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The Level Of Awareness And Response Mechanisms Of The Actors About The Impacts Of Climate Change On Tourism, The Case Of AntalyaZengin, Oznur 01 December 2009 (has links) (PDF)
The concept of &ldquo / climate change&rdquo / is, nowadays, seen as a global problem of the whole world.
It has impacts on the economic, social, and environmental life of human beings, and also on
the local life. As one of the sectors that are important for the local economies, &ldquo / tourism&rdquo / is
vulnerable to climate change due to being sensitive to the factors of climate and weather.
Therefore, to discuss the relation between the climate change and tourism is the aim of this
thesis. In this regard, the context of &ldquo / the awareness of the actors&rdquo / about the impacts of the
climate change becomes important. To evaluate the awareness of the actors, the research is
focused on &ldquo / the response mechanisms&rdquo / that they develop. The hypothesis is that although the
expected impact of climate change is very important, the level of awareness of the actors on
this sector is rather limited and this leads to limited action to mitigate the negative impacts of
climate change on tourism. In this regard, in this research, the main purpose is identified as
to discuss the impacts of climate change on tourism, and to evaluate the awareness of the
actors and the response mechanisms. It is researched that whether the actors are aware of the
current condition about climate change and tourism and whether the response mechanisms
that actors develop are effective on the impacts of climate change on tourism. As a sample in
Turkey, Antalya is defined as the case study area, and the impacts of climate change on
tourism are examined, and the awareness of the actors is analyzed. It is displayed, by the
results of the analysis, that which type of mechanisms the actors in Antalya have trend to
develop about climate change impacts.
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Evolution du cycle hydrologique continental en France au cours des prochaines décennies / Evolution of the continental hydrological cycle over France in the coming decadesDayon, Gildas 20 November 2015 (has links)
L'étude des impacts du changement climatique demande souvent de mettre en place de longues chaînes de modélisation. Du modèle qui servira à estimer les concentrations futures en gaz à effet de serre jusqu'au modèle d'impact. Tout au long de cette chaîne de modélisation, les sources d'incertitudes s'accumulent et compliquent l'exploitation des résultats pour l'élaboration de stratégies d'adaptation. Il est proposé ici d'évaluer les impacts du changement climatique sur le cycle hydrologique en France ainsi que les incertitudes qui y sont associées. La contribution de chacune des sources d'incertitudes n'est pas abordée, principalement celle associée aux scénarios d'émission de gaz à effet de serre, aux modèles climatiques et à la variabilité interne. Nous proposons dans ce travail une approche pour évaluer la transférabilité dans un climat futur de la méthode statistique de régionalisation des simulations climatiques. La vérification de l'hypothèse de transférabilité effectuée est l'une des principales sources d'incertitudes des méthodes statistiques de régionalisation. L'évaluation proposée ici s'appuie sur l'utilisation de modèles régionaux, dans un cadre dit de modèle parfait, et permet de montrer que l'utilisation de certain prédicteurs s'avèrent utile à assurer la transférabilité de la méthode de régionalisation dans un climat futur. Cette approche proposée pour une méthode de désagrégation statistique est également applicable à des méthodes de correction des biais des modèles régionaux. Les récentes réanalyses atmosphériques sur l'ensemble du XXème siècle, régionalisées avec la méthode développée dans ce travail, et associées aux observations de température et précipitations permettent de caractériser le cycle hydrologique en France. Elles permettent notamment de montrer que la variabilité multi-décennale des débits observés pendant le XXème siècle est généralisée à l'ensemble du pays et est liée à la variabilité des conditions atmosphériques. Cette variabilité multi-décennale des débits est généralement plus faible dans les simulations hydrologiques réalisées avec les simulations historiques des modèles climatiques. Les projections climatiques ont été régionalisées avec la méthode développée dans ce travail. La température sur l'ensemble du pays, en moyenne sur les modèles climatiques, augmente jusqu'à 3,5°C en hiver et 6,5°C en été d'ici la fin du siècle. Les précipitations vont diminuer sur l'ensemble du pays en été, de presque moitié sur le sud du pays pour le scénario le plus sévère. En hiver, elles augmentent sur la moitié nord du pays et diminuent légèrement sur la partie sud. Dès les prochaines décennies, la diminution des précipitations est importante en été, l'évolution est moins marquée pour les autres