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Indicator Assessment

Soil moisture deficit

Indicator Assessment
Prod-ID: IND-530-en
  Also known as: LSI 012
Published 22 Mar 2021 Last modified 23 Mar 2021
15 min read

Monitoring the pressure from soil moisture deficits can warn of potential impacts on plant development and soil health, supporting the assessment of drought-tolerant, resilient and vulnerable ecosystems. In 2000-2019, soil moisture in the growing season was several times below the long-term average in the EEA member countries plus the United Kingdom. The largest soil moisture deficits occurred in 2003, 2017 and 2019, affecting over 1.45 million km2 in 2019. Soil moisture content was also low in 2012, 2015 and 2018, contributing to increasingly frequent and intense drought pressure.

Long term average soil moisture and soil moisture trends, 2000-2019

Note: The maps show the long-term average soil moisture contents (left) and the trends in soil moisture values (right), aggregated by NUTS3 regions. Soil moisture is equal to 0 when the soil is severely dry (wilting point) and equal to 1 when the soil moisture is above the field capacity. Low long-term average soil moisture values indicate areas where during the 2000-2019 period the soil moisture deficit was the biggest problem. Trends are expressed in standard deviation from the long term average. Negative trends indicate that soil moisture values show a decreasing tendency during the 2000-2019 period. Areas with lower soil moisture content together with decreasing tendency in the soil moisture are in risk of loosing their land functions of supplying ecosystem services. See also: https://www.eea.europa.eu/data-and-maps/data/data-viewers/soil-moisture and Original dataset: https://edo.jrc.ec.europa.eu/documents/factsheets/factsheet_soilmoisture.pdf

Data source:

Soil moisture is essential for the development of plants. It regulates soil temperature, salinity, the availability of nutrients and the presence of toxic substances, and it gives structure to soil and contributes to preventing soil erosion. As soil moisture content is an important indicator of soil condition and the overall state of the land system, it determines land use suitability.

Droughts are relevant for several targets of the EU Biodiversity Strategy for 2030 related to protecting and restoring nature (EC, 2021). As droughts hamper nature's ability to deliver a wide range of environmental, social, climate change adaptation and mitigation, and biodiversity benefits, they affect the implementation of the EU strategy on green infrastructure (EC, 2013). Long-term objectives of the EU common agricultural policy (CAP) — viable food production, the sustainable management of natural resources, climate action and balanced territorial development — are also affected by droughts (EC, undated b).

During the period 2000-2019, the growing season soil moisture content of the 38 EEA member countries (EEA-38) plus the United Kingdom was several times below the critical level. Soil moisture content exhibited a strong decreasing trend in the northern Continental region and hence drought pressure intensity increased in these areas. Other than in 2003, the largest soil moisture deficits occurred in the final 9 years of the period, indicating that drought pressure frequency is increasing. The area affected by growing season soil moisture deficits also increased between 2000 and 2019, increasing most in the last 3 years of the period. An increase of 80 % occurred, from an estimated 800 000 km2 in 2017 to 1.45 million km2 in 2019.

The 6 years with the lowest growing season soil moisture contents, covering the largest areas, were 2003, 2010, 2014, 2016, 2018 and 2019. The most intense drought pressures occurred in 2003, 2017 and 2019, with the most intense drought, affecting the largest area, occurring in 2019 (Figure 1). Soil moisture deficits were also severe in 2012, 2015 and 2018, with the area affected reaching an estimated 1.2 million km2 in 2018.

Although the Mediterranean region experienced frequent and intense drought events, it was the continental and Fennoscandia regions that experienced much lower than average soil moisture content between 2000 and 2019, with a trend towards worsening soil moisture deficits.

Area of yearly soil moisture deficit per country and land cover, in % of the country area

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Between 2000 and 2019, the Baltic countries, Cyprus, Finland, Poland, Portugal and Sweden experienced significantly lower than average growing season soil moisture. Moreover, Cyprus, Czechia, Finland, Poland and Sweden showed strong decreasing trends and are therefore hotspots for potential impacts of drought. Belgium and the Netherlands did not have the lowest soil moisture deficits in the 27 EU Member States (EU-27) plus the United Kingdom, but decreasing trends indicate that conditions might become limiting for plant growth in the future.

These countries face increasing soil moisture pressures, potentially affecting sustainable food production on arable lands and the products and ecosystem services provided by forests.

Ireland and the United Kingdom were also among the countries with the lowest soil moisture deficits in the EU-27 and the UK, but increasing trends indicate that conditions might become more favourable for plant development. Austria, Bulgaria, Croatia, Greece and Romania showed improving soil moisture conditions during the 20-year period and, with the exception of Croatia, the long-term average soil moisture deficits were moderate in these countries.

