Using hydrologic model ensembles to better understand the impact of climate change on the hydrology of large river basins

Thesis (Ph.D.)--University of Washington, 2020Whether at the scale of a small watershed or a large multinational basin, it has become common practice for water managers to use ensembles of projections to plan for hydrologic change. Better understanding these ensembles can help improve the design of future hydrologic modeling studies. In this dissertation I will describe three uses of hydroclimate ensembles to support water resource planning efforts. In Chapter 2 I present a large ensemble of hydrologic climate change projections for the Columbia River basin within the hydroclimatically diverse Pacific Northwestern United States and Canada (PNW). I show how methodological decisions in the modeling process variously affect the projections of change depending on hydroclimatic regime and metric of interest. In Chapter 3 I delve deeper into the PNW to examine the impactful metric of changes in floods, determining how dominant flood generating processes will evolve under climate change. I also calculate first-order sensitivities of high flows to changes in climate. In Chapter 4, I apply the lessons learned from the first two studies, conducted within the transboundary Columbia River basin, to transboundary rivers around the world. I present a study identifying hot spots of changes in water availability and hydropolitical risk for over 80 rivers (esp. transboundary rivers) around the world as projected by results from the Coupled Model Intercomparison Project Phase 6. Finally, I present how the findings from this dissertation can contribute to improved hydroclimate impacts assessments