Comparative study of deep learning models for daily karst spring discharge forecasting: LSTM Versus Hybrid VMD–LSTM
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摘要: 岩溶泉流量具有强非平稳与多尺度耦合特征,给精确预测带来挑战。为同时提升预测精度与物理可解释性,文章提出将变分模态分解(VMD)与长短期记忆网络(LSTM)耦合的 VMD-LSTM 框架:先用 VMD 将泉流量序列分解为若干本征模态,再与降雨共同作为输入,驱动两层 LSTM 进行建模;并以标准 LSTM 为基线开展对比评估。以桂林寨底岩溶系统 2013—2023 年日尺度数据为研究对象,VMD-LSTM 在训练、验证与测试阶段均优于基线模型;其中测试期达到纳什效率系数=0.951、均方根误差=0.524,且峰值均方根误差(观测前5%)下降 75.2%,显著增强了对极端事件的刻画能力。结果表明:VMD 可有效缓解原序列的非平稳与模态混叠,使 LSTM 更稳定地捕捉“快响应—慢退水”的动力学过程。该方法对岩溶区洪水预警与水资源调度具有现实应用价值。Abstract:
The discharge process of karst spring is controlled by complex hydrogeological structure and multi-scale dynamic mechanisms,exhibits characteristics of non-stationary and strongly nonlinearity, posing significant challenges for high-precision predictive modelings. Conventional physics-based models rely heavily on extensive hydrogeological parameters and often struggle to accurately capture non-stationary processes during extreme events. Consequently,integrating signal decomposition techniques with deep learning has emerged as a promising approach to enhance both prediction accuracy and physical interpretability. This study develops a hybrid model that combines Variational Mode Decomposition (VMD) with a Long-Short-Term Memory (LSTM) networks, referred to as VMD-LSTM, aiming to address non-stationarity and multi-scale coupling issues in daily karst spring discharge forecasting. Through a system comparison of the performance of the VMD-LSTM model and standard LSTM model during training, validation, and testing phases, the study evaluates improvements in prediction accuracy, extreme events characterization, and model stability, while elucidating the mechanisms by which VMD enhances the modeling performance of LSTM. This study utilized daily spring discharge and corresponding precipitation data from the Zhaidi karst system in Guilin, Guangxi, spanning from 2013 to 2023. The original spring discharge series was decomposed using VMD into ten Intrinsic Mode Functions (IMFs). Among them,six modes(Mode 5 to Mode10), which collectively represent the dominant karst hydrodynamic processes, were selected as inputs to a two-layer LSTM network for modeling. The model was trained using the Adam optimizer and the mean squared error loss function. The dataset was chronologically partitioned into a training set (80%), a validation set (10%), and a testing set (10%). Model performance was comprehensively evaluated using metrics including RMSE, MAE, NSE, KGE, and peak RMSE (caculated for the top 5% of high-flow events). Results demonstrated that the VMD-LSTM model consistently outperformed the standard LSTM across all three phases of the training,validation and testing. During the testing phase, the VMD-LSTM achieved an NSE of 0.951 and an RMSE of 0.524, representing improvements of 57.0% and 64.6%, respectively, compared to the LSTM model. Notably, the hybrid model exhibited substantially enhanced capability in predicting extreme discharges, reducing the peak RMSE from 6.208 to 1.542(a decrease of 75.2%). The VMD decomposition effectively mitigated non-stationarity and mode mixing present in the original series, enabling the LSTM network to more reliably identify and simulate the "rapid response–slow recession" characteristcs inherent in karst hydrological processes. This approach significantly syppressed the systematic underestimation and error dispersion during high-flow events. The VMD-LSTM hybrid model not only markedly enhanced the forecasting accuracy and extreme event modeling for karst spring discharge but also exhibited strong cross-phase consistency and physical interpretability, demonstrating high generalizability and robustness in practical forecasting scenarios. Future research could focus on incorporating hydrological physical constraints, conducting uncertainty quantification analysis, and extending the framework to higher spatiotemporal resolutions and multivariable coupling to further enhance model applicability and forcasting reliability across diverse karst systems. -
表 1 VMD变分模态分解
Table 1. Summary of VMD
模态 贡献率/% 主导周期/d 物理意义 Mode1 45.91 362.2 年际/季度趋势 Mode2 14.53 28.7 中期影响 Mode3 10.69 14.1 中期影响 Mode4 7.86 8.3 中期影响 Mode5 6.94 5.1 短期响应 Mode6 5.15 4.1 短期响应 Mode7 3.56 3.8 短期响应 Mode8 2.35 3.2 短期响应 Mode9 1.67 2.6 降雨—补给事件 Mode10 1.35 2.2 降雨—补给事件 表 2 LSTM(i)与VMD-LSTM(ii)模型结果对比
Table 2. Comparison of the results from the LSTM (i) and VMD-LSTM (ii) models
LSTM VMD-LSTM 训练期 (i) 验证期 (i) 测试期(i) 训练期(ii) 验证期(ii) 测试期(ii) RMSE 1.458 1.024 1.482 0.339 0.357 0.524 MAE 0.565 0.425 0.515 0.189 0.181 0.267 NSE 0.532 0.512 0.606 0.975 0.941 0.951 KGE 0.616 0.653 0.603 0.978 0.968 0.962 峰值_RMSE (5%) 5.709 3.904 6.208 0.723 1.032 1.542 -
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