saisons. Enfin, les résultats des projections hydrologiques réalisées avec un modèle hydrologique et un ensemble de modèles climatiques sont présentés pour les prochaines décennies et également pour la fin du XXIème siècle. Sur la Seine, les résultats sont différents en hiver de ceux présentés dans de précédentes études. Ici, les précipitations et les débits augmentent en hiver et diminuent en été sur ce bassin versant. Ailleurs en France, les résultats convergent avec les études précédentes, à savoir une augmentation de l'évapotranspiration, une diminution généralisée des débits et un assèchement des sols. L'incertitude due aux modèles climatiques et à la variabilité interne sur les changements relatifs de débits augmente systématiquement pendant le XXIème siècle, jusqu'à atteindre plus de 20% en hiver pour le scénario le plus sévère. Dans les prochaines décennies, l'incertitude due uniquement à la variabilité interne sur les changements de débits est aussi forte que l'incertitude due aux modèles climatiques et à la variabilité interne. Dès les prochaines décennies, les changements de débits annuels sont plus forts sur la Loire, la Garonne et le Rhône que les changements maximaux observés pendant le XXème siècle. / The assessment of the impact of climate change often requires to set up long chains of modeling, from the model to estimate the future concentration of greenhouse gases to the impact model. Throughout the modeling chain, sources of uncertainty accumulate making the exploitation of results for the development of adaptation strategies difficult. It is proposed here to assess impacts of climate change on the hydrological cycle over France and associated uncertainties. The contribution of each sources of uncertainty is not addressed, mainly that associated with greenhouse gases emission scenario, climate models and internal variability. In the context of impacts of climate change on the hydrological cycle over France, it is possible to ask what is the contribution of each sources of uncertainty to the total uncertainty associated with mean changes. Is it possible to reduce, and if so how, the contribution of one source or another ? We propose in this work an approach to assess the transferability in the future climate of a statistical method to downscale climate simulations. The transferability assumption is one the main sources of uncertainty in statistical downscaling method. The assessment suggested here relies on the use of regional climate models, in a perfect model framework, and shows that some predictors are useful to ensure the transferability of the downscaling method in the future climate. This framework, proposed for a statistical downscaling method, is also applicable to bias correction methods in regional climate models. Recent atmospheric reanalyses of the 20th century are downscaled with the method developed in this work, associated with observations of temperature and precipitation. The hydrological cycle over France is characterized with these reconstructions. We show that the multi-decadal variability of observed streamflows during the 20th century is generalized to the whole country and is partly due to atmospheric variability. This multi-decadal variability of streamflows is generally weaker in hydrological simulations done with historical simulations from climate models. The climate projections have been downscaled with the method developed in this work. The temperature on the country, on average over climate models, could increased by 3,5°C in winter and 6,5°C in summer in the course of this century. Precipitations will decrease all over the country in summer, nearly by half on southern part of France for the most severe scenario. In winter, precipitations will increase in the northern part of the country and will decrease slightly in the southern part. In the next few decades, the decrease in precipitation is important in summer, and changes are less pronounced for other seasons. Results of hydrological projections done with one hydrological model and an ensemble of climate models are presented for the coming decades and for the end of the century. On the Seine river, results slightly differ in winter from those presented in previous studies. Here, precipitations and streamflow increase in winter and decrease in summer on that river basin. Elsewhere in France, results are consistent with previous studies, namely an increase in evapotranspiration, a decrease in streamflow and much drier soil. The uncertainty due to both climate models and internal variability on relative changes in streamflows always increase during the 21st century, to over 20% in winter for the most severe scenario. In the coming decades, the uncertainty due to internal variability only on streamflow changes is as strong as the uncertainty due to both climate models and internal variability. In the coming decades, annual streamflow changes of the Loire, Garonne and Rhône rivers are stronger than the maximum changes observed during the 20th century.
