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3. Assessment Results: Threat Ranks of Transboundary Lakes

The TWAP Lakes and Reservoirs Component provides lake rankings based on the magnitude of their threats as considered on the basis of the previously-noted 23 basin drivers and associated driver weights. The rankings are expressed in terms of the magnitudes of the Incident Human Water Security (HWS), Adjusted Human Water Security (Ad-HWS), and Biodiversity (BD) threats. Other weighting criteria, such as Human Development Index (HDI), may give a threat perspective not adequately reflected by any of the above three threats (i.e., the threat ranks on the basis of the potential threats stemming from inadequate socio-economic and human resource fulfillment).

The HWS, BD, and Adj-HWS threats to the transboundary lakes are summarized below in terms of:

  1. Transboundary Lakes Threat Ranks on the basis of: (a) Incident human Water Security [HWS] Threats, (b) Adjusted Human Water Security [Adj-HWS] Treats, and (c) Incident biodiversity [BD] Threats (Fig. 3-1), and
  2. Transboundary Lake threat Ranks on the basis of Multiple Ranking Criteria (Fig. 3-2).

Fig. 3-1 TWAP Transboundary Lakes Ranked on Basis of HWS Threats,
(b) Adj-HWS Threats, and (c) BD Threats

(Cont., continent; Eur, Europe; N.Am, North America; Afr., Africa; S.Am, South America;
Estimated threat risks: Red – highest; Orange – moderately high; Yellow – medium; Green – moderately low; Blue – low)

