Pumping groundwater for uses like irrigation has decreased streamflow and plant water availability in the United States, according to the first large-scale simulation of surface water systems' sensitivity to water changes below ground. The results demonstrate an often-ignored pathway through which human development has already altered the hydrologic landscape, and they offer a better understanding of the connection between ground and surface waters that could improve researchers' ability to manage both. Groundwater declines, a global problem, have received much attention. In the U.S. alone, more than one thousand cubic kilometers of groundwater have been lost from underground storage in the last hundred years. Key gaps remain in researchers' understanding of how these subsurface changes impact natural hydrologic processes, however. Here, Laura Condon and Maxwell Reed attempted to isolate the impact of groundwater storage losses on water processes in watersheds. Through a high-resolution modeling approach, they evaluated the impact of 100 years of groundwater declines across the continental U.S on streamflow and plant water availability. Watershed response to groundwater storage changes varied with season, climate, and hydrologic setting, but typically, groundwater loss led to stream flow decline - a more than 50% decline in some streams. Evapotranspiration also declined with groundwater loss in a pattern more closely tied to water table depth. "Given the ubiquity of groundwater pumping across the globe...it is critical that hydrologists work to understand the behavior of developed systems with the same physical rigor applied to natural ones," the authors say. Hydrologic models currently overlook linkages between ground and surface water systems, which needs to change.