Advances in Understanding the Causes and Impacts of Droughts in North America under Current and Future Climates

摘要

Droughts reduce water resources necessary for human survival, economic development, and to sustain healthy ecosystems. Our ability to monitor and forecast droughts has grown dramatically in the past decades due to improved hydrological modeling made possible by satellite data and high computing power. However, there is still a large gap of knowledge regarding the mechanisms behind drought onset, development, and recovery. This gap prevents us from being able to forecast every severe drought and from being more confident about the effects of climate change. This thesis proposes a paradigm shift from droughts as local events to droughts as dynamic hazards that can travel in space. In this framework, droughts become the frame of reference, opening new possibilities for drought assessment and forecasting. Here, droughts are shown to have traveled across continents between 1979---2009. Patterns of frequent and common directions of displacement are identified. Precipitation recycling is proposed as an important mechanism behind these observed dynamics, and a detailed study of moisture sources over North America from 1980---2016 is carried out. This work shows that drought conditions can propagate downwind, especially from the U.S. Southwest to the U.S. Midwest, and from the northwest of Mexico and Central America to the center and south of Mexico. The effect of local precipitation recycling on drought intensification is quantified and shown to be highest in the north of Mexico and the U.S. Southwest. In a study of climate change's impacts on droughts, large biases are found in the climate models' representation of the hydrologic cycle and land-atmospheric coupling. This is shown to affect the models' drought projections by the end of the twenty-first century. Finally, this thesis includes a study of drought impacts on electricity generation and on CO2, SO2, and NOx emissions from the power sector in the American West under current and future climates. This work advances the understanding of how droughts propagate through the hydrologic cycle locally and across continents, opening new opportunities for seasonal forecasting. It also includes a rigorous drought impact study on the electricity sector that provides useful information to stakeholders and decision makers.