Supporting information

Indicator definition

This indicator shows the annual deviation in soil moisture content of each 500-m grid cell from the long-term (1995-2019) average. Negative soil moisture anomalies indicate that the annual average availability of soil moisture to plants drops to such a level that it has the potential to affect terrestrial vegetation and, hence, cause persistent changes in ecosystem condition. Negative long-term averages and negative trends in the annual data indicate increasing pressures on vegetation and ecosystems, and thus represent a climatic driver that should be considered in EU nature restoration plans. Therefore, the indicator can inform policy action on ecosystem restoration in the EU but also on adaptation to climate change.

Units

Area measured in km2and standard deviation; extent measured as area affected by soil moisture deficit as a percentage (%) of total country area.


 

Policy context and targets

Context description

Although there are no specific targets related to this indicator, in May 2020, the EU adopted a biodiversity strategy to 2030, related to protecting and restoring nature (EC, 2021). The strategy states that ‘The biodiversity crisis and the climate crisis are intrinsically linked. Climate change accelerates the destruction of the natural world through droughts, flooding and wildfires, while the loss and unsustainable use of nature are in turn key drivers of climate change’. Droughts negatively affect agricultural ecosystems and food security, the resilience of forest ecosystems and the ability of green urban spaces to protect people against heatwaves. In particular, the impacts of extended droughts on ecosystems need to be assessed because they can lead to significant loss of vegetation productivity, irreversible damage to the condition of ecosystems and land degradation.

For the EU, the opportunity cost of not reaching the headline target of the 2020 biodiversity strategy of halting the loss of biodiversity and ecosystem services has been estimated at EUR 50 billion per year (EC, 2015) . In addition to undermining economic benefits, the continuing loss of biodiversity means that ecosystems and the societies that rely upon them will become more fragile and less resilient in the face of challenges such as climate change, pollution and habitat destruction. Droughts have an impact on several land and soil functions, as well as ecosystem services, both in urban and rural areas. For example, droughts have an impact on the availability of water resources for human use in agriculture, cause habitat loss, the migration of local species and their replacement by alien species in open rural systems, and consequently cause soil erosion and biodiversity degradation. By putting pressure on natural ecosystems, droughts have hampered the achievement of the 2020 EU biodiversity strategy’s objectives.

Pressure from droughts on natural ecosystems also plays an important role in the implementation of the EU strategy on green infrastructure. In contrast to the most common ‘grey’ (human-made, constructed) infrastructure approaches that serve one single objective, green infrastructure approaches promote multifunctionality, which means that the same area of land is able to perform several functions and offer multiple benefits if its ecosystems are in a healthy state. More specifically, green infrastructure aims to enhance nature’s ability to deliver multiple valuable ecosystem goods and services, potentially providing a wide range of environmental, social, climate change adaptation and mitigation, and biodiversity benefits. Drought diminishes the normal condition of ecosystems and their capacity to provide services that could be integrated into green infrastructures.

Under EU legislation adopted in May 2018, EU Member States have to ensure that greenhouse gas emissions from land use, land use change and forestry are offset by an at least equivalent removal of CO₂ from the atmosphere in the period 2021-2030. Ultimately, the capacity of forests and soils on a given area of land to remove carbon from the atmosphere will depend on a number of natural (regional/geographical) circumstances such as variations in growing conditions (temperature, precipitation and droughts) and natural disturbances (storms, fires) as well as past and present management practices (e.g. rotation lengths, which affect the distribution of age classes in forest stands). By measuring changes in emissions and removals relative to business-as-usual projections, these circumstances (such as drought pressure) will be ‘factored out’, so that only changes related directly human-induced activities are measured. This also provides incentives for improving the current situation and gives an equal value to mitigation whether through sequestration or conservation, or material and energy substitution.

The role of the CAP is to provide a policy framework that supports and encourages producers to address economic, environmental (i.e. relating to resource efficiency, soil and water quality, and threats to habitats and biodiversity) and territorial challenges, while remaining coherent with other EU policies. This translates into three long-term CAP objectives: viable food production, the sustainable management of natural resources and climate action, and balanced territorial development. Given the pressure from droughts on natural resources, agriculture must improve its environmental performance through more sustainable production methods. Farmers also have to adapt to challenges stemming from changes to the climate by pursuing climate change mitigation and adaption actions (e.g. by developing greater resilience to disasters such as flooding, drought and fire). Understanding the spatiotemporal distribution of drought pressures on land will contribute to a better, faster and more informed implementation of CAP reforms and improve the quality of life of rural populations in Europe.

Targets

There are no specific targets related to this indicator.