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<b>Evaluating resource competition of live oak (</b><b><i>Quercus virginiana </i></b><b>) regeneration to support maritime forest restoration </b>Brianne Nicole Innusa (18423570) 23 April 2024 (has links)
<p dir="ltr">Coastal ecosystems are critically important habitats for the services they provide on a global and local scale. Maritime forests are found within the southern Atlantic coast, and they serve as a boundary between the ocean and land. These forests stabilize coastlines, recharge groundwater, and provide a protective buffer against storm damage. Southern live oak (<i>Quercus virginiana</i>) was historically the dominant canopy species in maritime forests; however, previous land conversions to loblolly pine (<i>Pinus taeda</i>) plantations have shifted the abundance of loblolly pine to become the dominant canopy tree in maritime forests. Loblolly pines are fast growing, and they regenerate vigorously but they are not well adapted to coastal stressor. In recent decades, outbreaks of southern pine beetle (<i>Dendroctonus frontalis</i>) have provided restoration practitioners an opportunity to clear tracts of pine dominated maritime forest to restore live oak to the canopy. This research project is comprised of two experiments studying the performance of planted <i>Q. virginiana</i> seedlings on maritime forest restoration sites in coastal Georgia. The first experiment evaluated planting density (1-meter, 2-meters, 3-meters), mulch (with or without), and fertilizer (with or without). Overall seedling survival was 99% after four years. The application of fertilizer had an initial positive effect on seedling diameter after the first growing season. The application of mulch increased seedling height in the second to fourth growing seasons, diameter in third and fourth, and crown width in the fourth growing season. Planting density had no consistent effect over the first four years, and no biological significance was observed for foliar nutrient content. The second experiment examined eight different groupings of intra- and interspecific competition between <i>Q. virginiana</i> and <i>P. taeda</i> including: oak or pine alone; oak surrounded by oak, pine, or oak/pine; pine surrounded by pine, oak, or pine/oak at 0.5-m spacing between all seedlings. Two years after outplanting, survival did not vary by treatment. Oak centered competition plots were positively impacted by border tree height and diameter in year one and border height positively affected the center tree height in year two. Pine centered competition plots were positively impacted by border tree height in year one and year two. Oak centered competition plots with a mix of oak and pine on the border had significantly lower osmotic potential than other pine centric treatments after two years. Overall, oak centered treatments had lower osmotic potential than pine centered treatments. Ectomycorrhizal (EMF) species composition changed, and relative abundance increased from the initial planting to two years later but there was no variation between treatments and most EMF species were generalists. These results highlight the importance of mulch and fertilizer to reduce transplant shock and how competing seedlings can train seedlings to allocate photosynthate to shoot growth to help promote aboveground growth.</p>
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Abflußentwicklung in Teileinzugsgebieten des Rheins : Simulationen für den Ist-Zustand und für Klimaszenarien / Development of runoff in subcatchments of the River Rhine : simulations of the current state and for climate change scenariosSchwandt, Daniel January 2003 (has links)
Die vorliegende Arbeit
'Abflußentwicklung in Teileinzugsgebieten des Rheins - Simulationen für
den Ist-Zustand und für Klimaszenarien' untersucht Auswirkungen möglicher
zukünftiger Klimaänderungen auf das Abflußgeschehen in ausgewählten, durch
