The synoptic controls on the ice-jam hydrology of the Peace River Basin.

摘要

The synoptic controls on the occurrence of ice jam flood in the Peace River Basin (PRB) are investigated. Such events are critical for maintaining the ecosystem health of the Peace-Athabasca delta (PAD), one of the world's largest fresh water deltas. Although the importance of climate on river-ice hydrology is being increasing recognized, few studies have investigated the relationship between atmospheric circulation and ice-jam flood occurrence.; The objective of this dissertation was to identify the synoptic controls on the ice-jam hydrology of the PRB over the period 1963-1996. Given the complexity of this objective, ice-jam floods were separated into three components that dictate their development: the magnitude of the upstream winter snowpack, the timing and rate of upstream snowmelt, and the occurrence of contrasting melt conditions between upstream and downstream locations. The synoptic and broad-scale controls on each component were then examined. Synoptic controls for upstream components were identified using an eigenvector-based synoptic typing classification procedure.; Results illustrated that variations in both the magnitude of the winter snowpack and the timing and rate of spring snowmelt in the upper reaches of the PRB could be explained by variations in occurrence of synoptic circulation patterns. The surface-to-atmosphere approach also proved to be successful in identifying the synoptic controls on contrasting melt conditions between upstream and downstream locations on the PRB. The examination of broadscale controls revealed that the variations in the Pacific/North American pattern related to the occurrence of synoptic circulation patterns over western Canada, that control the three aforementioned ice-jam components.; In addition, results indicated that the climate of the PRB is changing. For example, it was corroborated that the magnitude of the upstream winter snowpack was significantly reduced after 1976. Furthermore, the initiation of melt in both upstream and downstream locations was shown to be occurring progressively earlier during the study period. This can be partially attributed to a significant increase in the occurrence of March upper-level ridging patterns, which are associated with above normal temperatures in the PRB. The present and future implications of these changes to the formation of severe ice jam floods in the PAD are discussed.