Over the past twenty years, the semi-arid to arid climate in Southwestern North America (SWNA) has been exceptionally dry in addition to being hotter than any time in the 20th century, suggesting the first anthropogenic megadrought. While past megadroughts in the 9th and 16th century have been devastating to entire populations of Native Americans, modern urban and agricultural water users have been able to largely circumvent water shortages from this megadrought by solidifying or expanding their dependence on groundwater resources. Groundwater use and megadrought pose a dual threat to groundwater-dependent ecosystems including fish habitat requiring minimum baseflow condition. For sustainable water management, better understanding of the contributions of 20th century groundwater development, 21st century changes in groundwater use, and recent climate change on instream flows is critical to develop alternative strategies, but also to engage local, state, and federal resources in support of these strategies (e.g., funding). Better understanding of the role of the megadrought in reducing instream flow conditions will also inform stakeholders that are divided over who is to blame – and therefore liable for the cost of alternative water management – for observed reductions in instream flow conditions: local groundwater users or society at large.

The Scott and Shasta Rivers in mountaineous Northern California are among few remaining streams in that state without large surface water storage facilities (dams) and have therefore remained a critical habitat for fall-run Chinook salmon and Coho salmon in the Klamath River basin. Other tributaries to the Klamath River also have significant spawning habitat for salmon. Among the various sub-watersheds in the Klamath River basin, the Scott and Shasta basins are the only basins with large intermontane valleys subject to irrigated farming and groundwater pumping. The objective of this thesis research is to investigate historic streamflow records for the various tributaries in the Klamath River basin and to compare the emergence of low summer and fall instream flows among undeveloped tributary sub-watersheds with those in the Scott and Shasta River over the past 60 to 80 years of stream records, with additional analyses of similar watersheds in Oregon and California.

Streamflow records going back to the 1940s are provided by the USGS and by the California Department of Water Resources. The work will build on previous studies, especially the previous comparative watershed analysis implemented by Van Kirk and Naman (2008), which largely preceded the current megadrought conditions. The initial step will be to repeat the analysis of Van Kirk and Naman (2008) with data through 2020, then consider analyses of additional watersheds to further confirm the findings in the Klamath River basin. Results provide important information to local Groundwater Sustainability Agencies that are in the process of developing Groundwater Sustainability Plans. Additional statistical work may expand on the analysis of factors contributing to baseflow conditions and the shape of spring recess, especially for the Scott River, to determine whether late summer and fall baseflow conditions can be reliably predicted on April 1 or May 1. This may provide an important decision-support tool to manage irrigation water use (surface water or groundwater).

The thesis will be conducted remotely following anticipated COVID-19 guidelines in Germany and California recommending to avoid any travel for the foreseeable future, at least through the end of 2020. The student will regularly meet with Prof. Thomas Harter via Zoom. The student is expected to have very good knowledge of the R programming language (Python or Matlab is also acceptable) and QGIS and have a strong interest and background in statistical analysis in hydrology. The thesis is expected to be a publishable manuscript. The student must therefore also have excellent English technical writing skills. The student will be part of the Siskiyou research team at UC Davis and have opportunities to observe local stakeholder meetings in the Scott and Shasta River valleys to the degree that they will be held publically online.

English

Thomas Harter, University of California, Davis (remote online supervision) (thharter@ucdavis.edu)