Water-cycle intensity may be increasing, say researchers

Researchers based primarily in California have published a global assessment of freshwater discharge to the oceans which suggests that the rate of the hydrological cycle may be increasing.

Every water engineer knows that the water cycle is the key to sustainability of ecosystems and supplies to maintain human life. However, according to the researchers in their paper published in the Proceedings of the US National Academy of Sciences on 4 October 2010, there is no comprehensive global river discharge observing system.

Instead, for a period spanning 1994-2006, the researchers used a combination of satellite precipitation, evaporation and sea-level data in an ocean mass balance to estimate freshwater discharge to the sea. Their results indicated that this discharge averaged 36,055 km³/year for the study period, though this varied from year to year primarily as a result of El Niño.

However, the team also found that global discharge increased by 540 km³/y over the 13-year period, largely due to a 768 km³/y increase in ocean evaporation across the globe. This was balanced by a 240 km³/y increase in precipitation.

“Global changes in river discharge impact fresh water availability,” say the researchers. “They also point to changes in the intensity of the global hydrologic cycle.”