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Prevention of soil water erosion and ensuring water flow quality (InVEST Sediment Delivery Ratio)
GIS modeling and analysis, presentation of results – Eduard Kazakov (NextGIS OÜ, Estonia);
Analysis and presentation of results – Elena Bukvareva (BCC-Armenia);
Assessment of the alignment of results with real watersheds in Armenia – Vardan Asatryan (NAS RA)
Assessment of the relevance of modeling results for Armenia – external expert Alexander Arakelyan (NAS RA)
Two ecosystem services – 1) prevention of soil water erosion and 2) ensuring water flow quality – were estimated and mapped using InVEST Sediment Delivery Ratio model. The InVEST SDR model focuses only on overland erosion. Outputs from the model include the sediment load delivered to the stream at an annual time scale, as well as the amount of sediment eroded in the catchment and retained by vegetation and topographic features. The main indicator of the ES of prevention of soil erosion is avoided erosion, and the main indicator of the ES of ensuring water flow quality is avoided sediment export to streams.
The main results of ES modeling and mapping
The presented results are obtained on the basis of the following open data sources
FAA – Forest atlas of Armenia (digital maps);
ARMSTAT – regional statistics of Armenia;
ESRI land cover – data for 2017 and 2023
WorldClim – World Maps, graphs, tables, and data of the global climate;
Weather in Armenia;
Global-AI-PET_v3 – Global Aridity Index and Potential Evapotranspiration Climate Database v3
Hydrosheds – boundaries of watersheds
InVEST model outputs are proxy variables that should be interpreted in relative terms, rather than physical quantities. Nevertheless, the identified values are useful for analyzing the spatial distribution of services across the country’s territory and their balance with indicators of service utilization by the population and the economy.
This section presents preliminary results of testing models for assessing and mapping ecosystem services. In the future, if a decision is made to use these models, they should be calibrated using hydrological measurements made in Armenia.
The methodology and results will be described in detail in a forthcoming publication.
1. ES evaluation and mapping in physical indicators
In 2023, total avoided erosion was estimated as 140 million tons, and total avoided sediment export to streams was estimated as 13 million tons.
Avoided erosion, tons/pixel/year Avoided export, tons/pixel/year
Figure 1. ES indicators with current land cover, 2023
For detailed maps see the section “Ecosystem Services – Sediment Delivery Ratio – Basic scenario 2023”
With the current land cover (2023) the highest rates of avoided erosion were calculated for watersheds Aghstev, Vorotan, and Debed and the corresponding provinces Tavush, Syunik, and Lori. The lowest values were found for watersheds Metsamor and Akhuryan and for the province Armavir.
The highest rates of avoided sediment export were calculated for the same watersheds and provinces Syunik, Vayots Dzor, and Lori. The lowest values were found for watersheds Metsamor and Akhuryan and for the province Armavir.
This pattern, in general, is also evident for the total values of avoided erosion and sediment export.
Figure 2. ES indicators by provinces and watersheds
The model estimates that vegetation prevents more than 90% of erosion in all watersheds and provinces (except for the Armavir province with 89%) and more than 95% of sediment export everywhere.
Erosion on bare ground, tons/pixel/year Actual erosion in 2023, tons/pixel/year
