Glacial melting can result in nuclear power plant shutdowns, agriculture and water resources being put at risk, and coastal cities being threatened by flooding.

To mark Friday's first-ever World Day for Glaciers, the United Nations' World Meteorological Organization (WMO) weather, climate and water agency, and its UNESCO culture agency, zoomed in on the impact shrinking glaciers can have on everyday lives.

- Natural disasters increase -

By releasing large amounts of water, the melting of glaciers can trigger natural disasters such as floods, landslides and avalanches.

The lakes that form risk overflowing, threatening towns and villages downstream, while the retreating glacier tongue reveals bare rock or sediments that can collapse, increasing the local hazard risk.

Such risks sometimes result in legal action.

This week in Germany, a Peruvian farmer is suing the German energy giant RWE -- one of the world's top emitters of carbon dioxide -- for "climate justice".

Saul Luciano Lliuya argues that RWE must pay towards the cost of protecting his hometown, Huaraz, from a swollen glacier lake at risk of overflowing from melting snow and ice.

- Water resources in peril -

The water released by melting glaciers will initially swell rivers and lakes -- but this source will eventually run dry.

"We think that the majority of catchments around the globe are going to reach this peak water within the century, and about 30 percent or more have already passed" the peak, said Michael Zemp, director of the World Glacier Monitoring Service.

The disappearance of glaciers will affect freshwater supplies, particularly in Central Asia and the central Andes, "where glaciers, in the hottest and driest months, are often the only water resource".

According to a report published Friday by UNESCO, mountains provide up to 60 percent of the world's annual freshwater flow. More than two billion people depend directly on water from the mountains for their drinking water, sanitation and livelihoods.

Half of the River Amazon's water comes from the Andes, noted Abou Amani, secretary of UNESCO's intergovernmental hydrological programme.

- Biodiversity disrupted -

The altitude of the snow line is rising, altering biodiversity.

Vegetation will be able to grow higher up in the mountains, while for some plants, "it will be too dry or too wet", said Zemp.

He said this could lead to major changes in the entire mountain ecosystem.

"The amount of change, and that the speed of the change -- this is going to be the huge challenge," he said.

- Changing mountain lives -

Water plays an vital role in many economic sectors, such as farming, forestry, tourism and energy production.

"In the Andean countries, 85 percent of hydropower is generated from mountain areas," says UNESCO.

For some high mountain communities, glacier retreat will alter pastoral practices, such as for the Aymara minority, many of whom are forced to leave their Andean villages for urban areas as their pastures degrade.

- Electricity and transport impact -

Glacier retreat also threatens hydroelectricity production and food security. Difficult choices lie ahead.

Globally, glacier retreat and reduced snowfall in the mountains will impact two-thirds of the world's irrigated agriculture, according to UNESCO.

Other water-dependent sectors are also affected.

For several years now in France, rising river temperatures during heatwaves, or low flow rates during droughts, can slow down production at nuclear power plants.

And in recent years, the low water level in Europe's River Rhine threatened waterborne transport.

"It happens sometimes now, but in the future, it might happen more and more often as hot and dry periods will increase, and the problems will be accelerated by the lack in glacial melt," said Swiss glaciologist Matthias Huss.

- Sea levels rising -

After seawater expansion caused by rising temperatures, glaciers are the second biggest contributor to rising sea levels, but they are expected to become the main driver "over the next decades", said Zemp.

Global sea level has gone up by 10 centimetres since 1993, according to NASA satellite observations.

"Each additional millimetre of sea level rise exposes an additional 200,000 to 300,000 people to annual flooding. So small number, big impact," said Zemp.

This can have far-reaching implications.

In 2011 in Bangkok, major flooding disrupted the supply of hard drives to computer manufacturers worldwide.

"That leads to increase of computer prices" and even challenges in car manufacturing due to the demand for hard disks, said Stefan Uhlenbrook, the WMO's water and cryosphere director.

"And you see in a globalised, interconnected economy, these changes are impacting everyone."