Protocol and criteria for the blinded second reading of candidate change locations (Section 2.4)

Unit of assessment
  Single 10 m pixel located within mapped Annex I grassland habitat polygons.

Evidence used
  Monthly median Sentinel-2 NDVI time series (2016-2025; cloud-free observations, Cloud Score+ >= 0.6), presented in anonymised code order (A01-A22) without map strata, coordinates or point identifiers.

Objective
  Re-evaluation of the 22 locations initially flagged as candidate change against a clarified reference definition to distinguish persistent land-cover conversion from grassland management, interannual climate variability or seasonal dynamics.

Reference definition of change
  - "change": Grass or shrub cover in the baseline window (2016-2018) followed by persistent arable cropping (ploughed/sown land), built-up or bare ground in the recent window (2023-2025).
  - "no change": Consistent land-cover regime across both windows (grassland in both, or arable in both). Fluctuations in management (grazing intensity, mowing/haymaking dates, abandonment, shrub encroachment) or drought response are not change. A pixel that was already arable in 2016-2018 is not change.
  - "uncertain": Ambiguous trajectory, insufficient cloud-free observations, or mixed/edge pixel signatures.

Diagnostic NDVI characteristics in Bulgaria
  - Grassland (grazed or mown): Spring green-up in March-April, peak in May-June, gradual summer decline, autumn regreening (October-November), and absence of a prolonged bare-soil phase in the growing season. Mowing produces temporary dips with subsequent recovery.
  - Winter cereals / rapeseed: Autumn emergence and high early-spring NDVI (0.40-0.80), peak in April-May, sharp harvest decline in June-July, followed by an extended ploughed/bare-soil phase (~0.10-0.25) before the next crop emerges.
  - Spring crops (maize, sunflower): Bare soil / low values (0.10-0.25) in March-May, peak in July-August, harvest decline in September-October.
  - Built-up / bare: Persistently suppressed NDVI (<0.20) throughout the growing season.
  - Winter dormancy / snow: Low NDVI in December-February is attributed to frost, snow or dormancy and is not evidence of tillage.

Recorded evaluation
  Labels and diagnostic notes are tabulated in second_reading_labels.csv.
  The second reading was done by the interpreter (M.T.), who inspected the series of every location and decided
  its label. The series were presented, and the labels and notes recorded, in one browser session with an AI
  assistant (Claude, Anthropic); every recorded label was checked by the interpreter.
