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Many upland headwaters of the UK drain areas of blanket peat, much of which has been degraded through atmospheric deposition of pollutants, vegetation change, peat extraction, artificial drainage and erosion. These areas are increasingly the focus of interventions to restore some of the multiple-benefits lost through degradation. Understanding their runoff generation processes underpins analysis of their wider benefits including their potential to mitigate downstream flooding.Using a series of multivariate analysis techniques we examine controls on storm runoff in ten blanket peat catchments of 0.2-3.9 hectares all within 5 km of one another. We find that: 1) rainfall intensity is the dominant hydro-meteorological driver for both magnitude and timing of peak discharge for all ten catchments, with antecedent rainfall only relevant in small storms; 2) most of the inter-catchment variability in discharge predictability from rainfall can be explained by catchment characteristics, particularly catchment area; 3) runoff responses, particularly in small storms, are sensitive to scale even in an apparently homogenous and saturation-excess overland flow dominated peatland landscape; 4) peak discharge in large storms is strongly controlled by attenuation processes associated with the travel time distribution, and thus drainage network geometry; 5) peak discharge in smaller storms underlines the importance of hydrological connectivity at scales Together these results suggest a switching in rainfall-runoff behavior within these catchments where peak discharge is controlled by: catchment storage, connectivity and antecedent conditions in small storms; but runoff attenuation, travel time and thus and network structure and scale in larger storms. In the context of Natural Flood Management, our findings suggest that enhancing depression storage by creating distributed shallow peatland pools in addition to existing restoration methods could raise the threshold storm size below which catchment storage, antecedent conditions and connectivity remain important. However, changes in surface roughness and other measures that target runoff velocities are likely to be more effective in the largest (and thus most flood relevant) storms.

Upland blanket peat is widespread in the headwaters of UK catchments, but much of it has been degraded through atmospheric pollution, vegetation change and erosion. Runoff generation in these headwaters is an important element of downstream flood risk and these areas are increasingly the focus of interventions to restore the peat ecosystem and to potentially mitigate downstream flooding. Here we use a series of multivariate analysis techniques to examine controls on storm runoff behavior within and between ten blanket peat catchments all within 5 km of one another and ranging in size from 0.2-3.9 hectares. We find that: 1) for all 10 catchments, rainfall intensity is the dominant driver for both magnitude and timing of peak discharge, and that total and antecedent rainfall is important for peak discharge only in small storms; 2) there is considerable inter-catchment variability in: runoff coefficient, lag time, peak runoff, and their predictability from rainfall; however, 3) a significant fraction of the inter-catchment variability can be explained by catchment characteristics, particularly catchment area; and 4) catchment controls on peak discharge and runoff coefficient for small storms highlight the importance of storage and connectivity while those for large events suggest that surface flow attenuation dominates. Together these results suggest a switching rainfall-runoff behavior where catchment storage, connectivity and antecedent conditions control small discharge peaks but become increasingly irrelevant for larger storms. Our results suggest that, in the context of Natural Flood Management potential, expanding depression storage (e.g. distributed shallow water pools) in addition to existing restoration methods could increase the range of storms within which connectivity and storage remain important and that for larger storms measures which target surface runoff velocities are likely to be important.