The technical achievement behind these numbers lies in the data fusion the researchers assembled. To identify where wetlands had been converted to crops, the team drew on GLC_FCS30D, a global land-cover dynamics product at 30-meter resolution built from dense time series of Landsat imagery, alongside GlobeLand30 and fine-resolution wetland maps that distinguish marshes, swamps, floodplains, and coastal and tidal wetlands. Crop productivity was estimated using satellite-derived net primary production from the GLASS dataset, cross-checked against CROPGRIDS, a geo-referenced global dataset covering 173 crops, and crop-calendar information from the GGCMI Phase 3 archive. Flood hazard came from three independent sources: the European Commission’s Joint Research Centre global flood hazard map for a 100-year return period, a global coastal flood map, and the satellite-based Global Flood Database, which records actual inundation events observed from orbit. By layering these datasets in Google Earth Engine and validating the results at case-study sites, the researchers produced the first globally consistent picture of what happens when wetlands become fields.

The productivity findings strike at the heart of the rationale for reclamation. The team compared yields on wetland-reclaimed croplands with those on existing croplands and with the yields achievable on other agricultural land, quantifying a local yield gap for each converted parcel. Nearly half of the reclaimed croplands showed lower yields than established farmland, and the penalty was especially severe where upland crops such as maize, wheat or soybeans were planted on soils that had spent millennia functioning as saturated wetland ecosystems. Waterlogged, often saline or organic-rich wetland soils are poorly suited to the root systems and drainage requirements of upland cereals, and the legacy hydrology of a drained wetland can suppress productivity for years after conversion. The aggregate result is stark: despite occupying real land area, wetland-reclaimed croplands contributed only about 0.1 percent of total global crop production between 2000 and 2022, a contribution so small that it barely registers in the global food ledger.

Against that marginal gain, the flood exposure numbers are alarming. More than half of the world’s wetland-reclaimed croplands face severe flood hazards, and their average flood exposure probability is 23 times higher than that of all croplands globally. This is not a coincidence of geography but a structural feature of the conversion itself. Wetlands occupy low-lying positions in the landscape, in river floodplains, lake margins, deltas and coastal zones, precisely the places where water accumulates during heavy rainfall, snowmelt, storm surges and high tides. Intact wetlands act as natural sponges and buffers, storing floodwater and releasing it slowly, a regulating service documented extensively in the hydrological literature. When the wetland is drained and planted, the land loses that buffering capacity while remaining in the flood’s path. The result is a double exposure: the crops are grown where floods naturally occur, and the removal of the wetland makes the surrounding landscape more flood-prone as well.

The study’s most consequential finding is what the researchers call dual vulnerability. Globally, 60 percent of wetland-reclaimed croplands suffer simultaneously from limited agricultural gains and high flood exposure, meaning they produce less food than conventional farmland while facing dramatically greater odds of inundation. Using a multi-objective trade-off analysis, the team identified hotspots where both problems converge, and those hotspots are not randomly distributed. They cluster disproportionately in food-importing countries and in low-income countries, places where the capacity to absorb crop losses is weakest and where dependence on domestic harvests is often highest. In such settings, a single flood event can wipe out harvests on fields that were already underperforming, compounding food insecurity rather than relieving it. The pattern inverts the usual logic of agricultural expansion, which assumes that bringing new land under cultivation adds resilience to the food system.

The historical context makes the new findings more urgent rather than less. Previous research, including a landmark 2023 analysis in Nature, estimated that extensive global wetland loss over the past three centuries has been driven substantially by agricultural conversion, and meta-analyses of wetland conversion drivers have consistently ranked crop cultivation among the leading causes worldwide. Climate change is now amplifying the stakes. Studies of global flood risk under warming scenarios project that extreme precipitation and rising sea levels will intensify flood hazards in exactly the low-lying coastal and deltaic regions where wetland reclamation has been most aggressive. Meanwhile, satellite observations have shown that the proportion of the global population exposed to floods has been increasing, and rapid development in flood zones continues worldwide. Draining wetlands in the twenty-first century therefore means farming land whose flood risk is rising, not static, and doing so at the cost of the very ecosystems that moderate that risk.