Related policy documents

  • COM(2013) 249 final Green infrastructure (GI): enhancing Europe’s natural capital
    EC, 2013, Communication from the Commission to the European Parliament, the Council, the European Economic and Social Committee and the Committee of the Regions — Green infrastructure (GI): enhancing Europe’s natural capital (COM(2013) 249 final of 6 May 2013).
  • Common agricultural policy
    The common agricultural policy is about our food, the environment and the countryside.
  • EU Biodiversity Strategy for 2030
    The European Commission has adopted the new  EU Biodiversity Strategy for 2030 and an associated Action Plan (annex)  - a comprehensive, ambitious, long-term plan for protecting nature and reversing the degradation of ecosystems. It aims to put Europe's biodiversity on a path to recovery by 2030 with benefits for people, the climate and the planet. It aims to build our societies’ resilience to future threats such as climate change impacts, forest fires, food insecurity or disease outbreaks, including by protecting wildlife and fighting illegal wildlife trade. A core part of the  European Green Deal , the Biodiversity Strategy will also support a green recovery following the COVID-19 pandemic.
  • SWD/2015/0187 final
    EC, 2015, Commission staff working document — EU assessment of progress in implementing the EU biodiversity strategy to 2020 (SWD(2015) 187 final).
 

Methodology

Methodology for indicator calculation

Data for this soil moisture deficit indicator are derived at the pixel level and express the average soil moisture deviation from long-term average conditions and relative trends in soil moisture anomalies during the vegetation growing seasons for the period 2000-2019. To estimate relative trends, it is assumed that the time series of soil moisture anomalies can be represented as a linear function of time (t), as follows:

(Y_t) ̂ = (β0 + β1)  × (t + ε)

where (Y_t ) ̂ denotes the estimated soil moisture anomaly for the growing season at yeart, β_0 is the estimated soil moisture anomaly att = 0, β_1*t represents the rate of change in soil moisture anomalies as a function of time and ε is the error term of the model. Once the model parameters β_0 and β_1 are estimated for each pixel through a least-squares fit, the relative soil moisture anomaly trend (rSMAt) can be computed as follows:

rSMAt = ((Y_19 ) ̂ - (Y_00) ̂)/(max┬(t∈{00,…,19})〖Y_t 〗 - min┬(t∈{00,…,19} )〖Y_t 〗 ) × 100

where (Y_00 ) ̂ and (Y_19 ) ̂ denote, respectively, the estimated soil moisture anomalies for the years 2000 and 2019, and max┬(t∈{00,…,19} )〖Y_t 〗 and min┬(t∈{00,…,19} )〖Y_t 〗 denote, respectively, the observed maximum and minimum soil moisture anomalies during the period 2000-2019. A relative trend was chosen instead of the absolute trend in standard deviations, to scale the indicator in a measurement unit that is independent of any associated statistical distribution.

The vegetation growing season period was derived from the MODIS 8-day plant phenology index (Jin and Eklundh, 2014), with data smoothed for each year in the period 2000-2019 with a double logistic fitting curve using TIMESAT software (Jönsson and Eklundh, 2004).

To account for outliers in the trends, which can occur by means of changes in land cover due to the impacts of natural events or human land use activities (such as irrigation or clear cuts), it was decided to remove all pixels for which land cover flows between 2000 and 2018 were identified by the Corine Land Cover accounting layers. Similarly, to avoid the inclusion of trends derived from spurious regressions, only statistically significant trends (p-value < 0.05) were included in the final indicator. The significance of the trends was based on the non-parametric Mann-Kendall trend test (Mann, 1945).

Methodology for gap filling

All input data sets were derived from global sources with wall-to-wall coverage of the land surface. No gap filling was needed.

Methodology references

No methodology references available.

 

Uncertainties

Methodology uncertainty

Accuracy is determined by the remote-sensing vegetation signal provided by the Copernicus Land Monitoring Service and by the precipitation and soil moisture values provided by the Copernicus Emergency Service.

Data sets uncertainty

The various conceptual generalisations and scientific assumptions that are intrinsic in the Distributed Water Balance and Flood Simulation Model (Lisflood) — for example regarding soil physics, land use, canopy cover and meteorological data interpolation — and also the calibration of the model, may produce in some cases large approximations of the actual soil moisture content, and a progressive divergence from the real conditions.

Rationale uncertainty

No uncertainty has been identified.

Data sources

Other info

DPSIR: Pressure
Typology: Descriptive indicator (Type A - What is happening to the environment and to humans?)
Indicator codes
  • LSI 012
Frequency of updates
Updates are scheduled once per year
EEA Contact Info info@eea.europa.eu

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Geographic coverage

Temporal coverage

Dates