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Techniques for assessing impacts of projected climate change on agrohydrological responses in the Limpopo catchment.Lekalakala, Ratunku Gabriel. January 2011 (has links)
Climate detection studies point to changes in global surface temperature and rainfall patterns
over the past 100 years, resulting from anthropogenic influences. Studies on the analysis of
rainfall patterns [1950 – 1999] in southern Africa’s summer rainfall areas show an increase in
the duration of late summer dry spells, and this change is in line with expected effects of global
warming. Observations of surface temperature increases are consistent with climate projections
from General Circulation Models (GCMs), as well as with overall changes in climate over the
past century. As such, the alterations in climate conditions have a potential to significantly
impact agro-ecosystems. The changes in these climatic patterns are projected to result in a
cascade of changes in crop responses, and their associated crop yield-limiting factors through
altering water available for agriculture, as well as yield-reduction factors by increasing
pest/disease/weed prevalence, both of which may lead to agricultural production being affected
severely. The objective of this study is to explore effects of scenarios of climate change on
agrohydrological responses in the Limpopo Catchment, with an emphasis on the development
and application of statistical modelling and analysis techniques.
The algorithms of temperature based life cycle stages of the Chilo partellus Spotted Stem Borer,
those for agricultural water use and production indicators, and for net above-ground primary
production (an option in the ACRU model) as a surrogate for the estimation of agricultural
production. At the time that these analyses were conducted, the downscaled daily time step
climate projections of the ECHAM5/MPI-OM GCM, considered to indicate projections that are
midway between the extremes from other GCMs for southern Africa, were the only scenarios
available at a high spatial resolution which had been configured for South Africa. Further, the
statistical analysis techniques conducted in the dissertation include quantitative uncertainty
analyses on the temperature and precipitation projections from multiple GCMs (the output of
which subsequently became available), as well as validation analyses of various algorithms by
comparing results obtained from the GCM’s present climate scenarios with those from
historically obtained climates from the same time period.
The uncertainty analyses suggest that there is an acceptable consistency in the GCMs’ climate
projections in the Limpopo Catchment, with an overall high confidence in the changes in mean
annual temperature and precipitation projections when using the outputs of the multiple GCMs
analysed. However, the means of monthly projections indicated varied confidence levels in the GCMs’ output, more so for precipitation than for temperature projections. Findings from the
Validation analyses of the ECHAM5/MPI-OM GCM’s present climate scenario estimations of
agricultural production and the agricultural yield-reduction (Chilo partellus) factor against those
from observed baseline climate conditions for the same time period indicated a positive linear
relationship and a high spatial correlation. This suggests that the ECHAM5/MPI-OM GCM’s
present climate scenario is relatively robust when compared with output from observed climate
conditions.
ECHAM5/MPI-OM GCM projections show that agricultural production in future might increase
by over half in the southern and eastern parts of the Limpopo Catchment compared to that under
present climate conditions. Findings from the projections of the yield-limiting factor
representing water available for agriculture over the Catchment suggest increases in the
agricultural water productivity indicator under future climate conditions, with pronounced
increases likely in the eastern and southern periphery. On the other hand, the agricultural water
use indicator maintained high crop water use over most of the Catchment under all climate
scenarios, both present and future. These positive effects might be due to this particular GCM
projecting wetter future climate conditions than other GCMs do. Similar increases were
projected for the yield-reduction factor, viz. the development of Chilo partellus over the growing
season. These results suggest an increase in the C. partellus development, and thus prevalence,
over the growing season in the Catchment, and this correlates spatially with the projected rise in
agricultural production. The projected positive effects on agricultural production are thus likely
to be reduced by the prevalence in agricultural yield-reduction factors and restricted by
agricultural yield-limiting factors.
The techniques used in this study, particularly the temperature based development models for
the agricultural yield-reduction factor and the agricultural water use/water productivity
indicators, could be used in future climate impact assessments with availability of outputs from
more and updated GCMs, and in adaptation studies. This information can be instrumental in
local and national policy guidance and planning.
