HR: 11:50h
AN: H41G-07 INVITED     [PDF]
TI: Spatial Heterogeneity of Overland Flow in Semi-arid and Humid Climates and its Implications for Vegetation Growth and Landform Evolution
AU: * Kirkby, M J
EM: mike@geog.leeds.ac.uk
AF: School of Geography, University of Leeds, Woodhouse Lane, Leeds, LS2 9JT United Kingdom
AU: Bracken, L J
EM: l.j.bracken@durham.ac.uk
AF: Department of Geography, University of Durham, Science Laboratories, South Road, Durham, DH1 3LE United Kingdom
AU: Brookes, C
EM: c.brookes@geog.leeds.ac.uk
AF: School of Geography, University of Leeds, Woodhouse Lane, Leeds, LS2 9JT United Kingdom
AB: Although sub-surface flow creates a systematic pattern of discharge in humid climate areas, the pattern of topography at 2-5 m resolution superimposes a high degree of heterogeneity of overland flow at each level of catchment deficit. Further heterogeneity comes from differences in soil transmissibility, increasing the potential to create poorly connected patches of overland flow, particularly far upslope. Semi-arid areas also show heterogeneity of overland flow generation due both to random patchiness of infiltration linked in this case to topographic and vegetation patterns at a fine scale and to the duration of bursts of intense rainfall at the hillslope scale. The pattern of runoff generation is more random than for humid areas, but the probability of connection to the channel is also biased towards downslope, because flow from upslope may re-infiltrate when rainfall intensity declines. Although the drivers and relevant scaling ratios are very different for humid and semi-arid runoff, both show a broadly similar type of response to increasing storm size. In both cases, the pattern of overland flow contains patches, some of which are connected and some disconnected from channels. The runoff delivered reflects the heterogeneity of this pattern and its connectivity, with a non-linear increase in contributing area as storm rainfall increases. Many areas can also show both types of behaviour, with a more `humid' response in wetter seasons and in larger storms. These runoff processes have important impacts on the hillslope scale, first for the evolution of micro-topography and vegetation patterns and second for the non-linear delivery of sediment and consequent landform evolution. It is vital for the next generation of models to integrate soil, vegetation, hydrology and sediment transport to forecast and understand the functional interactions which occur over decadal and longer time spans
DE: 1815 Erosion and sedimentation
DE: 1824 Geomorphology (1625)
DE: 1860 Runoff and streamflow
DE: 1866 Soil moisture
SC: Hydrology [H]
MN: 2003 Fall Meeting