Multi-year mapping of flood autumn irrigation extent and timing in harvested croplands of arid irrigation district

Flood irrigation after crop harvest, e.g. autumn (AI), is a common practice in arid and semi-arid regions like Hetao Irrigation District (HID) Northwest China to increase soil moisture leach salt. Detailed information about the extent, timing, amount of AI imperative for modeling agro-hydrological processes management. However, little attention given identification above factors. There are basically three major difficulties estimating annual changes AI, including suitable index identify temporal instability thresholds, an effective validation method timing. Therefore, this study proposes simple threshold-based extract extent timing HID using MODIS water indices at daily timescale. The Multi-Band Water Index (MBWI) time series first reconstructed adaptive weighted Savitzky-Golay filter then used time. proposed model has stronger generalization capability both space due robust thresholds selected from Z-score normalized feature variable. validated pixels generated by segmentation Sentinel-derived MBWI sampling points field survey. Results show that performed well with overall accuracy more than 90.0% area. accuracies 76.4% 91.7% based on middle-to-late whole periods, respectively. We found decreasing trend area gradual delay starting HID, mainly cropping patterns, climate, fees. Overall, promising identifying flood large districts helpful scheduling.