Simulating the Impacts of Changes in Precipitation Timing and Intensity on Tree Growth

The timing and intensity of precipitation varies from year-to-year and is expected to change in the future. Assessing the impacts of this moisture delivery variability on tree growth is important both for future forest health and for our interpretation of pre-instrumental tree-ring records. Here, we used the Vaganov-Shashkin model to investigate how changes in precipitation delivery impact tree growth at five sites representing four species in two North American river basins with high precipitation variability but different seasonal cycles. Evenly distributed precipitation increased tree growth in the Lower Sacramento watershed, while the water-limited South Platte benefited from concentrated precipitation early in the growing season. Although most experimental simulations retained the pattern of high- and low-growth years, tree growth was reduced with fewer, more intense precipitation events, which could affect interpretation of past climate extremes. Under the RCP4.5 scenario, projected warming offset the potential benefits of increased precipitation on tree growth.