To Burn or Not to Burn? A Case Study of Illilouette Basin

The state of California has a long history of fire suppression. At the same time, more than 60% of California's water comes from montane watersheds where fire suppression policies have drastically changed forest structure, and consequently water balance over time. Illilouette Creek Basin in Yosemite National Park is a unique watershed that lacks fire suppression since 1972 and has an extensive climatic, remote sensing, and hydrologic monitoring record that allows for fine spatiotemporal modeling. RHESSys, a distributed hydro-ecological model, was used to compare water balance between fire suppressed and fire unsuppressed IllIillouete Creek Basin. In the first modeling step, a fire suppressed landscape prior to 1972 was compared to a historical fire landscape of Illilouette Creek Basin, using observed climatic inputs from 1972 to 2012. In the second modeling step, the same comparison was made, however within the context of future climate; ensembles of future climate predictions for both medium and severe emission scenarios were used as model inputs for a period from 2030 to 2070. Results show that introducing natural fires to a montane watershed increases streamflow and soil storage, and decreases transpiration for both historical and future climates. The results of this study can aid forest managers in making decisions within the context of future climate. While natural fires will continue increasing downstream water yields, there will be more stress on the landscape due to hotter climate with more variable precipitation pattern.