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Upcoming Seminars
| Title: | A discrepancy in near-surface water vapor trends between models and observations
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| Speaker: |
Dr. Isla Simpson
Isla is section head of the climate analysis section in the climate and global dynamics laboratory of NSF NCAR. She obtained her PhD in 2009 from Imperial College London and then had postdoc positions at University of Toronto and Lamont-Doherty Earth Observatory, before joining NCAR in 2015. At NCAR she works on the representation of climate variability and change CESM and other models and the use of CESM in seasonal-to-decadal prediction.
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| Date/Time: |
Thursday, August 13, 2026 01:00 PM MDT (-0600)
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| Location: |
David Skaggs Research Center, Room GC402
Google Meet |
Abstract
Arid and semi-arid regions of the world are particularly vulnerable to greenhouse gas driven hydroclimate change. The American Southwest is a particularly clear example where recent drought has led to unprecedented water shortages in the Colorado River, and some of the most extreme wildfire seasons in recent history, and this has almost certainly been exacerbated by the substantial warming and aridification that has resulted from rising greenhouse gases. Climate models are our primary tool for projecting the future hydroclimate that society in these regions must adapt to, but here a concerning discrepancy between observed and model-based historical hydroclimate trends will be discussed. An expected consequence of a warming atmosphere is that atmospheric water vapor would rise as a result of the increased water-vapor holding capacity of the atmosphere. But this is only true if there is enough water available to satisfy the rising atmospheric demand. Earth System Models, indeed suggest that over the last four decades, atmospheric water vapor should have risen, even over arid and semi-arid regions, but in contrast, the observation-based record shows no evidence of rising humidity over arid and semi-arid regions of the world. This suggests that the availability of moisture to satisfy the increased atmospheric demand is lower in reality than in models in arid and semi-arid regions and it indicates a major gap in our understanding and modeling capabilities, which could have severe implications for hydroclimate projections, including fire hazard, moving forward. Ongoing work to identify the origins of this discrepancy will also be discussed. This includes the accompanying discrepancies in shortwave radiation trends, the potential role for inhomogeneities in the observational records and the role of mis-represented water availability from the land surface.
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