ETD Collection

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Author: search.filters.author.Fitchett, Jennifer MyfanwyHas files: Yes

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    Towards a multi-proxy holocene palaeoenvironmental and palaeoclimatic reconstruction for Eastern Lesotho
    (2016-01-20) Fitchett, Jennifer Myfanwy
    The eastern Lesotho highlands observe climate patterns distinct from adjacent lower altitude regions, representing a niche environment with unique biodiversity, comprising well-adapted but restricted biomes. With a heavy reliance on subsistence agriculture, Lesotho faces risks to both the economy and individual livelihoods, should current rates of climate change persist or intensify. Furthermore, eastern Lesotho serves as southern Africa’s primary water catchment, with precipitation exceeding evaporation. Any changes in the climate and hydrological systems, as are likely under climate change scenarios, would compromise biomes, livelihoods, and water security both locally and regionally. Climate change research in eastern Lesotho, is thus of particular value, yet meteorological data are sparse and the palaeoenvironmental history remains poorly resolved. This research presents the first multi-proxy Holocene palaeoenvironmental and palaeoclimatic reconstruction for eastern Lesotho. This reconstruction is developed from the results from pollen, diatom and sediment analyses, extracted from sediment cores obtained from two peat bogs at Sani Valley (~2,800 m.asl) and Mafadi Wetland (~3,390 m.asl), and from an exposed gully-sidewall profile at Sekhokong (~2,950 m.asl), approximately 1km south of the Sani Valley site. The reconstructions are temporally constrained by AMS radiocarbon dates obtained for all three sites. Mafadi Wetland demonstrates marked differences to the lower altitude sites, including slower sedimentation rates, a decrease in pollen and diatom taxa diversity, and an increase in the relative abundance of ice-tolerant diatom taxa. The microtopography of the three sites influences the rates of sedimentation, sediment properties, pollen composition, and distinct palaeoenvironmental and palaeoclimatic reconstructions for each site. The Sekhokong record commences in the late Pleistocene, with a wet period from ~13,180-10,850 cal. yr BP, interrupted by a dry period from ~13,080-12,830 cal. yr BP. From ~10,550-6,420 cal. yr BP, the Sekhokong record indicates a drier climate with a slow transition to warmer, wetter conditions. The Mafadi Wetland record commences with cold, wet conditions from ~8,140-7,580 cal. yr BP, followed by a warmer, drier period from ~7,520-6,680 cal. yr BP. Thereafter, greater microclimatic differences are apparent. For Sekhokong, warmer, dry conditions are inferred for ~6,420-6,000 cal. yr BP, followed by cold, wet conditions from ~6,000-5,450 cal. yr BP. Warmer, dry conditions commence earlier at Mafadi Wetland, from ~6,160-5,700 cal. yr BP, coinciding with the initiation of a longer wet period at Sani Valley, from ~6,200-4,900 cal. yr BP. At Sekhokong, a dry, warmer period follows from ~5,450-3,700 cal. yr BP. At Sani Valley, drier conditions are evident from ~4,770-4,470 cal. yr BP, followed by a cold, wet period from ~4,460-2,260 cal. yr BP. For Mafadi Wetland, these cold, wet conditions endure longer, from ~5,600-1,100 cal. yr BP. This overlaps with similarly cool, wet conditions at Sekhokong, from ~3,650- 1,200 cal. yr BP. By contrast, dry conditions are evident at Sani Valley, from ~2,260-1,350 cal. yr BP. For all three sites, ~1,000 cal. yr BP to present is characterised by progressive drying, with discrete wet events. Pronounced cold events are detected at ~12,660 cal. yr BP, ~8,400-8,000 cal. yr BP and ~150 cal. yr BP. The results of this study indicate similarities with records from adjacent studies in western Lesotho and South Africa, although with notable variability in the timing of events. The palaeoenvironmental reconstructions for eastern Lesotho, and their comparison with existing studies, provide valuable information to improve the understanding of southern African Holocene climates, and to facilitate the development of high resolution, accurate climate models for the eastern Lesotho region.
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    Phenological response of citrus flowering to climate variability and change in Iran: 1960-2010
    (2013-08-02) Fitchett, Jennifer Myfanwy
    Phenology refers to “the study of the timing of recurrent biological events, the causes of their timing with regard to biotic and abiotic forces, and the interrelationship among phases of the same or different species” (Badeck et al., 2004: 295). This discipline has recently gained popularity in bio-geographical climate change studies, as it is recognized as an accurate and easily measured signature of the impact that changing temperature and precipitation over recent decades have had on plants. A five-decadal dataset (1960-2010) comprising daily temperature and rainfall records, and of the annual timing of peak flowering of five citrus types (orange, tangerine, sweet lemon, sour lemon and sour orange) was acquired for the Iranian cities of Gorgan, Kerman and Shiraz. The cities are geographically and climatically distinct, with arid Kerman located on the central Iranian plateau, humid Gorgan on the Caspian lowlands and Shiraz situated at the foot of the Zagros Mountains with a semi-arid climate. These climate data for Kerman and Shiraz reveal strong, statistically significant increases in Tmax of 0.03°C/yr, and even stronger increases in Tmin of 0.05°C/yr-0.07°C/yr, whilst Gorgan presents a statistically significant decrease in precipitation of 4.69mm/yr over the study period. Significant increases in daily sunshine hours of 7.09h/yr and 19.01h/yr are demonstrated for Gorgan and Kerman respectively. Negligible delays in the timing of peak flowering for the five citrus types in Gorgan by 0.05-0.01d/yr, and more considerable advances in the timing of flowering for Kerman (0.12-0.17d/yr) and Shiraz (0.56-0.62d/yr), occur concurrently with these climate trends. These differences in the direction of shift in flowering dates, combined with differences in climate trends, highlight the extent to which the location of the crops, and the associated abiotic forces, influence flowering dates. Significant relationships between the flowering dates of the citrus types and Tmax are demonstrated for Kerman and Shiraz, equating to advances of 1.85-3.08d/°C and 6.14-7.86d/°C respectively, with similar advances in flowering dates associated with increases in Tmin. Significant relationships between the timing of peak flowering and precipitation are demonstrated for Kerman. Across the majority of the climate variables studied, the strongest monthly relationships with flowering dates were for the month in which peak flowering occurs, suggesting a direct effect on control over this phenophase. The development of multiple regression models facilitated the simultaneous analysis of the effects of all of the climate variables, and increased the associated explanatory potential. The rate of change in peak flowering dates observed for the period 1960-2010, and the relative influence of some climate variables over others, highlight the importance of monitoring fruit tree phenology in a water scarce region such as Iran. With decreases in precipitation, increases in Tmin and Tmax and the potential for heightened frost risk by the end of the century due to the increased likelihood of late-winter flowering, citrus cultivation in Kerman is under threat. Shiraz is likely to survive continued climate variability and change throughout the 21st century, provided that sufficient water is available either naturally or through irrigation. Gorgan demonstrates the greatest capacity to continue successful citrus farming, and the greater Caspian Lowlands hold potential as a suitable location for the expansion of citrus farming required to compensate for any yields lost in the more arid areas of Iran and the Middle East.