3.1.2. Temperature

Mean annual maximum temperature and minimum temperature are examined in a similar way to the precipitation. The mean of 10 RCP 4.5 projections in two future periods are compared with their counterparts in the historical period (Figure 6). Increases are expected for both maximum and minimum temperature in both future periods across all regions. The eastern regions (NL, SL, and CR) are generally expecting more significant warming compared to other regions. This is likely because of their geographic location (away from the Pacific Ocean, lacking ocean regulation). In contrast, the Coastal regions normally have the least significant warming except for the South Coast region which has similar climate pattern as the dry Tulare Lake region. Comparing two future periods, late-century is expecting more warming consistently for all regions, which is not surprising given

the accumulated effect of the greenhouse-gas emissions. The increases in minimum temperature and maximum temperature are generally comparable to each other. Statewide, the increases in the latter is slightly higher. Specifically, for maximum temperature, a 2.4 ◦C warming is projected statewide in the late-century versus 2.0 ◦C in mid-century. For minimum temperature, the statewide increases are expected to be 2.2 ◦C and 1.8 ◦C, respectively, in those two periods. This is somewhat different from previous studies which claimed that increases in minimum temperature are more pronounced [16], leading to smaller diurnal temperature ranges.

**Figure 5.** Box-and-whisker plots of percent differences (%) between historical and individual projections on: (**a**) annual precipitation; and (**b**) wet season precipitation. Yellow boxes represent mid-century results and orange boxes show late-century results.

In addition to the differences between mean RCP 4.5 projections and the historical baseline, the differences associated with the mean RCP 8.5 projections are also examined (Table 4). The messages are generally consistent with what the RCP 4.5 results (Figure 6) indicate. In general, warming (in both maximum and minimum temperature) is expected across all regions in both future periods. The inland eastern regions are projected to have the highest increases in temperature. The late-century is expecting more significant warming than the mid-century. Comparing RCP 4.5 and RCP 8.5 scenarios, warming of the latter is more pronounced in terms of increase amount. Specifically, for minimum temperature in the mid-century, RCP 8.5 scenario shows about 0.8 ◦C (for San Francisco Bay and Central Coast) to 1.1 ◦C (North Lahontan) warmer than the RCP 4.5 scenario; in the late-century, the range is from 1.9 ◦C (Central Coast) to 2.5 ◦C (North Lahontan). For maximum temperature, the differences between two scenarios are slightly higher than that of the minimum temperature.

**Figure 6.** Differences (◦C) between historical and mean RCP 4.5 projections on mean annual: (**a**) maximum temperature in mid-century; (**b**) minimum temperature in mid-century; (**c**) maximum temperature in late-century; and (**d**) minimum temperature in late-century.


**Table 4.** Differences (◦C) between historical and mean RCP 8.5 projections on annual maximum and minimum temperature.

Looking at individual projections on maximum (Figure 7a) and minimum temperature (Figure 7b), all of them show at least 1 ◦C warming. No projections indicate any decreases for any region, which is

different from precipitation projections that have no such consensus. This is also reported in previous studies [30,75–79]. Comparing two future periods, higher increases are expected in the late-century. On average, increases in maximum temperature are generally higher than increases the minimum temperature, which is particularly true for the eastern regions. Those observations are consistent with what is noted in Figure 6. Similar to precipitation projections, the warming range of late-century is larger than that of mid-century across all regions. This indicates that climate models tend to disagree more with each other further into the future because of increasing uncertainty in climate model forcing.

**Figure 7.** Box-and-whisker plots of differences (◦C) between historical and individual projections on mean annual: (**a**) maximum temperature; and (**b**) minimum temperature. Yellow boxes represent mid-century results and orange boxes show late-century results.

At the seasonal scale, the mean projection in mid-century shows at least 1 ◦C warming in both maximum and minimum temperature across all seasons (Figure 8a). In comparison, at least 2.5 ◦C warming is expected in late-century (Figure 8b). The highest increases (2.9 ◦C and 5.0 ◦C in mid-century and late-century, respectively) are expected to occur in Summer maximum temperature in the coolest region, North Lahontan. Comparing different regions, the eastern regions are expecting higher increases in both minimum and maximum temperature than other regions. This is consistent with what Figure 6 illustrates on the annual scale. Looking at different seasons, fall and summer are expecting relatively higher warming than winter and spring. Particularly, summer is expecting the highest increases. Statewide, an amount of 2.4 ◦C and 2.5 ◦C warming is projected in mid-century in summer minimum and maximum temperature, respectively. In late-century, the corresponding increases in summer are expected to be 4.2 ◦C and 4.3 ◦C, respectively.

**Figure 8.** Differences (◦C) between historical and mean (of all 20) projections on seasonal maximum temperature (Tmax) and minimum temperature (Tmin) in: (**a**) mid-century; and (**b**) late-century.
