[미국] 서부지역, 지하수 자원 고갈

캘리포니아 대학과 Irvine시, NASA 과학자의 연구에 따르면, 2004년부터 발생한 콜로라도 강 유역의 75% 이상의 물 손실은 지하수 자원으로부터 비롯됐다고 밝혔다. 지하수 고갈의 정도는 미국 서부지역의 물 공급에 문제가 될 수도 있다.

연구는 제일 처음 서부 주의 물 수요에 필요한 지하수의 양을 수량화하고 나사의  Gravity Recovery and Climate Experiment (GRACE) 위성의 데이터를 사용해서 물 및 지하수의 변화와 관련된 변화를 추적했다. 2004년 12~2013년 11월 동안 매달 변화된 물의 양은 담수에서 거의 5천300만 acre-feet으로 거의 국자 최대 저수지의 두배가 되는 양이고 전체의 4분의3인 약 4천 100만 acre-feet는 지하수에서 추출됐다.

According to a new study jointly conducted by the University of California, the city of Irvine and NASA scientists, more than 75 percent of the water loss in the drought-stricken Colorado River Basin since late 2004 has originated from underground resources. Accordingly, the extent of groundwater loss may pose a greater threat to the water supply of the western United States than previously considered.

The study is the first to quantify the amount that groundwater contributes to the water needs of western states. According to the U.S. Bureau of Reclamation, the basin has been suffering from prolonged, severe drought since 2000 and has experienced the driest 14-year period in the last hundred years.

The research team used data from NASA's Gravity Recovery and Climate Experiment (GRACE) satellite mission (see "NASA satellites detect possible disastrous flooding months in advance, finds research") to track changes in the mass of the Colorado River Basin, which are related to changes in water amount on and below the surface.

Monthly measurements in the change in water mass from December 2004 to November 2013 revealed that the basin lost nearly 53 million acre-feet (65 cubic kilometers) of freshwater -- almost double the volume of the nation's largest reservoir, Nevada's Lake Mead. Likewise, more than three-quarters of the total -- about 41 million acre-feet (50 cubic kilometers) -- was derived from groundwater.

Water aboveground in the basin's rivers and lakes is managed by the U.S. Bureau of Reclamation, and its losses are documented. Pumping from underground aquifers is regulated by individual states and is often not well documented.

"There's only one way to put together a very large-area study like this, and that is with satellites," said senior author Jay Famiglietti, senior water cycle scientist at JPL on leave from UC Irvine, where he is an Earth system science professor. Within a given region, the change in mass due to rising or falling water reserves influences the strength of the local gravitational attraction. By periodically measuring gravity regionally, GRACE reveals how much a region's water storage changes over time.

The Colorado River is the only major river in the southwest part of the United States. Its basin supplies water to about 40 million people in seven states, as well as irrigating roughly four million acres of farmland.

"The Colorado River Basin is the water lifeline of the western United States," said Famiglietti. "With Lake Mead at its lowest level ever, we wanted to explore whether the basin, like most other regions around the world, was relying on groundwater to make up for the limited surface-water supply. We found a surprisingly high and long-term reliance on groundwater to bridge the gap between supply and demand."

Famiglietti noted that the rapid depletion rate will compound the problem of short supply by leading to further declines in streamflow in the Colorado River. "Combined with declining snowpack and population growth, this will likely threaten the long-term ability of the basin to meet its water allocation commitments to the seven basin states and to Mexico," Famiglietti said.

[출처 = Water World / 2014년 7월 24일]