# How to calculate the surface area of a lake in an endorheic basin, where evaporation is the only "outflow"

So, I am essentially doing a project where the Western Amazon is an endorheic basin with the climate of the Sechura desert and wanted to see how large the surface area of the lake formed within would be and if there'll even be a lake there.

So, for constants like the river inflow rate I'll use the Sechura and for the temperature and evaporation rate, something between the Sechura, Sahara and Death Valley for the size and distance from the coast of this.

• Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer.
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Commented May 24 at 9:12
• I would turn the bit about salinity of an endoheric lake into a separate question to make this question work within the rules. Commented May 24 at 9:43
• For "the river inflow rate I'll use the Sechura": no such river is known to the usual sources of information. Could you please post a link to the description of this mysterious river where one can find its average flow rate? Commented May 24 at 12:36
• I wasn't clear, by Sechura I mean the river basins of the Sechura Desert. Commented May 27 at 15:16

Let's start by considering that, if there was the right orography to have an endorheic basin, we would notice it by the fact that one of the many rivers flowing in the Amazon basin would have formed a lake. Since this is not the case, we can conclude that, unless you change the orography, you cannot have the basin you are looking for.

That said, there is a pretty crude and simple method to estimate the surface of a region on a map:

• plot the contours of the region on paper or cardboard
• cut the paper/cardboard along those contours
• weigh the resulting shape
• knowing the scale of map you have printed, cut a square corresponding to 1/10/100 square km (it depends on the chosen scale)
• weigh the square
• you will find that the shape weighs n times the square. Its surface is also n time the surface of the square.

• There is no need to weigh anything, unless one absolutely abhors using computers; but in that case they would not be able to read the answer, would they? Get the map in a digital file, fill in the area with a distinctive color, and use your favorite image editor to count the pixels of that color. P.S. Remember to use an equal-area map projection; for areas smaller than about half of a hemisphere the azimuthal equal-area projection is perfectly adequate. Commented May 24 at 12:32

Deepends? Evaporation depends on surface and temperature. If the water is shallow, the surface below dark and manifold, or even heated by volcanics.. you get fast evaporation, which is then covered in salt. So, lets look at the real world- and there we have the salton sea and the dead sea.