Global coastal water clarity has increased due to human intervention

Communications Earth & Environment volume 6, Article number: 641 (2025) Cite this article

This article has been updated

Abstract

Climate change and human activity are reshaping coastal systems, yet global impacts on water clarity remain poorly quantified. Here we leverage remote sensing big data to develop a global model of coastal suspended particulate matter across continental coastal waters, and show that global coastal suspended particulate matter concentrations have declined by 0.28 mg L−1 annually since 2000, driven by natural processes and human intervention. Furthermore, the spatial extent of areas exceeding the 2000 global mean threshold has shifted landward at an average rate of 0.014 km year−1. Long-term sea level rise and diminished sediment delivery—driven by urbanization and expanding impervious surfaces—were the dominant drivers of this global clarification trend. In contrast, moderate increases in wave height and salinity enhanced resuspension, while larger shifts promoted suspended particulate matter settling. These findings provide a basis for tracking suspended particulate matter trends and guiding sustainable coastal management under urban and climatic pressures.

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Introduction

Global climate change, linked to substantial anthropogenic forcing1,2, has triggered cascading disruptions across Earth’s critical coastal interfaces—where 90% of marine biodiversity converges and 40% of humanity resides. As emphasized by the IPCC Sixth Assessment Report3, this rapid acceleration of climatic forcing has intensified terrestrial-oceanic couplings beyond historical analogs. However, the underlying processes governing these interactions remain poorly understood. Accelerated ice-sheet meltwater4 and intensified hydro-meteorological extremes5,6 have disrupted sediment delivery systems that stabilized nearshore ecosystems over millennial timescales7,8,9. Concurrently, rising sea levels and altered wind regimes10,11 are intensifying coastal erosion and wave-driven sediment remobilization. Together with expanding coastal urbanization12,13 these perturbations are reconfiguring sediment transport pathways and driving emergent degraded water quality hotspots characterized by suspended particulate matter (SPM) accumulation. Crucially, the nonlinear couplings between climate-driven hydrodynamic shifts14 and anthropogenic pressures on nearshore environments15,16 generate feedbacks that may exceed biogeochemical thresholds for coastal water clarity—a vital indicator of ecosystem health. These synergistic forces create intricate and spatially divergent patterns of material flux between land and sea, with some coastal regions experiencing sediment depletion while others exhibit localized accumulation or enhanced resuspension. Such heterogeneity underscores the need to better understand the long-term trends and multifactorial drivers shaping land–ocean exchanges.

Advances in remote sensing big data have transformed the monitoring of land–ocean interactions, providing high spatial and temporal resolution and deep insights into these dynamic exchanges. While agencies like the U.S. Environmental Protection Agency emphasize SPM as a key water quality metric, their understanding of how these fluxes respond to the combined pressures of human activities and climate change on a global scale remains limited. Satellite-derived data products, such as those tracking sediment transport, ocean currents, and land-ocean flux estimates, are indispensable for deepening our understanding of these interconnected systems. Despite advances in satellite-based coastal monitoring17,18, critical knowledge gaps persist in deciphering how these multiscale drivers synergistically govern global patterns of water clarity. The absence of a unified framework to reconcile localized sediment dynamics with planetary-scale transport mechanisms hinders predictive understanding of coastal ecosystem resilience, particularly in quantifying the relative contributions of climate forcing versus anthropogenic pressures on SPM budgets.

We focused on the 100 km marine ecotone along continental coastlines worldwide, leveraging 23 years (2000–2023) of consistent moderate resolution imaging spectroradiometer (MODIS) observations to track decadal-scale trends in coastal SPM, decode multiscale land–ocean coupling mechanisms, and assess their anthropogenic and climatic drivers. A remote sensing dataset for coastal suspended sediment concentration was developed to analyze spatiotemporal patterns of global coastal SPM levels, derived from the National Aeronautics and Space Administration (NASA)’s Terra and Aqua MODIS satellites’ global daily land surface reflectance (SR) products (500-m resolution). A coastal SPM retrieval algorithm, adapted from a global reference method18, was systematically implemented. Validation against in-situ SPM measurements from 1106 coastal observatories confirmed methodological robustness, demonstrating a median absolute percentage error (MAPE) of 21.1% across global heterogeneous marine environments. Our methodology quantifies coastal waters SPM transport using impervious surface area (ISA)19 as the human pressure index, while integrating sea surface height (SSH), wave height, and salinity as natural drivers. The analytical framework is grounded in established sediment transport models20,21,22 but innovates through global-scale big data spatio-temporal coverage and machine learning-enhanced pattern recognition.

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https://www.nature.com/articles/s43247-025-02638-x

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