Mittelgebirge geprägten Teileinzugsgebieten des Rheins: Mosel (bis Pegel
Cochem); Sieg (bis Pegel Menden 1) und Main (bis Pegel Kemmern).<br><br>In einem ersten Schritt
werden unter Verwendung des hydrologischen Modells HBV-D wichtige
Modellprozesse entsprechend der Einzugsgebietscharakteristik
parametrisiert und ein Abbild der Gebietshydrologie erzeugt, das mit
Zeitreihen gemessener Tageswerte (Temperatur, Niederschlag) eine Zeitreihe
der Pegeldurchflüsse simulieren kann. Die Güte der Simulation des
Ist-Zustandes (Standard-Meßzeitraum 1.1.1961-31.12.1999) ist für die
Kalibrierungs- und Validierungszeiträume in allen Untersuchungsgebieten
gut bis sehr gut.<br>Zur Erleichterung der
umfangreichen, zeitaufwendigen einzugsgebietsbezogenen Datenaufbereitung
für das hydrologische Modell HBV-D wurde eine Arbeitsumgebung auf Basis
von Programmerweiterungen des Geoinformationssystems ArcView und
zusätzlichen Hilfsprogrammen entwickelt. Die Arbeitsumgebung HBV-Params
enthält eine graphische Benutzeroberfläche und räumt sowohl erfahrenen
Hydrologen als auch hydrologisch geschulten Anwendern, z.B. Studenten der
Vertiefungsrichtung Hydrologie, Flexibilität und vollständige Kontrolle
bei der Ableitung von Parameterwerten und der Editierung von Parameter-
und Steuerdateien ein. Somit ist HBV-D im Gegensatz zu Vorläuferversionen
mit rudimentären Arbeitsumgebungen auch außerhalb der Forschung für Lehr-
und Übungszwecke einsetzbar.<br><br>In einem zweiten Schritt werden
Gebietsniederschlagssummen, Gebietstemperaturen und simulierte Mittelwerte
des Durchflusses (MQ) des Ist-Zustandes mit den Zuständen zweier
Klimaszenarien für den Szenarienzeitraum 100 Jahre später (2061-2099)
verglichen. Die Klimaszenarien beruhen auf simulierten Zirkulationsmustern
je eines Modellaufes zweier Globaler Zirkulationsmodelle (GCM), die mit
einem statistischen Regionalisierungsverfahren in Tageswertszenarien
(Temperatur, Niederschlag) an Meßstationen in den Untersuchungsgebieten
überführt wurden und als Eingangsdaten des hydrologischen Modells
verwendet werden.<br>Für die zweite Hälfte des 21.
Jahrhunderts weisen beide regionalisierten Klimaszenarien eine Zunahme der
Jahresmittel der Gebietstemperatur sowie eine Zunahme der Jahressummen der
Gebietsniederschläge auf, die mit einer hohen Variabilität einhergeht.
Eine Betrachtung der saisonalen (monatlichen) Änderungsbeträge von
Temperatur, Niederschlag und mittlerem Durchfluß zwischen
Szenarienzeitraum (2061-2099) und Ist-Zustand ergibt in allen
Untersuchungsgebieten eine Temperaturzunahme (höher im Sommer als im
Winter) und eine generelle Zunahme der Niederschlagssummen (mit starken
Schwankungen zwischen den Einzelmonaten), die bei der hydrologischen
Simulation zu deutlich höheren mittleren Durchflüssen von November bis
März und leicht erhöhten mittleren Durchflüssen in den restlichen Monaten
führen. Die Stärke der Durchflußerhöhung ist nach den individuellen
Klimaszenarien unterschiedlich und im Sommer- bzw. Winterhalbjahr
gegenläufig ausgeprägt. Hauptursache für die simulierte starke Zunahme der
mittleren Durchflüsse im Winterhalbjahr ist die trotz Temperaturerhöhung
der Klimaszenarien winterlich niedrige Evapotranspiration, so daß erhöhte
Niederschläge direkt in erhöhten Durchfluß transformiert werden können.<br>Der Vergleich der Untersuchungsgebiete zeigt in
Einzelmonaten von West nach Ost abnehmende Änderungsbeträge der
Niederschlagssummen, die als Hinweis auf die Bedeutung der
Kontinentalitätseinflüsse auch unter geänderten klimatischen Bedingungen
in Südwestdeutschland aufgefaßt werden könnten.<br>Aus den regionalisierten Klimaszenarien werden
Änderungsbeträge für die Modulation gemessener Zeitreihen mittels
synthetischer Szenarien abgeleitet, die mit einem geringen Rechenaufwand
in hydrologische Modellantworten überführt werden können. Die direkte
Ableitung synthetischer Szenarien aus GCM-Ergebniswerten (bodennahe
