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This publication is categorised as a CSO Frontier Series Output. Particular care must be taken when interpreting the statistics in this release as it may use new methods which are under development and/or data sources which may be incomplete, for example new administrative data sources.
The System of Environmental Economic Accounting - Ecosystem Accounting (SEEA-EA) is a spatially-based, integrated statistical framework for organizing biophysical information about ecosystems, measuring ecosystem services, tracking changes in ecosystem extent and condition, valuing ecosystem services and assets and linking this information to measures of economic and human activity. It is an integrated statistical framework adopted by the United Nations Statistical Commission.
The SEEA-EA outlines five sets of ecosystem accounts:
1. Ecosystem extent accounts
2. Ecosystem condition accounts
3. & 4. Ecosystem services flow accounts (physical and monetary)
5. Monetary ecosystem asset accounts
As part of a recent amendment to Regulation (EU) No 691/2011 on environmental economic accounts, it will be mandatory to report ecosystem extent, condition and services (physical flow) accounts in line with SEEA-EA. The monetary flow of ecosystem services and the monetary value of ecosystem assets will not need to be accounted for under the new regulation. Mandatory reporting by member states will commence in 2026.
The accounts produced here were done so in line with SEEA-EA principles. However, while methodology for the flood control ecosystem service were produced prior to the amendment of Regulation (EU) No 691/2011, the account was not adopted and is therefore not mandatory.
Corine Land Cover was used as the data source for ecosystems. A crosswalk was performed between the EU Level 1 ecosystem typology and the CLC Accounting Layers third level classes. This crosswalk has since been altered based on feedback from a national expert group, which recommended allocating the CLC code 243 (“Agriculture mosaics with significant natural vegetation”) to Grasslands rather than Croplands.
The resolution of the Corine Land Cover Accounting Layers is too low to capture most roads. Therefore, data was sourced from the Digital Landscape Models (DML) Core Data from Tailte Éireann.
The Irish Soil Information System is a 1:250,000 scale national soil map. The soil texture coupled with the land cover determines a curve number assigned to a given location (see Potential Runoff Retention Indicator). This map is an associative soil map, meaning it lists the different types of soils which may be found in a specified area. When this map is converted to a raster, the value at each pixel can be interpreted as the most likely soil texture to be found at that point.
Imperviousness Density of the soil is used to improve the accuracy of the curve number estimate. This data is sourced from Copernicus Land Monitoring Service (CLMS) in the form of a 10m x 10m raster file which is downscaled to 100m x 100m to match the scale of the other lower resolution datasets used.
A Digital Elevation Model (DEM) is a graphical representation of elevation data. A DEM for Ireland was sourced from Eurostat. The DEM is used to create a slope raster which is another necessary input for correcting the curve number to account for slope which is essential to model the directional relationship of the flood control ecosystem service.
Another Copernicus dataset was included which showed the locations of Riparian Zones.
Flood maps were created by combining the Catchment Flood Risk Assessment Management (CFRAM) flood maps and the National Indicative Fluvial Maps. These maps depict predicted flood events based on current climate conditions with a return period of one thousand years. The CFRAM flood maps were designed to meet the requirements of the 2007 EU Floods Directive (2007/60/EC).
The Irish Peat Soil Map is used to identify the locations of peat soils in Ireland.
Drained and undrained peat is delineated using the Water and Wetness Status raster from Copernicus. This dataset provides information on the occurrence of water and wet surfaces.
The potential runoff retention indicator is used to delineate the Service Providing Areas and can be interpreted as a score identifying a given location’s ability to retain water, where a higher value represents greater ability to retain water. It is calculated in five steps and incorporates different data inputs at each stage to improve accuracy.
The first step implements the Curve Number method, which assigns a curve number to each land cover and soil texture combination. Hydrological soil classes are created to categorise different soil textures. The curve numbers are a measure of the amount of runoff generated from a given combination of land cover and soil texture, with a higher curve number indicating a greater amount of runoff, and therefore a poorer ability to retain water. Curve numbers are initially assigned based on a default lookup table provided in Eurostat’s guidance note. See Table 5.1.
The accuracy of the curve numbers is then improved by adding corrections for soil imperviousness, slope, and riparian zones. Each of these corrections incorporate new data inputs which adjust the curve numbers according to formulae provided in the guidance note.
The final step involves reversing the scale of the curve number map such that higher scores indicate areas with high potential to supply the service. The Service Providing Areas are then delineated using threshold values of the potential runoff retention indicator (see below).
Service Providing Areas are delineated using threshold values from the potential runoff retention indicator. Threshold values are assigned to three broad categories of land cover types: Artificial, Agricultural, and Natural and Semi-Natural. The threshold values are determined by considering the sum1 of the mean and standard deviation of the potential runoff retention indicator values for each land cover type within the three categories and taking the average over the entire category.
