Water Sustainability Program Student Fellowship

1. Introduction In dry desert regions like the Southwest U.S., natural and human systems are particularly sensitive to variations in climate. The natural ecosystem of the Sonoran Desert is largely dependent on and adapted to monsoon precipitation, which is also needed to maintain water demand and agriculture from year to year. From a resource management perspective, the monsoon is relevant in the consideration of severe weather hazards, water supply, and extreme droughts, especially given that the monsoonal precipitation accounts for approximately 30-50% of the annual total. Recent projections from the Intergovernmental Panel on Climate Change (IPCC) suggest that precipitation in our region may be decreasing in the long-term due to anthropogenic climate change. However, how warm-season precipitation associated with the North American monsoon will change is a major uncertainty in the present IPCC projections. Therefore, assessing how the North American monsoon will change in the future is a pressing and difficult research challenge. Given that the global climate has already been measurably altered by human activity in the last thirty years, climate model projections must be considered in a complete framework of the existing observational and paleoclimate record to increase their credibility, both within the scientific community and by natural resource stakeholders. Thus, the scientific objective of this work was to characterize how climate change is affecting the intensity of summer monsoon precipitation. Consistent with emerging work that has characterized recent observational changes in monsoon precipitation globally, it was hypothesized that anthropogenic climate change is synergistically interacting with natural climate variability to intensify extreme weather and climate events—that may push the already vulnerable human and natural systems in the Southwest U.S to fail points.