How Green is Your Valley? Remote Sensing of Large Watershed Change for ecosystem management

This project looked for high-level indicators of watershed health that will be useful for natural resource
management of salmon. We use a well-established remote sensing indicator of the ‘greeness’ of
terrestrial vegetation from studies of forestry, agriculture, and climate change1 called the Normalized
Difference Vegetation Index (NDVI). We obtained a very large NDVI dataset assembled by the Canada
Centre for Remote Sensing from daily weather satellite imagery for 1985 to 2006, at 10-day and 1-km
resolution for all of BC. Following further corrections and quality control, we extracted spatially
averaged time series for several Fraser watersheds and developed a set of secondary indicators,
including the long-term trends and annual anomalies of summer greeness, and timing of spring ‘greenup’.
These show that dramatic, spatially varying, changes in vegetative cover have occurred within the
Fraser Basin since 1985. Comparison of with metrics of salmon abundance and survival at the
watershed level suggests that changes captured by the NDVI time series relate to salmon success.
Much work remains to be done, but these indicators can be mapped at the watershed, basin and
province level, and provide a completely new lens though which to examine the salmon life cycle. As
expected in an exploratory project taking a bottom-up data driven approach, we are generating more
questions than answers. The work is being followed up by DFO, using a more top-down approach. We
have generated mapped indices for use by the Nature Conservancy of Canada, Simon Fraser and
DFO, and will participate in the Annual FSWP Meetings to broadcast our results and seek further
collaborators.

1Myneni et al, 1997. Increased plant growth in the northern high latitudes from 1981 to 1991. Nature
386: 698-702.