Coupled community cohesion and surface water hydrology determinants of groundwater use sustainability

Water table elevations are dropping in irrigated locations of the western U.S. and the world where use exceeds recharge. Along the Rio Grande, community irrigation systems have been developed that are particularly suited to high interannual precipitation variability. These same systems that efficiently and equitable allocate surface irrigation water seem to also generate feedback loops that balance groundwater recharge with use. To identify drivers of groundwater sustainability, we studied the coupled human and natural system components of surface water - groundwater interactions at distinctive sites along the Rio Grande: vibrant community irrigation systems of northern New Mexico; separately controlled surface and groundwater irrigation systems of southern New Mexico; and groundwater irrigation systems that had entirely lost their historic community surface irrigation systems in northern Chihuahua, Mexico. At the northern New Mexico site we found both the hydrology and the community irrigation system generate positive feedback loops for sustainable groundwater and for return flow to the river that benefits downstream users. In southern New Mexico, positive feedbacks of reduced irrigation district surface deliveries lead to more groundwater pumping that in turn causes less efficient surface delivery, additional pumping and stressed groundwater systems. At the sites in Mexico, lack of community cohesion coupled with decades of groundwater pumping has led to negative feedbacks where additional pumping causes drops in groundwater levels that increase pumping costs and reduce the rate of groundwater declines. In ongoing work, we are using socio-cultural and hydrological data to inform a system dynamics model that will identify groundwater sustainability tipping points in terms of community cohesion and the balance between irrigation water use and groundwater recharge in surface water connected systems.