Location, location, location -- Considering relative catchment location
to understand subsurface losses
Abstract
The analysis of large samples of hydrologic catchments is regularly used
to gain understanding of hydrologic variability and controlling
processes. Several studies have pointed towards the problem that
available catchment descriptors (such as mean topographic slope or
average subsurface properties) are insufficient to capture
hydrologically relevant properties. Here, we test the assumption that
catchment location, i.e. the relative properties of catchments in
relation to their surrounding neighbours, can provide additional
information to reduce this problem. We test this idea in the context of
Great Britain for a widely discussed problem, that of catchment water
balance errors due to subsurface losses. We test three hypotheses while
considering different locational aspects (1) location to coast, (2)
location next a relevant neighbour and (3) location within the drainage
basin, utilizing only basic and widely available geological and
topographical information. We find that subsurface losses from
catchments with a highly permeable geology connection to the coast are
in order of 20% water balance error. We define a simple
topographic-geologic index that is able to partially explain water
balance issues between neighbours of highly permeable catchments. The
results imply that location, geology and topography combine to define
the differences of water balances of UK catchments compared to what we
would expect from their climatic setting alone. The simple index defined
here can easily be derived globally and tested regarding its wider
applicability.