ИСТИНА

Spatio-temporal change and variability of the total annual flow of rivers Vakhsh, Panj and Amudarya were examined by using measurements at three gauging stations (gs): 1. Komsomolabad, 2. Lower Panj, and 3. above the Karakum Canal. Basin area above each of the gs equals to respectively 29 500 km2, 113 000 km2 and 187 560 km2. Fluctuation in annual runoff Q analyzed for the period 1932-2009. The positive trend was revealed in the temporary change of Q on the 2-nd and 3-rd gs and a negative trend on the first gs. For each of the three gs were defined values P(Q) (the probability of not exceedance of a given Q value) during 1932-2009 years. Spatial variability of P(Q) values in normal and extreme years in the Amu Darya basin was calculated and described by data of 26 gs for the baseline climate period 1961-1990. A similar study carried out for long-term series of calculated annual volumes of glacial runoff VM in the Vakhsh and Panj river basins. The total quantity of glaciers within Vakhsh and Panj river basins was divided into 138 groups for calculations therein P(VM). Spatial variability P(VM) in normal years turned out much more significant than in minimal and maximal ones. This result is important for hydropower, because an even spatial distribution VM volumes in low water years has a stabilizing role for the balance of input and output of reservoirs. Small or large spatial variability P(VM) in extreme and normal years is influenced by the proper variability of air temperature and precipitation. Statistical probabilities of seasonal air temperature in normal and extreme years entirely corresponds to its role as index of ablation and runoff formation. Low water vegetation season is consequence of cool summer and vice versa. Total volume of glaciers melting in high water year equals to 26.89 km3 and 7.11 km3 in low water year.