The Volga River Water Runoff in Warm Epochs

Abstract

Similarities and differences in climatic conditions (air temperature and precipitation), annual and seasonal runoff, as well as hydrographs of the Volga River runoff near Volgograd in the epochs of global warming in the geological past, the period of modern warming (since 1981), and the scenario global warming in the 21st century are revealed. Changes in the runoff of the geological past and the scenario future were estimated on the basis of the monthly water balance model developed at the Institute of Geography of the Russian Academy of Sciences and the equation of the average long-term water balance. The results of traditional and model paleoclimatic reconstructions and climate scenarios of global warming in the 21st century were used as climatic conditions for assessing changes in runoff. Modern long-term changes in the Volga River runoff are analyzed on the basis of ideas about long-lasting contrasting phases. As a result of the analysis, it is shown that the annual Volga River runoff in the conditions of the warm epochs of the Mikulinsky interglacial and the Atlantic optimum of the Holocene (based on traditional paleoclimatic reconstructions) was lower than the modern one. Whereas, according to model paleoclimatic reconstructions of the warm epochs of the Holocene, climatic scenarios of anthropogenic warming, as well as in the conditions of modern global warming, the annual runoff of the Volga River is higher than in the base period. Significant differences in the changes in the seasonal distribution of the Volga River runoff between all the considered warm epochs were revealed. The different nature of these changes is characteristic of the warm epochs of the paleoepochs and in the conditions of scenario climatic changes in the 21st century. At the same time, changes in the seasonal distribution during modern global warming are similar to those that can be expected with scenario warming in the first third and middle of the current century (except snowmelt flood runoff). A close correlation was revealed between the anomalies of changes in the annual air temperature and the annual amount of precipitation in all the considered warm epochs. During the period of instrumental observations, the long-term phases of the increased or decreased water runoff of the Volga River are synchronous with the corresponding phases of the index of the North Atlantic oscillation and the periods of increase and decrease in the annual levels of the Caspian Sea.