Monitoring groundwater changes more precisely

Date:
July 15, 2020
Source:
GFZ GeoForschungsZentrum Potsdam, Helmholtz Centre
Summary:
A new method could help to track groundwater changes better
than before.

Researchers have compared gravity field data from the GRACE
and GRACE- Follow On satellite missions with other measuring
methods. They investigated the seasonal water storage in almost
250 river basins in Asia, whose water regime is dominated by
monsoon. The results allow the large-scale GRACE data to be scaled
down to smaller regions.



FULL STORY ==========================================================================
A new method could help to track groundwater changes better than
before. To this end, researchers from Potsdam and Oberlin, Ohio (USA),
have compared gravity field data from the GRACE and GRACE-Follow On
satellite missions with other measuring methods. They investigated the
seasonal water storage in almost 250 river basins in Asia, whose water
regime is dominated by monsoon. The results allow the large-scale GRACE
data to be scaled down to smaller regions.

The researchers report on this in the journal Earth and Planetary
Science Letters.


========================================================================== Knowledge of underground water storage is of existential importance
for agriculture as well as for the drinking water supply in many
regions. These reservoirs are replenished by precipitation and seeping
water, which in turn feeds rivers and lakes and allows rivers to flow in
dry seasons. Measurements, however, are difficult because it is difficult
to look into the earth, so one has to rely on either point values only
-- via boreholes and wells -- or on calculations from precipitation and
runoff data.

Since 2002 there has been another method of measuring groundwater changes:
Via the GRACE satellite missions (from 2002 to 2017) and GRACE-Follow On
(since 2018), the change in the amount of water in and on the earth can
be determined on the basis of its gravity field signal. But this method
also has its pitfalls. First, the mass changes measured by the GRACE-FO satellites say nothing about the depth in which the mass is located:
Do lakes empty at the surface? Is the level of rivers falling? Or does
water drain from deeper layers? Secondly, the GRACE-FO satellites provide
data for comparatively large areas of several tens of thousands of square kilometres. It is currently not possible to resolve the gravity field
data more precisely.

In a new study, Amanda H. Schmidt from Oberlin College, Ohio, together
with researchers from the German Research Centre for Geosciences, is
showing how different methods can be cleverly combined to obtain reliable groundwater data even for small river basins. They have examined monsoon rainfall data and seasonal water storage in almost 250 river basins in
Asia. The size of the individual areas varies from one thousand to one
million square kilometres. The study covers almost all of Asia.

The water balance on our planet is characterized by three main variables: precipitation, surface runoff and evaporation. The difference of these
goes into or flows out of various reservoirs, e.g. the groundwater. Time
series of measuring stations on rivers (hydrographs) after persistent precipitation show typical falling curves (so-called recession curves),
which reflect the emptying of water reservoirs. Groundwater fluctuations
can be estimated from these curves. Another method is the comparison
of precipitation and runoff values by the time delay of the runoff; the temporary intermediate storage results in a so-called P-Q hysteresis. P
stands for precipitation and Q for runoff. The area or size of the
hysteresis loop can be used as a measure for the intermediate storage.

The study in Earth and Planetary Science Letters now shows that the P-
Q hysteresis and the gravity field data of GRACE missions are strongly correlated. According to the study, both reflect seasonal groundwater
changes very well. As a consequence, this means that a combination of precipitation and runoff data and GRACE gravity field data can also be
used to record groundwater in catchment areas that are only about 1000
square kilometres in size.


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


========================================================================== Journal Reference:
1. Amanda H. Schmidt, Stefan Lu"dtke, Christoff Andermann. Multiple
measures
of monsoon-controlled water storage in Asia. Earth and Planetary
Science Letters, 2020; 546: 116415 DOI: 10.1016/j.epsl.2020.116415 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/07/200715111431.htm

--- up 1 hour, 55 minutes
* Origin: -=> Castle Rock BBS <=- Now Husky HPT Powered! (1337:3/111)