Famously sunny California has seasonal drought baked into its climate. Real drought - a relative shortage of winter rains for one, two, or more winters is also a common occurrence throughout California's history. Over the past century, we have learned to exploit groundwater as an insurance against drought, to grow crops and support cities. But groundwater resources are threatened by overuse, by pollution from urban and agricultural activities, and they are increasingly disconnected from rivers and ecosystems that rely on groundwater resources. This talk will provide an intuitive and illustrated journey to highlight the role of groundwater in managing cities, farms, and the environment under a Mediterranean climate, particularly in drought; explore existing challenges to protect groundwater resource; and outline promising approaches to sustainable groundwater management that also makes California more drought resilient as we perhaps face a Megadrought as the new normal.