Abstract
The amount of water taken from groundwater for agricultural irrigation is often not observed, while hydrological models have been extensively proposed to investigate the irrigation dynamics and impacts in agricultural areas. In this work, we propose an agro-hydrological model that integrates agricultural irrigation with the traditional Xin’anjiang (XAJ) hydrological model. In particular, the proposed model incorporates the FAO guidelines on crop evapotranspiration into hydrological routing of water balance and flow fluxes in unsaturated and saturated zones. The model was used to calibrate the groundwater irrigation amounts in terms of both the observed river discharge and the groundwater depth in the Xuanwu plain area of the Huaihe River Basin in China. The calibration and sensitivity analyses were performed by the shuffled complex evolution (SCE-UA) method. This method can be applied to a single-objective optimization of model parameters, based on either the river discharge or the groundwater depth, or to a multi-objective optimization of model parameters based on both of these objectives. The results show that the multi-objective calibration is more efficient than the single-objective method for capturing dynamics of the river discharge and the groundwater depth. The estimated means of the annual groundwater withdrawal for wheat and maize irrigations were found to be about 140.5 mm and 13.7 mm, respectively. The correlation between the groundwater withdrawal and the change in groundwater depth during crop growing seasons demonstrated that the groundwater withdrawal is the dominant factor for the groundwater depth change in the river basin, particularly in the winter wheat season. Moreover, model simulations show that the combined effects of the reduced precipitation and the increased groundwater withdrawal would lead to a decrease of the average annual runoff and an increase of the average groundwater depth. These estimates can greatly help in understanding the irregular changes in the groundwater withdrawal and offer a quantitative basis for studying future groundwater demands in this area.
Highlights
Agricultural needs account for about 70% of worldwide freshwater withdrawals, while irrigation water accounts for about 90% of all agricultural water usage [1]
As the Chinese government promotes the sustainable use of groundwater resources and prevents groundwater over-exploitation, estimation of groundwater withdrawal in irrigated fields is quite important for effective control of groundwater utilization in an appropriate level
The results show that single-objective parameter calibration methods cannot effectively simulate the dynamics of the river discharge and the groundwater depth at the same time
Summary
Agricultural needs account for about 70% of worldwide freshwater withdrawals, while irrigation water accounts for about 90% of all agricultural water usage [1]. Remote-sensing techniques have been applied to estimate crop transpiration and soil moisture (e.g., Cruz-Blanco et al [5]) These efforts can roughly estimate historical groundwater withdrawal for irrigation, but they need verifications of the groundwater withdrawal in relation to the consumptive water use of crops. Such relationship can be developed based on water balance analysis in cultivated areas. The aforementioned approaches are mostly applied to calibrate hydrological parameters and evaluate the effectiveness of hydrological simulations of the rainfall–runoff response and groundwater table dynamics These approaches are seldom used to evaluate water use in irrigated agriculture. The single-objective and multi-objective optimization approaches are constructed for model parameter calibration and validation against the catchment outlet discharge and the groundwater depth
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