A recent study from researchers at the University of California (UC) Irvine has found that since 1994, the overall amount of fresh water flowing into the world's oceans has increased significantly. They found that 18 percent more fresh water has reached the oceans between 1994 and 2006, an average annual rise of 1.5 percent.

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The biggest reasons for the increase are the more frequent and extreme storms which are attributable to global warming. It is also a consequence of melting polar ice. The research team, led by UC Irvine Earth System Science Professor, Jay Famiglietti, focused on the issue of greater storm water runoff reaching the oceans.

Unfortunately, the increased precipitation falls unevenly over the Earth's surface. This is a phenomenon of global warming; the higher-rainfall areas of the world get wetter, and the more arid regions get drier.

According to Famiglietti, "In general, more water is good. But here's the problem: Not everybody is getting more rainfall, and those who are may not need it. What we're seeing is exactly what the Intergovernmental Panel on Climate Change predicted â€“ that precipitation is increasing in the tropics and the Arctic Circle with heavier, more punishing storms. Meanwhile, hundreds of millions of people live in semiarid regions, and those are drying up."

The study found that global warming has triggered an acceleration of the evaporation and precipitation cycle. Higher temperatures over the oceans cause the fresh water to evaporate and form thicker clouds. It is then dumped on land in ferocious torrents, often in the form of hurricanes or monsoons (think Pakistan floods). The fresh water then finds its way back to the ocean via rivers and channels.

Therefore global warming should also increase river flow throughout wetter regions. However, there is no global system in place to measure river discharge levels, so no definitive data is available at this point.

What the study employed instead was NASA satellites and other satellites that are capable of tracking total water volume each month flowing from the continents into the sea. From the satellite data, the team assembled a 13-year record of sea-level rise, precipitation, and evaporation. The final conclusion is that rising temperatures accelerate the hydrologic cycle, the benefits of which are distributed unevenly over the globe.

The scientists admit, however, that despite their work spanning the longest time frame ever for this type of research, the 13-year study is still a relatively short period, and that more research is needed and is underway.

The UC Irvine study was done in conjunction with researchers from the University of South Florida, the Jet Propulsion Laboratory in Pasadena, and Remote Sensing Systems of Santa Rosa, CA. Funding was provided by NASA. The research is published in the journal, Proceedings of the National Academy of Sciences.