Keywords: Climate projections (scenarios), agricultural production, agricultural yield-reduction
(Chilo partellus) and -limiting factors, uncertainty analysis, validation analysis. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2011.
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Ecological relationships between the armadillo lizard, Cordylus cataphractus, and the southern harvester termite, Microhodotermes viatorShuttleworth, Cindy 12 1900 (has links)
Thesis (MSc (Botany and Zoology))--University of Stellenbosch, 2006. / The role of the southern harvester termite, Microhodotermes viator, and several climatic parameters in the distribution of the group-living lizard, Cordylus cataphractus, was investigated. Microhodotermes viator is considered the most important prey item of C. cataphractus and termitophagy as the causative agent in the evolution of group-living in this species. One would therefore expect a high degree of correspondence in the ranges of C. cataphractus and M. viator. As climate will also play a role in the distribution of any species, various climatic variables were investigated to determine their influence on the distribution of C. cataphractus. Species distributions were visualized using the minimum polygon technique and the degree of overlap was determined using standard geographic information systems (GIS) techniques. A total of 53 C. cataphractus localities were investigated for the presence of termites. The climatic limits of the geographical distribution of C. cataphractus were investigated by means of three models, namely Classification Trees, General Discriminant Analysis and Logistic Regression. The range of C. cataphractus was completely included within the range of M. viator Microhodotermes viator was included in the diet of C. cataphractus at 73 % of the localities sampled within the lizard’s range. The current geographical range of C. cataphractus is mainly correlated with two climatic factors, namely the low summer rainfall and high monthly solar radiation. The restricting role of both these factors can be directly linked to the group-living nature of C. cataphractus.
If termitophagy were the overarching cause of group-living in C. cataphractus, then one would expect a close relationship between termite density and lizard density and termite density and lizard group size. I investigated these relationships at both a local and regional scale. For the local scale study, 25 quadrats of 25 × 25 m were plotted at a selected site, and for the regional scale study, ten 35 × 35 m quadrats at sites throughout the lizard’s range were used. In each quadrat, a range of variables were recorded, the most important of which were lizard density, lizard group sizes, termite foraging port density, distance to nearest termite foraging ports, vegetation height and vegetation cover. I found that the density of termite foraging ports determines C. cataphractus density. Vegetation height and cover affects crevice selection by C. cataphractus groups, probably because an unobstructed view is necessary to locate termite activity at foraging ports.
I also investigated possible differences in the use of termites by different sized groups of C. cataphractus during different times of the year. Faecal samples, collected once a month at Eland’s Bay from small, medium and large groups from January 2005 to December 2005, were analysed for the presence of termite head material. I found that large groups fed on termites to a greater extent than small groups during certain times of the year and there was a general tendency for this phenomenon throughout the year.
The results collected in this study indicate that the southern harvester termite, M. viator, plays a central role in the ecology of the group-living lizard, C. cataphractus.
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Managing for Resistance and Resilience of Northern Great Lakes Forests to the Effects of Climate ChangeDuveneck, Matthew Joshua 09 January 2014 (has links)
Climate change is expected to drastically change the environmental conditions which forests depend. Lags in tree species movements will likely be outpaced by a more rapidly changing climate. This may result in species extirpation, a change in forest structure, and a decline in resistance and resilience (i.e., the ability to persist and recover from external perturbations, respectively). In the northern Great Lakes region of North America, an ecotone exists along the boreal-temperate transition zone where large changes in species composition exist across a climate gradient. Increasing temperatures are observed in the more southern landscapes. As climate change is expected to substantially affect mid-continental landscapes, this region is especially vulnerable to climate change. My research assessed the effects of climate change under business as usual (BAU) management as well as alternative management strategies. To do so, I simulated forest change in two landscapes (northeastern Minnesota and northern lower Michigan) under three climate change scenarios (current climate, low emissions, and high emissions), and four management scenarios (BAU, modified silviculture, expanded reserves, and climate suitable planting) with a spatially-explicit forest simulation model from year 2000 to year 2150. Specifically, I explored how climate change would affect relationships between tree species diversity and productivity; how expanded reserves and modified silviculture may affect aboveground biomass (AGB) and species diversity; how climate suitable planting may affect functional diversity, and AGB; and how alternative management may affect the resistance and resilience of forests to multiple disturbances interacting with climate change.
