Groundwater level observations due to the lack of synoptic water-level measurements are often available with irregular time intervals. The results lead to an inaccurate understanding of the parameters affecting groundwater level changes and their time delays. This paper presents a simple and low-cost approach to interpolate the irregular, periodic intervals of recorded groundwater level data for the Najafabad aquifer located in central Iran. Forty-six monitoring wells with an average of 20 years of data were used for this study. Piecewise cubic Hermite interpolating polynomial (PCHIP), cubic spline, linear, and nearest neighbor are the selected interpolation methods. Cross-validation with leave-one-out technique was also applied to evaluate the accuracy of the methods under three conditions, including low, average, and high groundwater level decline. The analysis proved that (1) PCHIP interpolation showed a high performance in all of the groundwater level decline conditions (0.22 < RMSE < 0.59 and 0.72 < R² < 0.98). (2) Under slight and without abrupt fluctuations of groundwater level conditions, cubic spline showed a better performance than the linear interpolation (R² = 0.98, RMSE = 0.49 for cubic spline and R² = 0.98, RMSE = 0.51 for linear). The selected approach reduces the uncertainty in the study of issues such as changes in groundwater recharge and storage, groundwater flow directions, surface–groundwater interaction, and groundwater modeling.

由于缺乏天气水位测量，地下水位观测通常以不规则的时间间隔进行。结果导致对影响地下水位变化及其时间延迟的参数的不准确理解。本文提出了一种简单且低成本的方法，用于对位于伊朗中部的 Najafabad 含水层的记录地下水位数据的不规则、周期性间隔进行插值。本研究使用了平均 20 年数据的 46 口监测井。分段三次 Hermite 插值多项式 (PCHIP)、三次样条、线性和最近邻是选定的插值方法。还应用留一法交叉验证来评估方法在三种条件下的准确性，包括低、平均、和高地下水位下降。分析证明：（1）PCHIP 插值在所有地下水位下降条件（0.22 < RMSE < 0.59 和 0.72 < R ²  < 0.98)。(2) 在地下水位轻微波动且无突变的情况下，三次样条比线性插值表现出更好的性能（ 三次样条R ² = 0.98，RMSE = 0.49  ，线性R ² = 0.98，RMSE = 0.51）。所选择的方法减少了研究地下水补给和储存变化、地下水流向、地表-地下水相互作用和地下水模型等问题的不确定性。