Developing Tree-Ring Based Streamflow Reconstructions for Large and Complex River Basins

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This project analyses the use of tree-ring derived streamflow information as an alternative technique to develop long-term records of river streamflow in temperate, complex river-basins. Better and longer stream-flow records will help improve water resource management in large and complex watersheds experiencing and anticipating drought and water supply shortages. In places where measured runoff records are limited, tree-ring based streamflow records can be used to understand the range of possible variability and to therefore improve water management planning and modeling. This technique has mostly been used in semi-arid environments with relatively simple surface hydrology. This project implements and analyses tree-ring based streamflow modeling techniques in temperate, hydrologically complex watersheds, to assess its effectiveness, and thereby improving drought mitigation in those basins. This research will be conducted in collaboration with local stakeholders, and has the potential to inform local water management plans, fish conservation, and ongoing negotiations of water and resource rights. Technical workshops will build capacity for stakeholders to incorporate these new records into their own decision-making framework. The project provides field and academic learning opportunities for an undergraduate student and supports the continuing research program of an early career female Postdoctoral Research Scientist. Large temperate watersheds are increasingly susceptible to the impacts of drought, but their complex hydrology complicates the application of flow reconstruction to water supply forecasting. To accomplish meaningful tree-ring modeling in these basins, where multiple, shifting sources of runoff across several sub-basins mean that water management is reliant on seasonal streamflow information, this project directly targets drought-season runoff and decomposes the study watershed basin into independent main-stem and sub-basin reconstructions. This project will compare a large network of tree-ring chronologies with meteorological, gridded climate, and instrumental streamflow data from the basin main-stem and sub-basin gauges. Using these relationships as a guide for targeted chronology resampling, paleoclimate reconstructions of past summer runoff and drought will be developed for each basin spanning the last several centuries. During the summer season a combination of snowmelt, air temperatures, and rainfall determine streamflow and each of these factors is also linked to radial tree growth. The reconstructions will be statistically compared against independent estimates of past hydro-climate variability, model simulations, and independently developed climate fields to determine whether recent droughts have been exceptional in the last several centuries, and whether medium- and long-term internal hydro-climate variability contains a forced anthropogenic signal. Updated chronologies will permit examination of a recent extreme drought event and estimates of the probability of similar-magnitude droughts in the future. By targeting one of the most complex river basins in the world, the Fraser River Basin (FRB), this project provides a sound framework for enhancing water management in temperate watersheds in the United States and around the globe.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.