Dendrochronological reconstruction of precipitation trends to 1591 AD in the Sooke Watershed, Vancouver Island, British Columbia
| Autor: | Farmer, Lauren Kirsten |
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| Jazyk: | angličtina |
| Rok vydání: | 2020 |
| Předmět: | |
| Druh dokumentu: | Diplomová práce |
| Popis: | By 2050, mean annual temperature on Vancouver Island, British Columbia is expected to rise by 1.5°C and summer precipitation is expected to decrease 14% below pre-industrial levels. The purpose of this thesis was to extend the Sooke Watershed precipitation record by developing proxy records from annual Douglas-fir tree rings, with the goal of being able to provide information about the pre-historical range of precipitation variation that could assist future water management decisions. Robust dendrohydrological relationships were established to extend the instrumental record of precipitation back to the year 1591. To provide geographic context for the hydrologic history of the Sooke Watershed, I examined Douglas-fir climate-radial growth relationships across western Canada to three monthly climate variables: precipitation, average air temperature, and Hargreaves Climatic Moisture Deficit (CMD). Ten study sites were chosen to represent a gradient of climate conditions where Douglas-fir grows in Alberta and British Columbia. In order to explore how growth sensitivities varied over time, long- and short-term climate-growth relationships at these study sites were analyzed and compared to those established for the Sooke Watershed. A short-term analysis of the radial growth of Douglas-fir trees in the Sooke Watershed revealed the presence of a negative climate-growth relationship to the June and July temperature of the growing year starting in 1990. Further, the radial growth of Douglas-fir trees at all sample sites was moisture limited, whereby they exhibited strong positive growing season correlations to precipitation and negative correlations to CMD. Lastly, lagged negative effects of August and September precipitation and CMD were present and related to the annual radial growth increments. These results signify that: the rise in air temperature in recent decades is limiting the radial growth of Douglas- fir trees in the Sooke Watershed; annual variation in ring-width increments is regulated by the amount of precipitation that falls near the end of the prior growing season; and, moisture availability in the spring of the current year of growth plays an important role in determining the annual increment of radial growth. Collectively, the results suggest that the radial growth of Douglas-fir trees within the Sooke Watershed are sensitive to interannual climate fluctuations and future growth is likely to be altered by changes in temperature and precipitation regimes. These climate-growth relationships justified the development of a May-June-July precipitation reconstruction for the Sooke Watershed. Using a novel detrending method, an Ensemble Empirical Mode Decomposition, I created a model that explained 28% of the May-June-July precipitation variability. Results from the dendrohydrological analyses extend the understanding of the water supply area May-June-July precipitation record to 1591. The reconstruction revealed four major summer drought episodes that exceeded severity during the instrumental record severity: 1594-1596, 1662-1665, 1796-1797, and 1898-1899. Four extreme summer pluvial episodes were also observed from 1646-1647, 1689-1690, 1793-1794, and 1920-1921. The findings of the research provide information about historical summer precipitation trends within the Sooke Watershed – the primary water supply area to Greater Victoria. Notably, the research places summer drought and pluvial events recorded within the instrumental record into a much longer context, permitting an understanding of natural frequency and duration of hydrological events in the Sooke Watershed. Graduate |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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