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Flood Risk Mitigation
The InVEST model Urban Flood Risk Mitigation (UFRM) calculates two main indicators:
– the Runoff retention, i.e. the amount of runoff retained by soil and vegetation compared to the storm rain volume in m3 (1 m3 of runoff is equal to 10 mm per one 10x10m pixel) and as proportion of retained precipitation);
– the Runoff (Q), mm, which is a potentially hazardous factor that can cause flooding.
The main results of ES modeling and mapping
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)
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
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
We tested the model for two scenarios—average and extreme spring rainfall. The highest precipitation in Armenia occurs in May and June. While precipitation levels vary significantly across different climatic zones, for the initial model testing, we considered it reasonable to use countrywide average values. During these months, an average rainfall event delivers 12 mm of precipitation. For the extreme rainfall scenario, we assumed approximately half of the monthly precipitation in either of these months, which is 50 mm.
(Table).
The average spring rainfall scenario (12 mm)
Precipitation is almost entirely retained by vegetation and soil. Quick runoff across most of Armenia is less than 1 mm, slightly exceeding this value in some valleys. Under the bare ground scenario (all natural vegetation is replaced with bare soil), runoff retention (RT) reduces very slightly. Quick runoff (Q) increases slightly in absolute terms, but the relative changes in some watersheds are noticeable.
Current land cover 2023
Runoff retention, m3 (1m3 = 10mm/pixel) Q, mm 
Bare ground scenario
Runoff retention, m3 (1m3 = 10mm/pixel) Q, mm 
Figure 1. Maps of ES indicators under the average spring rainfall scenario (12 mm). For detailed maps see the section “Ecosystem Services – Urban Flood Risk Mitigation – Scenario 2 (12 mm 2023) and Scenario 4 (12 mm no vegetation)
The ES provided by natural terrestrial ecosystems can be estimated as the difference in indicators between the current land cover 2023 and bare ground scenario. The ecosystem service is most pronounced in the Debed, Akhuryan, and Aghstev watersheds, reducing quick runoff by 55%, 74% and 83%, respectively. In other watersheds, the service is less significant.
Figure 2. ES provided by natural ecosystems, % relative to current land cover, 2023
Table 1. ES provided by natural ecosystems
| Difference LC 2023 – Bare ground | ||||
| Q, mm_sum | Q, mm_mean | RT, m3_sum | RT, m3_mean | |
| Aghstev | -2642473.79 | -0.06 | 264249.38 | 0.006 |
| Akhuryan | -2523669.01 | -0.08 | 252368.21 | 0.008 |
| Arpa | -272522.40 | -0.01 | 27254.20 | 0.001 |
| Debed | -2189224.99 | -0.06 | 218924.26 | 0.006 |
| Hrazdan | 266913.27 | 0.01 | -26690.17 | -0.001 |
| Metsamor | -1293014.33 | -0.02 | 129303.41 | 0.002 |
| Vorotan | -259641.64 | -0.01 | 25965.08 | 0.001 |
| Difference LC 2023 – Bare ground, % relative to 2023 | ||||
| Q, mm_sum | Q, mm_mean | RT, m3_sum | RT, m3_mean | |
| Aghstev | -82.53 | -82.53 | 0.59 | 0.59 |
| Akhuryan | -73.92 | -73.92 | 0.80 | 0.80 |
| Arpa | -3.94 | -3.94 | 0.06 | 0.06 |
| Debed | -54.91 | -54.91 | 0.56 | 0.56 |
| Hrazdan | 2.76 | 2.76 | -0.07 | -0.07 |
| Metsamor | -8.99 | -8.99 | 0.22 | 0.22 |
| Vorotan | -2.34 | -2.34 | 0.10 | 0.10 |
The extreme spring rainfall scenario (50 mm)
Precipitation is fully retained only in a small part of the territory (the darkest areas on the map of runoff retention). As a result, quick runoff (Q) exceeds 10 mm across most of the territory and exceeds 20 mm in a significant portion. If all natural vegetation is replaced with bare ground, runoff retention (RT) decreases significantly, and quick runoff (Q) also increases noticeably. For this scenario, ES is more pronounced and occurs in all watersheds, manifesting as an increase in RT by 9%–13% and a decrease in Q by 17–49%.
