In Denmark there are approximately 65,000 km of rivers. Whether a river has a good condition is among other things determined on basis of the fauna in the river. In this project trout is being inves-tigated, because of its very specific requirements for their habitat. A self-reproducing trout popula-tion indicates a good ecological state in the river. In Denmark work is being made to improve the rivers but knowledge about how climate changes will affect the individual rivers and their condition is limited.
This project is based on the river Kastbjerg Å that has its outlet in Mariager Fjord. Firstly it is inves-tigated whether or not the climate will change around Kastbjerg Å and if so how the changes will affect the trout habitats. The study is made based on the following hypothesis: Changes in the cli-mate will result in less favorable physical conditions for trout in the future.
The hypothesis is investigated using a rainfall-runoff model (NAM), which is bias corrected with the delta change method to simulate future climate based on historical data. A series of climate simula-tions made with different climate models so that the variation in estimations of the future is exam-ined. The estimates of the future are analyzed in relation to historical data from Kastbjerg Å. In or-der to estimate if the future climate will result in smaller trout habitats the habitat model CASiMiR is used to assess how the trout habitats will be altered at different discharges in a section of the river near the outlet.
Climate estimations made based on 11 climate models showed a great variation and thus there is a great uncertainty regarding, how the future climate is expected to be and thereby also whether the suitable trout habitats will be smaller in the future. If the future will become as projected by climate model ARPEGE-RM5.1 the changes in mean discharge will mean smaller habitat areas for trout fry and adults and slightly lager areas for juvenile. If the future on the other hand follows ECHAM5-REMO or ECHAM5-HIRHAM4 it will mean smaller habitat areas at mean discharge for juvenile trout and larger habitat areas for fry and adult trout.