For an ongoing project I had to calculate fractional snow cover transition dates across Alaska. These transition dates mark when snow levels drop below 5% coverage or when continuous accumulation of more than 5% starts. The period between these two dates can be considered snow free, and has the potential to support vegetation growth.
Below you see a snow cover trend map of the US and Canada, with earlier snow melt marked in red (-) and later snow melt marked in blue (+). Some patterns stand out, mainly mountain ranges in the West of the US have seen earlier and earlier snow melt dates. Alaska, doesn’t see very clear patterns, aside from earlier snow melt in the southern peninsula. Arctic Canada does see clear earlier snow melt throughout. Surprisingly, some later snow melt dates can be noted as well. From the middle of Alberta, Canada sweeping east to the great lakes a trend of later snow melt dates is noted. A word of caution is needed as these regions might be heavily influenced by the “polar vortex” in 2015, creating a long winter season, and potentially skewing the trend analysis. Furthermore, locations without data are places with a very short snow cover period, which were excluded for clarity (i.e. these are areas were snow cover has less of an influence on the growing season).
In short, as long as the analysis isn’t too complicated GEE is a quick way to get good and reproducible results. Sadly, the system does have it’s limitation and makes true time series analysis (with custom aggregation and curve fitting techniques) rather difficult if not impossible. I feel that these kinds of analysis are clearly outside the scope of the more GIS oriented GEE setup. I tip my hat to Google for providing this service, rather impressive I must say.