The aridity risk shows how dry the site's climate is at baseline: it compares the year's rainfall with the water that soil and plants could lose to evaporation (aridity index) and assigns the UNEP climate class, from humid (A) to hyper-arid (F). It changes over time with the climate model projections.
Indicator. Aridity index: annual precipitation divided by potential evapotranspiration (dimensionless). The lower it is, the drier the climate.
Data. Future Global Aridity Index and PET Database (Zomer et al. 2024): mean of the CMIP6 models for 2021–2040 and 2041–2060 under each scenario, at about 1 km, with Hargreaves potential evapotranspiration. Scenarios: SSP1-2.6 / SSP2-4.5 / SSP3-7.0 / SSP5-8.5.
Calculation.
(1) The aridity index is read in the site's 1 km cell; if the cell is sea the closest of the 8 adjacent land cells is used, and if they are all sea the site is on open water and the class is A.
(2) Up to 2040 the 2021–2040 period applies, then 2041–2060; after 2060 there are no published values and the 2041–2060 value is kept (a xNatura choice).
(3) The index is classed with the UNEP climate classes, the same used by the UN Convention to Combat Desertification (UNCCD, Article 1) and the IPCC (SRCCL).
Thresholds → level A–F.
• A: humid, index ≥ 0.65
• B: dry sub-humid, 0.5–0.65
• C: semi-arid, 0.35–0.5
• D: semi-arid, 0.2–0.35
• E: arid, 0.05–0.2
• F: hyper-arid, below 0.05.
Limits 0.05, 0.2, 0.5 and 0.65 from the UNEP classes (Zomer et al. 2022 give the same scheme with 0.03 as the hyper-arid limit); the split of semi-arid at 0.35 comes from the platform's aridity map legend, not from a paper.
From physical to impact. The physical level (A–F) is combined with the production process's sensitivity through the risk matrix (6 physical levels by 5 sensitivity bands) → impact level. Version 2025 also turned the impact level into a value at risk with a damage factor per class, a xNatura estimate without a published source: it is no longer used. Economic damage, Version 2026 xNatura estimate: 0 €, until a published method estimating the euro loss of a single site is chosen.
Economic damage. There is no Version 2026 estimate for this risk: published drought losses are totals by region and sector, mostly agriculture, energy and water supply, with negligible damage to buildings (Naumann et al. 2021); in high-income countries firm-level studies find no measurable effect of extreme dry days on sales (Gatti et al. 2024), and only extreme droughts lower regional growth (Zaveri et al. 2023). The risk therefore shows the class only, without a euro amount.
Sources.
• [Zomer et al. 2024, CMIP6-based global estimates of future aridity index and potential evapotranspiration for 2021-2060](Zomer et al. 2024, CMIP6-based global estimates of future aridity index and potential evapotranspiration for 2021-2060)
• [Zomer et al. 2022, Version 3 of the Global Aridity Index and Potential Evapotranspiration Database](Zomer et al. 2022, Version 3 of the Global Aridity Index and Potential Evapotranspiration Database)
• [UNCCD Article 1: Use of terms](UNCCD Article 1: Use of terms)
• [Special Report on Climate Change, Desertification, Land Degradation, Sustainable Land Management, Food Security, and Greenhouse gas fluxes in Terrestrial Ecosystems (SRCCL)](Special Report on Climate Change, Desertification, Land Degradation, Sustainable Land Management, Food Security, and Greenhouse gas fluxes in Terrestrial Ecosystems (SRCCL))
• [Naumann et al. 2021, Increased economic drought impacts in Europe with anthropogenic warming](Naumann et al. 2021, Increased economic drought impacts in Europe with anthropogenic warming)
• [Gatti et al. 2024, Thirsty Business: A Global Analysis of Extreme Weather Shocks on Firms](Gatti et al. 2024, Thirsty Business: A Global Analysis of Extreme Weather Shocks on Firms)
• [Zaveri et al. 2023, Droughts and Deficits: The Global Impact of Droughts on Economic Growth](Zaveri et al. 2023, Droughts and Deficits: The Global Impact of Droughts on Economic Growth).
