Spelling suggestions: "subject:"climate achange frocesses"" "subject:"climate achange eprocesses""
1 |
Toward better prediction and deeper understanding of human heat stressQinqin Kong (19185685) 22 July 2024 (has links)
<p dir="ltr">Robust and actionable information regarding how heat stress will change as climate warms is essential for informing impact assessments and heat mitigation and adaptation strategies. In meeting this demand, this dissertation has two mutually reinforcing goals: to improve heat stress prediction through a more comprehensive account of human heat stress, and to advance our understanding of the driving mechanisms of model-predicted heat stress changes.</p><p dir="ltr">As the initial step in achieving the first goal, we adopt the wet-bulb globe temperature (WBGT) as our preferred metric for heat stress. Then we (i) develop a fast, scalable Python implementation of the “gold standard” physics-based WBGT model, (ii) devise a straightforward, yet effective statistical bias-correction approach, and (iii) generate a global dataset of bias-corrected heat stress prediction at fine spatial and temporal resolutions based on a CMIP6 model ensemble. </p><p dir="ltr">To achieve our second goal of understanding the driving mechanisms of WBGT changes, we take advantage of the underlying physical relationship between WBGT and the simpler, wet-bulb temperature to gain insights into WBGT by first (i) investigating the soil moisture control of wet-bub temperature under present conditions and (ii) using CMIP6 results to understand future changes of wet-bulb temperature. Then, (iii) we develop a linear sensitivity framework that is used to disentangle WBGT changes into contributions from changes in temperature, humidity, wind, solar radiation and surface pressure. This disentanglement enables us to leverage existing theories and methods to understand the driving mechanism of WBGT changes.</p><p dir="ltr">Through this work we find several noteworthy conclusions, which is explained in depth in the rest of the dissertation, but we briefly summarize here. Wide-spread positive coupling between soil moisture and wet-bulb temperature are found over previously identified land-atmosphere coupling hotspots due to the effective control of soil moisture variations on surface energy partition and boundary layer dynamics. This implies that drying-induced amplified warming may be counteracted by relative humidity reductions, and a potential mismatch between relative hotspots of warming and intensifying heat stress. We confirm this hypothesis by showing distinctly different scaling patterns (with global warming) between dry-bulb temperature and WBGT based on a CMIP6 model ensemble. Regionally amplified warming in northern hemisphere mid-latitudes and the Amazon correspond to muted increases in WBGT. The central Sahel emerges as a strong local hotspot of WBGT scaling.</p><p dir="ltr">The sensitivity framework predicts close similarity between the scaling of black globe and natural wet-bulb temperature (two major components of WBGT) and that of dry- and wet-bulb temperature, if wind speed and solar radiation changes have a minor impact. This is confirmed to be the case in a CMIP6 model ensemble, with WBGT scaling primarily influenced by temperature and humidity changes. </p><p dir="ltr">Combining these results together holistically, we reach the following conclusions. Although the widely used and empirically well validated WBGT heat stress metric is a complex function of four environmental variables, as climate changes, the changes in WBGT predicted by climate models can be mostly understood in terms of changes in near-surface air temperature and humidity. Furthermore, the linear sensitivity framework and scaling analyses developed here allow us to partially attribute the WBGT scaling pattern to regional drying or wetting trends, and associated changes in surface energy balance and boundary layer dynamics. Thus, accurate prediction of WBGT changes is to first order largely a matter of getting those temperature and humidity correct and improvements to theories and models for those fields will directly translate to improvements in WBGT prediction as well. </p>
|
2 |
Assessment of land use urbanization impacts om surface temperature and hydrologyMohamed Atef Moham Aboelnour (8736174) 24 April 2020 (has links)
<p></p><p></p><p>Land use alteration and
climate change are major contributors to the hydrological cycle within
watersheds. They can influence the quantity and quality of water resources, the
ecosystem and environmental sustainability. Urban areas have expanded in recent
decades, accompanied by a noticeable increase in energy and water use. Such
changes in land use have many implications for humans to meet the increasing
share of the planet’s resources and water issues. Hence, distinguishing the
effects of land use change from concurrent climate variability is a particular
challenge for studies on operational management processes. In this work, some shortcomings related to climate
variability and land use change have been addressed, as applied to land surface
temperature (LST) and groundwater resources. Thus, the main goal
of this study is to evaluate the impacts of land use change on surface
temperature and the impact of urbanization and climate variation on hydrology. The research methodology included modeling
approaches that were used to estimate the land surface temperature and the
responses of hydrology to climate change and urbanization.</p>
<p>Land use maps
derived from Landsat datasets were analyzed using several classification
techniques to evaluate the intensity and pattern of urbanization and land
surface temperature in the Greater Cairo Region (GCR), Egypt. Accuracy of Landsat derived land use data were relatively
high and up to 96.5%. Findings indicated that the GCR land use alteration was
dynamic and that vegetation loss was the main contributor to urban expansion in
the GCR. Consequently, this led to increased LST and modified urban microclimate.
