Soil moisture (SM) plays a critical role in land-atmosphere interactions, influencing both water and carbon cycles. Accurate SM predictions are essential for effective disaster response, optimized irrigation practices, and progress in environmental research. Deep learning (DL) models have become increasingly popular for predicting SM. However, many existing approaches overlook the imbalance in observed data—where moderate moisture levels are far more common than extreme dry or wet conditions. This skewed distribution limits the models' ability to accurately capture rare but critical extremes, ultimately reducing their overall effectiveness. To overcome this limitation, we propose a Sampling-Weighted Sensitive Learning Strategy that improves model generalization by assigning greater importance to rare samples during training. We evaluated this approach using three widely used DL architectures: Long Short-Term Memory Network (LSTM), Bidirectional Long Short-Term Memory Network (BiLSTM), and Gated Recurrent Unit (GRU). To ensure consistency across experiments, the same random seed was applied throughout. Our results demonstrate notable improvements in prediction accuracy when applying the proposed strategy. The BiLSTM model, in particular, showed the most significant gains: unbiased Root Mean Square Error (ubRMSE) decreased by 7.38 %, and Bias was reduced by 11.64 %. Its Kling-Gupta Efficiency (KGE) improved by 2.73 %—slightly below the 5.35 % gain observed for the unidirectional LSTM—but regional results were particularly strong. In data-scarce areas, especially North Africa and Western Asia, BiLSTM KGE improvements frequently exceeded 20 %. Models trained with the proposed strategy also produced narrower 95 % confidence intervals during high-variability periods (e.g., summer and dry seasons), indicating greater predictive robustness under challenging environmental. These findings underscore the importance of addressing sample imbalance in training data and demonstrate the effectiveness of our strategy in enhancing DL models for SM prediction.
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