Eyes in the sky can track effectiveness of nature-based solutions

Combining data from ground-based techniques and remote monitoring using airborne devices offers new opportunities to monitor nature-based solutions (NbS) to mitigate floods, droughts, heatwaves, landslides, storm surges and coastal erosion, according to a new study.

According to the International Union for Conservation of Nature, NbS are actions to protect, sustainably manage, and restore natural and modified ecosystems that address societal challenges effectively and adaptively, simultaneously providing “human well-being and biodiversity benefits.” Since 2008, nature-based solutions (NbS) have emerged in the field of disaster risk reduction (DRR) and climate change adaptation (CCA) as a resource and cost-efficient measure to complement the limitations linked with the grey-engineered approach.

But their applicability and reproducibility are often hindered by the lack of standard monitoring methods, tools and indicators. Tracking how efficient these solutions are can help quash scepticism concerning the selection of NbS and address the imbalance between grey and green infrastructure, explained study lead author Prashant Kumar.

“By providing a wealth of good practice experiences and accompanying monitoring data, NBS assessment can create a gradual change in policy-makers and practitioners perception and therewith an increased wider uptake of NbS for their ecologic, socio-economic and monetary benefits,” Kumar, Associate Dean (International) and the Director of the GCARE at the University of Surrey told Mongabay-India.

Surrey’s Global Centre for Clean Air Research (GCARE) collaborated with experts from across Europe to analyse monitoring methods (ground-based, airborne and space sensors) that measure the success of NBS – such as wetlands, forest restoration projects and installation of green walls against five hydrometeorological risks: floods, droughts, heatwaves, landslides, and storm surges and coastal erosion. The review includes a few case studies from India where floods and tropical cyclones contribute almost 75 percent to the total mortalities per year due to EWEs; heatwaves and lightning are gaining importance.

Assessing what works and what doesn’t improve the confidence and competence associated with designing and implementing NbS. This could help appease existing hesitation and scepticism in choosing an NbS over grey-engineered alternative by providing evidence to questions of performance and related uncertainty, observed Prashant Kumar, noting the lack of globally accepted and standard approaches to NbS monitoring. But there are limitations to remote sensing measures in tracking the effectiveness of NbS in hydrometeorological hazards.

NbS science needs to trickle down into evidence-based policy-making. Additionally, experts have underscored the importance of the participation of local stakeholders for sustainable and equitable NbS.

Parvathi Preethan, Senior Project Associate with the Climate Resilience Practice team at WRI India, who was not associated with the study, agreed with the observations, particularly on making the case stronger for investments in nature-based solutions based on scientific data. “In addition to ensuring accountability, tracking and monitoring can also build evidence for the effectiveness of NbS, including their co-benefits, life cycle operational costs and economic contributions – thus making a stronger case for investment decisions, particularly by the private sector.”

“Currently, many developing countries find it difficult to assess the value of NbS and structure appropriate NbS investments. Having a set of common metrics to measure and track NbS would help to make more sound arguments for mobilising additional capital and resources needed,” Preethan told Mongabay-India.

Urban greenspace as a nature-based solution to warming

A range of remote sensing technologies (satellites, drones, and radars) can keep an eye on the effectiveness of NbS under conditions such as extreme weather and climate conditions (e.g. strong wind, heavy rainfall and snowfall), at night (e.g. active remote sensing tools), and over a larger area and inaccessible regions (e.g. monitoring NbS at regional scales such as river restoration, dunes or wildlands).

An example is the use of remote sensing technologies to judge if the green cover in urban areas can significantly lower warming in cities.

For instance, researchers used land surface temperature (LST) and a remote sensing vegetation index called Normalised Difference Vegetation Index (NDVI) to scrutinise the temperature distribution pattern in Nagpur in Maharashtra’s Vidarbha region where temperatures hit 50 degrees Celsius in summers. NDVI reflects the surface green cover and together with LST measurements, helps evaluate how efficient are urban greenspaces in controlling urban heating.

Review co-author Srikanta Sannigrahi, tapped into Landsat satellite data provided by USGS (United States Geological Survey) to calculate both LST and NDVI for Nagpur. In Nagpur, this high temperature is not well distributed across the city. The temperature is very high in the city centre or central part of the city and it is comparatively low in the regions with high vegetation cover.

