Gravimetry as a tool for hydrologic research

at the Sutherland Observatory

Andreas Güntner, Christoph Förste, Theresa BlumeGFZ German Research Centre for Geosciences

Gaathier Mahed, Maarten De Wit, Moctour DoucoureAEON / University of Cape Town

Quantifying variations in continental water storage

� Local to global water balances

� Water resources

� Flood risks

P: PrecipitationE: EvapotranspirationR: Runoff∆∆∆∆S: Water storage change

P = E + R + ∆S

Continental water balance

and their changes

in space and time

Motivation

Quantifying variations in continental water storage

Several storage components in ∆S:

• Snow and ice

• Groundwater

• Soil moisture

• Surface water storage

P: PrecipitationE: EvaporationR: Runoff∆∆∆∆S: Water storage change

Continental water balance

∆S = P – E – R∆S

GRACE satellite mission

(Gravity Recovery andClimate Experiment)

• Launched in March 2002

Water storage variations from satellite gravimetry

• Launched in March 2002

• Monitoring of temporal variations of the gravity fi eld of the Earthcaused by mass transport processes in the

- Earth's interior

- Atmosphere

- Oceans

- Ice caps

- Continental hydrology

Orders of magnitude of the different components of the gravity of the Earth:

g =9.807246731…m/s2

Static mass inhomogeneitiesMass changes

9.807246731…m/s• relativity, 1mm height difference

• ocean topography, polar motion

• hydrology (water storage changes)

• Earth and ocean tides, 1m height difference

• large water reservoirs

• mass inhomogeneities in the inner Earth

• mountains, deep ocean trenches, 1km height difference

• Earth flattening and rotation

Water storage variations on the continents from GRACE

ITG (Bonn) GRACE 2010 daily

Kalman smoother solutions

Geoid height changes

Linear Trends over 4 years

(2002 - 2006, expressed in cm water column)

+12 cmGlacier melting

in Alaska

Glacier melting

in Greenland

Sumatra earthquake 2004

Postglacial Uplift

Postglacial Uplift

Temporal gravity changes measured by GRACE

0

-12 cmSource: CNES/GRGS Toulouse

Depletion of groundwater resources in North-West In dia from GRACE(Indian States Rajasthan, Punjab and Haryana, 450 0 00 km²)

Rodell et al. (2009), Nature

Example Orange River Basin

GRACE data

Global hydrological models

Water storage variations from GRACE satellite gravi metry

Global hydrological models

Spe

iche

rano

mal

ien

(mm

)

Gravimeter Sutherland

Time-variable gravity data for hydrology

| Andreas Güntner | GFZ German Research Centre fo r GeosciencesGravimetric data in hydrology | 10

�Temporal variations of the gravity field of the Earth

�Water mass variations on the continents after removal of other mass components ∆∆∆∆S: Water storage change

P: PrecipitationE: EvaporationQ: Runoff

∆S = P - Q - E

Only integrative and large-scale measurement of ∆S for hydrology

Water storage variations from time-variable gravity

precipitation

evapotranspiration

GRACE

Gravimeter

surface runoff

Subsurface runoff

infiltration

goundwater storage variations

snow coverage and melt

soil moisture variations

Superconducting gravimeters

Superconducting gravitmeters allow

for extremly precise monitoring of

local gravity changes

Accuracy: ~ 10-12 g (1 nanoGal)

→ Measurement of temporal gravity

variations caused by e.g.

soil moisture and groundwater levelsoil moisture and groundwater level

changes

Superconducting

sphere

Superconducting

coils

Superconducting gravitmeters allow

for extremly precise monitoring of

local gravity changes

Accuracy: ~ 10-12 g (1 nanoGal)

→ Measurement of temporal gravity

variations caused by e.g.

soil moisture and groundwater level

Superconducting gravimeters

soil moisture and groundwater level

changes

gravimeter

World wide Superconducting gravimeter networkWithin the Global Geodynamic Project (GGP) of the IAG

GFZ Superconducting gravimeter station in Sutherland (South Africa)

• Since 2000• At the campus of the South African Astronomical Observatory (SAAO)• In cooperation with the National Research Foundation (NRF)

Part of the South African Geodynamic Observatory (SAGOS)

GFZ Superconducting gravimeter station in Sutherland (South Africa)

GFZ Superconducting gravimeter station in Sutherland (South Africa)

Hydrological monitoring in Sutherland / South Afric a

Climate

Gravimeter

Soil moisture

Groundwater Runoff

Climate

Effects of local water storage variations on gravim eter

Example station Wettzell, Germany

Snow

Soil 0-30cm

Soil 30-150cm

Saprolith 1.5 – 11m

Groundwater > 11m

Creutzfeldt et al., 2010, WRR; Creutzfeldt et al., GJI, 2010

Hydrological gravity effect

Gravimeter residuals

Examplegravimeter stations in Europe

Water storage variations from gravimeters and GRACE

GRACE

Hydrological modelGravimeter

Use of gravity data in hydrology - Summary

Gravimetry as a tool for hydrologic research

at the Sutherland Observatory

Andreas Güntner, Christoph Förste, Theresa BlumeGFZ German Research Centre for Geosciences

Gaathier Mahed, Maarten De Wit, Moctour DoucoureAEON / University of Cape Town