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Abstract: In the Northern Amudarya delta (Uzbekistan), the regulated hydrological regime is one of the main factors determining the ecological state of riverine ecosystems, such as the characteristic tugai forests. Euphratica poplar (Populus euphratica, syn. ariana) is the dominant tree species of tugai forests in Central Asia. A habitat suitability index for P. euphratica is developed to provide a measure for the evaluation of future water management alternatives as to their effects on the ecological situation in the delta region. The following environmental variables are chosen as determining parameters for habitat suitability: geomorphology, groundwater level and flooding regime (i.e. flooding frequency, timing and duration of the last flooding). Here, flooding frequency is a dynamic variable that reflects the flooding history at a given site. Collected semi-quantitative and qualitative knowledge about the impact of those variables on suitability of a site for P. euphratica is formalised using a fuzzy set approach. The resulting index is implemented in GIS and applied to a test period (1991–1999). The results are compared to the actual distribution of tugai forest in the year 2000 to check their plausibility. By these means a ‘virtual expert’ is created that enables a fast and simple evaluation of the habitat suitability for P. euphratica on a landscape scale. As part of an integrated simulation tool, the HSI shall support the ecological impact assessment of future water management strategies on the Northern Amudarya delta. [Copyright &y& Elsevier]