Under the BAU management scenario, I found that current and low emissions climate scenarios did not affect the relationship between species diversity and productivity; however, under a high emissions climate scenario, a decline in simulated productivity was coupled with a stronger positive relationship between diversity and productivity. Under the high emissions climate scenario, overall productivity declined in both landscapes with specific species declines projected for boreal species such as balsam fir (Abies balsamea) and black spruce (Picea mariana). Under alternative management scenarios, I simulated a limited ability to increase tree species and functional diversity, AGB, and net primary productivity under climate change. The limits of management were especially apparent under the high emissions climate scenario. In a novel approach to measuring resilience, I plotted the recovery of both initial species composition and AGB to stochastic fire events for each simulation. This approach assessed both a general response (i.e. AGB) with a more specific response (i.e. species composition). My results suggest that climate change will reduce the resilience of northern Great Lake forest AGB and species composition and that management effects will be largely outweighed by the declines expected due to climate change. My results highlight the necessity to consider even more innovative and creative solutions under climate change (e.g., planting species from even further south than I simulated).
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Biological soil crusts in forested ecosystems of southern Oregon : presence, abundance and distribution across climate gradientsOlarra, Jennifer A. 14 December 2012 (has links)
In arid and semi-arid deserts, soils are commonly covered with biological soil crusts. The
study of arid biocrusts and their ecological function has become increasingly common in
the literature over the last several decades. Interestingly, no mention is made of
biological soil crusts in forested ecosystems, raising the question as to whether they exist
in these areas and if they do, why they have yet to be recognized as such? Through the
use a parallel logic, this study finds that biocrusts do indeed exist in forests, a novel
relationship in forest ecology and seeks to determine if there exist ecophysical
explanations for the abundance and distribution throughout the forest landscape.
This study examined the effects of climate variables and substrate types on the
abundance, distribution and overall cover of forest soil biocrust at fifty-two sites in
southern Oregon, U.S.A. Sites were randomly selected within established buffer zones in
the Siuslaw, Rogue-Sisikyou, Umpqua, and Fremont-Winema National Forests. The
methods of Belnap et al 2001 were tested and then modified for application in forested
ecosystems. Data were collected on the relative abundance and distribution of biocrust
morphological groups across available substrates, community biocrust morphology,
aspect, elevation and soil texture, pH and organic matter content. Site-specific data on
average annual precipitation and minimum/maximum temperatures was collected using
the PRISM Climate Model.
This study found substrate colonization by specific morphological groups mixed across
the study; though dominant communities were observed for each substrate present,
substrate availability appears to be confounded by a number of variables (climate, stand
age and structure and litter layer) not controlled for in this study. Biocrust community
morphologies varied across sites, primarily influenced by the surface texture of the
substrate and morphology of the individual. Relatively smooth surfaces (rock, bare soil)
often resulted in smooth biocrust morphologies, whereas rough surfaces (dead wood, bare
soil) tended to result in a rolling morphology. Litter layer directly influenced the relative
proportion of substrates colonized, notably affecting dead wood and mineral soil
biocrusts. Total biocrust cover increased as precipitation increased as did biocrust
preference for dead wood substrates while mineral soil remained unchanged and rock
surfaces were negatively represented. Aspect generally followed the anticipated
distribution of total biocrust cover with the highest cover on N and NW aspects and
lowest on the W aspect. Increases in elevation were negatively related to overall biocrust
cover. Soil texture was not found to be directly related to overall biocrust cover,
attributed in part to the highly adaptive nature of the biocrust community. Soil organic
matter (SOM) influenced total biocrust cover with positive correlations between total
cover and increasing SOM content. Soil pH increased as expected across the
precipitation range (17 to 159 in/yr) of the transect. Total biocrust cover was found to
trend with soil pH, but is believed to be attributed to the parallel relationship between
precipitation and pH, rather than pH alone given the relative moderate pH range (4.39 to
6.54) of the study. The distribution and abundance of forest soil biocrusts is strongly
influenced by precipitation. The confounding influence of precipitation to litter layer
depth and organic matter content (through gradients of vegetative productivity) and soil
pH further are concluded to influence substrate preference by morphological groups.
