The fiscal case for nature, in plain English.

We need a shape on a map (or a postcode), the land cover inside it, the local climate, the air quality, the population nearby, and the local water bill. That is enough to start pricing what nature does for the place.

Standard: Inputs: OS MasterMap · Sentinel-2 land cover · Open-Meteo 1991–2020 climate normals · OpenAQ air quality · ONS LSOA population · the project's water company tariff.

We measure how much better the site becomes for nature after the intervention — counted in standard biodiversity units so a council or developer can use it for permits, offsets or net-gain reporting.

Standard: Defra Statutory Biodiversity Metric 4.0. Cross-checked against open species records (GBIF) and habitat connectivity (Conefor).

Rain that nature soaks up is rain the drainage network does not have to handle. We model how much runoff each intervention avoids and price it at the local water company's drainage tariff.

Standard: Soil Conservation Service Curve Number method (TR-55). Tariff example: Thames Water surface-water drainage 2025/26 = £1.69/m³.

Trees, green roofs and cool surfaces lower the felt temperature on a site. We translate that into kilowatt-hours of air-conditioning the buildings will not need to spend, then price it at the current non-domestic energy cap.

Standard: Town Energy Balance + Universal Thermal Climate Index (UTCI). Cooling-degree-day coefficient from Akbari–Pomerantz–Taha; Ofgem non-domestic price cap.

Vegetation removes fine particulates and nitrogen dioxide from the air. We count the kilograms each intervention takes out of the local air shed and value them using the UK government's official air-quality damage costs.

Standard: Nowak et al. (2014) i-Tree Eco deposition model. Pricing: DEFRA Air Quality Damage Costs (Jan 2023) — £75.5/kg PM2.5, £8.4/kg NO₂.

We estimate how much carbon the planted vegetation pulls out of the atmosphere over twenty years, set aside a buffer for losses, and price the rest at the UK government's traded carbon series.

Standard: IPCC 2019 Tier 1 biomass + i-Tree Eco allometrics; Bradley et al. (2005) UK soil-carbon factors; 20% buffer (Verra VM0047); UK DESNZ traded carbon central.

Lower heat and cleaner air mean fewer hospital admissions in a heatwave and more productive outdoor hours. We translate those into healthy-life-years gained and price them at the official Treasury rate.

Standard: Gasparrini et al. (2015) heat-mortality response on the 400 m resident population; HM Treasury Green Book 2022 (£70k per quality-adjusted life-year); productivity from Hsiang & Jina (2014).

Each benefit becomes a cashflow line: stormwater, pollination, recreation, air quality, carbon and avoided heat illness. Every line gets a confidence grade A-E so the reader knows where the evidence is strong and where it is provisional.

Standard: Pollination via Lonsdorf et al.; recreation via zonal travel-cost. Grades feed a dossier-level Rigor Index from 0 to 100.

We project the cashflows over twenty years, discount them with the rate finance teams already use, and report net present value, internal rate of return and lifetime cost per unit of service. These are the numbers a finance director can sign.

Standard: HM Treasury Green Book declining discount rates (3.5 / 3.0 / 2.5%) or a flat user rate. Capex/opex curves from CIRIA C753 and UKGBC nature-based-solutions guidance.

We do not pretend the answer is exact. We rerun the model 800 times, varying the seven inputs that move the answer most, and report a low / central / high band so reviewers can see the range, not just the headline.

Standard: Latin-hypercube Monte Carlo, N=800. Non-parametric P10 / P50 / P90 bands plus a tornado of variance contributions.

We back-tested the model against a 1.8-hectare mixed intervention in Marylebone twelve months after planting. The numbers were inside the published targets on canopy carbon, fiscal cashflows and biodiversity units.

Standard: City of Westminster T+12 month back-test: canopy carbon MAPE 11.3% (target ≤15%), cashflow total MAPE 18.7% (≤25%), biodiversity units MAPE 7.4% (≤10%). Inputs released CC-BY-4.0.

We use historical climate, not future scenarios. We do not yet model how people change behaviour around new green space. Where contractors have not quoted yet, we use sector-default costs. Planned additions include forward climate horizons, a Manchester pilot and an ISAE 3410 audit-readiness checklist.

Standard: Planned: UKCP18 RCP4.5/8.5 horizons; Greater Manchester pilot; ISAE 3410 readiness checklist.

Every number in a dossier traces back to a peer-reviewed paper, a government-published cost or a public standard. Open the technical appendix to see the full citation list.

Standard: Defra Statutory Biodiversity Metric 4.0 · DEFRA Air Quality Damage Costs · HM Treasury Green Book 2022 · TNFD LEAP v1.0 · Verra VM0047 · London Plan G5 · CIRIA C753 · IPCC 2019 · Nowak · Gasparrini · Hsiang & Jina · Lonsdorf · Masson · Bradley.