Daily water level forecasting is of significant importance for the comprehensive utilization of water resources. An improved least squares support vector machine (LSSVM) model was introduced by including an extra bias error control term in the objective function. The tuning parameters were determined by the cross-validation scheme. Both conventional and improved LSSVM models were applied in the short term forecasting of the water level in the middle reaches of the Yangtze River, China. Evaluations were made with both models through metrics such as RMSE (Root Mean Squared Error), MAPE (Mean Absolute Percent Error) and index of agreement (d). More accurate forecasts were obtained although the improvement is regarded as moderate. Results indicate the capability and flexibility of LSSVM-type models in resolving time sequence problems. The improved LSSVM model is expected to provide useful water level information for the managements of hydroelectric resources in Rivers. Energies 2019, 12, 112 2 of 11 artificial neural network (ANN) methods. Palani et al. [8] applied an ANN model for water quality estimation. Nourani et al. [9] established an ANN model for groundwater level prediction. Ivan and Gilja [10] showed good performance of ANNs for hydraulic parameter prediction. However, the model accuracy differs with neuron structures and parameter calibrations might be time-consuming.The support vector machine (SVM) has been used to address short-term forecasting problems since the 90s of the 20th century, on the basis of which LSSVM (least squares support vector machine) is put forward to overcome drawbacks (e.g., computation cost [11], uncertainties in structural parameter determination [12]) of SVM. LSSVM models solve a linear matrix equation with fewer constraint conditions and have been utilized in a variety of applications, e.g., forecasting of groundwater level fluctuations [13], river stage [14], and watershed runoff [15]. In the case of monthly flow forecasting, Noori et al. [16] discussed the influence of parameter selections on the model performance. Hybrid models have also been proved to be effective ways, such as SVM-Wavelet transform [17].Although the LSSVM models provide favorable solutions in hydrological forecasting problems, issues such as the kernel function and unbalanced features need to be carefully explored. Cheng et al. [18] improved LSSVM by integrating an adaptive time function. Thereby, the dynamic nature of the time series is considered by assigning an appropriate weight in the cash flow prediction for construction projects. To cope with low efficiency, Cong et al. [19] incorporated the fruit fly optimization algorithm (FOA) for appropriate parameter values of LSSVM. Comparison between LS-SVM-FOA and other models indicated the superiority of the improved model. Ghorbani et al.[20] modelled river discharge time series using SVM and ANN. The authors conclude that SVM and ANN have an edge over the results by the conventional RC (Rating Curve) and MLR (Multiple Linear Regression) models. This is mor...