Across the variables examined, similarities between the two communities (arid and
forest) in response to climate and soil chemistry show parallel relations, justifying the
formal establishment of biological soil crust community in forested regions. The
differences between communities related to the presence of trees validate the
establishment of forest soil biocrusts as distinct community in both form and ecological
function with the forests. / Graduation date: 2013
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Quantifying Twentieth Century Glacier Change in the Sierra Nevada, CaliforniaBasagic, Hassan J. 01 January 2008 (has links)
Numerous small alpine glaciers occupy the high elevation regions of the central and southern Siena Nevada, California. These glaciers change size in response to variations in climate and are therefore important indicators of climate change. An inventory based on USGS topographic maps (l :24,000) revealed 1719 glaciers and perennial snow and ice features for a total area of 39.l5 ±7.52 km2. The number of 'true' glaciers, versus non-moving ice, is estimated to be 118, covering 15.87 ± 1.69 Km2. All glaciers were located on north to northeast aspects, at elevations >3000 m. Historical photographs, geologic evidence, and field mapping were used to determine the magnitude of area loss over the past century at 14 glaciers. These glaciers decreased in area by 31% to 78%, averaging 55%. The rate of area change was determined for multiple time periods for a subset of seven glaciers. Rapid retreat occurred over the first half of the twentieth century beginning in the 1920s in response to warm/dry conditions and continued through the mid-1970s. Recession ceased during the early 1980s, when some glaciers advanced. Since the 1980s each of the seven study glaciers resumed retreat.
The uniform timing of changes in area amongst study glaciers suggests a response to regional climate, while the magnitude of change is influenced by local topographic effects. Glacier area changes correlate with changes in spring and summer air temperatures. Winter precipitation is statistically unrelated to changes in glacier area. Headwall cliffs above the glaciers alter the glacier responses by reducing incoming shortwave radiation and enhancing snow accumulation via avalanching.
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Influence of protein degradability and evaporative cooling on performance of lactating cows during hot environmental temperaturesTaylor, Ronald Brian, 1962- January 1989 (has links)
Two trials were conducted to determine the effect of protein degradability (low (LD) vs high (HD)) and evaporative cooling (shade cooling vs shade) on performance of 60 lactating Holstein cows in mid-lactation. Cooling and the LD diet increased milk production, 3.5% FCM and feed efficiency in trial 1 (24 cows) while in trial 2 (36 cows) LD diet increased milk production and feed efficiency and cooling did not exert a significant effect. Differences between trials were probably due to higher environmental temperature humidity indexes (77.0 vs 72.0), and a higher quality of the rumen bypass protein in the LD diet in trial 2 than trial 1. Cooling reduced respiration rates in trial 1 and respiration rates, rectal and inner ear temperatures in trial 2. Eating patterns were unaffected by protein degradability or cooling.
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Solar Tower Power Plant Performance CharacteristicsPretorius, Johannes Petrus 04 1900 (has links)
Thesis (MScIng)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: This study investigates energy generation by large-scale solar tower power
plants. The performance characteristics of a so-called reference plant with a
4000 m diameter glass collector roof and a 1500 m high, 160 m diameter tower
are determined for a site located in South Africa. The relevant draught and
conservation equations are derived, discretized and implemented in a numerical
model which solves the equations using speci ed meteorological input data and
determines the power delivered by the plant.
The power output of a solar tower power plant over a twenty-four hour
period is presented. Corresponding temperature distributions in the ground
under the collector are shown. Variations in seasonal generation are evaluated
and the total annual electrical output is determined. The dependency of
the power output on collector diameter and tower height is illustrated, while
showing that greater power production can be facilitated by optimizing the
roof shape and height. The minor in uence of the tower shadow falling across
the collector is evaluated, while the e ect of prevailing winds on the power
generated is found to be signi cant. / AFRIKAANSE OPSOMMING: Hierdie studie ondersoek elektrisiteitsopwekking deur grootskaalse sontoringkragstasies.
