This post was written by Andrea Becerra, who recently graduated from The Fletcher School at Tufts University with a Masters in International Environment and Resource Policy and Integrated Water Management. She is a consultant for NRDC focusing on urban and rural water management issues in Latin America.
Nature-based solutions are the focus of this year’s World Water Week in Stockholm, where thousands will gather to discuss critical challenges and innovative solutions for managing increasingly threatened water resources. Green infrastructure is central to nature-based solutions, because it capitalizes on nature’s ability to clean air, alleviate floods, filter water, and mitigate excessive heat. Two examples of green infrastructure that provide natural water management are green roofs and rain gardens, which help urban centers mimic the water cycle and improve a city’s capacity to re-direct, absorb, and re-use floodwater. This is an important tool for water-stressed cities like Santiago, Chile, that already grapple with both water scarcity and flooding—threats that will only intensify with climate change.
Urbanization coupled with climate change makes Santiago particularly vulnerable to flooding and the loss of valuable groundwater recharge. In order to accommodate a growing population, the city has expanded into the periphery, replacing natural landscapes and agricultural land with paved roads, residential buildings, and commercial centers. Heavy downpours and impermeable city streets leave little room for flood waters to exit during storms. At the same time, impervious surfaces decrease the rate of groundwater recharge.
As a result, in less than a decade Santiago has experienced three major flooding events that cut off water supplies to several hundred thousand people. The worst such flood, in 2017, left more than four million people without water. If the city’s current rate of expansion and construction continues, scientists at the Helmholtz Centre for Environmental Research predict that flooding hazards will increase. Beyond water disruptions, floods can also cause electricity cuts, increase the spread of water-borne illnesses, can be deadly and cause major and costly damages to infrastructure.
Meanwhile, the Maipo River basin, the most important water source for Santiago, is projected to experience a 40 percent reduction of its water balance by 2070 due to loss of precipitation and glacial retreat linked to climate change. The region has already experienced record dry years. From 2011 to 2015, Santiago experienced a prolonged drought known as the Mega Drought, characterized by 30-70 percent annual precipitation deficits and the warmest six-year period on record. Misallocated water resources compound the problem—a total of 20 aquifers in and around Santiago are over-extracted and water quantities are receding.
In drought- and flood-prone regions like Santiago, green infrastructure can serve the dual-purpose of alleviating flood damage while also replenishing receding groundwater supplies. Green infrastructure comes in many forms and scales, ranging from permeable parking lots to land conservation. Unlike pavement, forests and permeable parking lots retain water and slow runoff, reducing flood peaks. At the same time, water that is not lost as surface runoff can infiltrate soils and porous pavement, enhancing groundwater recharge.
The two panels in the infographic show mirror images of a city, one with green infrastructure and one without. In the left-hand scenario, stormwater quickly accumulates over impervious surfaces. On the right, an abundance of green infrastructure—trees, green rooftops, rain barrels, bioswales that line the streets, and a permeable parking lot—combines to slow, collect, and filter stormwater. The same storm that leads to a deluge of water in one setting barely disrupts the other.
This year’s World Water Week focuses on the importance of balancing green and grey solutions. Grey infrastructure made of concrete and steel, like pipelines and ditches, serves an important function across the world. However, it tends to serve the single purpose of channeling water, unlike the multiple societal benefits offered by green infrastructure.
Natural solutions that slow runoff and increase infiltration can also make cities healthier, cleaner, cooler in the summer, and more beautiful. A recent study documented an improvement in mental health in parts of Pennsylvania where vacant urban lots were converted to green space. Green infrastructure also helps purify the surrounding air. This is particularly important in central Chile, where particulate matter pollution levels contributes to some of the most toxic air in the Americas. In addition, water filtration through natural solutions can bring down greenhouse gas emissions from pumping and wastewater treatment.
Beyond environmental benefits, green infrastructure also makes financial sense. Both Lancaster, Pennsylvania, and Milwaukee, Wisconsin, have had success reducing wastewater treatment costs through green infrastructure, resulting in annual savings of $600,000 and $1.3 million respectively. On the other side of the world, coastal communities in Vietnam have turned to mangrove reforestation as a cost-effective flood mitigation strategy. One such community, Soc Trang, will save an estimated $1.8 million over 20 years by implementing mangrove rehabilitation instead of a traditional concrete dyke system.
It is not surprising that World Water Week 2018 will highlight the valuable role that nature can play in solving our most pressing water problems. Green infrastructure makes environmental, social, and economic sense. The Chilean government recognizes the importance of addressing flood risks and water scarcity in its climate change and adaptation plans. However, green infrastructure solutions are not explicitly mentioned as part of the solution. Chile has demonstrated leadership in many ways, from being the first South American country to implement a carbon tax to the first in opening a geothermal energy plant. It can continue demonstrating its commitment to sustainable development in the face of a changing climate by harnessing green infrastructure as a tool to increase water supply, restore aquifers, and reduce flooding.