The environmental costs extend well beyond flood regulation. Converting wetlands to cropland is known from global meta-analyses to increase greenhouse gas emissions, particularly when coastal wetlands, riparian zones and peatlands are drained, because the carbon accumulated in waterlogged soils oxidizes rapidly once exposed to air. Wetland conversion also alters soil microbial communities along entire soil profiles and disrupts the water-use balance between wetlands and surrounding agriculture, creating conflicts that have been documented from closed watersheds to large river basins. Biodiversity losses follow, which is why the researchers overlaid their maps with Ramsar sites, wetlands of international importance under the global conservation convention, and Important Bird Areas. The new study adds an economic dimension to this already long list of costs: if the land produces little food and frequently floods, then the carbon emissions, habitat destruction and hydrological disruption are being incurred for almost no agricultural return.

What makes the analysis particularly valuable for policymakers is its explicit treatment of trade-offs. Rather than presenting a single average, the team used a Pareto-based framework, drawing on multi-objective optimization methods, to map where agricultural gains and flood risks trade off against each other across regions and countries. The distribution of trade-off hotspots among regions with different food-production and consumption profiles revealed that the burden of bad conversions falls unevenly. Countries that import food, and countries with lower incomes, host a disproportionate share of the doubly vulnerable croplands, suggesting that wetland reclamation often occurs not where it makes agronomic sense but where land pressure and economic constraints push expansion onto marginal, flood-prone terrain. This echoes a broader finding in the sustainability literature that win-win outcomes are rare in complex environmental management, and that land-use decisions made under scarcity tend to externalize risks onto the most vulnerable.

The policy implications are direct. The authors argue that wetland reclamation should be recognized as an unsustainable agricultural expansion strategy and that food security and wetland conservation must be reconciled rather than treated as competing goals. Practical alternatives exist. Restoration of farmed wetlands can enhance flood resistance, as demonstrated by research on returning farmlands to lakes, which measurably improved agricultural flood protection in affected regions. Improving yields on existing cropland, reducing food waste, shifting diets and improving trade systems can all relieve the pressure that drives expansion onto wetlands in the first place. International frameworks, including the Ramsar Convention and national wetland protection policies, provide legal instruments, but the new evidence suggests they need to be integrated with agricultural planning so that subsidies and land-use permits stop incentivizing conversion of the world’s remaining wetlands.

For a planet that must feed nearly ten billion people by mid-century while halting catastrophic biodiversity loss, the study delivers a clear quantitative verdict: the world’s wetlands are a poor place to look for extra food and a dangerous place to farm. The full datasets and analysis code have been released publicly through Zenodo, allowing other researchers to scrutinize the findings and apply the framework to national and regional planning. As floods intensify under a warming climate, the fields carved out of the world’s marshes and deltas over the past two decades stand as a global natural experiment with an unambiguous result. The water, in the end, comes back, and it comes back to land that was never well suited to grow crops in the first place.

Subject of Research: Global assessment of crop productivity and flood exposure on wetlands converted to agriculture from 2000 to 2022

Article Title: Limited agricultural gains but high flood risk from global wetland reclamation

Article References: Zhang, X., Dong, J., Shang, Y., Chen, X., Wang, X., Singha, M., Peng, S., Fluet-Chouinard, E., Tellman, B., & Xiao, X. (2026). Limited agricultural gains but high flood risk from global wetland reclamation. Nature Sustainability. https://doi.org/10.1038/s41893-026-01965-x

Image Credits: AI Generated

DOI: 10.1038/s41893-026-01965-x

Keywords: wetlands, agriculture, flood risk, food security, land use change, cropland expansion, remote sensing, Nature Sustainability, ecosystem services, wetland conservation, sustainability, floodplain farming