Die uitsetkarakteristieke van 'n sogenaamde verwysings-kragstasie
met 'n 4000 m deursnee glas kollektor en 'n 1500 m hoë, 160 m deursnee toring
word ondersoek vir 'n spesi eke ligging in Suid-Afrika. Die toepaslike trek- en
behoudsvergelykings word afgelei, gediskretiseer en geimplementeer in 'n numeriese
rekenaarmodel. Die rekenaarmodel los die betrokke vergelykings op
deur gebruik te maak van gespesi seerde meteorologiese invoerdata en bepaal
dan die uitset gelewer deur die kragstasie.
Die uitset van 'n sontoring-kragstasie oor 'n periode van vier-en-twintig uur
word getoon. Ooreenstemmende temperatuurverdelings in die grond onder die
kollektor word geïllustreer. Die variasie in seisoenale elektrisiteitsopwekking
word ondersoek en die totale jaarlikse elektriese uitset bepaal. Die invloed wat
die kragstasie dimensies (kollektor deursnee en toring hoogte) op die uitset het,
word bestudeer en resultate getoon. Daar is ook bevind dat verhoogde uitset
meegebring kan word deur die vorm en hoogte van die kollektordak te optimeer.
Die geringe e ek van die toringskadu op die kollektor word bespreek, terwyl
bevind is dat heersende winde 'n beduidende e ek op die kragstasie uitset het.
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Site and vintage response of malic and tartaric acid in Vitis vinifera L. cv’s Cabernet Sauvignon and Sauvignon blancCoetzee, Zelmari 12 1900 (has links)
Thesis (MScAgric)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Acids are one of the major components that originate largely from the berry, that are found in
wine, and that influence the sensory perception. The presence of organic acids in adequate
concentrations in the grape berry, of which tartaric- and malic acid are the main organic acids
present, is important as this determines the potential of a must to produce a good and stable
wine.
The effect of temperature on the organic acid content of the must is widely discussed with
higher temperatures in general being associated with lower quantities of organic acids present
in the juice, and lower temperatures during ripening associated with higher quantities,
specifically in the case of malic acid.
Due to the topographical diversity of the Stellenbosch Wine of Origin district and the closeness
of the ocean and the occurrence of sea breezes, the mesoclimate differs greatly over short
distances. Sixteen sites, consisting of eight Sauvignon Blanc and Cabernet Sauvignon sites
respectively, were selected from a broader terroir study site network. Three vintages with
complete climatic datasets were selected for vintage comparisons. Climate in the study area
was monitored on differing scales, and data from a weather station network, as well as from
mesoclimatic dataloggers within the sites were available.
The available data was firstly compared to determine the variability of the data, not only
between the two climatic scales, but also between the sites. Different climate classification
indices and parameters available in literature were thereafter compared and evaluated for the
best representation in this area. The Huglin index was found to be a better representation
regarding the thermal climatic indices. Due to the great differences between temperatures noted
for the mesoclimatic loggers and the nearest automatic weather station, the use of mesoclimatic
logger data was preferred, and is advised in future studies where this scale of data is available.
Malic and tartaric acid has a definite synthesis period up until véraison, after which the content
of tartaric acid remains constant in the berry and the content of malic acid decreases until
harvest due to mainly respiration. The temperature data was therefore separated in a synthesis
period from flowering to véraison, and a ripening period from véraison to harvest.
In this study, clear differences were firstly seen in the climate as expected, not only between
sites per vintage, but in addition between vintages and between vintages per site. The
phenological differences between the sites could be largely attributed to the differences in
temperature as phenology and temperature was found to be highly correlated in this study.
Differences in the ripening parameters were noticed in addition to the contents of the organic
acids between sites, although no definite contribution of temperature was shown to affect the
contents of these compounds at either véraison or harvest. These differences may be attributed
to other factors such as the soil water content and the canopy architecture. In addition, these
factors all contribute in differing percentages to the differences found in the contents per site.
