Growing Water Risks Threaten UNESCO World Heritage Sites

Here, we look at how water stress, drought and floods are impacting these iconic landmarks, including the Ahwar of Southern Iraq, Mosi-oa-Tunya / Victoria Falls in southern Africa, the Chan Chan Archaeological Zone in Peru and the Migratory Bird Sanctuaries along the Coast of Yellow Sea-Bohai Gulf of China — along with some of the solutions aimed at ensuring these sites don’t disappear.

 Water Stress in the Ahwar of Southern Iraq

Hidden in the heart of the Middle East’s arid landscapes lies one of the world’s most extraordinary places — the Ahwar of Southern Iraq. In 2016, UNESCO added the Ahwar to the World Heritage list as a mixed site — recognized for both its natural values and cultural legacy. It’s one of about 470 UNESCO World Heritage Sites facing water scarcity due to issues like pollution and competition for its water resources.

Fed by the mighty Tigris and Euphrates rivers, the Ahwar is among the largest inland delta systems on Earth. These sprawling marshes are teeming with life that include millions of migratory birds like the rare basra reed warbler and large wild buffalo that wade through its reed beds.

But nature is only half the story.

This realm was also the birthplace of human civilization. The Sumerians, inventors of writing, the wheel and the first cities, built legendary settlements like Ur, Uruk and Eridu on the fertile fringes of these marshes.

Today, the Marsh Arabs (Ma’dan), using ancient traditions, depend on the water, crafting floating reed houses and raising the water buffalo for food and income. Their way of life, adapted to the wetlands, tells a story of resilience that spans millennia.

However, intensifying use of water resources is placing greater strain on the Ahwar. Water stress — the ongoing competition over water — increases water pollution and threatens the ecological integrity, biodiversity and cultural significance of the Ahwar.

According to data from WRI’s Aqueduct platform, the Ahwar marshes face extremely high water stress, where over 80% of the renewable supply is withdrawn to meet human demand. Over the years, upstream dam construction, agricultural water use and periods of political instability — including significant drainage of the marshes in the 1990s — have reduced the freshwater flowing into the region. As a result, the area remains highly vulnerable during times of drought. In 2023, 68,000 people from central and southern Iraq were displaced by drought.

What survives today of the Ahwar is largely due to the determined efforts of local communities, international allies and nature itself fighting to heal. But the region is still at risk. Looking forward, climate change will only make the region hotter and drier. The Intergovernmental Panel on Climate Change ranks southern Iraq as one of the five most likely places to be impacted by climate change. By 2050, the Aqueduct platform shows that water stress is expected to intensify throughout the region.

Drought at Mosi-oa-Tunya/Victoria Falls

Straddling the border between Zambia and Zimbabwe in southern Africa, Mosi-oa-Tunya (which means “the smoke that thunders”)/ Victoria Falls is more than a stunning waterfall. It was inscribed as a UNESCO World Heritage Site in 1989 for its vital ecosystem and essential source of livelihood for tens of thousands of people. Despite its reputation for massive cascading water, Mosi-oa-Tunya/Victoria Falls has faced recurring drought over the past decade and at times dried up to barely a trickle. 

Fed by floodwaters from the Zambezi River, Mosi-oa-Tunya/ Victoria Falls is crucial to the planet for several reasons.

Economically, Mosi-oa-Tunya/ Victoria Falls drives the tourism industry in both Zambia and Zimbabwe, drawing over 1 million visitors a year under normal conditions. Local tour guides, lodge owners, craft sellers and conservationists rely heavily on the flow of visitors. The water flowing from the falls also feed hydroelectric plants downstream that supply power to millions across southern Africa.

Ecologically, its riverine “rainforest” nurtures a rich diversity of wildlife and plants, including endangered and migratory birds like the Taita falcon. Rhinoceroses, elephants and lions roam the park in search of watering holes for drinking, bathing and hunting.

