Understanding the Role of Asymmetrical Warming on Streamflow Changes in the Western U.S. Using a Multi-model Approach
Abstract
Climate models project stronger warming in the warm than in the cold season over the Western U.S. Across much of this region, the dominant hydrologic signature of climate change is reduced winter snow accumulation and earlier streamflow peaks, which are mainly caused by cold season (October-March) warming. An obvious question is, how will warm season (April-September) warming affect the hydrology of the region? Earlier work has documented the seasonal warming signature over the major snowmelt dominated watersheds of the Western U.S. based on simulations using the Variable Infiltration Capacity (VIC) macroscale hydrology model. We show that while runoff timing shifts consistently earlier under cold season warming, runoff volume changes (mostly decreases) are less consistent, but are mostly attributable to warm season warming, and accompanying enhanced evaporative demand. However, the mechanisms that control runoff responses to asymmetrical (cold/warm season) warming remain unclear, as is the extent to which the previous results are model-dependent. Here, we expand on an earlier study to include experiments with Noah-MP, SAC-SMA, and Catchment land surface models over the major river basins of the Western U.S. (Columbia, Colorado, and Sierra Nevada (Southern and Northern)), and investigate the mechanisms that cause differences in annual and seasonal streamflow response to asymmetric seasonal warming. We find that the general features of the seasonal and annual runoff responses to asymmetric warming are consistent across models, although the magnitudes vary. We expand on the annual water balance to develop a seasonal ET-temperature response framework, which requires consideration of seasonal storage changes, primarily as SWE and soil moisture. We report a set of control experiments based on this framework, and found that basins with lower annual temperatures, greater warm season precipitation, larger change in basin average April 1st SWE between warming and baseline scenarios divided by warming magnitude (3 °C), and smaller summer vapor pressure deficits lead to stronger asymmetric streamflow response patterns, and in turn larger annual streamflow decreases under warm season contrasted with cold season warming.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.H23J2036B
- Keywords:
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- 1804 Catchment;
- HYDROLOGY;
- 1805 Computational hydrology;
- HYDROLOGY;
- 1847 Modeling;
- HYDROLOGY;
- 1855 Remote sensing;
- HYDROLOGY