ and South Asian monsoon in HadCM3
The role of global vegetation on the large-scale tropical circulation is examined in the version 3 Hadley Centre climate model (HadCM3). Alternative representations of global vegetation cover from observations and a dynamic global vegetation model (DGVM) were used as the landcover component for a number of HadCM3 experiments under a nominal present day climate state, and compared to the simulations using the standard land cover map of HadCM3. The alternative vegetation covers result in a large scale cooling of the Northern Hemisphere extra-tropics relative to the HadCM3 standard, resulting in a southward shift in the location of the inter-tropical convergence zone (ITCZ). A significant reduction in Indian monsoon precipitation is also found, which is related to a weakening of the South Asian monsoon circulation, broadly consistent with documented mechanisms relating to temperature and snow perturbations in the Northern Hemisphere extra-tropics in winter and spring, delaying the onset of the monsoon. The role of the Northern Hemisphere extra-tropics on tropical climate is demonstrated, with an additional representation of vegetation cover based on DGVM simulated changes in Northern Hemisphere vegetation from the end of the 21st Century. This experiment shows that through similar processes the simulated extra-tropical vegetation changes in the future contribute to a strengthening of the South Asian monsoon in this model. These findings provide renewed motivation to give careful consideration to the role of global scale vegetation feedbacks when looking at climate change, and its impact on the tropical circulation and South Asian monsoon in the latest generation of Earth System models
The impact of structural error on parameter constraint in a climate model
Uncertainty in the simulation of the carbon cycle contributes significantly to uncertainty in the projections
of future climate change. We use observations of forest fraction to constrain carbon cycle and land
surface input parameters of the global climate model FAMOUS, in the presence of an uncertain structural error.
Using an ensemble of climate model runs to build a computationally cheap statistical proxy (emulator) of the
climate model, we use history matching to rule out input parameter settings where the corresponding climate
model output is judged sufficiently different from observations, even allowing for uncertainty.
Regions of parameter space where FAMOUS best simulates the Amazon forest fraction are incompatible with
the regions where FAMOUS best simulates other forests, indicating a structural error in the model. We use
the emulator to simulate the forest fraction at the best set of parameters implied by matching the model to the
Amazon, Central African, South East Asian, and North American forests in turn. We can find parameters that
lead to a realistic forest fraction in the Amazon, but that using the Amazon alone to tune the simulator would
result in a significant overestimate of forest fraction in the other forests. Conversely, using the other forests to
tune the simulator leads to a larger underestimate of the Amazon forest fraction.
We use sensitivity analysis to find the parameters which have the most impact on simulator output and perform
a history-matching exercise using credible estimates for simulator discrepancy and observational uncertainty
terms. We are unable to constrain the parameters individually, but we rule out just under half of joint parameter
space as being incompatible with forest observations. We discuss the possible sources of the discrepancy in the
simulated Amazon, including missing processes in the land surface component and a bias in the climatology of
the Amazon.This work was supported by the Joint
UK BEIS/Defra Met Office Hadley Centre Climate Programme
(GA01101). Doug McNeall was supported on secondment
to Exeter University by the Met Office Academic Partnership
(MOAP) for part of the work. Jonny Williams was supported
by funding from Statoil ASA, Norwa
Changes in Climate and Land Use Over the Amazon Region: Current and Future Variability and Trends
This is the final version. Available on open access from Frontiers media via the DOI in this recordThis paper shows recent progress in our understanding of climate variability and trends in the Amazon region, and how these interact with land use change. The review includes an overview of up-to-date information on climate and hydrological variability, and on warming trends in Amazonia, which reached 0.6–0.7°C over the last 40 years, with 2016 as the warmest year since at least 1950 (0.9°C + 0.3°C). We focus on local and remote drivers of climate variability and change. We review the impacts of these drivers on the length of dry season, the role of the forest in climate and carbon cycles, the resilience of the forest, the risk of fires and biomass burning, and the potential “die back” of the Amazon forests if surpassing a “tipping point”. The role of the Amazon in moisture recycling and transport is also investigated, and a review of model development for climate change projections in the region is included. In sum, future sustainability of the Amazonian forests and its many services requires management strategies that consider the likelihood of multi-year droughts superimposed on a continued warming trend. Science has assembled enough knowledge to underline the global and regional importance of an intact Amazon region that can support policymaking and to keep this sensitive ecosystem functioning. This major challenge requires substantial resources and strategic cross-national planning, and a unique blend of expertise and capacities established in Amazon countries and from international collaboration. This also highlights the role of deforestation control in support of policy for mitigation options as established in the Paris Agreement of 2015.National Institute of Science and Technology for Climate ChangeFAPESPNational Coordination for High Level Education and Training (CAPES)Deutsche ForschungsgemeinschafNewton Fun
Mountain rock glaciers contain globally significant water stores
This is the author accepted manuscript. The final version is available from Springer Nature via the DOI in this recordGlacier- and snowpack-derived meltwaters are threatened by climate change. Features such as rock glaciers (RGs) are climatically more resilient than glaciers and potentially contain hydrologically valuable ice volumes. However, while the distribution and hydrological significance of glaciers is well studied, RGs have received comparatively little attention. Here, we present the first near-global RG database (RGDB) through an analysis of current inventories and this contains >73,000 RGs. Using the RGDB, we identify key data-deficient regions as research priorities (e.g., Central Asia). We provide the first approximation of near-global RG water volume equivalent and this is 83.72 ± 16.74 Gt. Excluding the Antarctic and Subantarctic, Greenland, and regions lacking data, we estimate a near-global RG to glacier water volume equivalent ratio of 1:456. Significant RG water stores occur in arid and semi-arid regions (e.g., South Asia East, 1:57). These results represent a first-order approximation. Uncertainty in the water storage estimates includes errors within the RGDB, inherent flaws in the meta-analysis methodology, and RG thickness estimation. Here, only errors associated with the assumption of RG ice content are quantified and overall uncertainty is likely larger than that quantified. We suggest that RG water stores will become increasingly important under future climate warming.This work was supported by the Natural Environment Research Council (grant number NE/L002434/1 to D.B.J.).
