Large-Scale Atmospheric Forcing of Recent Trends toward Early Snowmelt Runoff in CaliforniaSource: Journal of Climate:;1995:;volume( 008 ):;issue: 003::page 606DOI: 10.1175/1520-0442(1995)008<0606:LSAFOR>2.0.CO;2Publisher: American Meteorological Society
Abstract: Since the late 1940s, snowmelt and runoff have come increasingly early in the water year in many basins in northern and central California. This subtle trend is most pronounced in moderate-altitude basins, which are sensitive to changes in mean winter temperatures. Such basins have broad areas in which winter temperatures are near enough to freezing that small increases result initially in the formation of less snow and eventually in early snowmelt. In moderate-altitude basins of California, a declining fraction of the annual runoff has come in April?June. This decline has been compensated by increased fractions of runoff at other, mostly earlier, times in the water year. Weather stations in central California, including the central Sierra Nevada, have shown trends toward warmer winters since the 1940s. A series of regression analyses indicate that runoff timing responds equally to the observed decadal-scale trends in winter temperature and interannual temperature variations of the same magnitude, suggesting that the temperature trend is sufficient to explain the runoff-timing trends. The immediate cause of the trend toward warmer winters in California is a concurrent, long-term fluctuation in winter atmospheric circulations over the North Pacific Ocean and North America that is not immediately distinguishable from natural atmospheric variability. The fluctuation began to affect California in the 1940s, when the region of strongest low-frequency variation of winter circulations shifted to a part of the central North Pacific Ocean that is teleconnected to California temperatures. Since the late 1940s, winter wind fields have been displaced progressively southward over the central North Pacific and northward over the west coast of North America. These shifts in atmospheric circulations are associated with concurrent shifts in both West Coast air temperatures and North Pacific sea surface temperatures.
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contributor author | Dettinger, Michael D. | |
contributor author | Cayan, Daniel R. | |
date accessioned | 2017-06-09T15:25:02Z | |
date available | 2017-06-09T15:25:02Z | |
date copyright | 1995/03/01 | |
date issued | 1995 | |
identifier issn | 0894-8755 | |
identifier other | ams-4312.pdf | |
identifier uri | http://onlinelibrary.yabesh.ir/handle/yetl/4181868 | |
description abstract | Since the late 1940s, snowmelt and runoff have come increasingly early in the water year in many basins in northern and central California. This subtle trend is most pronounced in moderate-altitude basins, which are sensitive to changes in mean winter temperatures. Such basins have broad areas in which winter temperatures are near enough to freezing that small increases result initially in the formation of less snow and eventually in early snowmelt. In moderate-altitude basins of California, a declining fraction of the annual runoff has come in April?June. This decline has been compensated by increased fractions of runoff at other, mostly earlier, times in the water year. Weather stations in central California, including the central Sierra Nevada, have shown trends toward warmer winters since the 1940s. A series of regression analyses indicate that runoff timing responds equally to the observed decadal-scale trends in winter temperature and interannual temperature variations of the same magnitude, suggesting that the temperature trend is sufficient to explain the runoff-timing trends. The immediate cause of the trend toward warmer winters in California is a concurrent, long-term fluctuation in winter atmospheric circulations over the North Pacific Ocean and North America that is not immediately distinguishable from natural atmospheric variability. The fluctuation began to affect California in the 1940s, when the region of strongest low-frequency variation of winter circulations shifted to a part of the central North Pacific Ocean that is teleconnected to California temperatures. Since the late 1940s, winter wind fields have been displaced progressively southward over the central North Pacific and northward over the west coast of North America. These shifts in atmospheric circulations are associated with concurrent shifts in both West Coast air temperatures and North Pacific sea surface temperatures. | |
publisher | American Meteorological Society | |
title | Large-Scale Atmospheric Forcing of Recent Trends toward Early Snowmelt Runoff in California | |
type | Journal Paper | |
journal volume | 8 | |
journal issue | 3 | |
journal title | Journal of Climate | |
identifier doi | 10.1175/1520-0442(1995)008<0606:LSAFOR>2.0.CO;2 | |
journal fristpage | 606 | |
journal lastpage | 623 | |
tree | Journal of Climate:;1995:;volume( 008 ):;issue: 003 | |
contenttype | Fulltext |