Temperatur und Gesamtniederschlag) an einzelnen GCM-Gitterpunkten
erbrachte unbefriedigende Ergebnisse.<br>Ob, in welcher Höhe und zeitlichen Verteilung die in den (synthetischen) Szenarien verwendeten Niederschlags- und Temperaturänderungen eintreten werden, kann nur die Zukunft zeigen. Eine Abschätzung, wie sich die Abflußverhältnisse und insbesondere die mittleren Durchflüsse der Untersuchungsgebiete bei möglichen Änderungen entwickeln würden, kann jedoch heute schon vorgenommen werden. <br><br>Simulationen auf Szenariogrundlagen sind ein Weg,
unbekannte zukünftige Randbedingungen sowie regionale Auswirkungen
möglicher Änderungen des Klimasystems ausschnittsweise abzuschätzen und
entsprechende Risikominderungsstrategien zu entwickeln. Jegliche
Modellierung und Simulation natürlicher Systeme ist jedoch mit
beträchtlichen Unsicherheiten verknüpft. Vergleichsweise große
Unsicherheiten sind mit der zukünftigen Entwicklung des sozioökonomischen
Systems und der Komplexität des Klimasystems verbunden. Weiterhin haben
Unsicherheiten der einzelnen Modellbausteine der Modellkette
Emissionsszenarien/Gaszyklusmodelle - Globale
Zirkulationsmodelle/Regionalisierung - hydrologisches Modell, die eine
Kaskade der Unsicherheiten ergeben, neben Datenunsicherheiten bei der
Erfassung hydrometeorologischer Meßgrößen einen erheblichen Einfluß auf
die Vertrauenswürdigkeit der Simulationsergebnisse, die als ein
dargestellter Wert eines Ergebnisbandes zu interpretieren sind.<br><br>Der Einsatz <br>(1) robuster hydrologischer Modelle, die insbesondere temperaturbeeinflußte Prozesse adäquat beschreiben,<br>(2) die Verwendung langer Zeitreihen (wenigsten 30 Jahre) von Meßwerten und<br>(3) die gleichzeitige vergleichende Betrachtung von Klimaszenarien, die auf unterschiedlichen GCMs beruhen (und wenn möglich, verschiedene Emissionsszenarien berücksichtigen),<br>sollte aus Gründen der wissenschaftlichen Sorgfalt, aber auch der besseren Vergleichbarkeit der Ergebnisse von Regionalstudien im noch jungen Forschungsfeld der Klimafolgenforschung beachtet werden. / This thesis 'Development of
runoff in subcatchments of the River Rhine - simulations of the current
state and for climate change scenarios' investigates the impacts of
possible future climate changes on runoff and runoff regime in selected
subcatchments of the River Rhine. The regional climate in the selected
subcatchments Mosel (up to gauge Cochem), Sieg (gauge Menden 1) and Main
(gauge Kemmern) is affected by the middle mountain ranges.<br><br>In a first step, important model processes are parameterized according to catchment characteristics. A representation of the regional hydrology is then produced by using the hydrological model HBV-D. Based on time series of daily measurements (temperature, precipitation) at stations within the catchment, this representation can be used to realistically simulate time series of runoff and discharge. <br>In all examined areas, the quality of simulations of the calibration and validation periods for the current state (standard period of measurements 01/01/1961-12/31/1999) can be regarded as good to excellent. <br>To aid the catchment-specific, extensive and time-consuming data processing, a working environment for the hydrological model HBV-D has been developed. It is based on program extensions of the geographical information system ArcView and further programs. The working environment HBV-Params contains a graphical interface that gives both experienced hydrologists and students full control and enables them to flexibly derive parameter values and edit parameter and control files. In contrast to previous versions with only rudimentary working environments, HBV-D can therefore be utilized for research as well as for educational purposes. <br><br>In a second step, the current states of areal precipitation, areal temperature and simulated mean discharge (MQ) are compared to the corresponding states for two scenarios of future climate changes (100 years later, 2061-2099). These scenarios are based on simulated global circulations of one model run for each of two global circulation models (GCM). These global circulations are regionalized (downscaled) using a statistical approach into scenario time series of daily values (temperature, precipitation - input for the hydrological model) at control stations within the individual catchments. <br>For the second half of the 21st century, both regionalized climate change scenarios indicate increases in the mean annual areal temperature and mean annual sum of precipitation, along with a high variability of the latter. The seasonal (monthly) changes in temperature, precipitation and mean discharge between scenario state (2061-2099) and current state indicate increases in temperature (higher in summer than in winter) as well as a general increase in precipitation sums (strong fluctuations between individual months). In the hydrological simulations for all investigated catchments, this results in considerably higher mean discharges from November to March and small increases in mean discharge for the other months. The magnitude of the increases in discharge depends on the individual climate change scenario, one showing higher increases than the other during the summer half-year and vice versa for the winter half-year. The main reason for the simulated strong increase in mean discharge during winter half-year is, in spite of higher temperatures, the still relatively low evapotranspiration which allows higher precipitation to be directly transformed into higher discharges. <br>The comparison of the investigated catchments shows decreasing amounts of changes in the sum of precipitation from West to East in individual months. This indicates the importance of continentality under changed climatic conditions in Southwest Germany. <br>For the modification of measured time series (temperature, precipitation), which can be easily converted as synthetic scenarios into simulated hydrological results, amounts of change are derived from regionalized (downscaled) climate change scenarios. The derivation of synthetic scenarios directly from GCM output at individual GCM gridpoints yielded unsatisfactory results. <br>Only the future itself can show whether the timing and amount of changes in temperature and precipitation used in (synthetic) climate change scenarios come close to reality. An assessment of possible developments in runoff regime and specifically mean discharge under possible changed climatic conditions in the investigated catchments is already feasible today. <br><br>Simulations based on scenarios are one way to establish unknown future boundary conditions for the estimation of regional impacts of possible changes of the climate system. Nevertheless, all types of modeling and simulation of natural systems are linked with uncertainties. Rather large uncertainties persist regarding the future development of the socio-economic system and the complexity of the climate system and earth system. Furthermore, besides data uncertainties associated with the measurement of hydro-meteorological values, uncertainties associated with individual components of the model chain emission scenarios/gas cycle model - GCM/regionalization - hydrological model, which form a cascade of uncertainty, have a great influence on the trustworthiness of the simulation results (which are understood as one shown value within a range of results). <br><br>In the young field of climate impact research the use of <br>(1) robust hydrological models that adequately describe temperature-dependent processes,<br>(2) long time series (at least 30 years long) of measurements, <br>(3) concurrent comparisons of climate change scenarios, based on different GCMs (and, if possible, different emission scenarios)<br>should be considered for reasons of scientific thoroughness and to improve comparability of regional impact studies.
