STABLE ISOTOPES IN PRECIPITATION, SURFACE, AND GROUND WATERS: RECORDING THE NORTH AMERICAN MONSOON IN ARIZONA, NEW MEXICO, AND UTAH

Data show that during the past 100 years the Navajo Nation has experienced increasing temperatures and decreasing precipitation. The Navajo Nation’s precipitation stems from three components: 1) winter precipitation from the north Pacific, 2) winter precipitation from the tropical Pacific, and 3) summer monsoons from the Gulf of Mexico and the Gulf of California. There has been historical variability in precipitation in the southwestern United States. In Arizona, New Mexico and Utah, summer precipitation, also known as the North American monsoon, has ranged from weak monsoons causing drought to develop to strong monsoons causing flooding. I propose to conduct research to better understand patterns and changes in the North American monsoon by measuring stable isotope ratios of water on the Navajo Nation. For several decades hydrologists have recognized that stable isotope ratios of hydrogen and oxygen can be used to distinguish the origin of water in precipitation, surface and ground waters. Stable isotopic research will provide unique and critical information that will help us understand how different oceanic water sources contribute to monsoon precipitation in the Navajo Nation and how monsoon precipitation contributes to surface, ground and spring water sources. This work will address the following questions: Is there a mix of atmospheric water vapor sources contributing to monsoon precipitation in the Navajo Nation, and how does this vary geographically and with monsoon intensity? To what degree are different freshwater resources (streams, lakes, groundwater, and springs) derived from monsoonal precipitation, and which resources are likely to be most sensitive to future changes in the monsoon? There is a need for quantitative data to interpret monsoonal precipitation changes and its effect on Navajo Nation’s changing climate.