RECONSTRUCTING RUNOFF IN NORTHERN NEW MEXICO BASED ON DAILY PRISM PRECIPITATION

Groundwater is a crucial source of water for most of New Mexico, therefore understanding the rate and distribution of recharge to aquifers is crucial for sustainable development. The PyRANA (Python Recharge Assessment for New Mexico Aquifers) model was designed to estimate aquifer recharge by tracking the soil-water balance through time over the entire state. The main inputs are daily gridded precipitation data (PRISM), reference evapotranspiration (GADGET), and soil data. However, previous versions neglected focused recharge, which is an important contribution to groundwater recharge. Xu (2018) used a rainfall/runoff data set from Walnut Gulch, AZ to create a stochastic runoff generation algorithm, enabling the model to incorporate both diffuse recharge and transmission losses in first order and higher order basins. She also used rain gauge data to systematically adjust PRISM daily rainfall amounts. However, the factors influencing runoff in semiarid grass- and shrublands are different than those in wooded mountainous terrains. We have performed a similar analysis using rainfall and runoff data sets from the Santa Fe area and the Valles Caldera, and observed distinct differences from Walnut Gulch. All three mountainous basins analyzed exhibited clear relationships between rainfall and runoff with very similar slopes. The relationships for the three mountainous basins resembled each other much more than they resembled that of the Walnut Gulch area. And the systematic difference between PRISM and gauge data is somewhat different in the two regions. In the Walnut Gulch area, rainfall intensity is influential in runoff-generation process, but it appears to be much less influential in mountainous areas of northern New Mexico. These results support the hypothesis that two distinct rainfall/runoff relationships are required to reliably track soil moisture in these widely differing climate/vegetation zones.