The desertification risk estimates land degradation in drylands, i.e. where annual rainfall is between 5% and 65% of the water that soil and plants could lose to evaporation (UN Convention definition): elsewhere desertification does not occur and the risk is A. In drylands it combines rainfall scarcity (6-month SPI index) with the rarity of heat waves: when they occur together, the risk grows.
Indicator. Aridity index (annual precipitation / potential evapotranspiration), which tells whether the site is a dryland; Standardized Precipitation Index at 6 months (SPI-6), dimensionless; heat wave days (Warm Spell Duration Index, WSDI), the same as in the heat wave risk, expressed as a return period against the 1995–2014 climate.
Data. Aridity index from the 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. SPI-6 from the Copernicus Climate Data Store (CDS). Heat wave days from the CMIP6 extreme indices of the CDS: for each year the median across models of the centred 5-year mean of each model, as in the heat wave risk. Scenarios: SSP1-2.6 / SSP2-4.5 / SSP3-7.0 / SSP5-8.5.
Calculation.
(1) Drylands: under the UN Convention to Combat Desertification (UNCCD, Article 1) desertification is land degradation in arid, semi-arid and dry sub-humid areas, those with an aridity index between 0.05 and 0.65; the IPCC (SRCCL) uses the same definition. If the site's index in the period of the year is 0.65 or more (humid) or below 0.05 (hyper-arid desert, outside the definition), the site is not a dryland and the class is A. 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). If the site's 1 km cell is sea, the closest of the 8 adjacent land cells is used; if they are all sea, the site is on open water and the class is A.
(2) In drylands, SPI-6 and the heat wave days of the same year are taken. The return period is the one of the heat wave risk: the number of 1995–2014 years of all models divided by those with at least as many days, capped at 250 years.
(3) The conditions below are checked from the most severe: the first that holds gives the class.
Thresholds → level A–F.
• F: SPI-6 ≤ -2 and return ≥ 50 years
• E: SPI-6 ≤ -1.5 and return ≥ 50 years
• D: SPI-6 ≤ -1 and return ≥ 20 years
• C: SPI-6 ≤ -1.5 or return ≥ 20 years
• B: -1.5 < SPI-6 < 0 or return 5–20 years
• A: SPI-6 ≥ 0 and return < 5 years, or site not in a dryland (aridity index ≥ 0.65 or < 0.05, or open water).
SPI-6 limits, inclusive, from the WMO moderately, severely and extremely dry categories (McKee et al. 1993); the combination of the two drivers is a xNatura rule.
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.
• [Copernicus Climate Data Store (CDS)](Copernicus Climate Data Store (CDS))
• [Climate extreme indices derived from CMIP6 (Copernicus CDS)](Climate extreme indices derived from CMIP6 (Copernicus CDS))
• [United Nations Convention to Combat Desertification (UNCCD)](United Nations Convention to Combat Desertification (UNCCD))
• [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))
• [Future climate risk from compound events](Future climate risk from compound events)
• [The Relationship of Drought Frequency and Duration to Time Scales](The Relationship of Drought Frequency and Duration to Time Scales)
• [Standardized Precipitation Index User Guide](Standardized Precipitation Index User Guide)
• [UNCCD Article 1: Use of terms](UNCCD Article 1: Use of terms)
• [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)
• [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 / potential evapotranspiration), which tells whether the site is a dryland; Standardized Precipitation Index at 6 months (SPI-6), dimensionless; heat wave days (Warm Spell Duration Index, WSDI), the same as in the heat wave risk, expressed as a return period against the 1995–2014 climate.
Data. Aridity index from the 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. SPI-6 from the Copernicus Climate Data Store (CDS). Heat wave days from the CMIP6 extreme indices of the CDS: for each year the median across models of the centred 5-year mean of each model, as in the heat wave risk. Scenarios: SSP1-2.6 / SSP2-4.5 / SSP3-7.0 / SSP5-8.5.
Calculation.
(1) Drylands: under the UN Convention to Combat Desertification (UNCCD, Article 1) desertification is land degradation in arid, semi-arid and dry sub-humid areas, those with an aridity index between 0.05 and 0.65; the IPCC (SRCCL) uses the same definition. If the site's index in the period of the year is 0.65 or more (humid) or below 0.05 (hyper-arid desert, outside the definition), the site is not a dryland and the class is A. 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). If the site's 1 km cell is sea, the closest of the 8 adjacent land cells is used; if they are all sea, the site is on open water and the class is A.
(2) In drylands, SPI-6 and the heat wave days of the same year are taken. The return period is the one of the heat wave risk: the number of 1995–2014 years of all models divided by those with at least as many days, capped at 250 years.
(3) The conditions below are checked from the most severe: the first that holds gives the class.
Thresholds → level A–F.
• F: SPI-6 ≤ -2 and return ≥ 50 years
• E: SPI-6 ≤ -1.5 and return ≥ 50 years
• D: SPI-6 ≤ -1 and return ≥ 20 years
• C: SPI-6 ≤ -1.5 or return ≥ 20 years
• B: -1.5 < SPI-6 < 0 or return 5–20 years
• A: SPI-6 ≥ 0 and return < 5 years, or site not in a dryland (aridity index ≥ 0.65 or < 0.05, or open water).
SPI-6 limits, inclusive, from the WMO moderately, severely and extremely dry categories (McKee et al. 1993); the combination of the two drivers is a xNatura rule.
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.
• [Copernicus Climate Data Store (CDS)](Copernicus Climate Data Store (CDS))
• [Climate extreme indices derived from CMIP6 (Copernicus CDS)](Climate extreme indices derived from CMIP6 (Copernicus CDS))
• [United Nations Convention to Combat Desertification (UNCCD)](United Nations Convention to Combat Desertification (UNCCD))
• [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))
• [Future climate risk from compound events](Future climate risk from compound events)
• [The Relationship of Drought Frequency and Duration to Time Scales](The Relationship of Drought Frequency and Duration to Time Scales)
• [Standardized Precipitation Index User Guide](Standardized Precipitation Index User Guide)
• [UNCCD Article 1: Use of terms](UNCCD Article 1: Use of terms)
• [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)
• [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).