3.1 Rainfall and VPD
Total annual precipitation was 1027 mm in 2015 and 1178 mm in 2016 (Figure 2a and b). The daily growing season (from May to October) precipitation ranged from 0.2 to 47.2 mm in 2015 (total growing season precipitation = 424 mm), and 0.2 to 119.2 mm in 2016 (total growing season precipitation = 846 mm). These data contrasted with the average (2008-2016) growing season precipitation of 636 mm, and the average annual total precipitation of 1112 mm (Boggs et al., 2016). Thus, the 2015 growing season was 34% drier than average with only 424 mm of precipitation, while the 2016 growing season was 33% wetter than average with 846 mm.
Growing season VPD in the drier year of 2015 was significantly higher (p ≤ 0.05) than the growing season VPD in the wetter year of 2016 (Figure 2c). In 2015, the mean daily growing season VPD averaged 0.73 (standard error, 0.028) kPa and ranged from 0.01 to 1.7 kPa. In 2016, the mean daily growing season VPD averaged 0.65 (0.027) kPa and ranged from 0.01 to 1.5 kPa.