Richard Dallison
Dŵr Uisce research conducted by researchers in our Bangor team, and published last month in Hydrological Sciences Journal, has used hydrological modelling to characterise and quantify the potentially implications of worst-case future climate change on river systems in Wales. The work uses the Soil and Water Assessment Tool (SWAT) hydrological model to project daily streamflow in five Welsh catchments (Clwyd, Conwy, Dyfi, Teifi, Tywi) between 2021 and 2080. The analysis has characterised changes in future average, high, and low streamflows, as well as water quality impacts for key indicators. The work takes a worst-case scenario approach in terms of future climate change, with pessimistic global emission forecasts (Representative Concentration Pathway 8.5), using the latest projections from the UK Met Office.
Nowhere will escape the impacts of future climate change, with one of the key implications of this being alterations to rainfall pattern characteristics, in turn impacting river flows. Not only problematic in terms of available water resources, these alterations in precipitation and streamflow regimes will all also have an impact on water quality. In Wales, surface waters (rivers and lakes) are relied upon for a variety of purposes, so understanding how changes in rainfall will impact on river systems is crucial. In addition, as recent events have shown, living in close proximity to our waterways brings about hazards, so gaining greater clarity on change in future high flow event characterises in particular is especially important.
While the results show that annual average flows see only a small decline in the catchments studied (4% to 13% reduction), the results of seasonal analysis of extreme flows are more concerning. As Figure 1 shows, the modelling work suggests that the severity and frequency of very low river flows will increase in Wales under future climate change, especially in summer and autumn. This could potentially cause problems for organisations and people who abstract water directly from rivers. In addition, the severity and frequency of very high streamflows, those most likely to lead to flooding, is set to increase in the winter and spring (Figure 1). Both of these alterations will likely require adaptation measures, in terms of ensuring sufficient water resource supplies, and protecting against flood damage, respectively.
Figure 1: Overview of the direction, magnitude and significance of annual and seasonal trends in projected future (2021–2080) extreme streamflows, as detected by Mann-Kendall trend analysis.
When looking at the water quality findings (shown in Figure 2), nitrogen, phosphorus, and suspended sediment concentrations are all shown to increase across almost all catchments and seasons, suggesting a marked decline in future water quality. Dissolved oxygen levels, important for healthy aquatic life, are shown to markedly decrease, with this being linked to increasing nutrient levels in rivers and increased water temperatures, due to warming air temperatures. The findings have economic and environmental implications, for water abstractors in particular, as water resources could become more unreliable, seasonal, and polluted.
Figure 2: Overview of the direction, magnitude and significance of annual and seasonal average trends in projected future (2021–2080) water quality concentrations, as detected by Mann-Kendall trend analysis.
The results demonstrate that although perceived to be a country abundant in water resources, Wales will not escape the impacts of climate change induced streamflow reductions, especially in summer and autumn. Conversely, in winter and spring it is likely that high flow events will become larger and more frequent. This exaggeration of current seasonal streamflow patterns will require careful management moving forward, especially when combined with water quality deterioration.
The full open-access article can be found on the Hydrological Sciences Journal website, while more information on the implications of the climate change work being conducted by the Dŵr Uisce Project can be found on the Future Water Resources page of our website.