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Relative Humidity Has Uneven Effects on Shifts From Snow to Rain Over the Western U.S.
Author(s) -
Harpold A. A.,
Rajagopal S.,
Crews J. B.,
Winchell T.,
Schumer R.
Publication year - 2017
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1002/2017gl075046
Subject(s) - snow , relative humidity , precipitation , environmental science , humidity , atmospheric sciences , climatology , fraction (chemistry) , climate change , water equivalent , meteorology , chemistry , geography , geology , oceanography , organic chemistry
Abstract Predicting the phase of precipitation is fundamental to water supply and hazard forecasting. Phase prediction methods (PPMs) are used to predict snow fraction, or the ratio of snowfall to total precipitation. Common temperature‐based regression (Dai method) and threshold at freezing (0°C) PPMs had comparable accuracy to a humidity‐based PPM ( T RH method) using 6 and 24 h observations. Using a daily climate data set from 1980 to 2015, the T RH method estimates 14% and 6% greater precipitation‐weighted snow fraction than the 0°C and Dai methods, respectively. The T RH method predicts four times less area with declining snow fraction than the Dai method (2.1% and 8.1% of the study domain, respectively) from 1980 to 2015, with the largest differences in the Cascade and Sierra Nevada mountains and southwestern U.S. Future Representative Concentration Pathway (RCP) 8.5 projections suggest warming temperatures of 4.2°C and declining relative humidity of 1% over the 21st century. The T RH method predicts a smaller reduction in snow fraction than temperature‐only PPMs by 2100, consistent with lower humidity buffering declines in snow fraction caused by regional warming.