(A)Lakes Ranked on Basis of Incident Human Water Security (HWS) Threats   (B) Lakes Ranked on Basis of Adjusted Human Water Security (Adj-HWS) Threats   (C) Lakes Ranked on Basis of Incident Biodiversity (BD) Threats
Rank Lake Cont. Surface Area (km²) HWS Threat   Rank Lake Cont. Surface Area (km²) Adj-HWS Threat   Rank Lake Cont. Surface Area (km²) BD Threat
1CahulEur89.00.611SistanAsia488.20.981FalconN.Am120.60.62
2FalconN.Am120.60.612IhemaAfr.93.20.972ManglaAsia85.40.62
3ManglaAsia85.40.593AzueiS.Am117.30.963CahulEur890.61
4GalileeEur1620.594Rweru/MoeroAfr.125.60.963Neusiedler/FertoEur141.90.61
5Aras Su Qovsaginin Su AnbariAsia52.10.575CohohaAfr.64.80.965ErieN.Am26560.80.57
6Dead SeaEur642.70.576EdwardAfr.22320.946MichiganN.Am58535.50.56
7DarbandikhanAsia114.30.567Natron/MagadAfr.560.40.937GalileeEur1620.55
8Neusiedler/FertoEur141.90.548Abbe/AbheAfr.310.60.938DarbandikhanAsia114.30.54
9Szczecin LagoonEur822.40.549VictoriaAfr.66841.50.919Aras Su Qovsaginin Su AnbariAsia52.10.53
10Josini/Pongola-poort DamAfr.128.60.5210AlbertAfr.5502.30.9110OntarioN.Am19062.20.53
11Shardara/Kara-KulAsia746.10.5211KivuAfr.2371.10.9111Szczecin LagoonEur822.40.51
12ErieN.Am26560.80.5112Malawi/NyasaAfr.29429.20.9112MaggioreEur211.40.51
13Macro Prespa (Large Prespa)Eur2630.5013Dead SeaEur642.70.9013Dead SeaEur642.70.49
14AzueiS.Am117.30.5014TurkanaAfr.7439.20.9014Macro Prespa (Large Prespa)Eur2630.49
15OhridEur354.30.4915Aras Su Qovsaginin Su AnbariAsia52.10.8915OhridEur354.30.49
16MichiganN.Am58535.50.4816ManglaAsia85.40.8716ChamplainN.Am1098.90.49
17OntarioN.Am19062.20.4617GalileeEur1620.8717Josini/Pongola-poort DamAfr.128.60.48
18Caspian SeaAsia377543.20.4518DarbandikhanAsia114.30.8718HuronN.Am60565.20.47
19AmistadN.Am131.30.4219SelingueAfr.334.40.8712Shardara/Kara-KulAsia746.10.46
20VictoriaAfr.66841.50.4220Shardara/Kara-KulAsia746.10.8620Scutari/SkadarEur381.50.45
21IhemaAfr.93.20.4121Nasser/AswanAfr.5362.70.8621VictoriaAfr.66841.50.44
22SistanAsia488.20.4122ChilwaAfr.1084.20.8622IhemaAfr.93.20.44
23Scutari/SkadarEur381.50.4023Josini/Pongola-poort DamAfr.128.60.8523AzueiS.Am117.30.43
24MaggioreEur211.40.4024ChiutaAfr.143.30.8524Rweru/MoeroAfr.125.60.42
25HuronN.Am60565.20.4025ChadAfr.1294.60.8425ItaipuS.Am1154.10.42
26Rweru/MoeroAfr.125.60.4026Aral SeaAsia23919.30.8426CohohaAfr.64.80.41
27ChamplainN.Am1098.90.3927TanganyikaAfr.32685.50.8427Caspian SeaAsia377543.20.4
28CohohaAfr.64.80.3928AbyAfr.438.80.8328AmistadN.Am131.30.39
29ChadAfr.1294.60.3829CahulEur890.8229SistanAsia488.20.38
30ItaipuS.Am1154.10.3630ChungarkkotaS.Am52.60.8230AlbertAfr.5502.30.37
31ChungarkkotaS.Am52.60.3631TiticacaS.Am74800.8231ChadAfr.1294.60.36
32Natron/MagadAfr.560.40.3632SarygamyshAsia3777.70.8232AbyAfr.438.80.35
33AlbertAfr.5502.30.3533MweruAfr.5021.50.8133EdwardAfr.22320.35
34AbyAfr.438.80.3434Cahora BassaAfr.4347.40.7834KaribaAfr.5258.60.34
35EdwardAfr.22320.3435ItaipuS.Am1154.10.7535Lago de YacyretaS.Am1109.40.34
36KaribaAfr.5258.60.3336KaribaAfr.5258.60.7536Natron/MagadAfr.560.40.33
37TurkanaAfr.7439.20.3337Lago de YacyretaS.Am1109.40.7537KivuAfr.2371.10.33
38TiticacaS.Am74800.3338Lake Congo RiverAfr.3060.7538SelingueAfr.334.40.32
39KivuAfr.2371.10.3139Caspian SeaAsia377543.20.7339Nasser/AswanAfr.5362.70.32
40Lago de YacyretaS.Am1109.40.3140Salto GrandeS.Am532.90.6740Malawi/NyasaAfr.29429.20.32
41Abbe/AbheAfr.310.60.3141Scutari/SkadarEur381.50.6241ChungarkkotaS.Am52.60.31
42SelingueAfr.334.40.3042Neusiedler/FertoEur141.90.5842Cahora BassaAfr.4347.40.31
43Aral SeaAsia23919.30.3043Szczecin LagoonEur822.40.5343TurkanaAfr.7439.20.30
44Salto GrandeS.Am532.90.2944ErieN.Am26560.80.5144Salto GrandeS.Am532.90.30
45Nasser/AswanAfr.5362.70.2945Macro Prespa (Large Prespa)Eur2630.5145ChilwaAfr.1084.20.30
46Malawi/NyasaAfr.29429.20.2946FalconN.Am120.60.5048TiticacaS.Am74800.29
47Cahora BassaAfr.4347.40.2947AmistadN.Am131.30.4947Abbe/AbheAfr.310.60.29
48ChilwaAfr.1084.20.2848OntarioN.Am19062.20.4848TanganyikaAfr.32685.50.29
49SarygamyshAsia3777.70.2649OhridEur354.30.4743Aral SeaAsia23919.30.28
50ChiutaAfr.143.30.2550MichiganN.Am58535.50.4450MweruAfr.5021.50.28
51TanganyikaAfr.32685.50.2551HuronN.Am60565.20.4251ChiutaAfr.143.30.26
52MweruAfr.5021.50.2452MaggioreEur211.40.3352SarygamyshAsia3777.70.25
53Lake Congo RiverAfr.3060.2053ChamplainN.Am1098.90.2953Lake Congo RiverAfr.3060.20

The top dozen transboundary lakes exhibiting the greatest HWS threats were largely located in developed countries, including five European, four Asian, two North American and one African lake. Comparison of the HWS and Adj-HWS scores highlighted the positive impacts attributable to investments in measures to address the threatened transboundary lakes, resulting in a reduced number of threatened lakes in developed countries, while markedly increasing those in developing nations. The top dozen lakes exhibiting the greatest Adj-HWS threats included ten African, one Asian and one South American lake, highlighting their greater need for catalytic funding for transboundary lake management interventions. In regard to biodiversity, the top dozen lakes exhibiting the greatest Incident Biodiversity (BD) threats were also largely in developed countries, including five European, four North American and three Asian lakes. In contrast to their Adj-HWS threat rankings, the African transboundary lakes collectively exhibited lower BD threats than those in the developed countries, suggesting their biodiversity exhibited a more robust condition in spite of their greater human water security threats.

In addition to single ranking criteria, the transboundary lake threats were also ranked on the basis of simultaneous consideration of multiple filtering criteria, including the Adj-HWS threat and Human Development Index (HDI). It was not possible to develop an ‘adjusted biodiversity’ threat parameter similar to the Adj-HWS threat. Accordingly, a surrogate ‘Reverse Biodiversity’ (RvBD metric was developed to reflect the magnitude of the pristine nature of the biodiversity, with the lowest RvBD score indicating the greatest biodiversity threat. The computed ranks from these various parameters were also summed to obtain an overall threat ranking encompassing all of them.

