I have just started a course in hydrology (a totally different field from mine which is computer science) and I can't find the link between the fact that a river flows into a lake and the % of precipitation falling as snow. I'm really confused. Can someone explain the principle (questions a and b being trivial)? The problem is posed below:


A watershed has an area of 300 km2. Annual precipitation in this watershed has averaged 1039 mm over the past 30 years. Data from a stream gauging station at the outlet of this watershed indicate that the average flow rate has been 3,900 l/s over these 30 years.

a) What is the annual volume of precipitation in this basin in m3?

b) Estimate the total annual evapotranspiration from this pond in mm.

c) The stream in question drains into a Lake of 1000 km2; what is the average percentage of precipitation that falls as snow in this basin (to the nearest 10%)?

Thank you for sharing your expertise !


This is how I solve the two first questions

a) Volume = P * S

b) Water balance equation: P = Q + E Then E = P - Q where P in mm and Q in mm

c) I don't get the link.

  • $\begingroup$ I am curious as well. Is the precipitation measured in mm snow cover? $\endgroup$
    – fraxinus
    Jan 26 at 7:06


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