We apologize for possible errors in the machine translation of the site
Prevention of soil water erosion and sediment transport to waterbodies (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 ES – 1) prevention of soil water erosion and 2) ensuring water flow quality due to prevention of sediment transport to waterbodies – were estimated and mapped using InVEST Sediment Delivery Ratio (SDR) 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 (Figure 31A3-1).
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.
ES provided by terrestrial ecosystems
In 2023, total avoided erosion was estimated as 140 million tons, and total avoided sediment export to streams was estimated as 13 million tons. ES maps show that current erosion and sediment export are negligible, whereas avoided erosion and sediment export is many times higher (Figure 31A3-2, note that the scale values for current sediment export are one-tenth of those for avoided export). On average, ecosystems prevent about 95% of erosion and 96% of sediment export in Armenia (Table 31A3-1).
Table 31A3-1. ES indicators in Armenia
| Indicator | Land cover 2023 | Bare ground scenario | ES Provided by ecosystems | Change in ES due to ecosystem functioning % |
| Erosion | 2.3 t/ha/year 6.8 Mt/year | 48.6 t/ha/year 147.2 Mt/year | Avoided erosion −46.4 t/ha/year −140.4 Mt/year | −95% |
| Sediment export | 0.15 t/ha/year 0.47 Mt/year | 4.5 t/ha/year 13.5 Mt/year | Avoided sediment export −4.3 t/ha/year −13.0 Mt/year | −96% |
The SDR 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. 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 (Figures (Figure 31A3-3 and 31A3-4). This pattern, in general, is also evident for the total values of avoided erosion and sediment export (Tables 31A3-2 and 31A3-3).
Figure 31A3-2. ES indicators with current land cover, 2023. For detailed maps see the section “Ecosystem Services – Sediment Delivery Ratio – Basic scenario 2023” in the project Web GIS
Figure 31A3-3. ES indicators across watersheds
Figure 31A3-4. ES indicators across marzes
Table 31A3-2. Erosion in watersheds and provinces (Mt – million tons)
| 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 31A3-3. Sediment export in watersheds and provinces, 2023 (Mt – million tons)
| 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
Analysis of ES indicators across vegetation zones shows that the average avoided erosion is highest in forest and woodland zones, moderate in alpine and subalpine zones, and lowest in desert, semi‑ desert, and marshes (Figure 31A3-5 a). The range of values within individual polygons of certain vegetation zones is quite large — in semi-desert, forest, juniper, and broadleaf woodland zones. The ratio of avoided erosion to current erosion is highest in forest and woodland zones (avoided erosion is 96–97 times greater than current erosion), ranging from 93 to 95 in other zones (Figure 31A3-5 b). 
Figure 31A3-5. ES indicators across marzes
2. ES changes from 2017 to 2023
Changes in the landcover from 2017 to 2023 resulted in changes in avoided erosion and sediment export. The maps show that the changes are sporadic and oppositely directed (Figure 31A3-6). These changes represent only tenths of a percent of total ES volume, but can be important for tracking trends.
Figure 31A3-6. ES changes from 2017 to 2023: a) Changes in avoided erosion; b) Changes in avoided sediment export. For details see maps in the section “Sediment Delivery Ratio – Dynamics” in the project Web GIS
In absolute terms, the largest negative changes occurred in the Akhuryan and Vorotan watersheds, where erosion increased by 0.23–0.25 t/ha/yr. In the Debed watershed, erosion increased by 0.13 t/ha/yr. Small positive changes were observed in the Arpa watershed, where erosion decreased by 0.08 t/ha/yr. Changes in the other watersheds are negligible. Relative to 2017, erosion and sediment export increased the most in the Akhuryan watershed —by 21% and 13%, respectively. In the Vorotan watershed these indicators rose by 10% and 7%, respectively; in the Debed watershed —by 7% and 5%. In the Arpa watershed they decreased by 5% and 3%, respectively (Figure 31A3-7).
