Impact of Groundwater Management on Drought Responses in the Southwest

Long-term groundwater declines driven by human consumption are occurring around the world; however, the extent these trends are accelerated by drought conditions is less clear. In arid locations with limited reliance on surface water supplies, are groundwater declines still sensitive to drought conditions, or are trends driven solely by human con-sumption? Here, we use Arizona in the southwestern United States to explore drought response in a heavily groundwater-dependent arid system. We use a series of statewide, regional, and local case studies to perform a qualitative analysis on well data from 2000 to 2022 to illustrate how spatial variability in land use, surface water access, groundwater management, and policy impact groundwater. Areas with major characteristics are identified, and linear regression is performed on groundwater levels for each area over time. Across the state, groundwater levels have been declining for more than 50 years and persistent groundwater declines are noted in most large regions. Severe drought can further accelerate depletions beyond the long-term trends, especially in groundwater-dominated areas without pumping regulations. However, this is not the case everywhere. In major metropolitan areas, and in agriculturally dominated locations with direct access to regional surface water supplies (Colorado River), drought response is significantly dampened. In some locations, we show no added drawdown during drought or even a slight recovery. Overall, our results show that long-term groundwater declines can be exacerbated during drought periods, but spatial differences in our case studies highlight the importance of diverse water sources and local management decisions. Instances of groundwater recovery highlight the potential for sustainable groundwater management in water limited areas. SIGNIFICANCE STATEMENT: Groundwater levels are declining in many parts of the world. In many cases, declining trends are driven by sustained over pumping, and it is unclear how big an impact drought has relative to these human effects. Here, we perform a qualitative case study analysis to explore the impact of meteorological drought on groundwater levels in Arizona to better understand whether weather conditions are a major factor in accelerating groundwater declines. Arizona provides an excellent testing ground for this research due to its arid climate and groundwater dependence, as well as the spatial variability in groundwater governance and water availability.We use case studies with multiple major characteristics to illustrate the impact that land use, surface water access, groundwater management, and policy can have on groundwater outcomes. Our results show that drought does not always induce groundwater declines. Local groundwater policy and the diversity of the water supply portfolio can have a big impact on outcomes. Our findings are relevant for other arid locations struggling with groundwater sustainability and illustrate that there are multiple pathways to improving groundwater resilience.