Fig. 2.
Observed time-series of irrigated land cover in California and June–August temperature differences between intensively irrigated lands (CIF > 50%) and a reference area (0.1–10% CIF), both located in the Central Valley region (CV: 118.25–126.25°W, 34.75–40.25°N). Tmax (A) and Tmin (B) time-series are estimated by using UW (red), PRISM (green), CRU2.1 (blue), and CRU2.0 (brown) data below 500 m of elevation. Unfiltered (pale dotted lines) and low-pass-filtered averages (performed with a 11-point binomial filter, bright solid lines) are shown, both with climatology subtracted for clarity. Irrigation time-series (black line, right, vertical scale is reversed) is interpolated from data collected in a total of 12 U.S. Department of Agriculture censuses (represented by black dots). r numbers show correlation coefficients between irrigation and each filtered temperature time-series using the 12 paired observations. An asterisk indicates that temperature and irrigation are highly correlated (P < 0.01).