The results showed that vegetation cover decreased by 7.73% within a 26-year
timespan (1990-2016).</p>
<p>Land use alteration impacted
not only land surface temperature, but also, combined with variation in
climate, affected watershed hydrology, specifically streamflow and baseflow. Changes in streamflow and filtered baseflow in three
watersheds: Little Eagle Creek (LEC), Upper West Branch DuPage
River (UWBDR) and Walzem Creek watershed, from 1980
to 2017, caused by climate alteration and land use change were separated and
accessed using the SWAT (Soil and Water Assessment Tool) model.
Results showed that SWAT performed well in capturing the streamflow and
baseflow in urban catchments. SWAT model calibration and
validation was within acceptable levels for streamflow and baseflow. About 30%, 30% and 12% of the LEC, UWBDR and
Walzem Creek watershed areas changed from agricultural to urban areas. Findings
for the LEC watershed indicated that the variability in the baseflow and
streamflow appeared to be heavily driven by the response to climate change in
comparison to the variability due to altered land use. The contribution of both
land use alteration and climate variability on the flow variation was higher in
the UWBDR watershed. In Walzem Creek, the alteration in streamflow and baseflow
appeared to be driven by the effect of climate variability more than that of urbanization.</p>
<p>Finally, the impacts
of basin lithology and physical properties on baseflow were examined using
multiple regression models. Results suggest that the
baseflow index (BFI) can be predicted using the basin’s physical and geological
characteristics. This included different land uses and climate variables with
high accuracy and low relative errors. BFI was found to be highly driven by
precipitation and fractional areas of different lithologies in the basins in
various regions. These could be estimated with a high accuracy, as opposed to evapotranspiration that caused lower
model accuracy.</p>
<p>Information gleaned from these
outputs can help in understanding the dynamics of land use change and climate
variation, in order to help policy-makers predict and plan for future expansion
in developing countries and across the globe, in achieving long-term
sustainability of soil and water resources and their impact on climate change.
Increasing efforts to prevent further urbanization and vegetation loss should
be regarded as a practical management strategy and are of vital significance to
many communities. In addition, the regression models developed in this study
can be easily exploited in other areas with poor hydrological data quality and
ungauged sites in order to estimate the amount of groundwater discharge.</p><p></p><p></p>
|
3 |
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>
|
4 |
EFFECTS OF IMPERVIOUS SURFACES ON OVERWINTERING SURVIVAL OF EVERGREEN BAGWORM AND ABUNDANCE OF SCALE INSECT PESTS IN THE URBAN ENVIRONMENTSujan Dawadi (12218648) 18 April 2022 (has links)
<p>Urban areas are warmer than
surrounding rural areas. During the cold of winter, warming increases
surrounding host temperature and may improve the overwintering survival of marginally
hardy insects like evergreen bagworms. Similarly, during the summer, it has the
potential to increase the fecundity and abundance of sap feeding insect pests
such as scale insects in ways that change the capacity of their natural enemies
to regulate their populations. </p>
<p>Although in parts of Indiana
winters can be cold enough to kill bagworm eggs, they thrive in cities. I
conducted field experiments to determine the extent to which impervious surface
near an infestation could keep temperatures warm enough to affect bagworm survival
during cold of winter. My results suggest that the percentage of live eggs
inside overwintering pupae decreased as ambient temperature drops. This
response was moderated by the presence of impervious surface around an infested
plant. Eggs found in bagworms collected from host trees surrounded by more
impervious surface had a higher chance of survival than those collected from
trees with low levels of hardscape. However, impervious surface has its limit
such that egg mortality was not buffered by impervious surfaces at temperatures
at or below -21.67°C. Similarly, I also conducted field experiments with sap
feeding insects on honeylocust trees, a commonly planted tree in cities. Hot
sites had a mean daily temperature more than 1.5 °C warmer than cool sites and
scale insects were more abundant and fecund on trees in the hottest part of
Indianapolis compared to cooler areas. No differences were observed in rates of
parasitism on the scale insect. However, I found strong density dependence
relation between parasitoids and scales abundance at scale density at or below
the levels present in cool sites. The top-down regulation was prevalent at or
below a critical density of scale hosts. Conversely, bottom-up regulation was
prevalent above this host density as pests benefit from bottom-up factors. This
suggests that urban habitats helped the scales to escape biological control by
resident natural enemies above critical density of scale hosts. </p>
<p>My findings can be useful to
landscape designers to design landscapes that are less prone to insect pests. My
finding adds to a growing body of evidence that suggests that planting urban
trees with lesser amount of impervious surface can help reducing the urban
warming effect and increase the regulation from natural enemies. </p>
|
Page generated in 0.0509 seconds