Click here for recent article from the Bulletin of the American Meteorological Society:
Cayan, D.R., S.A. Kammerdiener, M.D. Dettinger, J.M. Caprio, and D.H. Peterson, 2001. Changes in the Onset of Spring in the Western United States. Bulletin of the American Meteorological Society, Vol. 82, No. 3, 399-415.
In the above paper, fluctuations in spring climate in the western United States over the last 4-5 decades are described by examining changes in the blooming of plants and the timing of snowmelt-runoff pulses. The two measures of spring's onset that are employed are the timing of first bloom of lilac and honeysuckle bushes from a long-term cooperative phenological network, and the timing of the first major pulse of snowmelt recorded from high-elevation streams. Both measures contain year-to-year fluctuations, with typical year-to-year fluctuations at a given site of one to three weeks. These fluctuations are spatially coherent, forming regional patterns that cover most of the west. Fluctutations in lilac first bloom dates are highly correlated to those of honeysuckle, and both are significantly correlated with those of the spring snowmelt pulse.
Last update: 1 September 2006
2002 Phenology
2003 Phenology
2004 Phenology
2005 Phenology
2006 Phenology
Phenology Climatology
1999-2001 Streamflow Timing
The lilac and honeysuckle phenology was recently updated for 2002-2006. The images below show the information from the Western Phenological Network observations. (This network was initiated by Dr. J. Caprio and the data was collected by Dr. M. Dettinger and Dr. D. Cayan for the California Applications Program.) The images below show the departure from 1983-1994 average phenological stage date for the: leafing of first bud, all leafed, first bloom, peak full bloom and withered. The circles indicate lilac observations and the triangles indicate honeysuckle observations.
The streamflow timing for the years 2003-2005 and 1999-2002 are shown below. The streamflow timing is based on when half of the water year's flow is done at each USGS streamflow gaging station. The climatology for the timing is based on the 1959-1993 average streamflow. Red shows stations which reached the half-year-flow earlier than normal and blue shows stations which reached the half-year-flow later than normal. The streamflow timing uses the USGS Hydroclimate Data Network sites. The timing is based on centroids of water-year hydrographs and is calculated by Dr. M. Dettinger and Dr. D. Cayan for the California Applications Program.
