Past Groundwater Drought in the North American Cordillera.

Groundwater level records in North America are relatively short (<60 years), preventing long‐term analysis of historical changes in groundwater levels associated with drought. In this study, tree ring widths are used to reconstruct groundwater levels in three regions in the North American Cordillera: Central British Columbia (BC), Canada, the Southern Interior Region of BC, and the San Luis Valley in Colorado, USA. Periods with severe drought conditions, identified using regime shift and threshold analyses were: 1890–1900 and 1950–1970 in Colorado, around 1920–1940 in the BC Interior, and 1935–1945 in Central BC. The groundwater level reconstructions are correlated with several climate indices and have similar regime shifts as identified in streamflow and drought records. The groundwater level reconstructions are strongly related to winter snowpack, suggesting that the observed trend of declining snowpack in recent years may lead to declining groundwater availability in these regions. Plain Language Summary: Long‐term records of observed groundwater levels are necessary to understand how groundwater resources may change over time. Unfortunately, many records in North America are considerably short (less than 60 years). This study uses tree ring widths to reconstruct groundwater levels in three mountainous regions of the North American Cordillera. We identify severe past groundwater drought conditions during: 1890–1900 and 1950–1970 in Colorado, around 1920–1940 in the British Columbia (BC) Interior, and 1935–1945 in Central BC, with some of these droughts being more severe than any that occurred in the observed records. We find that periods of groundwater drought in these regions are likely related to reduced winter snowpack, suggesting that future groundwater resources may be at risk, as climate change is already causing declining snowpack in these regions. Key Points: Tree ring records were used to reconstruct groundwater levels for three regions in the North American Cordillera from 1850 to 2002Some historical droughts are more severe than observed droughts, suggesting severe droughts could occur in the futureFuture groundwater levels in these regions will likely be negatively impacted by warming temperatures and declining snowpacks [ABSTRACT FROM AUTHOR]