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Dr. Hoerling is an Adjunct Lecturer in the Department of Civil, Environmental and Architectural  Engineering, at the University of ŷ���ڱ���Ƶ-Boulder.  Previously, he was meteorologist in NOAA's Physical Sciences Laboratory in Boulder, where he had worked from 1989-2023 receiving a Distinguished Career Award in 2021. He earned his PhD in meteorology from the University of Wisconsin-Madison in 1987. He is a Fellow of the American Meteorological Society and has published over 100 scientific papers exploring climate dynamics. These include studies on African and Indian monsoons, middle latitude variability linked to the El Niño phenomena, causes for drought and extreme climate events, climate predictability assessments, and hydro-climate variability of the ŷ���ڱ���Ƶ and Missouri River basins. His lecture course at ŷ���ڱ���Ƶ is titled “The ŷ���ڱ���Ƶ River Water Crisis.”

Abstract

Future ŷ���ڱ���Ƶ River Flows for an Upcoming Generation

The ŷ���ڱ���Ƶ River once fostered flourishing life in the 20^th Century, but it no longer meets all needs today. The roots for this water crisis are multifaceted – poor water policy and development law accumulated over a century, large natural swings in the basin’s hydrology lurching between excess flows and droughts, and emergent effects of human-induced climate change. The 1922 Compact Commissioners and subsequent decision makers could not foresee the threats to flows arising from anthropogenic climate change.  But today, increasing temperatures due to global warming have fueled fears that the ŷ���ڱ���Ƶ River will be permanently reduced.  A pressing question that is addressed in this short presentation is whether water resource recovery from low flows during the beginning of the 21^st Century is possible. Using empirical data, the sensitivity of the river (at Lee Ferry) to temperature and precipitation variability is first assessed.  These reveal the critical importance of precipitation via its strong constraint on river flows. Projections of temperature and precipitation are next examined using new suites of climate models, which are combined with the sensitivities to yield estimates of future flows.  Given current policy debates on operating guidelines for 2026-2050, the talk will offer a policy relevant analysis on how the river is likely to serve the needs for the upcoming generation.  

The new findings indicate that, owing to the critically important effects of precipitation variability, recovery of water resources from the recent severe drought state is indeed possible.  But any rebound will likely be muted owing to deleting effects of further warming.  The results also reveal a risk that flows could be materially lower than during the 2000-2020 period, exposing a threat of severely diminished flows when warming coincides with low precipitation.  Managing this wide range, especially considering increasing demands, is the pressing challenge for water managers in the basin. As stakeholders converge on post-2026 operating guidelines this study urge them to recognize and fully appreciate the ŷ���ڱ���Ƶ River’s intrinsic large variability in an even warmer world. A framework that incorporates such variability via risk-based management approaches can lead the basin and the region towards a future with sustainable water resources.