Let the water not runoff …

Our world’s soil is facing an existential crisis, its health has declined sharply and ruptured the fragile skin of the Earth. Land degradation has affected over 33% of top-soil and 90% could become degraded by 2050. An astonishing fact: It can take up to 1000 years to naturally form just two to three centimeters of top-soil.

Soil health decline can be due to a variety of causes: Soil erosion, excessive usage of chemical fertilizers without organic manure and an imbalance in fertilizer nutrients (nitrogen, phosphorous, potassium) to name a few. Widespread soil erosion due to water, wind induced erosion and chemical degradation affects both arable and open forest lands with estimates that suggest annual loss of 5.3 billion tons of top-soil and 8.0 metric tons of plant nutrients through water erosion in India.

Sponge cities as solutions: Green + Blue + Grey Infrastructure:

Our future is moving more towards urbanization and the proportion of world’s population living in cities is projected to grow two-thirds. Increased opportunities in cities, the flight from conflict, poverty and climate change events are driving more people to live or move to urban areas.

Is there an answer to livable cities that are sustainable despite frequent flood disasters, environment deterioration, water resource shortage and water ecological destruction?  There is good potential in the concept of ‘Sponge’ cities.

Sponginess of a city is determined by its natural ability to absorb rainwater and have least water run-off. A city’s assets can be classified as green and blue assets: its grass, trees, bushes, lakes, ponds, water bodies and grey assets: buildings, hard paved surfaces, concrete pipes etc. By calculating the % of green, blue, grey infrastructure, soil type and water runoff potential, a city’s natural absorbency from its green and blue spaces gives a higher sponginess ranking.

India faces extreme climates and Mumbai has a history of flooding during the monsoons with the heaviest-ever recorded 24-hour rainfall figures in the world. But the city benefits from a large quantity of green infrastructure, particularly tree cover. This is driven by large areas of woodland to the northeast and a large quantity of trees interspersed around buildings. The integration of green infrastructure across the urban areas helps give Mumbai city some resilience to storms but also urban heat island effects. Let us look at the sponginess score of Mumbai when compared to Auckland, Singapore, and few others.

Sponginess of Top Cities

Agricultural run-offs:

India has very high arable land (land that has a lot of crop rotation and is ploughed or tilled regularly) and hence the topic of soil erosion due to water, wind, deforestation, overgrazing and faulty methods of agriculture is critical to address.

Soil is eroded at an average annual rate of 16.35 tons per hectare which means around 5 billion tons per year for the country. Out of this, about 29 per cent is permanently lost to the sea, nearly 10 per cent is deposited in reservoirs (which means the storage capacity in lakes/rivers and waterbodies is reduced by 1-2 per cent annually) and the remaining 61 per cent of the eroded soil is merely shifted from one site to another.

Conservation or regenerative agriculture:

Conservation agriculture as a strategy to invert the soil degradation spiral is the preferred method adopted by most countries today. No-tillage systems which eliminates intensive tillage, maintaining crop residue cover to ensure water does not run-off with the soil, and proper crop rotation using native and perennial crops have reported to improve soil organic matter (SOM) levels with carbon accumulation in diverse soils that are resilient to climate change. The recent heat wave in India resulted in an abrupt decline in wheat outputs (The average temperature in April was consistently above the 40°C mark across Punjab) and all exports of wheat was prohibited. Sustainable residue management options where crop residues were not burnt making the land bare and exposed to soil erosion, but rather keeping the soil surfaces covered with crop residue during heavy rainfall/erratic heat conditions, nutrients in the soil would make the crops more resilient to such heat waves.

Parched land due to water runoff

Natural solutions for sustainable water resilience:

Our cities are not equipped to cope with the amount of water that needs to be treated in a short period of time during extreme rainfall. Our sewer systems cannot be stretched as in most cases it is financially unfeasible, and so what is the solution?

Stone wool usage in water management of urban areas:

Stone wool is a natural product made from rock basalt and sourced directly from our earth. It is sustainable and almost inexhaustible as basalt is produced naturally and 100% recyclable. Stone wool elements have been used in largescale water storage facilities in public areas and as infiltration systems in wadis and under large, paved surfaces. Stone wool has a remarkable insulation capacity that it does not absorb water but provides resistance that delays the water to be pushed down to sewer systems in a delayed manner.

Due to the delayed discharge, water slowly permeates below the ground and thanks to its high load bearing capacity even small spaces can be designed with stone wool filtration elements in urban areas to prevent flash flooding. Instead of dealing with water by trying to get rid of it quickly, sponge cities slow water, absorb rain and halt runoff, a major source of pollution in urban waterways.

Bio-diversity parks in cities, restoring our water bodies, installing rain gardens, green roofs , green infrastructure combined with strict urban planning that prevent encroachments can help save our ever-expanding cities.

In Conclusion: Moving away from traditional hard infrastructure methods of flood barriers, concrete walls, old sewer systems, traditional methods of farming and over application of chemical fertilizers , we need to bring in solutions that mimic nature as a sustainable way of securing our soil future. Natural disasters when they happen are overwhelmingly destructive and mother nature has shown us the right path and we just need to follow it.

Sponge city construct

Published by Meena Iyer

Sustainability champion and naturally committed to support the cause of healing our planet impacted due to climate change.

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