Change in runoff initiation probability over a severe drought in a peat soil - implications for flowpaths

Severe drying of soils can lead to cracking and thus the generation of new hydrological pathways. In soils that show hydrophobic behaviour upon drying, it is possible that such flowpaths survive beyond the period of the drought that caused the initial cracking. Change in flowpaths in peat following severe droughts has been proposed as an explanation for long-term increases in DOC concentration leaving peat-covered catchments across the Northern Hemisphere With changes in climate making dry summers and summer drought more likely in the UK, this study aims to understand whether there have been long-term flowpath changes in a peat soil following a 1 in 33 year drought. The measure used by this study to analyse changes in the flowpaths present in peat soils is the probability of runoff initiation. The probability of runoff initiation represents a method for comparing the occurrence of runoff from the catchment in comparison to the precipitation inputs relative to the antecedent conditions of the catchment. The study examines 1674 rainfall events over a five year period before and after a severe drought and shows that the most important factor for controlling runoff initiation is the total amount of rainfall in any event and that the system is capacity rather than rate limited. The time of year is found to have a significant influence upon the probability of runoff initiation above and beyond the effect of water table depth and rainfall character. However, the study can find no persistent effect of severe drought beyond the period of drought itself, suggesting that, in terms of the factors investigated here, peat flowpaths are stable against changes in drought frequency and severity with climate change and cannot contribute to long-term changes in DOC runoff