S.H. and R.A.B. received funding from the European Union Seventh Framework Programme FP7/2007-2013
under grant agreement no 603864 (HELIX: High-End cLimate Impacts and eXtremes; www.helixclimate.eu). The
work of R.A.B. forms part of the BEIS/Defra Met Office Hadley Centre Climate Programme GA01101
Impacts of climate extremes in Brazil the development of a web platform for understanding long-term sustainability of ecosystems and human health in amazonia (pulse-Brazil)
This is the final version of the article. Available from the American Meteorological Society via the DOI in this record.This work was funded by the joint FAPESP 2011/51843-2 and NERC NE/J016276/1 International Opportunities Fund. PULSE-Brazil development is also funded by the FAPESP grant (2012/51876-0) under the Belmont Forum Cooperation Agreement. Marengo and Aragão thank the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) for their Research Productivity Fellowship
Towards quantifying uncertainty in predictions of Amazon 'dieback'.
This is the final version of the article. It first appeared from The Royal Society via http://dx.doi.org/10.1098/rstb.2007.0028Simulations with the Hadley Centre general circulation model (HadCM3), including carbon cycle model and forced by a 'business-as-usual' emissions scenario, predict a rapid loss of Amazonian rainforest from the middle of this century onwards. The robustness of this projection to both uncertainty in physical climate drivers and the formulation of the land surface scheme is investigated. We analyse how the modelled vegetation cover in Amazonia responds to (i) uncertainty in the parameters specified in the atmosphere component of HadCM3 and their associated influence on predicted surface climate. We then enhance the land surface description and (ii) implement a multilayer canopy light interception model and compare with the simple 'big-leaf' approach used in the original simulations. Finally, (iii) we investigate the effect of changing the method of simulating vegetation dynamics from an area-based model (TRIFFID) to a more complex size- and age-structured approximation of an individual-based model (ecosystem demography). We find that the loss of Amazonian rainforest is robust across the climate uncertainty explored by perturbed physics simulations covering a wide range of global climate sensitivity. The introduction of the refined light interception model leads to an increase in simulated gross plant carbon uptake for the present day, but, with altered respiration, the net effect is a decrease in net primary productivity. However, this does not significantly affect the carbon loss from vegetation and soil as a consequence of future simulated depletion in soil moisture; the Amazon forest is still lost. The introduction of the more sophisticated dynamic vegetation model reduces but does not halt the rate of forest dieback. The potential for human-induced climate change to trigger the loss of Amazon rainforest appears robust within the context of the uncertainties explored in this paper. Some further uncertainties should be explored, particularly with respect to the representation of rooting depth
Noradrenergic-dependent functions are associated with age-related locus coeruleus signal intensity differences.
The locus coeruleus (LC), the origin of noradrenergic modulation of cognitive and behavioral function, may play an important role healthy ageing and in neurodegenerative conditions. We investigated the functional significance of age-related differences in mean normalized LC signal intensity values (LC-CR) in magnetization-transfer (MT) images from the Cambridge Centre for Ageing and Neuroscience (Cam-CAN) cohort - an open-access, population-based dataset. Using structural equation modelling, we tested the pre-registered hypothesis that putatively noradrenergic (NA)-dependent functions would be more strongly associated with LC-CR in older versus younger adults. A unidimensional model (within which LC-CR related to a single factor representing all cognitive and behavioral measures) was a better fit with the data than the a priori two-factor model (within which LC-CR related to separate NA-dependent and NA-independent factors). Our findings support the concept that age-related reduction of LC structural integrity is associated with impaired cognitive and behavioral function
The distribution and hydrological significance of rock glaciers in the Nepalese Himalaya
This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this record.In the Nepalese Himalaya, there is little information on the number, spatial distribution and morphometric
characteristics of rock glaciers, and this information is required if their hydrological contribution is to be
understood. Based on freely available fine spatial resolution satellite data accessible through Google Earth, we
produced the first comprehensive Nepalese rock glacier inventory, supported through statistical validation and
field survey. The inventory includes the location of over 6000 rock glaciers, with a mean specific density of 3.4%.