Applying this method nationally gives a map showing the locations of all the Service Providing Areas. These areas are interpreted as being capable of supplying some amount of flood control to downstream Service Demanding Areas.
1For the Natural and Semi-Natural categories the difference of the mean and standard deviation is used rather than the sum.
Service Demanding Areas are defined as economic assets which lie in floodplains. Economic assets correspond to the following land covers: Settlements & Other Artificial Areas, Croplands, and Sown Pastures & Other Grass. To find where these land covers lie in floodplains, flood hazard maps are incorporated.
Two flood hazard maps are used in conjunction with one another:
These are predictive flood maps, showing areas which are predicted to experience a theoretical flood event with an estimated probability. These maps use a value called the Annual Exceedance Probability (AEP) to describe the probability of a flood event of a specified severity or greater of occurring in a given year. In this model, the AEP was chosen to be 0.1%, also known as a 1000-year return period. In addition to this, these maps are filtered to only include fluvial (river) floods, and they are modelled based on current climate conditions.
The extent of the CFRAM flood maps are limited to Areas of Potentially Significant Flood Risk (APSFR) as designated under the EU Floods Directive. Therefore, it is necessary to complement these maps with the NIFMs to obtain a nation-wide flood map.
To map the Service Demanding Area, the Settlements & Other Artificial Areas, Croplands, and Sown Pastures & Other Grass ecosystem types are overlayed onto the flood maps, and the locations which overlap directly comprise the Service Demanding Area.
The flood control service flow is defined as the portion of the upstream area of the Service Demanding Area which is covered by Service Providing Areas. Delineating the upstream area is done using a method called Flow Accumulation.
Flow accumulation is a method by which the relative upstream area of every pixel in a map is calculated by counting the number of pixels which drain into each other. Draining pixels are found by considering the Flow Direction, a separate computation which uses a Digital Elevation Model (height map) to trace the direction of water flow. In this case, flow direction was determined by considering the neighbouring pixels in a Digital Elevation Model and noting either the greatest drop or smallest rise in elevation as the direction of flow.
To calculate the portion of the upstream area which is covered by Service Providing Areas, two flow accumulation maps are produced. The first map gives the flow accumulation for the entire country, while the second gives the flow accumulation using only the elevation data associated with the Service Providing Area. This will result in only upstream Service Providing Area pixels being counted towards the flow accumulation. The portion of upstream area covered by Service Providing Area for each Service Demanding Area pixel can then be computed by dividing the flow accumulation values of the two maps.
This calculation yields a map showing the ratio of the upstream area of each Service Demanding Area pixel which is covered by Service Providing Areas, and the service flow is calculated by summing all the individual values.
The allocation of the supply of the flood control ecosystem service to each ecosystem type is essentially a weighting of the total supply value to the different ecosystem types. Weights are chosen to reflect the relative importance and effectiveness different ecosystems have in providing the flood control service.
The first component of the computation is the correction factor. This is found using the following formula
| Correction factori | = | (100 - Average(CNj∈i)) / 100 |
where CNj∈i is the curve number of land cover j belonging to ecosystem type i. The average curve number is computed across all land covers belonging to a given ecosystem type.
The correction factor for each ecosystem type is then multiplied by the flow accumulation figure found by considering only the extent of that ecosystem type. The result of this product is the Weighted Extent.
Finally, the weighted extent for each given ecosystem type is expressed as a fraction of the sum of all the weighted extents to give the Allocation Coefficient for each ecosystem type. This ratio is multiplied by the total service flow figure to allocate the supply to each ecosystem type.
The geospatial model used to produce these figures distinguishes between drained peat and wet peat, with a further breakdown of the saturation levels of the wet peat. This was done to account for the sensitivity of peat soils hydrological properties. A new soil class in the curve number lookup table was created and applied to wet peat that was found to be saturated. Drained peat was delineated by considering all peat soils which were not located beneath Inland Wetlands. Wet peat was classified as all other peat soils outside of the drained selection. This peat was further separated into saturated and unsaturated classes depending on the surface wetness. These classes were defined using categories from the Water and Wetness Status raster from Copernicus which provides information on the occurrence of water and wet surfaces. Saturated peat was associated with the categories 'Permanent Water' and 'Permanent Wet', and unsaturated peat was assigned to the categories 'Dry', 'Temporary Water' and 'Temporary Wet'.
A new hydrological soil class E was created using the average curve numbers between classes C and D. This soil class was used to assign curve numbers to the previously identified drained peat. Saturated wet peat was assigned curve numbers from soil class D, highlighting the poor ability of a saturated soil to absorb any more water. Unsaturated wet peat was assigned to soil class A. See Table 5.1.
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