Hybrid Mechanistic-Statistical Approach to High Resolution Water Temperature and Flow Models: II. Vegetation x Climate Scenarios

Forest practices can exacerbate or moderate risks to coldwater habitat (CWH) related to climate variability, wildfire, and forest disease. We applied a high-resolution hybrid mechanistic/statistical stream network (SSN) model to evaluate effects of riparian management practices and future climate in the Upper Rogue, OR basin on flow and temperature. We compared recent (1990 – 2018) and 2040’s climate scenarios for temperature and precipitation, considering both average, minimum, and maximum based on the Palmer Drought Severity Index. Riparian management conditions included historical reference, current vegetation (CV), and vegetation managed via the Oregon Forest Practices (FPA) Act which prescribes minimum forest buffer widths of 100-110 ft for fish-bearing (F) and 35 ft for non fish-bearing (NF) streams. Under the 2040s scenario, flow will be lost by the end of August in 79% of F reaches and 93% of NF reaches in a dry year. Interannual variability of CWH extent will increase during the 2040s. In cool/wet years, core F CWH (< 16 0C) extent will decline by ~ 10 % while habitat > 18 0C will increase under the FPA scenario as compared to the current vegetation regime. For 2040s flowing streams under mean climate, the extent of NF reaches with <15 °C 7DADM will be reduced under the FPA to 2.2% of reaches as compared to current vegetation (4.5 % of reaches). Thus, reduced protections prescribed for NF streams will impact downstream CWH as well as headwater NF habitat.