A new method could help to track groundwater changes better than before.
A new method could help to track groundwater changes better than before. To this end, researchers from Potsdam and the 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.
Read more at GFZ German Research Centre for Geosciences
Photo: The dam on the river Koshi in Eastern Nepal was erected for irrigation and for protection of neighbouring India from flooding. CREDIT: Dr. Christoff Andermann
