Grid-based simulation of river flows in Northern Ireland: model performance and future flow changes

Study Region: Northern Ireland (NI), and sub-catchments in the Republic of Ireland that drain to NI rivers. Study Focus: Information on the potential future impacts of climate change on river flows is necessary for adaptation planning. There have been many such studies for Great Britain, but fewer for NI. Here, a grid-based hydrological model is configured for NI, and used to investigate changes in seasonal mean, extreme high and extreme low flows. New Hydrological Insights: When driven by observed climate data, the model shows good performance for a wide range of catchments, particularly where artificial influences are limited. When driven by ensemble data from the UKCP18 Regional (12km) projections, model performance for the baseline period (1981-2010) is similar to that using observed data, especially when using a simple precipitation bias-correction. Model projections for a future time-slice (2051-2080) generally suggest decreases in spring–autumn mean flows, especially in summer (median -44%), but possible increases in winter mean flows (median 9%), with some variation between ensemble members, particularly in winter when some show large increases to the west. Consistent with this are large projected reductions in 10-year return period low flows everywhere (median -45%), and large increases in 10-year return period high flows for some locations and ensemble members (median 16%). Future applications could include expanding the range of climate data applied.