Around 45,000 properties in Northern Ireland are at risk of flooding as the country braces for stormier and more extreme weather, a report said.
The main road between Coupar Angus and Blairgowrie has been closed by flooding.
Rail services have been called off, roads have been left impassable and a school was forced to shut after major flooding hit Perthshire.
Wales could face heavy downpours on Wednesday after a severe weather warning was issued in parts of the country.
Communities along the banks of the River Almond will be given greater protection from flooding following the opening of a £25 million protection scheme.
Flash flooding has hit a wildfire-scarred area of Northern California, forcing officials to deploy swift water rescue teams to save people stuck in vehicles and rescue them from homes.
Fifteen flood warnings covering almost all of Tayside's main rivers and several of the region's biggest towns are in force following an overnight downpour.
A storm named Diana has brought strong winds and heavy rain to parts of the UK as a number of flood warnings were issued for the South West.
Flood warnings have been issued for the rivers Tay, Isla, Lyon and Earn as Tayside endures a downpour of rain - with a local caravan park and golf course both said to be at risk.
At least 12 people have been killed after storms lashed Sicily, causing torrential floods.