Short intense downpours are becoming more common due to climate change. In towns and cities, with large areas of non-porous surfaces, heavy rainfall can only run over rather than into the ground. This can cause surface water flooding at any time of the year. In South Wales, towns like Maesteg, Merthyr, Aberdare, Treorchy and Ebbw Vale can be affected by flash floods creating dangerous torrents in streams or even along roads. The steep slopes in these areas make this problem worse.

Welsh rivers are at a high risk of flooding during storms. A big problem is that we have built more houses on their floodplains. This has created an even higher risk downstream by stopping flood water storage and redirecting it onto the next down-valley town. Rivers like the Severn in Newtown, the Afon Conwy in Llawrst, Taff in Pontypridd and the River Wye in Builth Wells have all flooded in recent years.

Sea levels are rising. Storms can cause waves and a surge of higher tides that threaten settlements and farms on the low lying coasts of South East and North East Wales. Towyn, near Rhyl which flooded in 1990, and the low, flat coastline east of Cardiff up to the M4 Severn Bridge are the most at-risk areas in Wales.