Any Difference Between Annual Average Temperature and Yearly Average Temperature

and especially could anyone tell me the data used to be averaged are from one year or years when calculating the annual average temperature or yearly average temperature?

The data is the average of the average monthly temperatures over the period in question.

I agree that any differences would be nearly insignificant. I'm guessing, but I see at least two possibilities:

1. Whoever wrote the document was simply not consistent, and considered the two terms synonymous. (Need to see the terms in context.)

2. One (I have no idea which) term could refer to the average from January 1st to December 31st, while the other could refer to the 365 day period ending on a given day, or possibly to some other period. (here in the USA, weather statistics are commonly calculated from July 1st to June 30th, producing what we call seasonal averages etc.)

Thanks, I do agree with you that extremes are more relevent, but that will be only one value to be listed in the document, let's say the maximum temperature of the hottest month in the last decades and lets assume that it happens to be the higest temperature in the past century, then this value will have no representativeness and will lead to bigger design margin. However if we apply the annually average highest temperature of the hottest month, that sounds more reasonable and will present more realistic data for reference.