Regarding Sacramento's tree canopy, the critical metric is not how much rain falls on Sacramento; it's about how much rainwater flows from, and snow melts down, the Cascade and Sierra Nevada mountains and then into the Sacramento and American rivers. Those rivers flow through the heart of Sacramento, and raise the local water table high enough to provide trees in the area with sufficient water to grow tall and sturdy in the California sunshine.
MIT found Sacramento's tree canopy covers
23.6% of the city. That is lower coverage than they found in Vancouver and Singapore, but higher coverage than they found in New York, Paris, Los Angeles, London, Boston, Seattle, Toronto, Geneva, Tel Aviv, Turin, Frankfurt and Amsterdam.