It was found though that temperature can be used as an indicator of the organic acid content in
the grape berry, considering that the temperature data is available on a mesoclimatic scale,
separated in a synthesis and period of degradation, and the number of hours within the
temperature thresholds are determined. Differences seen in the organic acid contents can
however not only be attributed to the differences in topography and the temperature as
discussed in this study. / AFRIKAANSE OPSOMMING: Sure is belangrike druifkomponente wat grootliks hul oorsprong in die korrel het, in die wyn
voorkom, en die sensoriese persepsie van die wyn beïnvloed. Die voorkoms van organiese
sure in genoegsame konsentrasies in die korrel, waarvan wynsteensuur en appelsuur die hoof
organiese sure is, is belangrik aangesien dit die potensiaal van die sap om ʼn goeie en stabiele
wyn te produseer, bepaal.
Hoe temperatuur die inhoud van organiese sure in die druiwesap affekteer is gereeld onder
bespreking, met hoër temperature in die algemeen geassosieer met ʼn laer inhoud van
organiese sure, terwyl laer temperature geassosieer word met ʼn hoër inhoud van organiese
sure in die sap, veral in die geval van appelsuur.
As gevolg van die topografiese diversiteit van die Stellenbosch Wyn van Oorsprong distrik,
asook die nabyheid van die oseaan met die gepaardgaande voorkoms van die seebries,
verander die mesoklimaat aansienlik oor klein afstande in hierdie area. Vir die studie was
sestien wingerde, wat bestaan het uit agt Sauvignon Blanc en agt Cabernet Sauvignon
wingerde, geselekteer vanuit ʼn groter terroir studie. Verder was drie seisoene, met volledige
klimaatsdatastelle, geselekteer vir die vergelyking van data tussen die seisoene.
Klimaat was op verskillende skale binne die studie area gemonitor en data van ʼn weerstasie
netwerk, sowel as van mesoklimaat dataversamelaars binne die wingerde, was beskikbaar. Die
beskikbare datastelle was vergelyk, asook geëvalueer, om die mees verteenwoordigende
datastel vir die area te bepaal. Met die oorweging van die termiese indekse was daar gevind dat
die Huglin indeks beter verteenwoordigend van die area was. Verder, as gevolg van die groot
verskille wat gevind is tussen die temperature gemeet met die mesoklimaat dataversamelaars
en die naaste outomatiese weerstasie, was daar besluit dat die gebruik van die mesoklimaat
data verkies is en is dit ook aan te beveel vir die gebruik in toekomstige navorsing indien die
tipe data beskikbaar is.
Wynsteen- en appelsuur het beide ʼn definitiewe sintese periode tot en met véraison, waarna die
hoeveelheid wynsteensuur in die korrel relatief konstant bly en die hoeveelheid appelsuur
afneem hoofsaaklik as gevolg van respirasie. Die temperatuur data was dus verdeel in ‘n
periode van sintese vanaf blom tot en met véraison, en ʼn rypwordingsperiode vanaf véraison tot
en met oes.
In hierdie studie was daar eerstens groot verskille waargeneem in die klimaat soos wat daar
verwag is. Hierdie verskille was nie net waargeneem as tussen die seisoene nie, maar ook
tussen die wingerde binne ʼn seisoen. Die fenologiese veskille tussen die wingerde wat ook
waargeneem is, kon hoofsaaklik aan die verskille in die temperatuur toegeskryf word en ʼn goeie
korrelasie tussen temperatuur en fenologie is opgemerk.
Merkwaardige verskille in die rypwordingsparameters, asook in die inhoud van die organiese
sure, was waargeneem, alhoewel die bydrae van temperatuur op die inhoud van hierdie
komponente by véraison of oes nie as definitief getoon is nie. Dit kan toegeskryf word aan die
bydrae van ander faktore, soos byvoorbeeld die grondwaterinhoud en die lowerargitektuur, op
die inhoud van hierdie komponente. Die addisionele faktore dra egter in verskillende
persentasies by tot die verskille waargeneem tussen die wingerde.