Figure 3. Erosion under bare ground scenario and current erosion in 2023
For details see maps in the section “Sediment Delivery Ratio – Basic scenario 2023”
Table 1. Erosion in watersheds and provinces, 2023
| Erosion under bare ground scenario, t/ha/year | Current erosion, t/ha/year | Avoided erosion, t/ha/year | Total erosion under bare ground scenario, Mt/year | Total current erosion, Mt/year | Total avoided erosion, Mt/year | Share of avoided erosion, % | ||
| Watersheds | Aghstev | 96.0 | 2.5 | 93.5 | 29.7 | 0.8 | 28.9 | 97.4 |
| Akhuryan | 24.7 | 2.0 | 23.0 | 6.6 | 0.5 | 6.1 | 92.0 | |
| Arpa | 49.6 | 2.5 | 47.0 | 21.1 | 1.1 | 20.1 | 95.0 | |
| Debed | 75.2 | 2.9 | 72.4 | 28.7 | 1.1 | 27.6 | 96.1 | |
| Hrazdan | 34.3 | 1.9 | 32.3 | 19.8 | 1.1 | 18.6 | 94.3 | |
| Metsamor | 20.3 | 1.3 | 19.0 | 7.1 | 0.5 | 6.6 | 93.6 | |
| Vorotan | 78.8 | 4.0 | 75.0 | 34.3 | 1.7 | 32.6 | 94.9 | |
| Provinces | Aragatsotn | 26.8 | 1.6 | 25.2 | 7.1 | 0.4 | 6.6 | 93.9 |
| Ararat | 33.8 | 1.7 | 32.1 | 6.9 | 0.3 | 6.5 | 94.9 | |
| Armavir | 3.9 | 0.4 | 3.5 | 0.5 | 0.1 | 0.4 | 89.1 | |
| Gegharkunik | 41.1 | 2.3 | 38.8 | 15.8 | 0.9 | 14.9 | 94.4 | |
| Kotayk | 37.7 | 2.0 | 35.7 | 7.7 | 0.4 | 7.3 | 94.6 | |
| Lori | 76.5 | 2.9 | 73.6 | 28.0 | 1.1 | 26.9 | 96.2 | |
| Shirak | 27.4 | 2.1 | 25.3 | 7.1 | 0.5 | 6.6 | 92.3 | |
| Syunik | 78.8 | 4.0 | 74.8 | 34.3 | 1.7 | 32.6 | 94.9 | |
| Tavush | 99.2 | 2.4 | 96.8 | 26.4 | 0.6 | 25.7 | 97.6 | |
| Vayots Dzor | 60.8 | 3.1 | 57.7 | 13.6 | 0.7 | 12.9 | 95.0 |
Table 2. Sediment export in watersheds and provinces, 2023
| Mean current sediment export 2023, t/ha/year | Mean avoided sediment export 2023, t/ha/year | Total current sediment export 2023, Mt/year | Total avoided sediment export 2023, Mt/year | Share of avoided sediment export, %* | ||
| Watersheds | Aghstev | 0.2 | 5.5 | 0.0 | 1.7 | 97.3 |
| Akhuryan | 0.1 | 2.9 | 0.0 | 0.8 | 95.3 | |
| Arpa | 0.2 | 5.2 | 0.1 | 2.2 | 96.7 | |
| Debed | 0.2 | 5.9 | 0.1 | 2.2 | 96.7 | |
| Hrazdan | 0.1 | 3.5 | 0.1 | 2.0 | 96.4 | |
| Metsamor | 0.1 | 2.1 | 0.0 | 0.7 | 96.1 | |
| Vorotan | 0.3 | 7.8 | 0.1 | 3.4 | 96.2 | |
| Marzes | Aragatsotn | 0.1 | 2.7 | 0.0 | 0.7 | 96.2 |
| Ararat | 0.1 | 3.5 | 0.0 | 0.7 | 96.5 | |
| Armavir | 0.0 | 0.5 | 0.0 | 0.1 | 95.1 | |
| Gegharkunik | 0.1 | 4.2 | 0.1 | 1.6 | 96.6 | |
| Kotayk | 0.1 | 3.6 | 0.0 | 0.7 | 96.1 | |
| Lori | 0.2 | 5.9 | 0.1 | 2.1 | 97.0 | |
| Shirak | 0.1 | 3.2 | 0.0 | 0.8 | 96.2 | |
| Syunik | 0.3 | 7.8 | 0.1 | 3.4 | 96.6 | |
| Tavush | 0.2 | 5.4 | 0.0 | 1.4 | 97.2 | |
| Vayots Dzor | 0.2 | 6.4 | 0.0 | 1.4 | 96.6 |
Mt – million tons
Current export are values with current land cover in 2023
A comparison of indicators for different vegetation types shows that this ecosystem service is performed most effectively in forest zone, while its effectiveness is minimal in desert, semi-desert and marsh areas. It is important to remember that this ES is determined not only by the type of vegetation, but also by other factors — namely, soil type, slope, and precipitation. In this model, all differences between types of herbaceous vegetation are determined not by the vegetation itself, but by the conditions in which it grows.
a b c d e
Figure 4, d, e. Mean values (red dots) and value ranges (colored bars) of indicators for different vegetation types
2. ES changes from 2017 to 2023
Changes in the landcover from 2017 to 2023 resulted in changes in avoided erosion and sediment export. These changes represent only tenths of a percent of ES volume, but can be important for tracking trends.
Changes from 2017 to 2023 (red indicates a decrease, blue indicates an increase.)
