Abstract:Highly variable water regimes, such as California's, contain distinctive problems in the pursuit of secure timing, quantities and distributions of highly variable flows. Their formal and informal systems of water control must adapt rapidly to forceful and unpredictable swings on which the survival of diversified ecosystems, expansive settlement patterns and market-driven economies depends. What constitutes resilient water governance in these high-variability regimes? Three bodies of theory-state resource government, resilience and social mediation-inform our pursuit of governance that adapts effectively to these challenges. Using evidence drawn primarily from California research and participation in the policy and practice of water governance, we identify two stark barriers to learning, adaptation and resilience in high-variability conditions: (1) the sharp divide between modes of governance for ecological (protective) and for social (distributive) resilience and (2) the separation between predominant paradigms of water governance in "basins" (shared streamflow) and in "plains" (minimized social risk). These sources of structural segregation block adaptive processes and diminish systemic resilience, creating need for mediating spaces that increase permeability, learning and adaptation across structural barriers. We propose that the magnitude and diversity of need are related directly to the degree of hydro-climatic variability.