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The influence of cross-winds on the performance of natural draft dry-cooling towers.Du Preez, Abraham Francois 12 1900 (has links)
Thesis (PhD (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 1992. / The effect of cross-winds on the performance of natural draft dry-cooling towers is studied by
means of isothermal model tests, a numerical simulation and full scale measurements. The
action of the wind on such towers is found to be complex and is influenced by a number of
different parameters including the wind speed, the shape of the approaching wind profile, the
inlet diameter to the inlet height ratio of the tower, the tower height, the shape of the tower
shell, the pressure loss coefficient of the heat exchangers and the amount of heat rejected by the
tower. For a horizontal arrangement of the heat exchangers the wind effect on the tower is
shown to be strongly dependent on both the shape and pressure loss coefficient of the tower
supports.
In practical cooling towers the heat exchangers are either arranged horizontally in the inlet
cross-section of the tower or vertically around the circumference of the tower and the wind
effect is found to be dependent on the particular layout. The wind effect on a tower is
furthermore found to increase if the heat exchangers are arranged in the form of A-frames.
Additional reductions in the heat rejection rate of the tower are caused by a non-uniform air
temperature distribution inside the tower and flow distortions through the heat exchanger.
Significant reductions in the wind effect on a cooling tower can be achieved by installing
windbreak walls below the heat exchangers if the latter are arranged horizontally in the tower
inlet.
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Life history trade-offs between survival, moult and breeding in a tropical season environmentStevens, Matthew C. January 2011 (has links)
The trade-off between current and future investment in reproduction lies at the heart of life history theory. The need to differentially allocate resources between these two options arises generally as a result of environmental pressures. Higher risk of mortality in adults is linked with increased investment in current reproduction, whereas the opposite is true where adults are long-lived (the r- K selection paradigm). Perhaps the most obvious factors influencing the environment stem from seasonality of the climate, since rainfall and temperature affect food availability, resulting in a higher risk of mortality. The available trade-offs that an organism can make will therefore be constrained by environmental variability potentially resulting in general adaptation and so ultimately influencing evolution of biome-specific life-history traits. In this thesis, I examine how the seasonality of a West African tropical savannah environment influences moult and breeding timing and duration, and survival in West African tropical savannah bird species. I show that moult in tropical birds follows the same basic descendant pattern through the wing feathers, but is a much lengthier process than for temperate species (mean = 131 ± 11 days, N = 29 species), and that it frequently overlaps with breeding activities. This suggests either that either the feathers of tropical species take longer to grow; that it is a relatively low-cost activity and has little influence on life history trade-offs; or that individuals further aim to reduce mortality risk by attempting to maintain high flight capability at all times. Breeding also occurred over a longer season than for temperate species, although an obvious peak in occurrence was identified to coincide with the food-abundant period of the late rains and early dry season. Lengthy breeding seasons may indicate an increased tendency to re-nest (possibly as a result of higher nest predation levels), and we also identified a prolonged immature plumage phase – potentially indicating an extended duration of parental care. Survival rates were calculated from mark-recapture models based on mist-netting data. Previous work has focussed on the use of incorporating mark-resighting data alongside that obtained by standard mark-recapture techniques. Here, I assess the models applied in those methods, identify problems associated with over-paramaterisation, goodness of fit and the generation of biologically unrealistic estimates, and so provide suggestions on how to improve the protocol. Average survival from my study (40 species: 0.63 ± 0.02) was higher than previous estimates obtained from this site and were comparable with estimates from other Afrotropical and Neotropical areas, although rates varied greatly between species. Juvenile survival (13 species) was similar or possibly lower than adult survival. I then used my empirically derived estimates of moult, breeding and survival life history traits to identify potential trade-offs between traits. Overall I was unable to identify significant relationships between any of the life history trait estimates, other than between adult survival and clutch size. In this, the results followed those of previous researchers in identifying a pattern of lower investment in current reproduction (clutch size) and maximisation of adult survival in tropical species. My study, however, demonstrates for the first time how moult and breeding duration are likely to be less constrained in tropical environments.
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