Changes in local climate in the neighbourhood of the Ust-Ilimsk water reservoir on the Angara, Russia

The paper presents results of investigations on microclimate over one of the largest artificial water reservoirs in the world - Ust-Ilimsk on the Angara in Russia. It is located in the western edge of the Central Siberian Upland in the northern part of Irkutsk Oblast. The area of reservoir at a normal level of water damming (296 m a.s.l.) amounts to 1873 km2, the capacity of stored water - 59,4 km3, and the shoreline length is equal to 2384 km. The evaluation of the influence of the water reservoir on local climate was based on the analysis of data collected over many years measurements of a series of particular elements of the climate and carried out in the direct neighbourhood of the reservoir before (1936-1975) and after its construction in 1977. From the research the results show that the Ust-Ilimsk water reservoir distinctly influences the local climate of adjacent areas. The differences are mostly connected with the increase in total radiation and changes in the radiation balance of the reservoir, and the larger heat capacity of the water mass in comparison to land. As data from meteorological stations indicate, the climate in the neighbourhood of this water reservoir gains many new features and generally becomes milder. The average annual increase in air temperature over the reservoir shores reached 1.3°C, whereas with in land it was only 0.4°C. At every meteorological station (inshore and continental), in the summer period and during the whole year as well, the average sum precipitation decreased by 7-14%. In the winter, when polynya exist, the number of days with fogs increases over the reservoir. Fogs in the shore zone of the Ust-Ilimsk reservoir delay the coming of frosts by 1-2 weeks.