The river basin drains some 533,000 square miles (1,380,000 square kilometres), stretching from the Valdai Hills and Central Russian Upland in the west to the Ural Mountains in the east and narrowing sharply at Saratov in the south.
From Kamyshin the river flows to its mouth uninterrupted by tributaries for some 400 miles.
Four geographic zones lie within the Volga basin: the dense, marshy forest, which extends from the river's upper reaches to Nizhny Novgorod (formerly Gorky) and Kazan; the forest steppe extending from there to Samara (formerly Kuybyshev) and Saratov; the steppe from there to Volgograd; and semidesert lowlands southeast to the Caspian Sea.
The course of the Volga is divided into three parts: the upper Volga (from its source to the confluence of the Oka), the middle Volga (from the confluence of the Oka to that of the Kama), and the lower Volga (from the confluence of the Kama to the mouth of the Volga itself).
The Volga is a small stream in its upper course through the Valdai Hills, becoming a true river only after the entrance of several of its tributaries. It then passes through a chain of small lakes, receives the waters of the Selizharovka River, and then flows southeast through a terraced trench.
Past the town of Rzhev, the Volga turns northeastward, is swelled by the inflow of the Vazuza and Tvertsa rivers at Tver (formerly Kalinin), and then continues to flow northeastward through the Rybinsk Reservoir, into which other rivers, such as the Mologa and the Sheksna, flow.
From the reservoir the riverproceeds southeastward through a narrow, tree-lined valley between the Uglich Highlands to the south and the Danilov Upland and the Galich-Chukhlom Lowland to the north, continuing its course along the Unzha and the Balakhna lowlands to Nizhny Novgorod. (Within this stretch the Kostroma, Unzha, and Oka rivers enter the Volga.)
On its east-southeastward course from the confluence of the Oka to Kazan, the Volga doubles in size, receiving waters from the Sura and Sviyaga on its right bank and the Kerzhenets and Vetluga on its left.
At Kazan the river turns south into the reservoir at Samara, where it is joined from the left by its major tributary, the Kama. From this point the Volga becomes a mighty river, which, save for a sharp loop at the Samara Bend, flows southwestward along the foot of the Volga Hills in the direction of Volgograd.(Between the Samara Bend and Volgograd it receives only the relatively small left-bank tributaries of the Samara, Bolshoy Irgiz, and Yeruslan.)
Above Volgograd the Volga's main distributary, the Akhtuba, branches southeastward to the Caspian Sea, running parallel to the main course of the river, which also turns southeast. A floodplain, characterised by numerous interconnecting channels and old cutoff courses and loops, lies between the Volga and the Akhtuba.
Above Astrakhan a second distributary, the Buzan, marks the beginning of the Volga delta, which, with an area of more than 7,330 square miles, is the largest in Russia. Other main branches of the Volga delta are the Bakhtemir, Kamyzyak, Staraya (Old) Volga, and Bolda.
The Volga is fed by snow (which accounts for 60 percent of its annual discharge), underground water (30 percent), and rainwater (10 percent). The natural, untamed regime of the river was characterized by high spring floods (polovodye). Before it was regulated by reservoirs, annual fluctuations in level ranged from 23 to 36 feet on the upper Volga, from 39 to 46 feet on the middle Volga, and from 10 to 49 feet on the lower Volga.
At Tver the average annual rate of river flow is about 6,400 cubic feet (180 cubic metres) per second, at Yaroslavl 39,000 cubic feet per second, at Samara 272,500 cubic feet per second, and at the river's mouth 284,500 cubic feet per second. Below Volgograd the river loses about 2 percent of its waters in evaporation. More than 90 percent of annual runoff occurs above the confluence of the Kama.
The climate of the Volga basin changes significantly from north to south. From its source to the Kama confluence, it lies within a temperate climatic zone characterized by a cold, snowy winter and a warm, rather humid summer. From the Kama to below the Volga Hills, hot, dry summers and cold winters with little snow prevail. Toward the south and east, temperatures increase and precipitation decreases.
The average temperatures in the river's upper reaches range from 19° F (?7° C) to 6° F (-14° C) and those of July from 62° F (17° C) to 68° F (20° C), while on its lower reaches at Astrakhan corresponding temperatures are 19° F (?7° C) and 77° F (25° C).
Annual rainfall ranges from 25 inches (635 millimetres) on the northwest to 12 inches on the southeast. Evaporation of precipitation ranges from 20 inches in the northwest to eight inches in the southeast.
The upper and middle courses of the Volga begin to freeze at the end of November, the lower reaches in December. The ice breaks up at Astrakhan in mid-March, at Kamyshin at the beginning of April, and everywhere else in mid-April.
The Volga is generally free of ice for about 200 days each year and for about 260 days near Astrakhan. As great masses of water accumulated within the reservoirs constructed during the Soviet period, however, the temperature regime of the Volga was so changed that the duration of ice increased on the headwaters of the reservoirs and decreased on the stretches below the dams.