GYA temperatures have risen (Chang and Hansen 2015), the amount of snowmelt has declined (Tercek et al. Previous work in the GYA shows similar trends, which we examine here in detail.
Collectively these observations confirm that even a modest rise in temperature is already transforming the hydrology of the West. 2007 Udall and Overpeck 2017), and enhanced evaporation (Golubev et al. 2014), diminished the volume of snowmelt, pushed the timing of peak streamflow earlier in the year (Stewart et al. 2018 Milly and Dunne 2020), increased winter rainfall (Knowles et al. Instrumental records from across the western states show that rising mean annual temperature has reduced snowpack (Mote et al. The trends parallel climate and hydrological changes that have occurred in recent decades throughout the western United States. In this chapter we examine recent climate and hydrologic trends in the GYA as recorded by observations at weather stations and streamgages. Īnnual streamflow today is similar to that of the mid-20 th century, but on average over the GYA the timing of peak flow has shifted earlier in the year by 8 days (range of 1-15 days in the HUC6 watersheds), extending the length of the water-limited warm season. Much of the snowfall decline occurred in spring when warming was greatest. Īs the climate has warmed, mean annual snowfall in the GYA has declined by 3.5 inches (8.9 cm) per decade. It has declined by 17 and 11% in June and July, respectively.
Īverage annual total precipitation has remained near 15.9 inches (40.5 cm), but precipitation has increased in spring and fall, by 17-23% in April and May and 42% in October. Īverage precipitation across the GYA has not changed significantly and remains near 15.9 inches (40.5 cm) with year-to-year variability of 2.2 inches (5.6 cm) based on the standard deviation of the meteorological record average. Meteorological records, averaged across the GYA, show that the mean annual temperature in the GYA has increased by 2.3☏ (1.3☌) at a rate of 0.35☏ (0.19☌) per decade. Trends at weather stations and streamgages show that temperature has risen, snowfall has declined, and peak streamflow has shifted earlier into the spring in the GYA’s watersheds since 1950. Release of the Madison River from Ennis Lake dam and powerhouse near Ennis, Montana. David Liefert, Bryan Shuman, Steven Hostetler, Rob Van Kirk, and Jennifer L.
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