Abstract
California’s Central Valley (CV) is one of the most productive agricultural regions in the world, enabled by the conjunctive use of surface water and groundwater. We investigated variations in the CV’s managed surface water diversions relative to climate variability. Using a historical record (1979−2010) of diversions from 531 sites, we found diversions are largest in the wetter Sacramento basin to the north, but most variable in the drier Tulare basin to the south. A rotated empirical orthogonal function (REOF) analysis finds 72% of the variance of diversions is captured by the first three REOFs. The leading REOF (35% of variance) exhibited strong positive loadings in the Tulare basin, and the corresponding principal component time-series (RPC1) was strongly correlated (ρ > 0.9) with contemporaneous hydrologic variability. This pattern indicates larger than average diversions in the south, with neutral or slightly less than average diversions to the north during wet years, with the opposite true for dry years. The second and third REOFs (20% and 17% of variance, respectively), were strongest in the Sacramento basin and San Francisco Bay−Delta. RPC2 and RPC3 were associated with variations in agricultural- and municipal-bound diversions, respectively. RPC2 and RPC3 were also moderately correlated with 7-year cumulative precipitation based on lagged correlation analysis, indicating that diversions in the north and central portions of the CV respond to longer-term hydrologic variations. The results illustrate a dichotomy of regimes wherein diversions in the more arid Tulare are governed by year-to-year hydrologic variability, while those in wetter northern basins reflect land-use patterns and low-frequency hydrologic variations.
Highlights
California’s Central Valley (CV), including the San Francisco Bay and Sacramento−San Joaquin Delta, is one of the world’s most productive agricultural regions, enabled by a complex engineered network of dams, reservoirs, and aqueducts, as well as numerous groundwater wells that provide irrigation supply
Temporal Variability of Surface Water Diversions Long-term (1979−2010) mean annual diversion volumes were highly variable from site to site, ranging from 0.01 to 86.6 thousand acre-feet (TAF; Figure 3)
We investigated the associations of climate variability and changing societal water-use patterns with regional aggregated diversions over major river basins within the CV and the Bay/ Delta
Summary
California’s Central Valley (CV), including the San Francisco Bay and Sacramento−San Joaquin Delta, is one of the world’s most productive agricultural regions, enabled by a complex engineered network of dams, reservoirs, and aqueducts, as well as numerous groundwater wells that provide irrigation supply. Surface water rights allocations exceed water supply by a factor of five in California (Little Hoover Commission 2010; Grantham and Viers 2014), while groundwater pumping has been largely unmonitored statewide and generally not monitored at all in the CV This lack of comprehensive data on the CV hydrologic system has led to persistent uncertainties in how groundwater storage fluctuates over time, and in response to droughts or extreme precipitation years, and in how to manage regional water resources (Faunt et al 2009; Faunt et al 2015; Xiao et al 2017)
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