Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Why how much water runs down the rivers

22.10.2008
Humans are increasingly altering the amount of water that runs from the land to the sea or inland waters. Calculations with a global vegetation and hydrology model indicate that precipitation had the largest impact on global river discharge over the 20th century.

Regionally, however, discharge varied according to factors such as land use change and irrigation practices, temperature, and the concentration of the greenhouse gas carbon dioxide (CO2), researchers from the Potsdam Institute for Climate Impact Research (PIK) report in the journal "Geophysical Research Letters". The impact of these mainly anthropogenically driven factors on discharge and the availability of water for human use is expected to grow in the future.

"How much the subtle increase in discharge during the 20th century is due to the rising CO2 concentration is the subject of scientific debate," says Dieter Gerten, lead author of the study. His team studied the effects of changes in climate, CO2 concentration, land cover and land use on river discharge using the dynamic global vegetation model LPJmL ("Lund-Potsdam-Jena managed Land" model). "Modelling shows that an increase in global precipitation was the driving force for the increase in river discharge", says the geographer and hydrologist.

The researchers used data from the Climatic Research Unit (CRU) at the University of East Anglia in Norwich, UK, a standard data set used in global modelling, as input to the vegetation model for simulating river discharge patterns. The simulations show large changes in the amounts of discharge during the last century in many regions of the world. In line with observations, river discharge decreased in North and West Africa, Central and Eastern Europe and parts of South Asia. It increased in parts of Siberia, as well as North and South America.

Global river discharge normally amounts to 35,000 to 40,000 cubic kilometres annually. According to the CRU climate data it increased by 7.7 percent during the last century, the researchers report. Approximately 95,000 to 110,000 cubic kilometres of precipitation fall on land surface each year. However, because regional amounts of precipitation and trends vary between different data sets, and other data do not indicate a clear global trend, it remains unclear whether there is actually an increase in global river discharge.

Following precipitation, land use had the largest impact on river discharge. During the last century, humans have increased global discharge by 1.7 percent, especially by deforestation. While irrigation caused significant regional decreases in discharge, its global effect on river discharge was negligible.

Over the last century, global warming decreased river discharge by 0.9 percent. This trend, due basically to increased evapotranspiration, was strongest at high latitudes and in parts of Central Asia. The global temperature signature has become increasingly evident in recent decades, the researchers write. Calculations based on three IPCC scenarios indicate that this trend will continue and that global warming alone could reduce global river discharge by six percent by the end of the 21st century.

Theoretically, the rise in the concentration of CO2 could reinforce this trend. The greenhouse gas could have a fertilizing effect that leads to an expansion of vegetation cover. On a regional level, more plants would take more water from the soil and thus decrease river discharge. Globally, however, the fertilization effect is negligible. Another direct effect of increased CO2 concentration has increased discharge by more than one percent between 1901 and 2002: under a higher concentration of CO2 plants need to open their stomata less in order to take up enough CO2 for growth. Therefore, evapotranspiration decreases and they take less water from the ground.

"The net effect of the rising CO2 concentration in the atmosphere could increase global river discharge by a further five percent by 2100," says Dieter Gerten. Globally, this would probably compensate the negative impacts of temperature. However, temperature and CO2 effects would not necessarily affect the same regions. The researchers are planning further studies to investigate possible developments of future water availability and demand worldwide.

"Currently, our model is the only one that can take the effects of all these factors into account," says Wolfgang Lucht, chair of the PIK research domain "Climate Impacts & Vulnerabilities". To achieve this, knowledge about hydrology needs to be combined with knowledge about vegetation dynamics. "The calculations indicate that human activities are having an increasing impact on the Earth's water balance", says Lucht. To be able to make more precise projections of future water availability, more methods of measurement and more data are needed. The researchers therefore call for a stop to the current deconstruction of the global meteorological network.

Article:
Gerten, D., S. Rost, W. von Bloh, and W. Lucht (2008), Causes of change in 20th century global river discharge, Geophysical Research Letters, 35, L20405, doi:10.1029/2008GL035258.
For further information please contact the PIK press office:
Phone: +49 331 288 2507
E-mail: press@pik-potsdam.de

Patrick Eickemeier | idw
Further information:
http://www.agu.org/journals/gl/
http://www.pik-potsdam.de/news/press-releases/why-how-much-water-runs-down-the-rivers?set_language=en

More articles from Earth Sciences:

nachricht Massive impact crater from a kilometer-wide iron meteorite discovered in Greenland
15.11.2018 | Faculty of Science - University of Copenhagen

nachricht The unintended consequences of dams and reservoirs
14.11.2018 | Uppsala University

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: UNH scientists help provide first-ever views of elusive energy explosion

Researchers at the University of New Hampshire have captured a difficult-to-view singular event involving "magnetic reconnection"--the process by which sparse particles and energy around Earth collide producing a quick but mighty explosion--in the Earth's magnetotail, the magnetic environment that trails behind the planet.

Magnetic reconnection has remained a bit of a mystery to scientists. They know it exists and have documented the effects that the energy explosions can...

Im Focus: A Chip with Blood Vessels

Biochips have been developed at TU Wien (Vienna), on which tissue can be produced and examined. This allows supplying the tissue with different substances in a very controlled way.

Cultivating human cells in the Petri dish is not a big challenge today. Producing artificial tissue, however, permeated by fine blood vessels, is a much more...

Im Focus: A Leap Into Quantum Technology

Faster and secure data communication: This is the goal of a new joint project involving physicists from the University of Würzburg. The German Federal Ministry of Education and Research funds the project with 14.8 million euro.

In our digital world data security and secure communication are becoming more and more important. Quantum communication is a promising approach to achieve...

Im Focus: Research icebreaker Polarstern begins the Antarctic season

What does it look like below the ice shelf of the calved massive iceberg A68?

On Saturday, 10 November 2018, the research icebreaker Polarstern will leave its homeport of Bremerhaven, bound for Cape Town, South Africa.

Im Focus: Penn engineers develop ultrathin, ultralight 'nanocardboard'

When choosing materials to make something, trade-offs need to be made between a host of properties, such as thickness, stiffness and weight. Depending on the application in question, finding just the right balance is the difference between success and failure

Now, a team of Penn Engineers has demonstrated a new material they call "nanocardboard," an ultrathin equivalent of corrugated paper cardboard. A square...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

“3rd Conference on Laser Polishing – LaP 2018” Attracts International Experts and Users

09.11.2018 | Event News

On the brain’s ability to find the right direction

06.11.2018 | Event News

European Space Talks: Weltraumschrott – eine Gefahr für die Gesellschaft?

23.10.2018 | Event News

 
Latest News

Purdue cancer identity technology makes it easier to find a tumor's 'address'

16.11.2018 | Health and Medicine

Good preparation is half the digestion

16.11.2018 | Life Sciences

Microscope measures muscle weakness

16.11.2018 | Life Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>