Global analysis of how effective and topographic catchment areas differ


Date:
September 22, 2020
Source:
University of Freiburg
Summary:
Topographically sketched catchment areas are a spatial unit
based on the shapes of the earth's surface. They show how human
activities and climate change influence the available quantities
of water. Knowledge of these units is fundamental to sustainable
water management. However, due to underground connections, some
catchment areas accumulate water from areas beyond their topographic
boundaries, while others are effectively much smaller than their
surface topography would suggest. Currently, most hydrological
modelling strategies do not take these groundwater connections
into account, but assume that the catchments are independent of
their surroundings.



FULL STORY ========================================================================== Topographically sketched catchment areas are a spatial unit based on
the shapes of the earth's surface. They show how human activities and
climate change influence the available quantities of water. Knowledge of
these units is fundamental to sustainable water management. However, due
to underground connections, some catchment areas accumulate water from
areas beyond their topographic boundaries, while others are effectively
much smaller than their surface topography would suggest. Currently,
most hydrological modelling strategies do not take these groundwater connections into account, but assume that the catchments are independent
of their surroundings. For this reason, Dr.

Yan Liu and Assistant Professor Dr. Andreas Hartmann from the Chair
of Hydrological Modeling and Water Resources at the University of
Freiburg, together with a team of researchers from the University of
Bristol in England and Princeton University in the US, have introduced
the Effective Catchment Index (ECI). Using this new metric, they were
able to determine how topographic and actual catchment areas differ when analyzing a global data set. The team recently published the results in
the journal Environmental Research Letters.


========================================================================== Using the ECI, the team led by Liu and Hartmann was able to demonstrate
that the assumption of a closed water balance, i.e. that the level of
a river changes only through precipitation and evaporation from its
topographic area, for example, does not apply to a considerable number
of catchments around the world. Every third catchment studied has an
effective catchment area that is even greater than twice or less than
half its topographical area. The scientists recognized that these areas influence or are influenced outside their topographical boundaries by
water management activities such as pumping groundwater and, for example, deforestation or reforestation.

With their analysis, the researchers show that the ECI they have
redefined is suitable for investigating how drought can spread across topographical boundaries as a result of water exchange. It can also be
used in the analysis of the effects of climate and land use changes on cross-boundary water exchange. "This is how we have seen where we need to further investigate underground networks across topographical boundaries
in order to support sustainable water management," says Hartmann.


========================================================================== Story Source: Materials provided by University_of_Freiburg. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Yan Liu, Thorsten Wagener, Hylke E Beck, Andreas Hartmann. What
is the
hydrologically effective area of a catchment? Environmental Research
Letters, 2020; 15 (10): 104024 DOI: 10.1088/1748-9326/aba7e5 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/09/200922112232.htm

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