Lack of Mechanistic Understanding
The reliance on machine learning models without incorporating mechanistic insights limits the understanding of the underlying physical processes driving soil salinity. While ML models can capture trends from data, they don't explain *why* those trends occur. This makes it harder to generalize findings and predict responses to novel situations.
The accuracy of global-scale salinity predictions can be limited by inconsistencies in soil data. Different labs might use varying methods, impacting the data's reliability and leading to inaccurate trends being captured by the models.
Using a 5-year moving average for spatiotemporal predictors can introduce bias, potentially smoothing out important short-term fluctuations in factors like rainfall and temperature that significantly impact soil salinity.
The limited number of GCMs with projected sea salt deposition rates adds uncertainty to salinity predictions. A larger ensemble of GCMs is needed to fully capture the range of possible future scenarios.
The study primarily focuses on soil salinity based on electrical conductivity (EC) measurements. Other important aspects like sodicity (measured by exchangeable sodium percentage) and alkalinity are not considered. This provides an incomplete picture of salt-affected soils.
The lack of spatially explicit uncertainty maps for the predictions makes it difficult to assess the reliability of the results in different regions. Users don't know where the predictions are more or less likely to be accurate.
The overestimation of salinity for low EC values during model fitting introduces bias into the predictions. This is problematic because accurate prediction at low salinity levels is important for early detection and management of salinization.
Geographic Bias in Training Data
The model training dataset might be biased towards North America and Australia due to greater data availability in these regions. This raises concerns about the generalizability of the model's predictions to other parts of the world, particularly data-sparse areas.