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SPECIES- TO COMMUNITY-LEVEL RESPONSES TO CLIMATE CHANGE IN EASTERN U.S. FORESTSJonathan A Knott (8797934) 12 October 2021 (has links)
<p>Climate change has dramatically altered the ecological landscape of the eastern U.S., leading to shifts in phenological events and redistribution of tree species. However, shifts in phenology and species distributions have implications for the productivity of different populations and <a></a>the communities these species are a part of. Here, I utilized two studies to quantify the effects of climate change on forests of the eastern U.S. First, I used phenology observations at a common garden of 28 populations of northern red oak (<i>Quercus rubra</i>) across seven years to assess shifts in phenology in response to warming, identify population differences in sensitivity to warming, and correlate sensitivity to the productivity of the populations. Second, I utilized data from the USDA Forest Service’s Forest Inventory and Analysis Program to identify forest communities of the eastern U.S., assess shifts in their species compositions and spatial distributions, and determine which climate-related variables are most associated with changes at the community level. In the first study, I found that populations were shifting their spring phenology in response to warming, with the greatest sensitivity in populations from warmer, wetter climates. However, these populations with higher sensitivity did not have the highest productivity; rather, populations closer to the common garden with intermediate levels of sensitivity had the highest productivity. In the second study, I found that there were 12 regional forest communities of the eastern U.S., which varied in the amount their species composition shifted over the last three decades. Additionally, all 12 communities shifted their spatial distributions, but their shifts were not correlated with the distance and direction that climate change predicted them to shift. Finally, areas with the highest changes across all 12 communities were associated with warmer, wetter, lower temperature-variable climates generally in the southeastern U.S. Taken together, these studies provide insight into the ways in which forests are responding to climate change and have implications for the management and sustainability of forests in a continuously changing global environment.</p>
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QUANTIFYING CARBON FLUXES AND ISOTOPIC SIGNATURE CHANGES ACROSS GLOBAL TERRESTRIAL ECOSYSTEMSYoumi Oh (9179345) 29 July 2020 (has links)
<p>This thesis is a collection of three research
articles to quantify carbon fluxes and isotopic signature changes across global
terrestrial ecosystems. Chapter 2, the first article of this thesis, focuses on
the importance of an under-estimated methane soil sink for contemporary and
future methane budgets in the pan-Arctic region. Methane emissions from
organic-rich soils in the Arctic have been extensively studied due to their
potential to increase the atmospheric methane burden as permafrost thaws.
However, this methane source might have been overestimated without considering
high affinity methanotrophs (HAM, methane oxidizing bacteria) recently identified
in Arctic mineral soils. From this study, we find that HAM dynamics double the
upland methane sink (~5.5 TgCH<sub>4</sub>yr<sup>-1</sup>) north of 50°N in
simulations from 2000 to 2016 by integrating the dynamics of HAM and
methanogens into a biogeochemistry model that includes permafrost soil organic
carbon (SOC) dynamics. The increase is equivalent to at least half of the
difference in net methane emissions estimated between process-based models and
observation-based inversions, and the revised estimates better match site-level
and regional observations. The new model projects double wetland methane
emissions between 2017-2100 due to more accessible permafrost carbon. However,
most of the increase in wetland emissions is offset by a concordant increase in
the upland sink, leading to only an 18% increase in net methane emission (from
29 to 35 TgCH<sub>4</sub>yr<sup>-1</sup>). The projected net methane emissions
may decrease further due to different physiological responses between HAM and
methanogens in response to increasing temperature. This article was published
in <i>Nature Climate Change</i> in March
2020.</p>
<p>In Chapter 3, the second article of this
thesis, I develop and validate the first biogeochemistry model to simulate
carbon isotopic signatures (δ<sup>13</sup>C)
of methane emitted from global wetlands, and examined the importance of the wetland
carbon isotope map for studying the global methane cycle. I incorporated a carbon isotope-enabled module into an
extant biogeochemistry model to mechanistically simulate the spatial and
temporal variability of global wetland δ<sup>13</sup>C-CH<sub>4</sub>. The new
model explicitly considers isotopic fractionation during methane production,
oxidation, and transport processes. I estimate a mean global wetland δ<sup>13</sup>C-CH<sub>4</sub> of
-60.78‰ with its seasonal and inter-annual variability. I find that the new
model matches field chamber observations 35% better in terms of root mean
square estimates compared to an empirical static wetland δ<sup>13</sup>C-CH<sub>4</sub> map.
