Martin Robert Tillotson

Rapid urbanisation and climate-induced extreme weather events have intensified urban stormwater runoff challenges. Biofiltration systems have emerged as effective, sustainable urban drainage solutions for mitigating these impacts. A total of 78 peer-reviewed studies were assessed to synthesise findings on how design parameters influence pollutant removal performance in biofiltration systems treating urban stormwater runoff. Peer-reviewed articles published from 1 January 1995 to 3 June 2025 were retrieved from Scopus and Web of Science (WoS). Non-peer-reviewed, non-empirical, incomplete, or non-relevant studies were excluded. Rigorous application of a standardised review protocol and predefined criteria was employed to mitigate bias. The findings reveal high removal efficiencies for certain trace metals, ammonium, Escherichia coli (E. coli), hydrocarbons, and microplastics, with inconsistent removal for total nitrogen, nitrates, and phosphorus. The primary pollutant removal mechanisms were adsorption, ion exchange with select media, and denitrification in saturated zones. Only 22% of the reviewed studies incorporated a saturated zone, while 18% included a protective surface layer, despite both design elements being associated with improved pollutant removal performance. Variations in media composition and stormwater quality limit comparability across studies. This review highlights the need for context-specific design guidance and further exploration of multi-functional media to enhance multi-pollutant removal.

This study quantifies nine key nutrient gaps by comparing national demand and domestic production in each of Africa’s 54 countries. While different countries exhibited varying degrees of nutrient gaps for different nutrients, all countries were deficient in at least one nutrient, with eight being deficient in all nutrients. Based on current agricultural productivity, only seven African nations would be able to satisfy their nutrient gaps through production expansion given water and land constraints.

Water scarcity is a global challenge in many emerging economies, including China. China is one of the most extensive freshwater users and has set water efficiency improvement goals for 2030 at the prefecture level. However, no systematic water use and savings comparison exists across prefectures and sectors. Here, we used datasets of water withdrawal for 10,608 industrial and 1715 agricultural sub-sectors for 343 prefectures, and explored the opportunities to reduce water use. Results show that 10% of the least water-efficient industrial sub-sectors represent a disproportionate 46% water use. 18.9 km³ (±3.2%) water saving in industry and 50.3 km³ (±2.3%) in agriculture could be achieved, equivalent to Russia’s annual demand. A minority of sectors, including cloth(ing)- and chemical-manufacturing, rice-, vegetable- and fruit-cultivation, could contribute the most to water savings. Our study is essential for identifying water use and efficiency information for individual prefectures and sectors.

Consumption behaviours exert pressure on water resources both locally and globally through interconnected supply chains, hindering the achievement of Sustainable Development Goals 6 (Clean water and sanitation) and 12 (Responsible consumption and production). However, it is challenging to link hotspots of water depletion across spatial scales to final consumption while reflecting intersectoral competition for water. In this study, we estimated the global exceedance of regional freshwater boundaries (RFBs) due to human water withdrawal at a 5-arcmin grid scale using 2015 data, enabling the identification of hotspots across different spatial scales. To reduce uncertainty, we used average estimates from 15 global hydrological models and 5 environmental flow requirement methods. We further attributed the hotspots of exceedance to final consumption across 245 economies and 134 sectors via the multi-region input–output model EMERGING. Our refined framework revealed previously unknown connections between regional hotspots and consumption through international trade. Notably, we found that 24% of grid-level RFB exceedance (718 km³ yr⁻¹; 95% confidence interval of 659–776 km³ yr⁻¹) was outsourced through trade, with the largest flows (52 km³ yr⁻¹; 95% confidence interval of 47–56 km³ yr⁻¹) from water-stressed South and Central Asia to arid West Asia. The demand for cereals and other agricultural products dominated global consumption-based RFB exceedance (29%), while the exports of textiles and machinery and equipment exacerbated territorial exceedance in manufacturing hubs within emerging economies. Our methodology facilitates the tracing of global hotspots of water scarcity along supply chains and the assignment of responsibilities at finer scales.