Fig. 3-2 Transboundary Lake Threat Ranks by Multiple Ranking Criteria

(Cont., continent; Eur, Europe; N.Am, North America; Afr, Africa; S.Am, South America;
Adj-HWS, Adjusted Human Water Security threat; HWS, Incident Human Water Security threat; BD, Incident Biodiversity threat;
HDI, Human Development Index, RvBD, surrogate for ‘Adjusted’ Biodiversity threat;
Estimated risks: Red – highest; Orange – moderately high; Yellow – medium; Green – moderately low; Blue – low)

Cont. Lake Name Adj-HWS Threat RvBD Threat HDI   Adj-HWS Rank HDI Rank RvBD Rank   Sum Adj- HWS + RvBD Relative Rank   Sum Adj-HWS + HDI Relative Rank   Sum Adj- HWS + RvBD + HDI Overall Rank
AfrAbbe/Abhe0.930.710.4777141143211
AfrTurkana0.90.70.41131092222310322
AfrSelingue0.870.680.36162153111185333
AfrMalawi/Nyasa0.910.680.4291214233219354
AfrChiuta0.850.740.4123932653215354
AfrCohoha0.960.590.38342831271354
AfrKivu0.910.670.3812618308184367
AfrRweru/Moero0.960.580.364330341672378
AfrLake Congo River0.750.780.34351136183619378
AfrTanganyika0.840.710.42686321434174010
AfrEdward0.940.650.43613222871964111
AfrChilwa0.860.70.41211110311032144212
AfrMweru0.810.720.383354372138204212
AsiaSistan0.980.620.46120252662184614
AfrNatron/Magadi0.930.670.518231725431134815
AfrNasser/Aswan0.860.680.43201616361936185216
AfrAlbert0.910.630.46101924341529125317
AfrIhema0.970.560.442183335172075317
S.Am,Azuei0.960.570.4652131362026115719
AsiaAral Sea0.840.620.627265321353315820
AsiaSarygamysh0.820.750.672929231958326021
AfrCahora Bassa0.780.690.43341513472549256222
AfrVictoria0.910.560.47112232432433166523
AfrChad0.840.640.43251723482642216523
AfrKariba0.750.660.43361419553050286925
S.AmTiticaca0.820.710.7132328402225357226
AfrAby0.830.650.52282421492752307327
S.AmChungarkkota0.820.690.71313312432364347628
AsiaShardara/Kara-kul0.860.540.65222835573150278529
EurDead Sea0.90.510.72143438522948248630
AfrJosini/Pongola-poort Dam0.850.520.61242737613451298831
S.AmSalto Grande0.670.70.74403811512878398932
AsiaDarbandikhan0.870.460.68173046633547239333
S.AmLago de Yacyreta0.750.660.73383620583274389434
AsiaAras Su Qovsaginin Su Anbari0.890.470.73153544593350269434
AsiaMangla0.870.380.54182553713943229636
S.AmItaipu0.750.580.733737296637743710337
AsiaCaspian Sea0.730.60.773941276636804010738
EurGalilee0.870.450.881946476638653611239
EurCahul0.820.390.693031518142613311239
EurScutari/Skadar0.620.550.784142347541834111741
N.AmAmistad0.490.610.864745267340474011842
EurMacro Prespa (Large Prespa)0.510.510.754440408443844212443
EurOhrid0.470.510.744939398846884412744
EurSzczecin Lagoon0.530.490.834343438644864312945
N.AmHuron0.420.530.9351503687451015113746
EurNeusiedler/Ferto0.580.390.884247509247894513947
N.AmOntario0.480.470.924849459348974914248
EurLake Maggiore0.330.50.8952484294501005014248
N.AmFalcon0.50.380.854644529853904614248
N.AmErie0.510.430.934551499451964814551
N.AmChamplain0.290.510.9453524194491055314652
N.AmMichigan0.440.440.9450534898521035215153
Relative Risk Category
Low
Moderately Low
Medium
Moderately High
Highest

Based on these criteria, the African transboundary lakes are collectively the most threatened, comprising 21 of the top 25 most threatened lakes. The remaining lakes include three Asian and one South American lake. However, the relative threat ranks differ when the Adj-HWS, RvBD or HDI are considered individually, with the developed countries generally exhibiting lower threat ranks. As previously noted, because the context under which the transboundary lake threat rankings should be interpreted must be determined by the user of the ranking results, based on selected weighting criteria and relevant regional physical and socioeconomic factors.

These factors, considered alone or collectively, can readily lead to erroneous conclusions regarding the comparative transboundary lake threats. Thus, the calculated lake threats presented below represent only one approximation of the actual threat rankings. As demonstrated in the transboundary lakes assessment, different rankings, sometimes striking, can be obtained when different ranking factors are considered in the ranking calculations.