Subsidence monitoring in transboundary aquifers

An environmental drill behind the US/Mexico border wall as construction of the new section of wall begins at the Organ Pipe National Monument, August 23, 2019. Photo credit: AZCentral.com

Some aquifers compact when groundwater is pumped out of water wells too quickly. Termed, “groundwater overdraft,” this overpumping causes the level of the ground to sink on the order of centimeters each year and is exemplified through this iconic photo illustrating the long-term implications of subsidence in California’s Central Valley.

Subsidence in the San Joaquin Valley, California. Photo credit: USGS

In transboundary aquifers - regions where different diplomatic entities share groundwater - there is often a gap in the sharing of data across political boundaries, especially where those boundaries delimit geopolitical tension. A number of these aquifers are also the type of aquifer that will compact irreversibly due to groundwater overdraft.

Transboundary aquifers of the world and two that I highlighted in this study. The location of the drilling photo at the top of this post is marked in the lower left hand panel. Data: UN-International Groundwater Resource Assessment Center

Drawing from political scientific research into the governing characteristics of political institutions that successfully manage common pool resources, I sought to use methods in satellite radar remote sensing to fill a key characteristic of governing institutions for water sustainability: unbiased monitoring of the condition of the shared resource.

In October 2019 I travelled to Valencia, Spain to give an oral presentation on monitoring subsidence in transboundary aquifers at the American Geophysical Union’s Chapman Conference on the Quest for Sustainability in Heavily Stressed Aquifers.

To illustrate the potential value for diplomatic accountability using this technique, I ran subsidence analyses using data from the Sentinel-1 constellation and the Stanford Method for Persistent Scatterers in two regions with shared aquifers and geopolitical tension: the US/Mexico border and the southern Jordan River Valley.

I found mean subsidence rates of 5 cm/year near a cluster of pivot-irrigated agricultural fields just on the Mexico side of the border with New Mexico.

Mean subsidence velocity at the US/Mexico border (2018)

In the region of the Dead Sea, I found subsidence mirroring the political boundaries drawn during the Oslo Accords around the ancient city of Jericho in the Israeli-occupied West Bank. Agricultural regions in Jericho subsided at a rate of 10 cm/year in 2018.

(Left) Setting image from Sentinel-2. (Middle) Boundaries drawn during the Oslo Accords and Israeli settlement outlines (blue). Area A is under Palestinian National Authority administration and Area C is controlled militarily by Israel. Area B, with mixed administration, is not included in the study region. (Right) Mean subsidence velocity in the southern Jordan River Valley (2018). Subsidence is focused along the movement barrier (a ditch to prevent vehicle crossings) in Jericho and in Jordan, near the Dead Sea.

Subsidence around Jericho is likely driven by Palestinian reliance on groundwater resources from shallow Holocene alluvial aquifers underlaying agricultural regions of date palm cultivation in eastern Jericho. Interestingly, in regions of date palm cultivation under the control of Israeli settlers, there is not such dramatic subsidence.

In their research on the political role of date palm agriculture in the West Bank, Julie Trottier, et al, explain that the Israeli Water Authority and Israeli settlers are advancing recycled wastewater reservoirs for date palm irrigation but Palestinian farmers are reduced to using shallow saline groundwater or available springwater.

Subsidence monitoring in transboundary aquifers can be used, where applicable, for an unbiased monitor of aquifer condition in pursuit of transparency, accountability, and sustainability of shared water in stressed aquifers.

Corey Scher
Corey Scher
PhD Student in Earth and Environmental Science