If selective pressure and genetic diversity support it then evolution proceeds (realizing that actual speciation may also require isolation of a sub-group). However, the underlying premise of a linear process is not how evolution works.

For CA ag we absolutely depend on the storage and planned release of winter snowpack; balanced to also provide flood protection from those same reservoirs. LA sucks from both sides of the Rockies and both sides of the Sierra, so there is that! (too many people in too dry an area). That said, "drought" is a human concept related to ag and city water supply. Extended lack of precip absolutely hurts local animal and plant (including fish) communities. Our attempts to engineer out of extended drought and climate change are very dicey (probably less snow, MAYBE less total precip) . The tunnels project and Delta pumping are an expensive, highly-contested mess. Conservation and less-water crops and desal are likely the eventual solutions in CA. IMHO. The "which is more important" answer is it depends where you live.