Abstract <p>A methodology is proposed and an assessment of water balance elements of the local catchments of the Kuibyshev, Saratov, and Volgograd reservoirs is carried out based on the data of the regional offices of Roshydromet. The studies were developed for the period of 1966–2017. The methodology is based on taking into account the data on atmospheric precipitation, evaporation, and runoff from the local catchments of the lower Volga reservoirs. Evaporation from the catchment areas is estimated using the method of A.R. Konstantinov taking into consideration the respective series of air temperature and pressure of water vapor. The balance element, taking into account the accumulation (loss) of water content within the local catchments, was determined by the difference between atmospheric precipitation and the sum of runoff and evaporation. When moving upriver from the Volgograd Reservoir to the Kuibyshev Reservoir, evaporation from the catchments under consideration, as well as the correlation of its time series with atmospheric precipitation, consistently decrease. Accordingly, precipitation, local runoff, and their correlation increase. Simultaneously, for the reservoir catchments, the groupings of years of high, low, and close to average values for 1966–2017 were estimated for precipitation, evaporation, and runoff. It was concluded that the presence of these groupings during this period is strictly individual. The lengths and different sequences of alternation of groupings of years of the water balance elements can be signs of certain patterns in their fluctuations. This article estimates the probabilities of transition of water balance components from one range of values to another. In some cases, the probability of transition of a water balance element from one range to another, or its preservation in the current range, is quite high and amounts to 50% or more, or it may be small (close to 0). Such information can be useful in predicting the transition with the appropriate lead time.</p>