Current land cover 2023
Runoff retention, m3 (1m3 = 10mm/pixel) Q, mm
Bare ground scenario
Runoff retention, m3 (1m3 = 10mm/pixel) Q, mm
Figure 3. Maps of ES indicators under the extreme spring rainfall scenario (50 mm). For detailed maps see the section “Ecosystem Services – Urban Flood Risk Mitigation – Scenario 1 (50 mm 2023) and Scenario 5 (50 mm, no vegetation)
Figure 4. Total values of ecosystem functions and ES provided by natural ecosystems
Figure 5. ES provided by natural ecosystems, % relative to the total values of ecosystem functions
Table 2. ES provided by natural ecosystems
| Difference LC 2023 – Bare ground | ||||
| Q, mm_sum | Q, mm_mean | RT, m3_sum | RT, m3_mean | |
| Aghstev | -226460024.7 | -5.1 | 22646007.5 | 0.5 |
| Akhuryan | -139056519.5 | -4.4 | 13905656.2 | 0.4 |
| Arpa | -232059662.9 | -5.3 | 23205971.4 | 0.5 |
| Debed | -167505046.9 | -4.3 | 16750512.0 | 0.4 |
| Hrazdan | -113526172.9 | -3.1 | 11352621.6 | 0.3 |
| Metsamor | -220867993.8 | -3.7 | 22086804.6 | 0.4 |
| Vorotan | -79787700.0 | -2.9 | 7978773.5 | 0.3 |
| Difference LC 2023 – Bare ground, % relative to 2023 | ||||
| Q, mm_sum | Q, mm_mean | RT, m3_sum | RT, m3_mean | |
| Aghstev | -43.3 | -43.3 | 13.2 | 13.2 |
| Akhuryan | -32.8 | -32.8 | 11.9 | 11.9 |
| Arpa | -49.0 | -49.0 | 13.4 | 13.4 |
| Debed | -32.0 | -32.0 | 11.6 | 11.6 |
| Hrazdan | -21.8 | -21.8 | 8.7 | 8.7 |
| Metsamor | -27.5 | -27.5 | 10.1 | 10.1 |
| Vorotan | -17.4 | -17.4 | 8.6 | 8.6 |
The loss of EU that occurred in historical times can be assessed as the difference between the EU indicator values for the 2023 land cover and the fully natural land cover where all croplands and built-up areas are replaced with grasslands. This ratio shows that a significant part of the service is still preserved at present.
As expected, the most significant loss of EU occurred in areas that are currently built-up. For croplands, the loss of EU is less substantial.
2. ES changes from 2017 to 2023
Changes in the landcover from 2017 to 2023 resulted in changes in runoff retention (RT) and quick runoff (Q). These changes in most watersheds and provinces are around 1% or less, but can be important for tracking trends. In all watersheds except Arpa, and in all provinces except Vayots Dzor, ES weakened as RT values decreased and Q values increased. The most significant changes occurred in the Akhuryan watershed and the Vayots Dzor province.
| Changes in absolute terms | Changes in relative terms, % relative to 2017 | ||||||||
| Total quick runoff Qsum, mm | Quick runoff, Q, mm | Total runoff retention, RTsum, m3 | Runoff retention, RT, m3 | Total quick runoff Qsum | Quick runoff, Q | Total runoff retention, Rtsum | Runoff retention, RT | ||
| Watersheds | Aghstev | 3695334.006 | 0.083 | -369533.450 | -0.008 | 0.712 | 0.712 | -0.215 | -0.215 |
| Akhuryan | 1168730.457 | 0.037 | -116873.088 | -0.004 | 0.277 | 0.277 | -0.100 | -0.100 | |
| Arpa | -540886.772 | -0.012 | 54088.842 | 0.001 | -0.114 | -0.114 | 0.031 | 0.031 | |
| Debed | 6613157.466 | 0.168 | -661315.935 | -0.017 | 1.278 | 1.278 | -0.458 | -0.458 | |
| Hrazdan | 8848607.245 | 0.243 | -884860.753 | -0.024 | 1.730 | 1.730 | -0.675 | -0.675 | |
| Metsamor | 8775668.887 | 0.147 | -877566.932 | -0.015 | 1.104 | 1.104 | -0.399 | -0.399 | |
| Vorotan | 15077382.948 | 0.545 | -1507738.364 | -0.055 | 3.395 | 3.395 | -1.607 | -1.607 | |
| Prrovinces | Aragatsotn | 6380583.199 | 0.234 | -638058.439 | -0.023 | 1.720 | 1.720 | -0.643 | -0.643 |
| Ararat | 885512.409 | 0.042 | -88551.026 | -0.004 | 0.357 | 0.357 | -0.110 | -0.110 | |
| Armavir | 2302985.854 | 0.182 | -230298.494 | -0.018 | 1.180 | 1.180 | -0.527 | -0.527 | |
| Gegharkunik | 4984155.795 | 0.125 | -498415.690 | -0.012 | 1.089 | 1.089 | -0.324 | -0.324 | |
| Kotayk | 1631821.499 | 0.077 | -163182.179 | -0.008 | 0.532 | 0.532 | -0.217 | -0.217 | |
| Lori | 6383285.157 | 0.170 | -638328.701 | -0.017 | 1.308 | 1.308 | -0.458 | -0.458 | |
| Shirak | 15920566.788 | 0.590 | -1592056.743 | -0.059 | 3.722 | 3.722 | -1.728 | -1.728 | |
| Syunik | 3659796.336 | 0.082 | -365979.684 | -0.008 | 0.706 | 0.706 | -0.213 | -0.213 | |
| Tavush | 321776.033 | 0.012 | -32177.603 | -0.001 | 0.084 | 0.084 | -0.033 | -0.033 | |
| Vayots Dzor | -373092.509 | -0.016 | 37309.252 | 0.002 | -0.157 | -0.157 | 0.041 | 0.041 | |
