The boundaries of drainage basins shifted faster during past episodes of climate change, according to a new theory by Ben-Gurion University geologists

Using a unique field site in the Negev, Ben-Gurion University of the Negev geologists have presented the first-ever time-dependent record of drainage divide migration rates. Prof. Liran Goren, her student Elhanan Harel, and co-authors from the University of Pittsburgh and the Geological Survey of Israel, further demonstrate that episodes of rapid divide migration coincide with past climate changes in the Negev over the last 230,000 years (unrelated to present-day climate change).

It is an astounding achievement that will accelerate our understanding of how climate affects the Earth's surface.

Their findings were just published in PNAS (Proceedings of the National Academy of Sciences).

The researchers focused on the migration rate of drainage divides—the topographic boundaries separating neighboring drainage basins. Drainage basins are hydrologic units that accumulate surface water into a single outlet. As divides shift, they reshape basin boundaries and redistribute surface water, rock particles, and ecological niches across landscapes. Until now, the state of the art has been limited to long-term average divide migration rates.

However, a unique site presenting a sequence of terraces in the Negev desert of Israel has provided the first traceable record of divide location at different snapshots in time, constraining a time series of divide migration rate. Combining field observations, river terrace dating, and numerical simulations, they were able to infer divide migration dynamics in the Negev Desert, over the last 230,000 years. By doing so, they discovered for the first time that episodes of accelerated migration, more than twice the rate of other episodes, coincide with regional climate fluctuations indicated by regional paleoclimate proxies.

"It's an exciting discovery," says Prof. Liran Goren of the Department of Earth and Environmental Sciences, "We were not expecting to discover the correlation with climate fluctuations nor the speed with which the divide shifted during that time. It adds to our knowledge of the drivers affecting the Earth's surface evolution in fascinating ways."

"I think what’s fascinating about this research is that a small channel in the Negev desert, which at first glance doesn’t seem particularly remarkable, can actually hold such an impressive record of drainage divide migration along its course," says Elhanan Harel. "The findings from this study are important for better understanding the nature of divide migration, while also contributing to the ongoing scientific discussion about the climatic history of the Negev."

Additional researchers include Onn Crouvi and Naomi Porat of the Geological Survey of Israel, Tianyue Qu and Eitan Shelef, of the University of Pittsburgh, and Hanan Ginat of the Dead Sea and Arava Science Center.

This research was supported by the United States–Israel Binational Science Foundation (BSF), grant number 2019656 and the United States National Science Foundation (NSF-Geomorphology and Land-use Dynamics), grant number 1946253.