Mosi-oa-Tunya/ Victoria Falls experienced droughts as recently as 2016, 2019 and 2024. Research on rainfall patterns near Mosi-oa-Tunya/Victoria Falls shows that the onset of the rainy season, normally in October, is arriving later in the year. That means in a drought year, it takes longer for relief to arrive; and the longer a drought continues, the more it affects the people, crops and economy around it.

In 2019, more than 300 people in Zimbabwe were attacked by animals in search of food and water; 45 million people in southern Africa were in need of food aid amid crop failures; and in Zimbabwe and Zambia, hydroelectric power shutdowns caused blackouts up to 18 hours a day — affecting millions while posing significant challenges to development and climate adaption goals.

An Aqueduct analysis found that Mosi-oa-Tunya/ Victoria Falls ranks as a medium drought risk, below the more than 430 UNESCO World Heritage Sites that rank as a high drought risk. This is primarily because relatively low population density and limited human development immediately surrounding the site reduces overall exposure. However, the site faces increasing pressure from tourism-related infrastructure development and data shows the probability of drought occurrence ranks high — a finding reinforced by the many recent droughts that have plagued the region.  

Climate change is not only expected to make these droughts more frequent, but recovery is expected to last longer, especially in places that aren’t prepared.  The time between droughts may not be long enough for the ecosystem to recover — which is particularly concerning for Mosi-oa-Tunya/ Victoria Falls.

River Flooding in the Chan Chan Archeological Zone

Before the Inca carved their stone temples into the heights of Cusco and Machu Picchu in Peru, the Chimú sculpted an empire from sunbaked earth called Chan Chan (which means “Sun Sun”). Nestled between the Pacific Ocean and the foothills of the Andes Mountains, the desert city of Chan Chan was once the largest city in pre-Colombian South America.

Today, it remains the largest adobe ruins in the world and a marvel of urban planning. The site was inscribed on the UNESCO World Heritage List in 1986 and simultaneously placed on the List of World Heritage in Danger, due to its overall vulnerability to natural erosion and extreme climatic events associated with the El Niño–Southern Oscillation phenomenon.

Behind its intricately carved walls lies a complex cityscape of palaces, temples, homes, workshops and storehouses. Stretches of farmland once surrounded Chan Chan, supported by a sophisticated irrigation system that diverted water from the Moche and Chicama rivers. These advanced water management systems not only sustained the Chimú with water during times of drought, but may have also protected the city from El Niño flooding. 

But the1,000-year-old adobe walls of Chan Chan were not built to withstand the intensified El Niño flooding of the 21st century. 

The El Niño climate pattern warms the ocean and upends wind patterns, especially in the Pacific. In Peru, the warmer sea temperatures transform the normally dry winds into humid air that gathers in the foothills of the Andes. When fully saturated, this tropical atmosphere can release up to 10 times more rain than usual. Mountain rivers swell, hurtling toward the coast as torrents of water, mud and rock. Known locally as huaycos, these destructive mudslides sweep away everything in their path, from homes and roads to hospitals and schools.

Chan Chan is no exception. According to WRI’s Aqueduct platform, the UNESCO site and its surrounding region in La Libertad face extremely high risk to river flooding, a threat that is only expected to grow and is shared by more than 390 sites on the UNESCO World Heritage list. By 2050, the population affected by floods each year in an average, non- El Niño year in La Libertad is expected to double from 16,000 to 34,000 due to a combination of human activity and climate change. In an El Niño year, that increase may be much higher.

Modern agriculture has dramatically expanded around Chan Chan. All that irrigation has pushed up the groundwater level, leaving less room in the soil to absorb rainfall during storms. The result: more surface runoff and greater flood risk. At the same time, warming global temperatures are projected to make El Niño events more frequent and intense.

Some experts warn that Peru’s coast is already offering a glimpse of what climate change looks like in real time. Despite having disaster preparedness plans in place, Peru was hit hard by El Niño floods in both 2017 and 2023. Hundreds of people were killed, thousands were displaced — some permanently — and millions of residents were affected. From space, the scars of swollen rivers and devastating huaycos are visible near Chan Chan. On the ground, caretakers report that the site’s delicate adobe structures are deteriorating from heavy rainfall and erosion.

