Integrated Science Assessment Model (ISAM) is a coupled biogeochemical and biogeophysical model with 0.5° × 0.5° spatial resolution and multiple temporal resolutions ranging from a half-hour to yearly time steps. It simulates C, N, energy, and water budgets for various terrestrial ecosystems through photosynthesis, surface hydrology, radiative transfer, carbon allocation, and ecosystem respiration (Barman et al., 2014a, 2014b; Yang et al., 2009). Moreover, ISAM incorporates crop growth processes for C3 and C4 food crops (maize, soybean, wheat, and rice) and bioenergy grasses (miscanthus, cave-in-rock, and alamo), which are evaluated at site-level, regional, and global scales (Gahlot et al., 2020; Lin et al., 2017; Niyogi et al., 2015; Song et al., 2013, 2015, 2016). Some of the important features, unique to ISAM and critical for crop yield calculations, include (i) dynamic crop-specific phenology and carbon allocation schemes (Song et al., 2013, 2015), accounting for the sensitivity of different crops to extreme environmental conditions; (ii) dynamic vegetation structures, which better capture seasonal variability in leaf area index (LAI), canopy height, and root depth; (iii) dynamic root distribution processes at the depth that improve simulated root-mediated soil water uptake and transpiration.
