Subject: Reservoir evaporation Posted: 6/23/2016 Viewed: 11232 times
I would like to ask how WEAP calculate reservoir evaporation, I read WEAP's manual, but still not clear. I know that may be WEAP based on volume - elevation curve to calculate reservoir evaporation. However, I'm wondering that whether WEAP also need based on temperature, wind speed and humidity to calculate reservoir evaporation?
In addition, WEAP also require input Net evaporation, so are there any related to this term?
I ask this question because I try run WEAP model to simulate impacts of climate change on water shortage at the downstream of the reservoir. In my case, rainfall tend to increase lead to reservoir inflow increase in in the future, temperature also increase 1 oC. However, water shortage at the downstream of the reservoir is increase compare to baseline. Normally, water shortage should be decrease when reservoir inflow increase. So I think this because temperature increase lead to increase reservoir evaporation.
Hope you can help me clear this problem.
WEAP does not calculate reservoir evaporation data, that is why the user has to enter net evaporation (which combines both the rainfall on the reservoir and the evaporative losses). For this, WEAP uses the volume-elevation curve to figure out the losses/gains of water to the reservoir. You could make an expression that responds to climate in a nearby catchment, but that's not the default.
I see you have increased inflow to the reservoir - this could indeed result in increased outflow over time, although the stored water could be impacted by higher evaporation under the volume-elevation curve that you entered. Can you compare the river reach data just below the reservoir? There are many reasons that your demand sites downstream may have higher water shortages; it may not be the reservoir releases are decreasing.