Fig. 4

Distribution of Arid Zones and changes in cropland and forestland cover within the GGW Region. (a) Map of aridity. The bioclimatic zone is defined by the Aridity Index (AI) following the classification developed by FAO. The red solid line represents “Boundary”. (b) The variation of RI of CFC and FFC with latitude. We only considered areas where forestland or cropland existed. The dashed line represents the mean RI along the latitude direction, while the intersection points of the fitted lines (solid lines) for forestland and cropland RI are marked by red dots. (c) Map of significant changes in forestland and cropland cover, detailed in Supplementary Fig. 6. Utilizing sen’s slope estimator and the Mann-Kendall (M-K) trend test, we obtained the trends of cropland and forestland fractional changes between 2015 and 2022. (d) The percentage of change type north and south of the “Boundary”. (e) Statistics of categories and slope conditions on both sides of the “Boundary”. The subscript “P” denotes significant results from the M-K test, while the subscripts “N” and “S” represent areas north and south of “Boundary”, respectively. *P < 0.001. In addition, Cliff’s Delta can be used to calculate the effect size of the Mann-Whitney U test. The larger the effect size, the greater the difference. ■: Large effect size.