SUMMARY
Water purity and availability determines health and life quality of humans, biodiversity and existence of plants and animals. The results of global climate change have been registered all over the world as progressive warming with fast heat waves, accelerated glacier ice melting, variations in the global ocean streams and heat balance, droughts and lack of drinking water, damage to plants and animals. Mathematical modeling of the water exchange in local ecosystems is a very important constituent of detailed analysis of different scenarios of water availability at various trends in the weather change.The work is aimed at mathematical modelling of water balance in an urban ecosystem accounting for global climate changes. A brief review of the models is presented, and a synthetic model for the water balance on the urban territory of Kharkiv city (Ukraine) based on the statistical dependencies, compartmental system dynamics approach and hydrological equation with probabilistic description of the input parameters is developed. The monthly and year averaged temperature and precipitation curves, time series on downpours, droughts and storms over the Kharkiv region and Kharkiv city during 1908-2012 years were collected from the open databases and analyzed. Gradual increase in the annual temperature was confirmed.Different scenarios of the regional development (population growth and industry development with increased water demands) and weather changes were tested, and availability of water has been estimated. It was established by numerical simulations, the water insufficiency in the region in 2040 could reach 10-17 % if the mean annual air temperature increases in 0.5-2.5 °T. This will cause damage for plants, animals, and human health. The obtained results are important for decision making by official planning authorities and regional administration