The effect of interactions between rainfall patterns and land-cover change on flood peaks in upland peatlands

Flood processes in catchments are driven by a combination of rainfall and landscape characteristics. Upland peatlands are source areas of flooding but there is lack of understanding of how different rainfall intensities and temporal patterns may interact with land-cover configurations to influence flood peaks. Using spatially distributed (SD-) TOPMODEL we investigated these interactions for a case study peatland catchment. For each of four rainfall depths ranging from 20 mm to 50 mm, four storm rainfall patterns were applied (rainfall that was uniform, rainfall with an early peak intensity during the storm, middle peak and late peak). Late peak rainfall resulted in the highest river flow peaks at the catchment outlet studied, followed by middle and early rainfall peak patterns, while uniform rainfall through time gave the lowest flow peaks. A key factor was synchroneity of overland flow movement and concentration. The impact on river flow peaks of land-cover change on riparian zones and on gentle gradient slopes was larger than that for other parts of the catchment under different rainfall intensities and patterns. The impacts of land-cover change on proportional change in flood peaks in these sensitive areas became smaller when rainfall intensity increased, but absolute changes in flow peaks became larger. Land-cover change in sensitive areas under middle and late peak rainfall had a larger impact on river flow peaks than for early peak rainfall. It was possible to identify the ‘worst’ rainfall patterns for a particular case of land-cover change which may be useful for practitioners to help manage expectations of flood response to nature-based solutions.