Chan Chan has weathered centuries of time, wind and desert sun. Bold conservation and climate resilience measures are needed to prevent this ancient city — once a marvel of water mastery — from falling victim to the very element it once controlled.

Coastal Flooding Impacting the Migratory Bird Sanctuaries of the Yellow Sea and Bohai Gulf Coast of China

In 2022, a bar-tailed godwit known as B6, being studied by the U.S. Geological Survey, captured global attention with an astonishing feat of endurance: On his very first migration, the 4-month-old bird flew nonstop from Alaska to Australia — a staggering journey of over 8,425 miles completed in just 11 days, setting a new world record.

But B6’s journey didn’t end there. He still had to return home and would likely need additional rest and fuel to make the equally long journey back. Like other bar-tailed godwits, B6 could have stopped in the intertidal wetlands of China’s Yellow Sea–Bohai Gulf coastline to feed and rebuild his strength before completing his migration.

For 50 million migratory waterbirds like B6 that pass through this region each year, these tidal flats are more than just a pit stop, they are a lifeline that also provide shelter and breeding grounds.

However, the Migratory Bird Sanctuaries along the Yellow Sea and Bohai Gulf Coast of China, which was added to the UNESCO World Heritage list in 2019, have faced pressures from nature and human activities. Large-scale development and encroaching coastal flooding are squeezing the wetlands to death.

For decades, land reclamation — converting sea areas into land by filling in marshes for agriculture, industry or urban development — led to the loss of extensive mudflat habitats. In 2018, China responded by banning land reclamation in Bohai Bay, a move widely praised by conservation groups.

But another challenge is harder to control: coastal flooding, which is currently impacting close to 50 sites on the UNESCO World Heritage list. Sea levels in Bohai Bay have risen at least 6 inches (about 0.15 meters) since 1980, driven in large part due to climate change. Even without storms, tidal conditions have temporarily raised sea levels by up to 1 meter (3.2 feet) in some areas, flooding the nearby cities.

As the sea pushes inland, it leaves less exposed mudflats where birds can find food — especially where protective infrastructures like seawalls and levees prevent wetlands from naturally shifting further inland. While essential for protecting human communities, these structures limit coastal habitats from adapting to rising seas. Losing this flyway could lead to a dramatic decline in bird populations, potentially reducing numbers by as much as 72% according to a study in the Royal Society B: Biological Sciences.

The effects of coastal flooding aren’t limited to birds. In Shandong Province, which includes parts of the Bohai wetlands, an estimated 21,000 residents are affected by coastal flooding each year, according to Aqueduct Floods data. That number could increase tenfold by 2050 due to a combination of climate change, sinking land — known as land subsidence — and population growth.

Despite the challenges, there are reasons for optimism. The 2018 ban on land reclamation was a major step forward, and local restoration projects are beginning to show positive results. In Nandagang Industrial Park, for example, coastal development was halted in 2015 to allow wetland restoration. In 2019, around 20,000 birds visited the site and by 2023, that number grew to 100,000.

Acting for the Future

Every World Heritage Site, shaped by the people and nature that created it, has the power to transport you to a time and place. Yet many of these sites are facing their own distinct challenges over water. While the stories vary, the path forward is the same — solutions that can be implemented today to protect our heritage for future generations.

• Locally: restore vital landscapes that support healthy, stable water. Invest in nature-based solutions like planting trees to restore headwater forests or revitalizing wetlands to capture flood waters and recharge aquifers. These approaches can build resilience to extreme weather and address multiple water challenges simultaneously.
   
• Nationally: enact conservation policies to protect vital landscapes from unsustainable development.
   
• Internationally: elevate water’s status as a global common good. Establish equitable transboundary agreements on sharing water across borders.

Data visualizations by Sara Staedicke; story edited by Alicia Cypress.