Extreme rainfall and its impact on cultivated landscapes with particular reference to Britain

摘要

Extreme rainfall events (> 50 mm day(-1)) falling on cultivated land which is relatively bare of vegetation cover, typically give rise to networks of rills and gullies with ephemeral gullies in depressions and valley bottoms. Farming practices such as the removal of field boundaries, the presence of wheelings and rolled surfaces encourage runoff. The coincidence of vulnerable crops such as maize, potatoes and sugar beet with erodible soils and sloping sites may lead to high rates of erosion associated with single events or wet seasons. Not all extreme rainfall events lead to runoff and erosion, this depends on timing with respect to the growing crop. Rates of erosion associated with extreme events may be high but when placed in a long-term temporal context, they tend to be quite low. Extreme events frequently lead to off-site impacts most notably muddy flooding of properties and the pollution of watercourses. Landscapes may be protected from extreme events by standard soil conservation techniques; off-site impacts may similarly be alleviated by flood-protection measures. In both cases, the challenge is to put in place adequate economic incentives, social pressures and governmental policy frameworks to incentivise effective action. Predicted rainfall changes in the future include wetter winters and increases in rain per rain-day. In this case, the risk of erosion on cultivated land will increase. However, erosion mitigation strategies should still address the issue of the incidence of high-risk crops on vulnerable sites. Copyright (c) 2015 John Wiley & Sons, Ltd.