Changes by marz generally mirror those in the corresponding watersheds: Shirak marz — Akhuryan watershed; Syunik marz — Vorotan watershed; Lori marz — Debed watershed; Ararat and Vayots Dzor marzes — Arpa watershed (Figure 31A3-8). An important management-relevant case arises in the marzes of Gegharkunik and Kotayk where opposite changes occurred, which compensated for each other within the Hrazdan watershed, to which these provinces belong. In the marzes of Aragatsotn and Armavir, both within the Metsamor watershed, we also observe changes in opposite directions: the marked deterioration in Armavir relative to 2017 is offset by relatively modest improvements in Aragatsotn, owing to its larger area. Changes in Tavush marz differ from those in the Aghstev basin because the Getik—a major tributary of the Aghstev—lies within Gegharkunik marz.
Figure 31A3-7. ES changes from 2017 to 2023 across watersheds
Figure 31A3-8. ES changes from 2017 to 2023 across marzes
Table 31A3-4. ES changes from 2017 to 2023 across watersheds and marzes
| 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
Terrestrial ecosystems reduce sediment export by 0.7–2.8 kg per cubic meter of river flow (Table 31A3-5; Figure 31A3-9). The value of 6.5 for the Aghstev watershed is not representative, because total amount of sediment export was calculated for an area larger than the actual Aghstev River watershed for which river flow data are available. The true value for that area is clearly lower.
In total, terrestrial ecosystems annually prevent about 3.2 million tonnes of sediment from entering the water that is consumed (Table 31A3-5). This ES is most important in Arpa watershed, where ecosystems annually prevent the export of 1.5 million of tons of sediment to the water used, and lowest in the Debed and Akhuryan watersheds, where this indicator is less than 100 thousands of tons (Table 31A3-5; Figure 31A3-10). However, the share of avoided sediment export in water use everywhere exceeds 95%, which means that the need for this ES is being met.
Figure 31A3-9. Sediment carried by river flow and avoided due to terrestrial ecosystems
Figure 31A3-10. Total amount of sediment avoided in the volume of water consumed
Table 31A3-5. ES supply-use balance
| Total water consump-tion*, mln m3 | River flow* mln m3 | Total sediment export, tons/year | Total avoided sediment export, tons/year | Sediment export per 1 m3 of river flow, kg/m3 | Avoided sediment export per 1 m3 of river flow, kg/m3 | Total amount of sediment avoided in the volume of water consumed, tons/year | The share of avoided sediment per 1 m3 of river flow, % | |
| Aghstev (a part of the marz Tavush) | 20.90 | 260.00 | 46926.1 | 1691482.9 | 0.18 | 6.5 | 135969.2 | 97.3 |
| Akhuryan (marz Shirak) | 63.10 | 700.70 | 37652.6 | 766472.4 | 0.05 | 1.1 | 69023.0 | 95.3 |
| Arpa (marzes Ararat and Vayots Dzor) | 835.90 | 1177.00 | 74243.8 | 2199773.9 | 0.06 | 1.9 | 1562269.4 | 96.7 |
| Debed (marz Lori) | 18.00 | 960.00 | 75937.3 | 2235907.1 | 0.08 | 2.3 | 41923.3 | 96.7 |
| Hrazdan (marzes Kotayk and Gegharkunik) | 218.60 | 712.20 | 74077.3 | 1964292.1 | 0.10 | 2.8 | 602912.5 | 96.4 |
| Metsamor (marzes Armavir and Aragatsotn) | 769.10 | 1043.30 | 29705.2 | 731035.0 | 0.03 | 0.7 | 538904.5 | 96.1 |
| Vorotan (marz Syunik) | 89.50 | 1319.60 | 131836.5 | 3383691.3 | 0.10 | 2.6 | 229494.1 | 96.2 |
| Total | 2015.10 | 6172.80 | 470378.9 | 12972654.7 | – | – | 3180495.8 | – |
