Western USA Groundwater Regulation and Infrastructure for Irrigated Agriculture

More than 2/3 of US groundwater use is attributed to the western 17 states—an area with many key regions for agricultural production and unsustainable groundwater pumping. Although there is increasing acknowledgement of the importance of more intensive management, the western US remains a patchwork of diverse and imperfect governance and legal strategies. Water quantity is regulated at the state level, so obtaining the right to withdrawal groundwater ("permitting") can be vastly different from one state to the next. Much attention has been devoted to quantifying rates of groundwater depletion across the west, but little is known about the spatiotemporal patterns of groundwater drilling and permitting. While many local agencies have a plethora of knowledge about groundwater infrastructure and regulation, most of this knowledge is hearsay or locally disseminated, and it is difficult to obtain groundwater data—physical and legal—comprehensively across large regions. Here we explore and map groundwater infrastructure and permitting approaches across the western US, focusing specifically on the importance of groundwater to sustaining agriculture in key producing regions (e.g., High Plains). We analyze over four million groundwater-drilling records and relate these data to geographically defined subareas ("special permitting areas") within states that have been designated legally due to concerns about the effects of groundwater withdrawal. Our work indicates that the default set of laws and regulations within states is often of lesser importance because of the extent of and legal powers granted within special permitting areas. We also find areas with significant groundwater drilling that do not fall within special permitting areas, indicating that special permitting areas are not all-inclusive of intensive use. Our work has practical implications, highlighting the effects of regionalized laws on a resource not confined physically by jurisdictional boundaries.