“Using LST and NDVI, we found that LST is quite high in the urban built-up area than that of vegetation area in April 2000, 2010, and 2015. Our results indicate that urban greenspace can substantially reduce urban heating and can act as a nature-based solution for handling the growing problem of urban heating,” explained Sannigrahi, of the Spatial Dynamics Lab, at School of Architecture, Planning and Environmental Policy, University College Dublin, Ireland.

Challenges in monitoring

But remote monitoring against hydro-meteorological hazards does have its share of limitations. For instance, the Advanced Very High-Resolution Radiometer (AVHRR) scanner-based flood imageries are often distorted by cloud cover and lack good spatial resolution. In terms of monitoring hydrological drought, satellite data fails to capture river flow rates or aquifer levels.

“Satellite-based monitoring can reasonably monitor hydrological droughts at the catchment scale, but is not adequate to capture the more localised scale NbS (green roofs/walls),” elaborated Prashant Kumar. Unmanned Aerial Vehicle-based photogrammetry (relying on photographs) lacks the canopy penetration capacity of LiDAR signals; while satellite radar can monitor floods and droughts in adverse weather conditions, the data analysis can be intricate and even strenuous to inexperienced analysers.

There are also cost concerns. If instruments and sensors deployed for other purposes (weather-related conditions) are used to monitor NbS performance as an offshoot then it comes at zero cost. But planning for special airborne equipment “only for the purpose of NbS efficiency monitoring has high purchase and operational costs,” noted Kumar. He, however, emphasised that investments in monitoring NbS benefit governments and society in the long run even if the initial costs are high.

Policy shifts required

NbS is not quite there yet: at a stage where it can compete with long-established approaches and standards used in the civil engineering domain. “Not now, but through time, we can arrive at a holistic methodology that could be used to monitor the entire components of NbS performance, through working with scientists, software engineers, remote sensing engineering/aerospace engineering, policy-makers and end-users in a collaborative process. It is possible to implement NbS that are both climate effective and will ensure environmental justice,” asserts Kumar.

While in India, there has been a recent shift towards acknowledging the role of nature in urban planning and policy-making (Bengaluru, Surat, Hyderabad, and Gorakhpur), there isn’t a specific integrated policy for measuring the effectiveness of NbS.

“There is a gap between the NbS science and its usage in evidence-based policy-making, resulting in ambiguous and contradictory information on the role of NbS for DRR, such as quantification of ecosystem value and services to reduce vulnerability. Hence, policies need to be recrafted for including the NbS concept and its relevance in the Indian context. Related research and policy issues are essential for successful amalgamation of NbS indigenous knowledge in resource conservation and climate change adaptation,” he added.

The lack of a coherent institutional policy means NbS projects remain largely sporadic and scattered, observed Preethan; urban development schemes introduced by the government, such as the Green India Mission and Atal Mission for Rejuvenation and Urban Transformation (AMRUT) can unlock the potential of NbS.

“Funding for NbS currently is predominantly on a case-by-case basis, and mainstreaming NbS into existing development schemes would help tap their budgets and generate a steady flow of resources. This can also help identify green investment opportunities –for example identifying opportunities to develop green infrastructure to complement existing grey infrastructure going forward, under development schemes,” Preethan said.

Japan-based Rajib Shaw, disaster and environmental management expert, who was not associated with the review believes that the composite deployment of grey and green infrastructure solutions to firm up the policy discourse. “Urban-rural partnership/resource connectivity becomes crucial and we also need to consider the public dimension such as awareness, understanding, commitment to successfully implement NbS,” Shaw, professor in Graduate School of Media and Governance in Keio University, told Mongabay-India.

In an essay,  University of Oxford’s Nature-based Solutions Initiative Director Nathalie Seddon underscored that to “qualify as an NbS, an action must sustainably provide one or more benefits for people while causing no loss of biodiversity or ecological integrity compared to the pre-intervention state.” To be sustainable and equitable, NbS must also be designed, implemented, managed and monitored by or in partnership with indigenous peoples and local communities through a process that fully respects and champions local rights and knowledge, and generates local benefits, the essay adds.

Banner image: Airborne measurements can help sense how efficient are urban green spaces in tackling urban heating, such as in Nagpur, Maharashtra. Photo by Ganesh Dhamodkar/Wikimedia Commons.