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Analysis of the spatial and temporal variability of terrestrial water storage and snowpack in the Pacific Northwestern United States
Citation:
Eric A., S., S. Leibowitz, J. Wigington, P. Sopan, AND R. Comeleo. Analysis of the spatial and temporal variability of terrestrial water storage and snowpack in the Pacific Northwestern United States. Presented at American Geophysical Union, December 03 - 07, 2012.
Impact/Purpose:
The climate of the Pacific Northwestern (PNW) United States provides a surplus of water during the wet winter months. However during the dry summer months water supply is at its minimum while demand is at its maximum. Because the supply and demand of water in the PNW are seasonally misaligned, it is critical to understand water storage in the region. Much of the water available during the summer is winter surplus stored as terrestrial water and mountain snowpack. Snowmelt recharges terrestrial water and, despite its importance, a basin-scale approach to understanding inter-connections between snowmelt and terrestrial water does not exist for the PNW. To realize this goal, novel techniques that provide new measurements of water fluxes are needed. Geophysical monitoring can accomplish this at local scales, but are logistically unable to provide data at broad spatial scales. Data from NASA’s Gravity Recovery and Climate Experiment (GRACE) satellite provide measurements of the Earth’s water storage at the global scale. Analysis of GRACE data at the regional scale helps provide spatial and temporal estimates for terrestrial and snow water fluxes. This more nuanced understanding of the fluxes of water across the landscape can help identify scarcity with regards to time and space. In turn, this knowledge can help develop adaptive use and management strategies to deal with potential scarcity in present and projected climates The research described builds upon efforts in the Freshwater Ecology Branch of the EPA to develop and apply a hydrologic classification scheme for the PNW. The goal of this classification system is to provide a basic understanding of streamflow in each classification unit. However one of the limiting components is understanding the fluxes of water storage (terrestrial and snow). This research will aid in improving the classification system.
Description:
The spatial and temporal variability of terrestrial water storage and snowpack in the Pacific Northwest (PNW) was analyzed for water years 2001–2010 using measurements from the Gravity Recovery and Climate Experiment (GRACE) instrument. GRACE provides remotely-sensed measurements of monthly fluxes in terrestrial water storage (TWS). In the PNW between 50-60% of annual precipitation falls as snow during the winter and spring months. Melt water from this snowpack is a key component of the hydrologic cycle that recharges aquifers and sustains streams during the more arid summer months, when demand for water is high. The motivation for this research is to improve our understanding of the spatial and temporal connections between variability in winter snowpack and TWS in the PNW. Initial results show distinct spatial patterns of intra-annual TWS variability running both North-to-South and West-to-East, and partially suggest the influence of seasonal snow water storage. The influence of fluxes in snow storage was removed from the GRACE data using a regionally validated temperature-precipitation-based snow model. Analytic and statistical assessment of snow water and GRACE data are presented. Future work including soil moisture, surface water and human consumptive use will further improve our understanding of groundwater variability in the region. These methods and initial results provide a novel approach to understanding the timing and location of regional storage patterns of TWS. This in turn will be applied to hydrologic classification frameworks for the region and used to identify snowpack characteristics indicative of potential water scarcity in the PNW.