Soil moisture

Assessment versions

Published (reviewed and quality assured)

• No published assessments

Rationale

Justification for indicator selection

Water retention is a major hydrological property of soil that governs soil functioning in ecosystems. Maintaining water retention capacity and porosity in soils can also reduce the effects of extreme precipitation events. While water retention capacity is an intrinsic soil property based on clay content, structure and organic matter levels, soil moisture content is highly dynamic and is, if based on natural factors only, the balance between rainfall, evapotranspiration, surface run-off and deep percolation. Changes in temperature as well as precipitation patterns and intensity will affect evapotranspiration and infiltration rates, and thus soil moisture.

Although soil moisture constitutes only about 0.005 % of global water resources, it is an important part of the water cycle and a key variable controlling numerous processes and feedback loops within the climate system. When depleted owing to a lack of precipitation, increased evapotranspiration or increased run-off, soil moisture starts to constrain plant transpiration, growth and, thus, productivity of natural and managed ecosystems. Therefore, information on soil moisture content can be used as a proxy for agricultural droughts.

Scientific references

• No rationale references available

Indicator definition

• Past trends: modelled trend in soil moisture over a depth of one metre

• Projections: change in the Palmer Drought Severity Index

Units

• Past trends: litres per cubic metre per decade (l/m³/decade)

• Projections: Palmer Drought Severity Index (unitless)

Policy context and targets

Context description

In April 2013, the European Commission (EC) presented the EU Adaptation Strategy Package. This package consists of the EU Strategy on adaptation to climate change (COM/2013/216 final) and a number of supporting documents. The overall aim of the EU Adaptation Strategy is to contribute to a more climate-resilient Europe.

One of the objectives of the EU Adaptation Strategy is Better informed decision-making, which will be achieved by bridging the knowledge gap and further developing the European climate adaptation platform (Climate-ADAPT) as the ‘one-stop shop’ for adaptation information in Europe. Climate-ADAPT has been developed jointly by the EC and the EEA to share knowledge on (1) observed and projected climate change and its impacts on environmental and social systems and on human health, (2) relevant research, (3) EU, transnational, national and subnational adaptation strategies and plans, and (4) adaptation case studies.

Further objectives include Promoting adaptation in key vulnerablesectors through climate-proofing EU sector policies and Promoting action by Member States. Most EU Member States have already adopted national adaptation strategies and many have also prepared action plans on climate change adaptation. The EC also supports adaptation in cities through the Covenant of Mayors for Climate and Energy initiative.

In September 2016, the EC presented an indicative roadmap for the evaluation of the EU Adaptation Strategy by 2018.

In November 2013, the European Parliament and the European Council adopted the 7^th EU Environment Action Programme (7^th EAP) to 2020, ‘Living well, within the limits of our planet’. The 7^th EAP is intended to help guide EU action on environment and climate change up to and beyond 2020. It highlights that ‘Action to mitigate and adapt to climate change will increase the resilience of the Union’s economy and society, while stimulating innovation and protecting the Union’s natural resources.’ Consequently, several priority objectives of the 7^th EAP refer to climate change adaptation.

Targets

No targets have been specified.

Related policy documents

• 7th Environment Action Programme
  DECISION No 1386/2013/EU OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL of 20 November 2013 on a General Union Environment Action Programme to 2020 ‘Living well, within the limits of our planet’. In November 2013, the European Parliament and the European Council adopted the 7 th EU Environment Action Programme to 2020 ‘Living well, within the limits of our planet’. This programme is intended to help guide EU action on the environment and climate change up to and beyond 2020 based on the following vision: ‘In 2050, we live well, within the planet’s ecological limits. Our prosperity and healthy environment stem from an innovative, circular economy where nothing is wasted and where natural resources are managed sustainably, and biodiversity is protected, valued and restored in ways that enhance our society’s resilience. Our low-carbon growth has long been decoupled from resource use, setting the pace for a safe and sustainable global society.’
• Climate-ADAPT: Adaptation in EU policy sectors
  Overview of EU sector policies in which mainstreaming of adaptation to climate change is ongoing or explored
• Climate-ADAPT: Country profiles
  Overview of activities of EEA member countries in preparing, developing and implementing adaptation strategies
• DG CLIMA: Adaptation to climate change
  Adaptation means anticipating the adverse effects of climate change and taking appropriate action to prevent or minimise the damage they can cause, or taking advantage of opportunities that may arise. It has been shown that well planned, early adaptation action saves money and lives in the future. This web portal provides information on all adaptation activities of the European Commission.
• EU Adaptation Strategy Package
  In April 2013, the European Commission adopted an EU strategy on adaptation to climate change, which has been welcomed by the EU Member States. The strategy aims to make Europe more climate-resilient. By taking a coherent approach and providing for improved coordination, it enhances the preparedness and capacity of all governance levels to respond to the impacts of climate change.
• EU Common Agricultural Policy (CAP) reform - basic regulations
  References to climate change particularly in Regulation 1307/2013 (direct payments for farmers), Regulation 1306/2013 (so-called horizontal issues such as funding and controls: Articles 12 and 93, Annex I) and Regulation 1305/2013 (rural development: Articles 5, 7, 15, 28, 34, 35, 53 and 55).
• European Drought Observatory (EDO)
  The European drought observatory (EDO) is a service run by the EC’s Joint Research Centre. The EDO pages contain drought-relevant information such as maps of indicators derived from different data sources (e.g., precipitation measurements, satellite measurements, modelled soil moisture content).

