Dynamic response characteristics of the plynlimon catchments and preliminary analysis of relationships to physical descriptors

Abstract

Assessment of the impacts of environmental change on hydrological systems at regional or national scale requires a modelling technique capable of spatial extrapolation. Few such techniques, providing a regional or national picture of hydrological impact, are currently available. The proposed regionalization methodology, outlined in Jakeman et al. (1992), is being applied to up to 100 gauged UK catchments of various size, geology, topography and climate using a rainfall-runoff model IHACRES (a program for Identification of unit Hydrograph And Component flows from Rainfall, Evapotranspiration and Streamflow data). Dynamic response characteristics (DRCs), such as the proportion of slow flow, identified by the model are being related to physical catchment descriptors (PCDs) such as soil type, slope and area, obtained from a geographical information system (GIs). Extrapolation to ungauged catchments should then be possible and the resulting hydrological GIS of the UK would allow spatial analysis of the hydrological impact of environmental changes in climate and land use. This paper presents a preliminary application of the methodology using the Plynlimon experimental catchments in central Wales for which good hydrological and physical descriptor records exist. Eight catchments are modelled: the headwaters of the Wye and Severn rivers and the three main subcatchments of each, the Gwy, Cyff and Iago and Hafren, Hore and Tanllwyth, respectively. Relationships between DRCs and PCDs are investigated and interpreted in the context of the wider project.