Healthy soils for healthy cities: Restoring urban ground to prevent floods
Every 5 December, World Soil Day serves as a reminder of one of the most overlooked foundations of food security, climate resilience and urban well-being: healthy soil. The 2025 campaign, “Healthy Soils for Healthy Cities,” underscores a simple but urgent message. Soil is not just “dirt” or farmland. It is a living system that underpins water, climate and human health. Over 95% of our food comes from soil, and it supplies nearly all the nutrients plants need. Just as critically, soil regulates water: healthy soil absorbs rainfall like a sponge, filters it, and releases it slowly to recharge aquifers and sustain vegetation. Yet a third of global soils are degraded, while urban areas continue to seal the ground beneath concrete and asphalt, weakening nature’s ability to manage water.
Over 95% of our food comes from soil, and it supplies nearly all the nutrients plants need
In cities, this hidden function of soil becomes a frontline issue. UN Water notes that beneath pavements lies soil that could absorb rain and mitigate heat if left permeable and vegetated. When urban soil is sealed, however, it loses these functions, and stormwater has nowhere to go. Instead of soaking in, rainfall races across hard surfaces, overwhelming drains and turning streets into temporary rivers. The U.S. EPA warns that urbanization sharply reduces infiltration and increases surface runoff, one of the key drivers of modern urban flooding.
By contrast, open, healthy urban soils act like natural reservoirs. Research from FAO’s Global Soil Partnership shows that compacted soils shed water, while vegetated soils dramatically boost infiltration. Parks, street trees, rain gardens, green roofs and other porous features catch rainfall, slow runoff, and guide water back into the ground. This not only reduces flood peaks but also replenishes groundwater for dry periods.
Climate change further heightens this urgency. More intense downpours, combined with paved land and lost vegetation, are already accelerating erosion and washing away precious topsoil on city edges. UNEP warns that when ground permeability is lost, flood risk and land instability escalate. However, restoring soils and planting vegetation can turn cities into “sponge cities.” Nature-based planners use green infrastructure to store and filter rainwater through parks, swales, planted medians, wetlands and infiltration basins. Even small interventions, rain gardens, bioswales, and meadow strips, provide significant benefits.
SuDS (Sustainable Drainage Systems) form an essential part of this approach. Widely used in the UK and increasingly adopted globally, SuDS are designed to mimic natural hydrology by slowing, storing and filtering rainwater before it reaches sewers or waterways. Techniques such as permeable pavements, infiltration trenches, detention basins, green roofs, and bioretention cells enhance soil infiltration while improving water quality. SuDS not only prevent floods, but they also recharge groundwater, support biodiversity and create greener, cooler urban environments. In essence, SuDS operationalize the idea that healthy soils are the foundation of resilient cities.
Key benefits of healthy urban soils and SuDS:
- Flood reduction: Enhanced infiltration lowers runoff and eases pressure on drainage systems.
- Urban cooling: Moist soils and vegetation reduce heat islands.
- Water filtration: Soil microbes break down contaminants and clean stormwater.
- Carbon storage: Organic-rich soils help capture carbon.
- Biodiversity: Soil-based green spaces support pollinators, trees and urban wildlife.
- Groundwater recharge: Rainwater is stored and released slowly into aquifers.
World Soil Day, officially designated by the UN in 2014, highlights soil’s essential role in healthy environments, from rural farmland to dense cities
Evidence from China’s sponge city pilots, European SuDS projects, and U.S. soil-friendly farming practices shows these methods work. Engineered soils and nature-based designs consistently reduce runoff, improve infiltration, and increase resilience to heavy storms.
World Soil Day, officially designated by the UN in 2014, highlights soil’s essential role in healthy environments, from rural farmland to dense cities. This year’s theme invites planners, policymakers, communities and citizens to rethink city design from the ground up. With two-thirds of humanity expected to live in cities by 2050, healthy soils are one of our most powerful, natural defenses against flooding.