Hello everyone,

I am working with WEAP on a lake system, specifically Lake Guiers in Senegal. I have a question about how WEAP calculates and varies basin precipitation (Inflow from pluie bv) and net evaporation across prospective scenarios. In my model, these two parameters are introduced only in the reference scenario. I did not modify them in the other prospective scenarios (S1 to SX). However, when I examine the results, particularly the Reservoir Inflows and Outflows for the different scenarios, I notice that the values of Net Evaporation and Inflow from pluie bv vary from one prospective scenario to another. For some scenarios, net evaporation is higher or lower than in others, and the same applies to basin precipitation/runoff.

I would therefore like to understand how WEAP calculates these two parameters in prospective scenarios when their input data have not been explicitly modified between scenarios.

More specifically:

How does WEAP calculate Inflow from pluie bv (basin precipitation/runoff) for each scenario?
How does WEAP calculate Net Evaporation for the reservoir?
Can these values vary between scenarios as a result of changes in reservoir storage, water level, surface area, or other scenario-dependent variables, even when the climatic input data remain unchanged?
Thank you in advance for your help and explanations.

The volume change in the reservoir volume due to net evaporation is a function of the net change in depth from both precipitation and evaporation multiplied by the reservoir surface area. It is likely that your reservoir surface area (which changes as the simulated reservoir volume varies across your scenarios) is changing, which is changing your evaporation results.

This may be tied to the precipitation result as well. Can you tell me more about what object in WEAP you are looking at the inflow from precipitation result for?