Opportunities for natural infrastructure to improve urban water security in Latin America

Abstract

Governments, development banks, corporations, and nonprofits are increasingly considering the potential contribution of watershed conservation activities to secure clean water for cities and to reduce flood risk. These organizations, however, often lack decision-relevant, initial screening information across multiple cities to identify which specific city-watershed combinations present not only water-related risks but also potentially attractive opportunities for mitigation via natural infrastructure approaches. To address this need, this paper presents a novel methodology for a continental assessment of the potential for watershed conservation activities to improve surface drinking water quality and mitigate riverine and stormwater flood risks in 70 major cities across Latin America. We used publicly available geospatial data to analyze 887 associated watersheds. Water quality metrics assessed the potential for agricultural practices, afforestation, riparian buffers, and forest conservation to mitigate sediment and phosphorus loads. Flood reduction metrics analyzed the role of increasing infiltration, restoring riparian wetlands, and reducing connected impervious surface to mitigate riverine and stormwater floods for exposed urban populations. Cities were then categorized based on relative opportunity potential to reduce identified risks through watershed conservation activities. We find high opportunities for watershed activities to mitigate at least one of the risks in 42 cities, potentially benefiting 96 million people or around 60% of the urbanites living in the 70 largest cities in Latin America. We estimate water quality could be improved for 72 million people in 27 cities, riverine flood risk mitigated for 5 million people in 13 cities, and stormwater flooding mitigated for 44 million people in 14 cities. We identified five cities with the potential to simultaneously enhance water quality and mitigate flood risks, and in contrast, six cities where conservation efforts are unlikely to meaningfully mitigate either risk. Institutions investing in natural infrastructure to improve water security in Latin America can maximize their impact by focusing on specific watershed conservation activities either for cleaner drinking water or flood mitigation in cities identified in our analysis where these interventions are most likely to reduce risk.

Urban streams in Latin America: Current conditions and research needs

“…Direct discharges of sewage and other untreated wastewater into urban streams are major cause of degradation in all Latin American countries (Lee, 2000;Rodríguez & Martine, 2008;Noyola et al, 2012;Tellman et al, 2018;UN, 2019;Rodríguez et al, 2020). Our findings indicate that there is a wide range of management strategies for dealing with sewage in the area, ranging from household septic tanks to city-wide sewerage collection and water treatment plants.…”

“…In general, urban streams seem to conform to characteristics associated with the urban stream syndrome even though most studies have focused on streams in higher-income economies (Walsh et al, 2005;Roy et al, 2016). Urban streams in Latin America are characterized by altered channel morphology (e.g., channelization), inputs of pollutants and sewage, and altered hydrology due to the rapid movement of runoff into streams, indicating that urbanization is affecting Latin American streams similar to streams in other regions of the globe (Romulo et al, 2018;Tellman et al, 2018). Although our survey of researchers in Latin America provides a coarse scale picture of the current status of rivers in the region, the results agree with previous studies that focused on specific cities or regions.…”

“…For example, various reviews of superficial waters in Latin America (e.g., Noyola et al, 2012 (Bower, 2014;Mena-Rivera et al, 2018). As urban sprawl continues to increase in Latin America, freshwater resources will continue to degrade and lose their value as sources of ecosystem services to humans (Lee, 2000;McDonald et al, 2011;Wade, 2012;Tellman et al, 2018;Rodríguez et al, 2020).…”

“…Green infrastructure projects may help to reduce runoff and protect streams. This type of management strategy is becoming popular in Latin America, with examples from cities like Bucaramanga (Colombia), Maracaibo (Venezuela), Quito (Ecuador), Tegucigalpa (Honduras) and San Juan (Puerto Rico) (Tellman et al, 2018). Runoff impacts stream ecosystems via two main mechanisms: by altering the natural flow regime and by transporting pollutants (Peña-Guzmán et al, 2016).…”

“…Stream conservation in the region requires appropriate management strategies to protect sources of water and effectively manage streams receiving wastewater. Most urban areas in Latin America lack legal commitments or resources allocated to protect streams (McDonald et al, 2011;Noyola et al, 2012;McDonald & Shemie, 2014;Tellman et al, 2018). Although we still have limited knowledge of streams in urban areas of Latin America, we expect most to be degraded.…”