The uplands of the oceanic temperate-humid zone, on which this book is focused, are dominated either by thin soils on steep slopes, or where slopes are more gentle, by thicker organic soils which range from raw peats and earthy peats to organo-mineral soils. Where slopes are gentle and soils in the uplands are deep, they tend to be dominated by organic matter (e.g. Paramo ecosystem of the Andes; Buytaert et al., 2006). Organic soils of the uplands tend to have a large water content and are quickly saturated during rainfall thereby generating fast moving surface or near-surface hillslope runoff. This is characteristic both for gentle upland slopes with deep organic soils and steeper slopes with thin soil layers and creates a system allowing water to be rapidly shed from headwater catchments. This means that even without management intervention or future climate change, such systems remain source areas for flooding. The impact of management practice on flood risk depends on a number of factors including drainage network structure, local topography and location of a given management practice with respect to these landscape features.
Over the last century there have been changes in upland management with increased drainage, grazing, liming and coniferous afforestation, which has lead to changes in the vegetation cover, structure and hydrology of these soils in many parts of the world (Buytaert et al., 2006; Holden et al., 2007a). The hydrology of organic soils is not only fundamental for their development and decay, as it is the semi-waterlogged nature of the soils that helps them remain in place, but the hydrology is also important for their function as a carbon store (see also Worrall, this volume) and as a source area for river and drinking water downstream. Changes in the hydrology of the uplands may drive changes in the hydrological, ecological and hydrochemical functions in other parts of the upland and lowland system. Therefore, in order to predict the consequences of environmental change on the uplands and the connected downstream impacts, an understanding of the temporal and spatial variability of hydrological processes is required. While this chapter will reference material from a range of international sources, it will focus on material from the UK uplands to illustrate the discussion. In particular it will examine the nature of research into impacts of management and climate change on hydrological processes in UK uplands.