Indicator. Aridity index: annual precipitation divided by potential evapotranspiration (dimensionless). The lower it is, the drier the climate.
Data. Future Global Aridity Index and PET Database (Zomer et al. 2024): mean of the CMIP6 models for 2021–2040 and 2041–2060 under each scenario, at about 1 km, with Hargreaves potential evapotranspiration. Scenarios: SSP1-2.6 / SSP2-4.5 / SSP3-7.0 / SSP5-8.5.
Calculation.
(1) The aridity index is read in the site's 1 km cell; if the cell is sea the closest of the 8 adjacent land cells is used, and if they are all sea the site is on open water and the class is A.
(2) Up to 2040 the 2021–2040 period applies, then 2041–2060; after 2060 there are no published values and the 2041–2060 value is kept (a xNatura choice).
(3) The index is classed with the UNEP climate classes, the same used by the UN Convention to Combat Desertification (UNCCD, Article 1) and the IPCC (SRCCL).
Thresholds → level A–F.
• A: humid, index ≥ 0.65
• B: dry sub-humid, 0.5–0.65
• C: semi-arid, 0.35–0.5
• D: semi-arid, 0.2–0.35
• E: arid, 0.05–0.2
• F: hyper-arid, below 0.05.
Limits 0.05, 0.2, 0.5 and 0.65 from the UNEP classes (Zomer et al. 2022 give the same scheme with 0.03 as the hyper-arid limit); the split of semi-arid at 0.35 comes from the platform's aridity map legend, not from a paper.
From physical to impact. The physical level (A–F) is combined with the production process's sensitivity through the risk matrix (6 physical levels by 5 sensitivity bands) → impact level. Version 2025 also turned the impact level into a value at risk with a damage factor per class, a xNatura estimate without a published source: it is no longer used. Economic damage, Version 2026 xNatura estimate: 0 €, until a published method estimating the euro loss of a single site is chosen.
Economic damage. There is no Version 2026 estimate for this risk: published drought losses are totals by region and sector, mostly agriculture, energy and water supply, with negligible damage to buildings (Naumann et al. 2021); in high-income countries firm-level studies find no measurable effect of extreme dry days on sales (Gatti et al. 2024), and only extreme droughts lower regional growth (Zaveri et al. 2023). The risk therefore shows the class only, without a euro amount.
Sources.
• [Zomer et al. 2024, CMIP6-based global estimates of future aridity index and potential evapotranspiration for 2021-2060](Zomer et al. 2024, CMIP6-based global estimates of future aridity index and potential evapotranspiration for 2021-2060)
• [Zomer et al. 2022, Version 3 of the Global Aridity Index and Potential Evapotranspiration Database](Zomer et al. 2022, Version 3 of the Global Aridity Index and Potential Evapotranspiration Database)
• [UNCCD Article 1: Use of terms](UNCCD Article 1: Use of terms)
• [Special Report on Climate Change, Desertification, Land Degradation, Sustainable Land Management, Food Security, and Greenhouse gas fluxes in Terrestrial Ecosystems (SRCCL)](Special Report on Climate Change, Desertification, Land Degradation, Sustainable Land Management, Food Security, and Greenhouse gas fluxes in Terrestrial Ecosystems (SRCCL))
• [Naumann et al. 2021, Increased economic drought impacts in Europe with anthropogenic warming](Naumann et al. 2021, Increased economic drought impacts in Europe with anthropogenic warming)
• [Gatti et al. 2024, Thirsty Business: A Global Analysis of Extreme Weather Shocks on Firms](Gatti et al. 2024, Thirsty Business: A Global Analysis of Extreme Weather Shocks on Firms)
• [Zaveri et al. 2023, Droughts and Deficits: The Global Impact of Droughts on Economic Growth](Zaveri et al. 2023, Droughts and Deficits: The Global Impact of Droughts on Economic Growth).