European and UK policies towards land management increase the likelihood of flooding, according to George Monbiot:-
The story begins with a group of visionary farmers at Pontbren, in the headwaters of Britain's longest river, the Severn. In the 1990s they realised that the usual hill-farming strategy – loading the land with more and bigger sheep, grubbing up the trees and hedges, digging more drains – wasn't working. It made no economic sense, the animals had nowhere to shelter, and the farmers were breaking their backs to wreck their own land.
So they devised something beautiful. They began planting shelter belts of trees along the contours. They stopped draining the wettest ground and built ponds to catch the water instead. They cut and chipped some of the wood they grew to make bedding for their animals, which meant that they no longer spent a fortune buying straw. Then they used the composted bedding, in a perfect closed loop, to cultivate more trees.
One day a government consultant was walking over their fields during a rainstorm. He noticed something that fascinated him. The water flashing off the land suddenly disappeared when it reached the belts of trees the farmers had planted. This prompted a major research programme, which produced the following astonishing results: water sinks into the soil under trees at 67 times the rate at which it sinks into the soil under grass. The roots of the trees provide channels down which the water flows, deep into the ground. The soil there becomes a sponge, a reservoir which sucks up water and then releases it slowly. In the pastures, by contrast, the small sharp hooves of the sheep puddle the ground, making it almost impermeable, a hard pan off which the rain gushes.
One of the research papers estimates that – even though only 5% of the Pontbren land has been reforested – if all the farmers in the catchment did the same thing, flooding peaks downstream would be reduced by about 29%. Full reforestation would reduce the peaks by about 50%. For the residents of Shrewsbury, Gloucester and the other towns ravaged by endless Severn floods, that means – more or less – problem solved.