Natural capital: defined by a recent World Bank/WRI report as “the planetary resources (e.g. plants, animals, air, water, soils, minerals) that sustain life and well-being. Natural capital underpins clean air, water and energy security, shelter, medicine, and more. Natural capital concepts are increasingly applied in national and corporate accounting to keep track of society’s dependence and impact on these vital resources.”

Nature-based solutions: defined by the IUCN as “…actions to protect, sustainably manage, and restore natural or modified ecosystems that address societal challenges effectively and adaptively, simultaneously providing human well-being and biodiversity benefits”.

Green infrastructure: defined by a recent World Bank/WRI report as infrastructure that “…intentionally and strategically preserves, enhances, or restores elements of a natural system, such as forests, agricultural land, floodplains, riparian areas, coastal forests (such as mangroves), among others, and combines them with gray infrastructure to produce more resilient and lower-cost services”.

Gray infrastructure: defined by a recent World Bank/WRI report as “… built structures and mechanical equipment, such as reservoirs, embankments, pipes, pumps, water treatment plants, and canals. These engineered solutions are embedded within watersheds or coastal ecosystems whose hydrological and environmental attributes profoundly afface the performance of gray infrastructure”.

While substantial evidence exists on the function of vegetative planting and other NBS methods for landslide risk, cost-effectiveness information is more limited. However, evidence suggests that disaster risk mitigation before an event occurs can be more cost effective than addressing social, environmental, and economic damage post-disaster, and the evidence for this, especially in developing countries, is an area of continued research (for example, see Shreve and Kelman 2014 who note that most cost-benefit analyses of disaster risk mitigation measures focus on flood, drought, and earthquakes). While not specific to landslide risk, some research has pointed to NBS as a cost-effective alternative to grey infrastructure. For example, WRI has estimated lower costs associated with green infrastructure development for filtering drinking water (US$1.5 billion for watershed conservation vs. US$8-10 billion to develop a new water filtration plans), reducing nutrient pollution (US$3.10 per pound of nitrogen reduced from forest buffers vs. US$8.56 per pound of nitrogen reduced from wastewater treatment plan upgrades) and treating wastewater (US$0.47 per 1,000 gallons of wastewater treated from wetlands vs. US$3.24 per 1,000 gallons of wastewater treated from a conventional wastewater treatment system) in the U.S. Increasing disaster risk and more frequent costly events may likely shift the balance in favor of proactive risk reduction measures in many cases. Shreve and Kelman 2014 also note the relative lack of information on the benefits of “ecosystem-based” disaster risk reduction, including measures such as reforestation and mangrove protection.

Evidence on the cost-effectiveness of NBS for landslide risk in growing but requires more research. Nehren and Mojica 2021 have conducted a global analysis of NBS for shallow landslide risk mitigation and note the need for additional research into the cost-effectiveness of these measures as compared to grey infrastructure. Singh 2010 provides evidence of bioengineering as a cost-effective solution with a high cost-benefit ratio, particularly when combined with traditional grey landslide risk reduction methods.