Identification of cultivated land change trajectory and analysis of its process characteristics using time-series Landsat images: A study in the overlapping areas of crop and mineral production in Yanzhou City, China

Abstract

Most studies have extensively evaluated the extent and direction of land-use change in coal mining areas; however, they did not adequately describe the time dimension of cultivated land changes at the pixel scale. In this study, we reconstructed the time-series of the normalized difference vegetation index (NDVI) using best index slope extraction-wavelet transform (BISE-WT) filtering. The trajectory type of cultivated land change was identified based on the time-series curves of those original cultivated land pixels using the modified normalized difference water index (MNDWI), normalized differences building index (NDBI), and bare soil index (BSI). Additionally, the time nodes of cultivated land changes were detected based on the NDVI time-series data, MNDWI, NDBI, and BSI. The results showed that this clustering method had the highest overall accuracy (89.90%) and the highest kappa coefficient (86.36%) of those three methods. Moreover, the overall accuracy of different trajectory types, time node detection in cultivated land converted to other lands, and the restored cultivated land from other lands were 0.9005, 0.9438, and 0.9430, respectively, and the kappa coefficient were 0.8803, 0.9390, and 0.9371, respectively. The conversion from cultivated land to non-cultivated land mainly occurred during 1989–2005, while the reclamation of cultivated land mainly occurred in 2009, 2011, and 2013. Permanent cultivated land accounted for the highest proportion (56.26%) of the five trajectory types. The proportion of cultivated land converted to non-cultivated land to cultivated land was 18.51%, and the proportion of disturbed cultivated land that was not reclaimed was 25.23%. The proportion of cultivated land converted to the developed was the comparatively high (17.73%), and that of the restored cultivated land after conversion from cultivated land to waterbody was the lowest (0.53%). The results of this study provide a scientific basis for guiding land reclamation, ecological restoration, and evaluating sustainability in the overlapping areas of crop and mineral production.