Methodology

Methodology for indicator calculation

Past trends

Soil moisture was estimated using an algorithm for calculating the water balance at the surface and in the sub-surface horizons (up to 1m depth). The model uses the recommendations of the Food and Agriculture Organisation of the United Nations (FAO) for estimating the available water content in soils. It calculates soil moisture by adding and subtracting the losses and gains in the various parameters of the soil water budget, expressed in terms of the water column (in millimetres).

Written in volumetric units, the soil water balance (SWB) can be represented by Equation 1:

D * Capital delta_SWB / Capital delta_t = RR(t) – ET_A(t) – SRO(t) – DP(t) (1)

where D (in millimetres) is the depth of the modelled soil profile (root zone), and Capital delta_SWB (in cubic metres per cubic metre) is the change of the water volume over an area with depth D between two consecutive steps (Capital delta_t). RR (in millimetres per day) is the amount of precipitation at the surface, ET_A (in millimetres per day) is the actual evapotranspiration, SRO (in millimetres per day) is the surface runoff and DP (in millimetres per day) is the deep percolation.

Thus, as precipitation increases, actual evapotranspiration (ET_A), total runoff (SRO) and deep percolation (DP) decrease the soil moisture content in the root zone. Pedotransfer functions were used to calculate the field capacity, wilting point and soil saturation point characteristics required to calculate the SWB.

In addition to climate data, the equation takes account of other parameters such as, land cover, phenological phases, and hydrological soil properties.

Input data: The model uses a range of inputs. Daily meteorological station data were obtained from the European Climate Assessment and Data set (ECA&D), compiled by the Royal Netherlands Meteorological Institute (KNMI). Land cover information from the Corine Land Cover 2006 project (CLC2006) was used to identify the type of land cover and to calculate the crop coefficient for three phenological stages (start, middle and end of season). Intra-annual variation of the crop coefficient k_c was calculated from the Normalised Difference Vegetation Index (NDVI), applying the same linear relationship between k_c and NDVI for all stations and over the whole validation period. Hydrological soil properties (namely soil saturation point, field capacity and wilting point) were calculated using soil characteristics (soil texture and soil organic matter) from the European Soil map (ESDB version 2.0).

Projections

Calculation of the Palmer Drought Severity Index (PDSI) opposes atmospheric water supply to soil water demand using a rather simple soil-water balance model.

The PDSI measures the deviation from climatically normal soil moisture conditions for the current month without regarding conditions of preceding months, accounting for local climate features.

Methodology for gap filling

Not applicable

Methodology references

No methodology references available.

Data specifications

EEA data references

• No datasets have been specified here.

External data references

• An assessment of actual evapotranspiration and soil water deficit in agricultural regions in Europe (dataset URL is not available)
• The future of dry and wet spells in Europe

Data sources in latest figures

Uncertainties

Methodology uncertainty

Soil moisture can be measured or estimated by various methods, based either on in-situ measurements, spatially continuous information derived from satellite imagery, or hydrological and land surface models. 

Soil moisture measurements are expensive and do not provide a good spatial representation of the soil wetness conditions due to the high variability of soil moisture on a local scale. In most of the studies, soil moisture is simulated by land surface, hydrological and soil water balance models. Modellers can choose the spatial and temporal resolutions of the end product, depending on the resolution of the input data and the computation capacities. The vertical distribution of the soil moisture can be represented with different compartments within the model.

Specifically for the projections (Palmer Drought Severity Index), regional climate model (RCM) simulations provided by the ENSEMBLES project are used to analyse changes in dry and wet conditions in Europe by the mid of the 21st century under the A1B emission scenario. Eight RCMs are selected to capture the uncertainties of the projected changes. 

Data sets uncertainty

Quantitative information, from both observations and modelling, on the past trends and impacts of climate change on soil and the various related feedbacks is very limited. For example, data have been collected in forest soil surveys, but issues with survey quality — at least in the first European forest soil survey — makes comparison between countries (and between surveys) difficult. To date, assessments have relied mainly on local case studies that have analysed how soil reacts under changing climate in combination with evolving agricultural and forest practices. Thus, Europe-wide soil information to help policymakers identify appropriate adaptation measures is absent. There is an urgent need to establish harmonised monitoring networks to provide a better and more quantitative understanding of this system. Currently, EU-wide soil indicators are (partly) based on estimates and modelling studies, most of which have not yet been validated. It is still common to use precipitation (sometimes combined with evaporation-based indicators, such as the SPI or the Palmer Drought Severity Index) to describe changes in soil moisture, despite the high sensitivity of the assessment to the specific method used.

When documenting and modelling changes in soil, biodiversity and forest indicators, it is not always feasible to track long-term changes (signal) given the significant short-term variations (noise) that may occur (e.g. seasonal variations of soil organic carbon as a result of land management). Therefore, detected changes cannot always be causally attributed to climate change. Human activity, such as land use and management, can be more important for terrestrial ecosystem components than climate change, both for explaining past trends and for future projections.

Rationale uncertainty

No uncertainty has been specified