Ecohydrology

One of the main objectives of the study presented is to characterize the hydrologic interactions between the uplands and the downstream irrigated valleys in semiarid watersheds of the southwestern United States. A combined, intensive field data collection and modeling, approach is being used for better understanding the hydrologic connectivity between the headwaters and traditionally-irrigated valleys in three watersheds of northern New Mexico. Study results show a strong hydrologic connectivity between surface water and groundwater in the lower agricultural valleys that follows a seasonal pattern, driven primarily by irrigation contributions to the shallow aquifer.  In one of the irrigated valleys, results showed that for separate irrigation events at the field scale, shallow aquifer recharge ranged from 1 to 230 mm and that for the cumulative irrigation season at the valley scale, aquifer recharge ranged from 1044 to 1350 mm yr-1. Runoff contributions from rain storms can also be a significant source of streamflow in these semiarid watersheds. A significant increase in river stage (0.3 m) was observed in response to runoff from a higher elevation frontal storm that yielded peak discharge of 17.9 m3 s-1 at a tributary monitoring station near the convergence with the Rio Grande. Also, preliminary results using a system dynamics model indicate a strong hydrologic connectivity between snow-melt driven runoff in the headwaters and the recharge of the shallow aquifer in the valley, mainly driven by the use of traditionally-irrigated agriculture systems. This study adds to the understanding of the interconnectedness of different hydrologic components and of the mechanisms of water distribution in semiarid landscapes.