Because of a scarcity of uniform data for the transboundary study lakes, it was not possible to evaluate the threats to the lakes on the basis of their in-lake conditions. Rather, the assessment approach for evaluating the relative threats to the transboundary lake basins was based on consideration of the conditions of their surrounding drainage basins, utilizing a modification of the global-scale database derived by Vӧrӧsmarty et al. (2010) on the basis of 23 basin drivers.
The threats to the transboundary lakes were based on calculating the incident Human Water Security (HWS) and Biodiversity (BD) threats to the lakes. The analysis also considered the ability of the basin countries to undertake investments in water infrastructure to address their transboundary water problems, in the form of an Adjusted Human Water Security (Adj-HWS) threat, which differs significantly between the developed and developing nations.
A scenario analysis framework was used to characterize and quantify multiple drainage basin-scale stressors to calculate their cumulative impacts on the transboundary lakes contained within them.
The 23 drivers, grouped under four major thematic areas, used to calculate the incident Human Water Security (HWS) and Biodiversity (BD) threats are summarized below. The definition of these terms is presented by Vӧrӧsmarty et al. (2010) and in the TWAP Transboundary Lakes Technical Report.
|Impervious Surfaces||River Fragmentation|
|Livestock Density||Consumptive Water Loss|
|Wetland Disconnectivity||Human Water Stress|
|Pollution||Soil Salinization||Agricultural Water Stress|
|Nitrogen Loading||Flow Disruption|
|Phosphorus Loading||Biotic Factors||Non-Native Fish#|
|Mercury Deposition||Non-Native Fish%|
|Pesticide Loading||Fishing Pressure|
|Sediment Loading||Aquaculture Pressure|
The relative risk categories were based solely on comparison of the relative calculated numerical threat scores, with the highest scores suggesting the greatest threat, and the lowest score suggesting the least threat. It is emphasized, however, that these calculated scores do not consider the context under which they were evaluated within the scenario analysis framework.
Based solely on drainage basin characteristics, they do not take in-lake conditions into account, nor do they consider the capacity of lakes and other lentic water systems to buffer basin-derived stresses.
Thus, some transboundary lakes whose calculated threat scores suggest they are only moderately threatened on the basis of their basin characteristics may actually be seriously degraded, while some transboundary lakes experiencing serious threats may not be identified as such because of insufficient data.
Differing regional physical and socioeconomic perspectives also can result in classifying a lake as being threatened in one region, but which may not be considered threatened elsewhere. These factors, considered alone or collectively, can readily lead to erroneous conclusions regarding the transboundary lake threats unless they are appropriately considered in properly interpreting the calculated lake threats. Without appropriately consideration of the context under which they were developed, therefore, the calculated lake threats represent only one approximation of the actual risks (although a high threat rank may signify future degradation under a ‘business-as-usual’ scenario). More definitive conclusions can only be derived from more intensive lake data compilation and analyses on a global scale.
|Relative Risk Category|