Effects of Future Climate Change on a River Habitat in an Italian Alpine Catchment

Abstract

The impact of prospective climate change on the hydrological and ecological status of the mountain stretch of the Serio river (ca. 300 km2) in the Northern Italian Alps was investigated. A hydrological model was used to mimic theflow regime, and experimental suitability curves were used to assess weighted usable area (WUA) for brown trout (Salmo trutta) in different stages (adult, young, and spawning), and four macroinvertebrates families (Leuctridae, Heptageniidae, Limnephilidae, and Limoniidae). Discharge-WUA curves were obtained using instream flow incremental methodology/physical habitat simulation system (IFIM-PHABSIM), and a seasonal WUA assessment was carried out. The future (until 2100) hydrological cycle was projected using outputs from two general circulation models from Assessment Report 5 of the Intergovernmental Panel on Climate Change (IPCC). The results display a potential for a large flow decrease yearly, until −60% at 2050 and −56% at 2090. Spring melt peaks will be largely dampened, with the largest projected decrease of −60% in 2050 and −66% in 2090. Also fall flows will be largely smoothed, down to −70% for 2050 and −56% for 2090. To quantify habitat quality, a specific quantile WUA20%, was used and exceeded presently for 292 days in a year, and the percentage of critical days nc% when WUA<WUA20%. Adult trouts will have decreasing nc% yearly (from 20% now to down to 13% in 2090), increasing in winter and spring and decreasing in fall. Young trouts will have decreasing nc% yearly (from 20% now to down to 2% in 2040 and 2090), but increasing in winter. Spawning, occurring in winter, will have lower nc% (from 16% now, to down to 8% in 2090). Macroinvertebrate families will have constant nc% yearly, unless for Leuctridae (from 20% now to up to 38% in 2050), and noticeable decrease of nc% in winter for Leuctridae until 2090, increase in spring and summer, and decrease in fall for all families until 2090. Correlation analysis of the WUA against weather and hydrological variables displayed that temperature is the most influencing variable, decreasing habitat suitability for all species in fall, and increasing suitability in spring, unless for young trouts.