Microclimate-adjusted carbon density modeling improves carbon density estimation for photovoltaic-impacted grasslands in Inner Mongolia.

Conventional assessments of carbon-pool change at photovoltaic (PV) facilities typically assign static carbon-density values to broad land-cover transitions. They do not explicitly represent microclimatic modifications associated with PV arrays. This limitation may be important in drylands, where reflectance-related thermal conditions and vegetation responses vary among land-cover settings and precipitation conditions. Carbon-pool changes within 189 confirmed PV facilities covering 254 km2 in Inner Mongolia are evaluated using a conventional static land-cover carbon-density approach M1 and a microclimate-adjusted approach M2. M2 incorporates a signed microclimate adjustment term δmicro into M1 to represent net responses associated with PV-related differences in reflectance, thermal conditions, and vegetation-related conditions. Across land-cover transitions, δmicro ranged from +36.2% for bare-land-to-grassland transitions to -12.6% for grassland-to-bare-land transitions. Field-based evaluation at 42 PV facilities showed that M2 had higher agreement with measured carbon densities than M1 (R2 = 0.730 vs. 0.624; RMSE = 2.130 vs. 2.512 kg C m-2; MAE = 1.706 vs. 1.896 kg C m-2). M2 also showed lower site-level absolute errors in paired tests (p = 0.041 for the paired t-test and p = 0.037 for the Wilcoxon signed-rank test). Relative microclimate adjustments are largest in the low-precipitation group, whereas the central tendency of estimated carbon-pool change is greater in the high-precipitation group. These findings indicate that microclimate-adjusted accounting can improve carbon-pool assessment at PV facilities and provide context-sensitive information for post-construction vegetation management and land-use screening in dryland grasslands.