Context:

• NASA’s GRACE mission has confirmed that a massive redistribution of freshwater is occurring across the Earth, with middle-latitude belts drying and the tropics and higher latitudes gaining water supplies.

Cause and Concern:

• A combination of the effects of climate change, vast human withdrawals of groundwater and simple natural changes are behind this.
• If this continues, it could have profound consequences leading to a situation in which some highly populous regions could struggle to find enough water in the future.

Key Findings:

• The resulting map of the findings shows an overall pattern, in which ice sheets and glaciers lose by far the most mass at the poles, but at the same time, middle latitudes show multiple areas of growing dryness even as higher latitudes and the tropical belt tend to see increases in water.
• The study emphasizes that the 34 separate changes that it detects do not all have the same cause – not even close.
• There’s very strong suspicion that the melting of glaciers and ice sheets is tied to climate change. On land, it’s possible that some droughts and rainfall increases may be also, though the study is cautious about that, noting that natural variability can also be a major factor here.
• There are also some major cases of humans increasing water storage in the landscape, particularly in China, where massive dam construction has created enormous reservoirs.
• Mainly, though, what’s striking about the map is the way that a combination of human-driven water withdrawals and droughts seem to be punishing the central latitudes of the northern hemisphere in particular, but also the southern hemisphere to a significant extent.

GRACE mission:

• The GRACE mission was selected as the second mission under the NASA Earth System Science Pathfinder (ESSP) Program in May 1997. Launched in March of 2002, the GRACE mission mapped variations in Earth’s gravity field. Designed for a nominal mission lifetime of five years, GRACE operated in an extended mission phase till 2017.
• GRACE is a joint partnership between the National Aeronautics and Space Administration (NASA) in the United States and Deutsche Forschungsanstalt für Luft und Raumfahrt (DLR) in Germany.
• GRACE consists of two identical spacecraft that fly about 220 kilometers (137 miles) apart in a polar orbit 500 kilometers (310 miles) above Earth. GRACE maps Earth’s gravity field by making accurate measurements of the distance between the two satellites, using GPS and a microwave ranging system.

Source:Economic Times & Wiki