Charles (Charlie) Luce of the USFS recently presented a talk at OSU based on the paper 'The Missing Mountain Water: Slower Westerlies Decrease Orographic Enhancement in the Pacific Northwest USA' by C.H. Luce, J.T. Abatzoglou and Z.A. Holden, Science 342: 1360-1364 (13 December 2013).
Supplementary materials: Download Luce.SM
Trends in streamflow timing and volume in the Pacific Northwest United States have been attributed to increased temperatures, because trends in precipitation at lower-elevation stations were negligible. We demonstrate that observed streamflow declines are probably associated with declines in mountain precipitation, revealing previously unexplored differential trends. Lower-troposphere winter (November to March) westerlies are strongly correlated with high-elevation precipitation but weakly correlated with low-elevation precipitation. Decreases in lower-tropospheric winter westerlies across the region from 1950 to 2012 are hypothesized to have reduced orographic precipitation enhancement, yielding differential trends in precipitation across elevations and contributing to the decline in annual streamflow. Climate projections show weakened lower-troposphere zonal flow across the region under enhanced greenhouse forcing, highlighting an additional stressor that is relevant for climate change impacts on hydrology.
Read what Michael Dettinger of the USGS says about this:
Damn! I knew that precipitation was somewhere!
Important stuff in here:
Although the consequences of increased temperature for mountain snow are relatively well understood and severe, poor information about both historical and projected changes in mountain precipitation may lead to substantial misjudgment of risks and maladaptation. In particular, ecosystems and water supplies may be more sensitive to declines in precipitation than to increases in temperature. (Luce et al., p. 1360)
'Maladaptation' - I like that word.
Enjoy! Or not.
"The analysis of disparate streamflow and precipitation records in this region, encompassing much of the headwaters of the Snake and Columbia River basins, highlights a change of substantial magnitude with considerable ecological and economic consequences that has heretofore been ignored or dismissed. At the same time, we note new utility for streamflow data and a potential approach for the assessment of orographic precipitation changes related to in- creased radiative forcing using macroscale wind information." - C. Luce et al., (from the paper, p. 1363)