More than one-sixth of the global population depends on meltwater for their water supply, and ecosystems are often highly responsive to changes in water availability. Therefore, shifts in snow and river flow can have substantial consequences, as in many parts of the world snowmelt is a critical water source to sustain agriculture, industrial water uses, and household water supply. As climate warms and river flows change, many regions will undergo more seasonal water scarcity. Across the Northern Hemisphere, peak river flows shift consistently towards earlier in the year and less water is available during summer, the paper published in Nature shows.
Systematic changes
The research demonstrates systematic snow and river flow changes in a warming climate across hundreds of river basins in the Northern Hemisphere. ''As the climate warms, the part of precipitation falling as snow shrinks, snowpacks melt earlier, and winter rainfall increases. Consequently, river flows peak earlier in the year and summer flows are shrinking. Such changes are occurring across most snowy river basins in the Northern Hemisphere'', Berghuijs explains. In contrast, most year-to-year variations in snow conditions are controlled by variability in precipitation timing rather than temperature, and this leads to much more diverse impacts on river flow, but these do not reflect impacts of climate warming the paper shows.
How climate change influences water resources
As the (already reduced) snowpacks melt earlier in the year, water availability from rivers moves from summer, when society’s water demand is typically highest, towards winter, when water demands are typically much lower. In many parts of the world, snowmelt-derived river flow is a critical water source, and acknowledging there are systematic shifts toward earlier river flow makes water less available when it is most needed for irrigated agriculture. ''Especially in places like the western US this means water rights should vary seasonally, and these seasonal rights need to shift towards other times of the year. So, these findings contribute to a clearer understanding of how climate change influences water resources, which can support water management and policy development'', says the earth scientist.
Database monitoring
This study uses existing open-access national and global databases of snow, river flow, and weather conditions. These databases contain daily values monitored over long periods, often multiple decades per river basin. These data are collected for, for example, operational water management and weather monitoring, but they also provide valuable sources for scientific research.