This corresponds to an areal coverage of 1371 km². Our approach subsampled approximately 20% of the total
identified rock glacier inventory (n = 1137) and digitised their outlines so that quantitative/qualitative landform
attributes could be extracted. Intact landforms (containing ice) accounted for 68% of the subsample, and the
remaining were classified as relict (not containing ice). The majority (56%) were found to have a northerly aspect
(NE, N, and NW), and landforms situated within north- to west-aspects reside at lower elevations than those
with south- to- east aspects. In Nepal, we show that rock glaciers are situated between 3225 to 5675 m a.s.l.,
with the mean minimum elevation at the front estimated to be 4977±280 m a.s.l. for intact landforms and
4541±346 m a.s.l. for relict landforms. The hydrological significance of rock glaciers in Nepal was then established
by statistically upscaling the results from the subsample to estimate that these cryospheric reserves store
between 16.72 and 25.08 billion cubic metres of water. This study, for the first time, estimates rock glacier water
volume equivalents and evaluates their relative hydrological importance in comparison to ice glaciers. Across
the Nepalese Himalaya, rock glacier to ice glacier water volume equivalent is 1:9, and generally increases
westwards (e.g., ratio = 1:3, West region). This inventory represents a preliminary step for understanding the
spatial distribution and the geomorphic conditions necessary for rock glacier formation in the Himalaya. With
continued climatically-driven ice glacier recession, the relative importance of rock glaciers in the Nepalese
Himalaya will potentially increase.This work was supported by the Natural Environment Research Council (grant number:
851 NE/L002434/1 to DBJ); the Royal Geographical Society (with IBG) with a Dudley Stamp Memorial Award
852 (awarded to DBJ); the European Union Seventh Framework Programme FP7/2007-2013 (grant number: 603864
853 to SH and RAB [HELIX: High-End cLimate Impacts and eXtremes; www.helixclimate.eu]). The work of RB forms
854 part of the BEIS/Defra Met Office Hadley Centre Climate Programme GA01101.
The numerical control of the motion of a passive particle in a point vortex flow
This work reports numerical explorations in the advection of one passive tracer by point vortices
living in the unbounded plane. The main objective is to find the energy-optimal displacement
of one passive particle (point vortex with zero circulation) surrounded by N point vortices. The
direct formulation of the corresponding control problems is presented for the case of N = 1, N = 2,
N = 3 and N = 4 vortices. The restrictions are due to (i) the ordinary differential equations that
govern the displacement of the passive particle around the point vortices, (ii) the available time
T to go from the initial position z0 to the final destination zf; and (iii) the maximum absolute
value umax that is imposed on the control variables. The resulting optimization problems are
solved numerically. The numerical results show the existence of nearly/quasi-optimal control.info:eu-repo/semantics/publishedVersio
El Niño Driven Changes in Global Fire 2015/16
This is the final version. Available on open access from Frontiers Media via the DOI in this recordData Availability Statement:
The JULES code used in these experiments is freely available on the JULES trunk from version 5.4 onward. The rose suite used for these experiments is u-bh074. Both the suite and the JULES code are available on the JULES FCM repository: https://code.metoffice.gov.uk/trac/jules (registration required). The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation, to any qualified researcher upon request.El Niño years are characterized by a high sea surface temperature anomaly in the Equatorial Pacific Ocean, which leads to unusually warm and dry conditions over many fire-prone regions globally. This can lead to an increase in burned area and emissions from fire activity, and socio-economic, and environmental losses. Previous studies using satellite observations to assess the impacts of the recent 2015/16 El Niño found an increase in burned area in some regions compared to La Niña years. Here, we use the dynamic land surface model JULES to assess how conditions differed as a result of the El Niño by comparing simulations driven by observations from the year 2015/16 with mean climatological drivers of temperature, precipitation, humidity, wind, air pressure, and short and long-wave radiation. We use JULES with the interactive fire module INFERNO to assess the effects on precipitation, temperature, burned area, and the associated impacts on the carbon sink globally and for three regions: South America, Africa, and Asia. We find that the model projects a variable response in precipitation, with some areas including northern South America, southern Africa and East Asia getting drier, and most areas globally seeing an increase in temperature. As a result, higher burned area is simulated with El Niño conditions in most regions, although there are areas of both increased and decreased burned area over Africa. South America shows the largest fire response with El Niño, with a 13% increase in burned area and emitted carbon, corresponding with the largest decrease in carbon uptake. Within South America, peak fire occurs from August to October across central-southern Brazil, and temperature is shown to be the main driver of the El Niño-induced increase in burned area during this period. Combined, our results indicate that although 2015/16 was not a peak year for global total burned area or fire emissions, the El Niño led to an overall increase of 4% in burned area and 5% in emissions compared to a “No El Niño” scenario for 2015/16, and contributed to a 4% reduction in the terrestrial carbon sink.Newton FundNatural Environment Research Council (NERC)São Paulo Research Foundation (FAPESP)Brazilian National Council for Scientific and Technological Development (CNPq)Inter-American Institute for Global Change Research (IAI
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