Land use change and hydrological response in the Camel catchment, Cornwall

Abstract The paper attempts to determine the extent to which rainfall trends and land use changes influence the river flow regime and flood response of a predominantly agricultural catchment (210 km 2 ) in southwest England. Temporal changes in daily rainfall totals were analysed over annual, seasonal and monthly timescales but although annual average October rainfalls exhibited a weak rising trend ( r =0.3, p >0.05), no long-term patterns were observed. Analysis of daily mean discharge data for the River Camel over the period 1965–2000, using the Gumbel distribution, revealed an increase in the magnitude and frequency of peak flows. Land use changes were examined using Agricultural Census Data for 1969, 1979, 1988, 1997 and 2000. Both the number of stock and the area under cereals increased from 1969 to 1997, but cereal production declined substantially between 1997 and 2000. Spatial response patterns were also examined through a comparison of the flow response of the entire Camel catchment with its more complex land use, with the predominantly pastoral De Lank headwater sub-catchment (22 km 2 ), to ascertain the amount of change due to increased livestock numbers alone. No single factor was found to be responsible for the increases in flood frequency and magnitude in the River Camel. Rather, long-term changes in the response of the Camel system appear to emanate from the cumulative impact of subtle changes in climate, combined with increased farming activity plus urban expansion. The paper highlights the inherent difficulties of attempting to disentangle the precise effects of individual land uses on flood responses at the catchment scale and underlines the need for a holistic approach to the management of floods. By the same token, sustainable catchment management can only be achieved through greater awareness of the potential for complex, small-scale land use decisions to result in large-scale hydrological changes.