Mapping Cropping Intensity Transitions in the Philippines from 2001 to 2024 Using Harmonic Analysis of MODIS NDVI Time Series Arlo Jayson Sabuito 1,3, Ainalyn Nerves 1,2, Keith Ann Cabello 1, Ariel Blanco 1,3
1 Philippine Space Agency (PhilSA)
2 Marine Science Institute, College of Science, University of the Philippines
3 Department of Geodetic Engineering, College of Engineering, University of the Philippines
Abstract
This study aims to track and analyze changes in cropping intensity across the Philippines to understand spatial and temporal patterns of agricultural practice. This analysis uses MODIS Terra surface reflectance data from 2001 to 2024 to derive a nationwide NDVI time series. The data were grouped into 3-year periods to model dominant crop cycle patterns using Harmonic analysis, and a moving maximum filter was applied to enhance the detection of vegetation peaks. The first derivative of the filtered temporal signal was computed, and sequences of zero slope segments were extracted to represent valid crop cycles. Cropping Intensity (CI) was calculated averaging the detected crop cycles per year, resulting in values of 1, 2, or 3 cycles per year. Transition analysis across CI maps revealed that 2 cycles/year was the most stable class, consistently accounting for 45-54% of valid pixels. Frequent transitions occurred between CI=2 and CI=3, and between CI=1 and CI=2. However, the portion of pixels retained in CI=1 declined over time: from 6.5% in 2001-2004 to 2.6% in 2020-2022. This suggests a reduction in areas with single cropping cycles and a general shift toward more intensive cropping. Latitudinal and longitudinal averages of cropping intensity throughout the years were also computed to assess general regional patterns. The temporal profiles for both latitudes and longitudes aggregates show increasing trend in cropping intensity across most regions over the study period. The results support the use of remote sensing derived cropping intensity monitoring as a tool for assessing agricultural dynamics in the country and its potential in guiding sustainable agricultural planning. As a next step, the approach can be extended to support land use change analyses and broader assessments relating to the overall agricultural shifts in practices and trends in the Philippines.
