When Rain Fails, Rivers Depend More on Water From Underground

Under severe drought, most of the world's monitored rivers take a larger share of their flow from water seeping in from below ground, according to a global analysis of stream gauges published Oct. 5, 2026, in Communications Earth & Environment.

The paper set out to pin down how much that slow, underground-fed flow, which hydrologists call baseflow, props up a river once rainfall fails, and whether the support holds as the climate warms. The authors describe both questions as unresolved across regions.

Muhammad Abrar Faiz, Liangliang Zhang and colleagues at Northeast Agricultural University in Harbin, China, with co-authors at the Chinese Academy of Sciences, combined streamflow gauge records from around the world with data on water stored on land and with a standard set of climate model runs. The team reports that under severe meteorological drought, a deep rainfall shortfall, 74.2% of gauging stations shifted toward a stronger baseflow share of their flow, 13.1% moved the other way, and 12.7% changed little.

The shift is a change in proportion, not a gain in water. The baseflow share climbed as low flows and streamflow shortfalls grew more severe, while the groundwater still reaching the river was itself shrinking: quick runoff from rainfall dropped away faster than the slow part did.

The authors also report that how a river basin divides its flow today set limits on how its slow flow behaved in the warmer simulations, which they read as evidence that the filling and emptying of underground storage is what keeps water in a river through a long drought. That half of the work is modeled rather than measured.

The paper is open access, and the journal posted its peer-review file alongside it. The version online is the accepted manuscript, which the journal says will be replaced by the final edited text.