Seventy years of drought impacts on resilience and groundwater storage across New Mexico, USA

Abstract:

New Mexico has experienced intermittent drought during the late 20^th century and has arguably been in a megadrought for nearly two decades. To understand long-term resilience of groundwater basins, we present a state-wide, aquifer-by-aquifer groundwater storage change analysis from the 1950s to the late 2010s. New Mexico is a rural state with diverse hydrogeology, access to surface water, and water management. While New Mexico operates under uniform prior appropriations law, the implementation and enforcement vary widely, from poor reporting and little to no enforcement in parts of New Mexico to fully adjudicated and carefully managed basin. This diversity of supply, use, and regulations, combined with historical, state-wide water level measurements allowed us to understand the controls on the resilience of groundwater-dependent regions during drought. We compiled and reviewed water-level data from all high quality sources, and found the decadal median water level of each well. Water levels were interpolated using inverse distance weighting or kriging. Decadal water level surfaces were differenced. Changes in water level were summed and multiplied by regional specific yields or specific storages to determine groundwater storage changes We also discussed regional water management schemes with state regulators and local water managers. From the 1950s to the present, we observed changes of between 0 km³ to 16 km³. 30% of the state lacked sufficient data. Regions with the smallest storage changes either had low populations or access to surface water. Regions with the largest (>2.5 km³) storage changes had high populations or intensive irrigated agriculture without recharge. Storage declines in basins with a mixed water sources and active water management were stopped or even reversed. Basins with passive or legally incoherent water management had the most dramatic declines. Basins that lack surface water and have intensive agriculture show the largest declines but simultaneously show little change in rates of decline during drought. We argue that these basins are both the most fragile and the least impacted by drought—they will simply be pumped dry under current water management strategies regardless of external environmental pressures