Sorry for the next question, but i need to solve it. What is the measure in units for the time span in water yield, hydropower production? Years, days… and if results in hp_value are in this time span or annual. Thank you.

# Annual Water Yield, Time span question

Hi @KevinChaEs -

Time span is in years (since the model provides annual average outputs), and value is given as net present value over the whole time span. Sorry that’s not clear in the User Guide Data Needs section (I’ll update that), but if you read the section that describes methods for calculating value, it says this:

*Td indicates the number of years present landscape conditions are expected to persist or the expected remaining lifetime of the station at dam d (set T to the smallest value if the two time values differ)… The value of each subwatershed for hydropower production over the lifetime of dam d is calculated similarly:…*

~ Stacie