The model also reasonably reproduces the regional heterogeneity of wetland δ<sup>13</sup>C-CH<sub>4</sub> in
Alaska, consistent with vertical profiles of δ<sup>13</sup>C-CH<sub>4</sub>
from NOAA aircraft measurements. Furthermore, I show that the latitudinal
gradient of atmospheric δ<sup>13</sup>C-CH<sub>4</sub> simulated by a chemical
transport model using the new wetland δ<sup>13</sup>C-CH<sub>4</sub> map
reproduces the observed latitudinal gradient based on NOAA/INSTAAR global
flask-air measurements. I believe this study is the first process-based
biogeochemistry model to map the global distribution of wetland δ<sup>13</sup>C-CH<sub>4</sub>,
which will significantly help atmospheric chemistry transport models partition
global methane emissions. This article is in preparation for submission
to <i>Nature Geoscience</i>.</p>
<p>Chapter 4 of this thesis, the third
article, investigates the importance of leaf carbon allocation for seasonal
leaf carbon isotopic signature changes and water use efficiency in temperate
forests. Temperate deciduous trees remobilize stored carbon early in the
growing season to produce new leaves and xylem vessels. The use of remobilized
carbon for building leaf tissue dampens the link between environmental stomatal
response and inferred intrinsic water use efficiency (iWUE) using leaf carbon
isotopic signatures (δ<sup>13</sup>C). So far, few studies consider carbon
allocation processes in interpreting leaf δ<sup>13</sup>C signals. To
understand effects of carbon allocation on δ<sup>13</sup>C and iWUE estimates,
we analyzed and modeled the seasonal leaf δ<sup>13</sup>C of four temperate
deciduous species (<i>Acer saccharum, Liriodendron tulipifera, Sassafras
albidum, </i>and <i>Quercus alba</i>)
and compared the iWUE estimates from different methods, species, and drought
conditions. At the start of the growing season, leaf δ<sup>13</sup>C values
were more enriched, due to remobilized carbon during leaf-out. The bias towards
enriched leaf δ<sup>13</sup>C values explains the higher iWUE from leaf
isotopic methods compared with iWUE from leaf gas exchange measurements. I
further showed that the discrepancy of iWUE estimates between methods may be
species-specific and drought sensitive. The use of δ<sup>13</sup>C of plant
tissues as a proxy for stomatal response to
environmental processes, through iWUE, is complicated due to carbon
allocation and care must be taken when interpreting estimates to avoid proxy
bias. This
article is in review for publication in <i>New
Phytologist</i>.</p>
<p> </p>
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Dynamics of Forest Ecosystems Under Global Change: Applications of Artificial Intelligence in Mapping, Classification, and ProjectionAkane Ota Abbasi (17123185) 10 October 2023 (has links)
<p dir="ltr">Global forest ecosystems provide essential ecosystem services that contribute to water and climate regulation, food production, recreation, and raw materials. They also serve as crucial habitats for numerous terrestrial species of amphibians, birds, and mammals worldwide. However, recent decades have witnessed unprecedented changes in forest ecosystems due to climate change, shifts in species distribution patterns, increased planted forest areas, and various disturbances such as forest fires, insect infestations, and urbanization. These changes can have far-reaching impacts on ecological networks, human well-being, and the well-being of global forest ecosystems. To address these challenges, I present four studies to quantify forest dynamics through mapping, classification, and projection, using artificial intelligence tools in combination with a vast amount of training data. (I) I present a spatially continuous map of planted forest distribution across East Asia, produced by integrating multiple sources of planted and natural forest data. I found that China contributed 87% of the total planted forest areas in East Asia, most of which are located in the lowland tropical/subtropical regions and Sichuan Basin. I also estimated the dominant genus in each planted forest location. (II) I used continent-wide forest inventory data to compare the range shifts of forest types and their constituent tree species in North America in the past 50 years. I found that forest types shifted more than three times as fast as the average of their constituent tree species. This marked difference was attributable to a predominant positive covariance between tree species ranges and the change of species relative abundance. (III) Based on individual-level field surveys of trees and breeding birds across North America, I characterized New World wood-warbler (<i>Parulidae</i>) species richness and its potential drivers. I identified forest type as the most powerful predictor of New World wood-warbler species richness, which adds valuable evidence to the ongoing physiognomy versus composition debate among ornithologists. (IV) In the appendix, I utilized continent-wide forest inventory data from North America and South America and the combination of supervised and unsupervised machine learning algorithms to produce the first data-driven map of forest types in the Americas. I revealed the distribution of forest types, which are useful for cost-effective forest and biodiversity management and planning. Taken together, these studies provide insight into the dynamics of forest ecosystems at a large geographic scale and have implications for effective decision-making in conservation, management, and global restoration programs in the midst of ongoing global change.</p>
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