July 19 () –
The water resources will increasingly fluctuate and become increasingly difficult to predict in snow-dominated regions across the Northern Hemisphere later this century, according to a comprehensive new study on climate change led by the National Center for Atmospheric Research (NCAR), in the United States, published in ‘Proceedings of the National Academy of Sciences’.
The research team found that even in regions that continue to receive the same amount of rainfall, river flows will be more variable and unpredictable. As snow cover recedes in a warmer future and no longer provides reliable runoff, the quantity and timing of water resources will increasingly depend on periodic rainfall events.
“Water managers will be at the mercy of rainfall, instead of having four or six months in advance to anticipate melting ice and runoff says NCAR scientist Will Wieder, lead author. Water management systems in snow-dominated regions are based on the predictability of snow cover and runoff, and much of that predictability could disappear with climate change.”
Observations show that the snow cover is already melting earlier, and even decreasing in many regions. This decline will be so steep by the end of the century that the amount of water contained in snowpack at the end of an average winter in parts of the US Rocky Mountains could plummet by almost 80%, according to scientists.
Changes in runoff and stream flow could have cascading impacts on ecosystems that depend on snow water, the study warns. Although changes will not be uniform across regions, increased snow-free days and longer growing seasons will put pressure on water resources, dry out soils in many areas, and increase fire risk.
The study assumes that greenhouse gas emissions continue at a high rate (scenario known as SSP3-7.0). According to Wider, the most serious effects on snow cover, runoff, and ecosystems would likely be avoided if society succeeded in reducing greenhouse gas emissions.
Scientists relied on an advanced set of computer simulations to fill in the details about the future of water resources, showing the extent to which changes in temperature and precipitation will alter snowpack and runoff patterns in the Northern Hemisphere. Although previous research has analyzed the effects of climate change on water availability, the new study focuses on the increasing variability of water resources.
Many regions of the Earth depend on the accumulation of snow during the winter and its subsequent melting in the spring and summer. to regulate runoff and river flow.
However, scientists have been warning for years that the snow cover will get thinner and melt sooner as precipitation in the colder months falls as rain instead of snow, and as melting occurs in occasions during the winter rather than in the spring runoff season.
To determine how reduced snow cover will affect water resource variability, Wieder and his co-authors turned to a powerful NCAR-based climate model: the Community Earth System Model, version 2.
They used a newly created database of simulations, known as CESM2 Large Ensemble, to compare a past period (1940-1969) with a future period (2070-2099). The simulations were performed on the Aleph supercomputer at the Institute of Basic Sciences in Busan, South Korea.
The results highlight the extent to which there will be widespread changes in the calendar and extent of water flows across much of the world by 2100. There will be an average of about 45 more snow-free days per year in the Northern Hemisphere, assuming greenhouse gas emissions are high.
The largest increases will occur in the mid-latitudes, which are relatively warm, and in high-latitude maritime regions, influenced by changes in sea ice..
Many regions that rely heavily on predictable snowpack-runoff relationships will experience the greatest loss of predictability due to a sharp decline in reliable pulses of spring runoff.
These regions include the Rocky Mountains, the Canadian Arctic, eastern North America, and eastern Europe. The authors warn that this will substantially complicate the management of freshwater resources, both for society and for ecosystems.
“We are in a race with predictability when it comes to stream flow because we are trying to improve our forecasts through better data, models, and physical understanding., but these efforts are being canceled by the rapid disappearance of our best predictor: snow, explains Flavio Lehner, a professor of earth and atmospheric sciences at Cornell University and a co-author of the study. It may be a race that we will lose, but we are trying to win it, and so we need to study these issues.”
Although reduced runoff will lead to drier soil in summer across much of the Northern Hemisphere, simulations showed that certain regions — including eastern Asia, the Himalayas, and northwestern North America — will hold moisture from the soil due to increased rainfall.
“Snow-related measurements are essential to inform society about the management of valuable water resources“, emphasizes Keith Musselman, hydrologist at the University of Colorado Boulder and co-author of the study.
“As utilities and civil works agencies plan new reservoirs and other infrastructure to accommodate a changing climate, we must address basic research questions about the changing characteristics of winter snowpack and the resulting water flow in which we have relied on for a long time,” he suggests.
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