Nearly 30 percent of Peru’s glaciers have melted away since 2000, threatening a critical source of drinking water and irrigation for millions of people downstream, according to a new study published in the journal The Cryosphere. Overall, the country lost nearly 8 gigatons of ice from 2000 to 2016, with 170 glaciers — covering an area equivalent to 80,000 soccer fields — disappearing entirely.

Scientists warn that the melting of Peru’s glaciers is only getting worse — ice loss from 2013 to 2016 was four times faster than the previous four-year period. The new research, led by scientists at the Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU) in Germany, is the first region-wide assessment of glacier retreat in the Peruvian Andes, which is home to 92 percent of the world’s tropical glaciers.

Peru’s glaciers have always served as an important source of water for communities downstream, from the Andes to the country’s coastline, particularly during the dry season. But as glacier melt increased in the 1970s in response to global warming, this extra water fueled urban growth and large-scale agriculture and led to the construction of several new hydroelectric dams.

But scientists warn that as these glaciers continue to melt, this once seemingly endless water supply could run dry in the coming decades, with significant socio-economic impacts. A shorter-term risk, they say, is that meltwater lakes are becoming increasing swollen, which can lead to outburst flooding in downstream communities. In the Cordillera Blanca area of Peru, glacier-related natural disasters claimed more than 25,000 victims from 1941 to 2003.