Changes in avoided erosion Changes in avoided sediment export 
For details see maps in the section “Sediment Delivery Ratio – Dynamics”
Current erosion and sediment export increased in Akhuryan, Vorotan, and Debed watersheds as well as in Shirak, Syunik, Lori, and Gegharkunik provinces. In other watersheds and provinces, these indicators have decreased. Avoided erosion changed oppositely to current erosion but to a lesser extent in relative terms. Avoided sediment export changed in the same direction as current erosion and export. In provinces Gegharkunik and Kotayk, opposite changes occurred, which compensated for each other within the Hrazdan watershed, to which these provinces belong.
| Changes in absolute terms, t/ha | Changes in %, relative to 2017 | ||||||||
| Avoided erosion | Current erosion | Avoided sediment export | Current sediment export | Avoided erosion | Current erosion | Avoided sediment export | Current sediment export | ||
| Watersheds | Aghstev | -0.006 | 0.006 | 0.018 | 0.000 | -0.01 | 0.26 | 0.33 | -0.28 |
| Akhuryan | -0.228 | 0.228 | 0.190 | 0.025 | -0.99 | 12.99 | 6.94 | 20.82 | |
| Arpa | 0.081 | -0.081 | -0.066 | -0.008 | 0.17 | -3.13 | -1.25 | -4.53 | |
| Debed | -0.126 | 0.126 | 0.055 | 0.013 | -0.17 | 4.51 | 0.95 | 7.18 | |
| Hrazdan | 0.012 | -0.012 | -0.010 | -0.001 | 0.04 | -0.62 | -0.27 | -0.68 | |
| Metsamor | -0.012 | 0.012 | 0.005 | 0.002 | -0.06 | 0.93 | 0.24 | 1.98 | |
| Vorotan | -0.248 | 0.248 | 0.388 | 0.028 | -0.33 | 6.64 | 5.22 | 10.28 | |
| Provinces | Aragatsotn | -0.015 | 0.015 | 0.004 | 0.002 | -0.06 | 0.92 | 0.16 | 1.88 |
| Ararat | 0.078 | -0.078 | -0.064 | -0.008 | 0.24 | -4.35 | -1.80 | -5.97 | |
| Armavir | 0.020 | -0.020 | -0.019 | -0.001 | 0.59 | -4.54 | -3.73 | -5.78 | |
| Gegharkunik | -0.078 | 0.078 | 0.076 | 0.008 | -0.20 | 3.54 | 1.83 | 5.43 | |
| Kotayk | 0.077 | -0.077 | -0.053 | -0.007 | 0.22 | -3.63 | -1.46 | -5.09 | |
| Lori | -0.132 | 0.132 | 0.071 | 0.014 | -0.18 | 4.81 | 1.23 | 7.58 | |
| Shirak | -0.254 | 0.254 | 0.210 | 0.027 | -0.99 | 13.68 | 7.03 | 21.68 | |
| Syunik | -0.247 | 0.247 | 0.388 | 0.028 | -0.33 | 6.62 | 5.21 | 10.25 | |
| Tavush | 0.070 | -0.070 | -0.082 | -0.008 | 0.07 | -2.86 | -1.51 | -5.13 | |
| Vayots Dzor | 0.079 | -0.079 | -0.058 | -0.009 | 0.14 | -2.51 | -0.90 | -3.78 | |
3. Supply – use balance
This section is based on a comparison of estimates of avoided sediment export in streams by the SDR InVEST model and data on water consumption from ArmStat regional statistics. Taking into account water use in the marzes, the ES of ensuring runoff quality is most important in the Lori marz, where ecosystems prevent the export of 119 kg of sediment per 1 m3 of water use, and least in the Armavir marz, where this indicator is only 0.1 kg/year.
The degree of satisfaction of the need for this ES everywhere exceeds 95%
| Sediment export per m3 of total water use, 2023, kg/m3/year | Avoided sediment export per m3 of total water use, 2023, kg/m3/year | Share of avoided sediment export per m3 of water use, % | |
| Aragatsotn | 0.1 | 3.1 | 96.2 |
| Ararat | 0.0 | 0.9 | 96.7 |
| Armavir | 0.0 | 0.1 | 95.4 |
| Gegharkunik | 1.1 | 29.1 | 96.5 |
| Kotayk | 0.2 | 4.4 | 96.3 |
| Lori | 4.0 | 119.1 | 96.8 |
| Shirak | 0.6 | 13.0 | 95.4 |
| Syunik | 1.7 | 42.6 | 96.3 |
| Tavush | 1.8 | 67.6 | 97.4 |
| Vayots Dzor | 2.0 | 59.5 | 96.7 |
