# Hansen Global Forest Change - Forest Loss Year - Dates Clarification

I have scoured both the GFC website, research papers and Stack Exchange, but haven't been able to find a clear and reliable explanation of what the "Year of gross forest cover loss event" pixel values represent.

Using V1.6 as an example, if I download the "lossyear" dataset, I see values in the range of 0-18: Assuming 0 equals no loss, does 18 equal a loss event between 1st January 2018 and 31st December 2018? Or does 18 equal a loss event between 1st January 2017 and 1st January 2018?

People I have spoken to regarding this have assumed that pixel value 18 equals a loss within the year of 2018, so 1st Jan 2018 to 31st Dec 2018. But looking at a chart from the paper has confused me.

According to this, I would expect loss between 2000 and 2001 to be value 1, so therefore in my dataset a pixel value of 18 would represent loss that occurred between 2017 and 2018.

Can anyone clarify this for me?

Assuming 0 equals no loss, does 18 equal a loss event between 1st January 2018 and 31st December 2018?

My understanding is that this is correct. Those values from 0-18 indicate the year in which the loss occurred.

I think the tricky concept here is that the "loss" occurs when looking at the difference between two different years of data. So that 2018 might be the first year in which the "loss" occurs, i.e. an area that was previously forested is no longer so.

The chart seems to indicate this as well, so that the column entitled "00-01" is looking at the difference between years 2000 and 2001, and counting pixels which were forested in 2000 but no longer forested in 2001.

You could verify by looking at the individual year layers and noting where & what time the forest loss occurs, and if that does correspond to the loss year that they're indicating.

Matt Hansen kindly responded to an email and clarified that it is indeed as Mike N detailed. The pixel value refers to the calendar year that loss was observed. Therefore 18 equals a loss event between 1st January 2018 and 31st December 2018.

Year of gross forest cover loss event (lossyear) Forest loss during the period 2000–2018, defined as a stand-replacement disturbance, or a change from a forest to non-forest state. Encoded as either 0 (no loss) or else a value in the range 1–17, representing loss detected primarily in the year 2001–2018, respectively. So, 1 = 2001 calendar year, and so on. Note 'primarily' as our detection of loss can be delayed and we misallocate a portion of the disturbance events.