Where will the flow go after the snow? Case study of the Diguillín Watershed, Central Chile

There is broad consensus that mountains are a key vulnerability for water resources security in a changing climate. Advances in telemetry and remote sensing have allowed us to further our understanding of surface processes, such as precipitation variability, forest evapotranspiration (ET) fluxes, and snow cover and real-time snow water equivalent (SWE) measurements. However, we are far less advanced in our understanding of surface water-groundwater interactions and deep subsurface flow in the mountains, owing to the assumption that mountain bedrock is impermeable. This limits our ability to project the holistic hydrologic response to a warming climate. We present a case study in which the mountain, and the alpine watershed that drains it, is by no means impermeable. The Diguillín watershed, comprised of the Alto Diguillín and Renegado subwatersheds, is a highly permeable volcanic basin typical of the Andes Mountain range, but also analogous to the California and Oregon Cascades, which experiences a Mediterrenean climate and significant interannual variability in precipitation related to ENSO. The abundance of springs indicative of a large volume of subsurface storage in both subwatersheds compensate for the seasonally dry summers and the interannually dry years, which is a key source of irrigation and drinking water in the summer for the communities in the Chilean Central Valley. We develop a 3-D integrated hydrologic model of the system, perform successive warming scenarios, and track the cascading response of snowpack, recharge, runoff, and groundwater storage. We also present a forest management scenario as a potential climate change mitigation strategy for augmenting recharge in headwaters systems. These results represent initial steps towards better understanding where the flow will go after the snow in permeable alpine systems.