LAUSR

This study investigated two popular satellite-derived vegetation indices (VIs), MODIS NDVI and EVI, as tools for monitoring crop growth at the Thapanzeik Dam irrigation district in Myanmar, where quality ground data are difficult to obtain. The time-series analysis for seasonal peak VIs presented a considerable improvement in paddy cultivation during 2001–2020 in the irrigation district during summer and monsoon. Fields outside the district had a much lower improvement ratio. Within the irrigation district, a canal with limited water supply was identified via peak and average VIs evaluation. The evaluation of precipitation impact on crop growth demonstrated an opposite impact on crop growth in summer and monsoon cultivations. Water is one of the limiting factors in summer in the irrigation district; thus, precipitation improves water conditions. However, water is not the limiting factor in monsoon; thus, extra water from precipitation, both hydraulically and meteorologically, negatively impacts crop growth. Compared to NDVI, EVI better captured crop growth in densely vegetated surfaces. Meanwhile, information degradation might have occurred with 250 m EVI, using 500 m blue-band reflectance as an input. Thus, the best vegetation index to use depends on the purpose of monitoring and the site situation.