Recharge and frozen ground in the PNW

Science Center Objects

The Issue: Seasonally frozen ground occurs over approximately one-third of the contiguous United States, and the extent and duration of frozen ground have been decreasing as a result of global warming. In semi-arid regions such as the Columbia Plateau and Snake River Plain in the Pacific Northwest, nearly all natural recharge occurs between October and March when intermittent or seasonal frozen-ground is commonplace and precipitation is relatively abundant. Thus, there is a potentially significant but poorly understood connection between climate change, frozen ground, and groundwater recharge to principal aquifers in the Pacific Northwest.

How USGS will help: This investigation will improve our understanding and our ability to monitor the linkages between climate change, frozen ground, and groundwater recharge to principal aquifers in the Pacific Northwest, including the Columbia Plateau and eastern Snake River Plain Regional Aquifer Systems.

9722-E3X - Monitoring Effects of Climate Change on Groundwater Recharge in the Pacific Northwest through Remote Sensing of Frozen Ground - Completed FY2014

Problem - Seasonally frozen ground occurs over approximately one-third of the contiguous United States, and the temporal and spatial distribution of frozen ground has been changing as a result of global warming. Increased runoff as a result of frozen ground has been well documented, and a simple water-balance evaluation suggests a corresponding decrease in groundwater recharge due to rejected infiltration. In semi-arid regions such as the Columbia Plateau and Snake River Plain in the Pacific Northwest, nearly all natural recharge occurs between October and March when intermittent or seasonal frozen ground is commonplace and precipitation is relatively abundant. Thus, there is a potentially significant but poorly understood connection between climate change, frozen ground, and groundwater recharge to principal aquifers in the Pacific Northwest.

Objectives - This investigation will improve our understanding and our ability to monitor the linkages between climate change, frozen ground, and groundwater recharge to principal aquifers in the Pacific Northwest. The scope of the investigation will include: 1) evaluating different remote-sensing-based methods to monitor freeze-thaw cycles in the study area, 2) incorporating a frozen-soil algorithm into the USGS Groundwater Surface Water Flow (GSFLOW) model, 3) analyzing recent (about the past 20 years) historical trends in frozen-ground and groundwater recharge across the study area, and 4) developing a first-tier strategy for monitoring trends in groundwater recharge from precipitation over time in areas subject to frozen ground. The intensive study areas include the Potholes Reservoir basin in Washington and the Reynolds Creek Experimental Watershed in Idaho, located within the Columbia Plateau and eastern Snake River Plain Regional Aquifer Systems, respectively.

Relevance and Benefits - This study is consistent with the national USGS mission and goals identified in the USGS Science Strategy document. The study will help clarify the record and assess consequences of climate variability and change on groundwater availability in the semi-arid regions of the Pacific Northwest. The study will provide information that advances the understanding of hydrologic processes, will enhance the USGS modeling capability for the northern tier of the US, and will develop a framework for future monitoring of climate change impacts on groundwater resources.

Approach - The primary tasks in this approach are processing historical remote sensing imagery using available algorithms to create time series of frozen-soil conditions; evaluating the accuracy of the method(s) using available soil temperature, frost tube, and similar data; assisting NRP Researchers with incorporating a frozen-soil algorithm into PRMS/GSFLOW; estimating historical groundwater recharge with the PRMS at selected locations; and evaluating the linkages between climate change, frozen ground, and recharge to develop a feasible strategy for monitoring trends in groundwater recharge as influenced by frozen ground.