For decades, the common perception in hydrology has been that deforestation in such areas made seasonal floods bigger on average, but had little effect on the number of large floods over time, said geoscientist Kim Green of the University of British Columbia.
But a new study by Green and her co-author Younes Alila published today in Water Resources Research, a journal of the American Geophysical Union, suggests that deforestation consistently causes more floods – both big and small. In the interior regions of North America, many creeks and rivers get most of their flow from melting snow accumulated during winter storms in mountainous areas.
How much water flows down these streams depends not only on how much snow falls upstream, but how fast the snow melts. But deforestation shines a new – and glaring – light on this water source. While ordinarily the trees keep the melting under control by shielding snow from the sunlight, “as soon as you get rid of the trees, the snow melts faster,” said Green. “It’s that simple.”
The difference between Green and Alila’s study and what hydrologists have historically done is how they crunched the data. In the past, hydrologists used a technique called chronological pairing – they compared each year’s flood data from a stream in a deforested area to that year’s data from a nearby, fully forested stream. This allowed the scientists to describe how floods become larger on average in deforested areas. But chronological pairing doesn’t deduce how much more frequent these floods might be. For this, scientists need a method called frequency pairing.
In frequency pairing, researchers review a decade or more of data all at once to determine a flood’s return period – how often a flood of a given size recurs. Green’s study is the first to use frequency pairing to explore how deforestation affects flood frequencies in streams in mountainous regions where at least half the annual precipitation falls as snow. She analyzed data from four creeks – Camp Creek, Redfish Creek and 240 Creek in British Columbia and Fool Creek in Colorado. With two creeks, Fool and Camp, she studied data from the past few decades in comparison to nearby, similar creeks where the terrain had not been deforested. With the other two, Redfish and 240, she used flood data generated by a computer model to study the simulated effect of deforestation of the terrain over more than 90 years.
The analysis showed that, in all four waterways, deforestation turned 10-year floods into three-to- five-year floods. Twenty-year floods recurred every 10 to 12 years. Most dramatically, in 240 Creek, 50 year floods happened every 13 years, almost four times as often. “Once you look at how the frequency has changed,” Green said, “you start to realize that deforestation has had a pretty dramatic effect on floods.”
Green’s model for how deforestation affects the flow of water is “something that’s going to be tested in other places many times, to see if their theory actually holds,” said Sandy Verry, a retired U.S. Forest Service hydrologist in Grand Rapids, Minn., who was not involved in the study but has studied streams using chronological pairing in the past. Verry said he believes Green’s conclusions about flood rates to be reasonable.
Until recently, the decades of data needed for frequency pairing data was scarce, Verry said, because hydrologists only started recording stream measurements in the North American West about 50 years ago. He expects there will be a “plethora” of further studies that study the frequency of floods over a broad array of deforested landscapes, including streams that flow into farmlands and cities. “There’s a whole realm of application to forest landscapes at lower elevations and flatland that this can be applied to,” Verry said.
Notes for JournalistsJournalists and public information officers (PIOs) of educational and scientific institutions who have registered with AGU can download a PDF copy of this paper by clicking on this link:
http://dx.doi.org/10.1029/2012WR012449Or, you may order a copy of the paper by emailing your request to Sean Treacy at
Neither the paper nor this press release are under embargo.Title:
Sean Treacy | American Geophysical Union
Novel method for investigating pore geometry in rocks
18.06.2018 | Kyushu University, I2CNER
Decades of satellite monitoring reveal Antarctic ice loss
14.06.2018 | University of Maryland
Moving into its fourth decade, AchemAsia is setting out for new horizons: The International Expo and Innovation Forum for Sustainable Chemical Production will take place from 21-23 May 2019 in Shanghai, China. With an updated event profile, the eleventh edition focusses on topics that are especially relevant for the Chinese process industry, putting a strong emphasis on sustainability and innovation.
Founded in 1989 as a spin-off of ACHEMA to cater to the needs of China’s then developing industry, AchemAsia has since grown into a platform where the latest...
The BMBF-funded OWICELLS project was successfully completed with a final presentation at the BMW plant in Munich. The presentation demonstrated a Li-Fi communication with a mobile robot, while the robot carried out usual production processes (welding, moving and testing parts) in a 5x5m² production cell. The robust, optical wireless transmission is based on spatial diversity; in other words, data is sent and received simultaneously by several LEDs and several photodiodes. The system can transmit data at more than 100 Mbit/s and five milliseconds latency.
Modern production technologies in the automobile industry must become more flexible in order to fulfil individual customer requirements.
An international team of scientists has discovered a new way to transfer image information through multimodal fibers with almost no distortion - even if the fiber is bent. The results of the study, to which scientist from the Leibniz-Institute of Photonic Technology Jena (Leibniz IPHT) contributed, were published on 6thJune in the highly-cited journal Physical Review Letters.
Endoscopes allow doctors to see into a patient’s body like through a keyhole. Typically, the images are transmitted via a bundle of several hundreds of optical...
Light detection and control lies at the heart of many modern device applications, such as smartphone cameras. Using graphene as a light-sensitive material for...
Water molecules exist in two different forms with almost identical physical properties. For the first time, researchers have succeeded in separating the two forms to show that they can exhibit different chemical reactivities. These results were reported by researchers from the University of Basel and their colleagues in Hamburg in the scientific journal Nature Communications.
From a chemical perspective, water is a molecule in which a single oxygen atom is linked to two hydrogen atoms. It is less well known that water exists in two...
13.06.2018 | Event News
08.06.2018 | Event News
05.06.2018 | Event News
18.06.2018 | Earth Sciences
18.06.2018 | Process Engineering
18.06.2018 | Life Sciences