MODELING NISQUALLY GLACIER SURFACE-ELEVATION AND LENGTH CHANGES USING A MASS-BALANCE RECORD DERIVED FROM REANALYSIS AND WEATHER-STATION DATA

Nisqually glacier, located on the southern slopes of Mt. Rainier in Washington State, USA, has a long history of observations and research; the first recorded observation of its terminus position was in 1857. Since then, numerous research efforts have collected glacier data including terminus position and measurements of ice-surface elevation across three transverse profiles. Daily weather observations are nearly continuous since 1916 at the Paradise (elevation 1600 m) and Longmire (842 m) ranger stations. The National Park Service has maintained a glacier mass-balance-stake measurement program since 2003.

We have analyzed the weather records from Longmire and Paradise, which show recent (1970 – 2015) warming and drying. We used these ground data in addition to upper-air reanalysis data to derive an extended (1917 – 2015) Nisqually Glacier summer, winter and annual mass-balance record. This record shows that the annual mass balance was on average −0.64 m w.e. a^-1 from 1917 to 1946; -0.37 m w.e. a^-1 from 1947 to 1986; and -0.85 m w.e. a^-1 from 1987 to 2015. These differences are driven by changes in the summer mass balance. Our record is consistent with weather observations from Paradise, where there are trends of higher temperature and lower precipitation, as well as glacier observations of ice thickness and length, which show the glacier thickening and advancing from ~1950 to 1980 and thinning and retreating since then. Finally, we use our mass-balance record to force a 1-D glacier-flowline model, which shows good agreement with thickness and length observations.