Dear WEAP community, I am modeling a reservoir in WEAP and I am having difficulty reproducing the observed storage.

Reference Scenario: 1980–2021
Observed reservoir storage: 2004–2020 only
I have the elevation-storage curve of the reservoir.
Storage capacity: 56 Mm³
Initial storage: 24 Mm³
Top of Buffer: 20 Mm³
Top of Inactive: 5 Mm³

The two upstream rivers have already been calibrated and validated, and their simulated inflows are used as inflows to the reservoir.

My problem is that the simulated outflow is almost equal to the inflow, so the reservoir storage does not reproduce the observed fluctuations during 2004–2020.I have downstream irrigation and domestic water demands, My questions are:

Where should I enter the observed reservoir inflowhm3 data in WEAP?
How should I represent the observed AEP, irrigation, leakage and evaporation data?
Should these data be entered as demands, transmission links, reservoir evaporation, or another WEAP component?
Why does the reservoir release almost all the inflow instead of storing water?
How can I calibrate the reservoir storage when the Reference Scenario starts in 1980 but observed storage is available only from 2004?

Any advice would be greatly appreciated.

Observed reservoir inflow would be a streamflow gauge object on the river just upstream of the reservoir. A reservoir has a parameter for net evaporation. You could enter leakage as loss to groundwater if it does not enter downstream, or, if the leakage water enters downstream you could enter it in a demand site with 0% consumption and add a return link to the river downstream and a transmission link from the reservoir.

Irrigation demands are handled by the demand site objects. 

If your reservoir is showing outflows similar to inflows, it is likely that either your storage is nearly or completely full, or that this level of outflow is needed to fulfill your downstream demands. To compare your scenario results against your observed storage, simply focus on the results from 2004-2020 when you have data. You could also adjust the dates of your model run to match those years temporarily while you calibrate.

 I recommend to explore our free, online WEAP tutorial https://www.weap21.org/tutorial/, where we have chapters on demand sites,  reservoirs, and calibration.

Hope this helps!