Impacts of drought can linger in rivers for years

A recent study from UC Riverside has revealed that the effects of drought can linger in streams and rivers for up to 3.5 years, regardless of intervening storms. Contrary to common belief, the research highlights that a lack of rainfall is not the sole indicator of drought. 

Focus of the study

The study, published in the Journal of Hydrology, introduces a new approach to understanding and measuring drought. The research focuses on two crucial factors: total water level and baseflow in streams.

Total water level, often analyzed by researchers, is influenced by both snowmelt and rainfall. Baseflow, which is less frequently examined due to previous measurement challenges, represents the segment of streamflow originating from groundwater. 

Measuring baseflow 

With baseflow being integral to water management and ecosystem services due to its strong connection with groundwater, the UC Riverside team initiated a closer examination of this overlooked aspect.

“People often just use rain as an indicator of drought because it’s easier to measure. But there are other kinds of drought that each have their own impacts,” said study co-author Professor Hoori Ajami. “We needed a new way to see how long it takes for one form of drought to become another form.”

Hydrological drought 

The researchers pointed out that baseflow is part of a category called hydrological drought, which has significant implications for water availability for consumption, irrigation, and hygiene. 

It also considerably affects the health of wildlife, plants, and ecosystems at large. More critically, severe hydrological drought poses a threat to infrastructure stability.

Decades of data

In an effort to better define hydrological drought’s commencement and conclusion, the UC Riverside team examined three decades worth of data from over 350 locations nationwide. Their investigation exclusively encompassed the baseflow in streams or rivers unaffected by human activities, with no reservoirs or dams present.

What the researchers learned 

The findings revealed that the onset and termination of hydrological droughts are influenced by an area’s typical climate and geography. 

Recovery times post-rainfall drought varied, with some areas like parts of Kansas taking up to 41 months to recuperate, while others like the Arroyo Seco area near Pasadena, California, recovering in nearly a year.

Study insights 

Study lead author Sanghyun Lee emphasized the importance of adopting site-specific water management strategies instead of a universal solution. 

“When we are looking at water management strategies, it is clear we cannot implement a one-size-fits-all solution everywhere, for every stream. Our approaches need to be site specific,” said Lee. 

“When I first came to California in 2016, people asked me, ‘Is the drought over?’ They wanted to know if our watersheds had recovered. This new study shows it may take another few years until they get back to normal,” said Ajami.  

Study implications 

The study’s results align with past research, indicating a delayed response of underground aquifers to rainfall shortages. As these aquifers are vital for agriculture, providing the baseflow for rivers, over-extraction of groundwater during drought can lead to the development of sinkholes, thereby endangering infrastructure.

“One key message we want to send is that people must be careful about managing the water they have,” said Lee. 

“Because of rising temperatures, baseflow drought is getting longer and more severe in many parts of the country. And because watershed boundaries often cross state or international lines, preserving precious water resources will require more cooperation.”

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