https://doi.org/10.24124/2025/59596

This dissertation provides a comprehensive analysis of atmospheric rivers (ARs) and
their impacts on the Nechako River Basin (NRB) in British Columbia (BC), Canada. The study
is divided into three main components: (1) the spatio-temporal distribution and trend analyses
of AR types impacting the NRB, (2) AR contributions to the NRB's water budget input and
their trends, and (3) the synoptic setting and hydrological responses in the NRB to three
exceptional AR events.
Initially, the spatio-temporal distribution and trends of ARs of various categories were
examined. The study found a notable shift from mid- to low-intensity AR types in several sub-
basins of the NRB. This shift suggests a potential impact on the regional water budget, as lower-
intensity ARs are mostly beneficial and less likely to cause hazardous impacts but may also
bring less water vapour to precipitate over the NRB. Spatial analysis revealed that the western
and northern parts of the NRB are most affected by ARs, mainly in the fall and winter, with
November experiencing the highest average AR intensity for the region.
Moreover, the contributions of ARs to the NRB's water budget and their trends were
assessed. AR days impacting the NRB are estimated at ~35 AR days yearly, on average,
accounting for approximately one-fifth of the total annual precipitation, bringing predominantly
rain in the fall and a mix of rain and snow in winter. Additional analyses indicated increasing
trends in total precipitation linked to low-intensity ARs in the northern and western sectors of
the NRB. The study highlights significant spatial variations in AR contributions to the NRB’s
hydrological cycle, impacting total precipitation, snowpack formation, runoff, and the overall
regional water budget.
The synoptic setting and hydrological responses in the NRB to three exceptional AR
events that occurred in 1952, 1978, and 2009 were also explored. These exceptional AR events
depict the dual role of ARs in contributing to water replenishment while causing natural
hazards. The exceptional ARs significantly contributed to snowpack formation and water
replenishment to the Nechako Reservoir, averaging total precipitation accumulations of 81 mm
(1.14 km3) in the Upper Nechako, highlighting their importance for regional water storage.
However, these events also underscored the potential for flash floods and landslides,
particularly during rain-on-snow conditions or when ARs make landfall on saturated soils and
steep terrain. The findings of this dissertation emphasize the critical role of ARs in shaping the
water budget of the NRB. The increasing frequency of some AR types, while others are
diminishing, shows the changing nature of ARs, which may require adaptive water management
strategies to balance the beneficial and detrimental impacts of these river-shaped storms.
Enhanced understanding of AR dynamics and their impacts can inform the development of
more effective flood prevention, water storage, and resource management practices, ensuring
sustainable water supply for various stakeholders. The insights gained are particularly valuable
for managing the Nechako Reservoir, where accurate water management is crucial for
balancing agricultural, industrial, residential, and ecological needs in central BC.

https://doi.org/10.24124/2025/59596