The uncertainty of gis-based interpolation methods in constructing shallow groundwater distribution map: A case study at Pleiku city, Gia Lai province

Four interpolation methods are applied to interpolate shallow groundwater level in Pleiku city, including inverse distance weighted, tension spline, universal kriging, and ordinary kriging. The cross-validation results record that the ordinary kriging is the best interpolation method which is shown by the lowest RMSE value, the highest R2 value. It is selected to assess the shallow groundwater level in spatial and seasonal change. Based on the groundwater level interpolated by the ordinary kriging, the groundwater level is divided into the northern and southern parts of the study area. The distribution of groundwater level is shallower than that in the southern part wheret groundwater depth is around less than15 m while in the southern part, most of the groundwater level is higher than 18 m. The elevation of groundwater level is found in rainy season; the elevated area accounts for 72.6% of natural area. Additionally, the groundwater level also declines in the rainy season at some region, focusing on Bien Ho lake region and two regions in the southern part of the city whose area accounts for 27.4% of the natural area.

Delineation of Hydraulic Flow Regime Areas Based on the Statistical Analysis of Semicentennial Shallow Groundwater Table Time Series

Shallow groundwater acts as an important source of water for the ecosystem, agriculture, drinking water supply, etc.; it is, however, among those water resources most sensitive to climate change, and especially to aridification. In the present study, the delineation of regional recharge and discharge zones of the Danube–Tisza Interfluve (Hungary, 8000 km2) is presented via the combination of multivariate time series and geomathematical methods to explore the subregions most sensitive to dewatering. The shallow groundwater level time series of 190 wells, covering a semicentennial period (1961 to 2010), were grouped into three validated clusters representing characteristically different subregions. Then, the subregions’ means and individual shallow groundwater level time series were investigated for long-term trends and compared with local meteorological variability (precipitation, evapotranspiration, etc.) to determine their regime characteristics. As a result, shallow recharge and discharge zones, a gravity-driven flow system, and the discharge zone of a deeper, overpressured flow system could be discerned with distinctive long-term changes in water levels. The semicentennial trends in shallow groundwater levels were significant (p < 0.05) in the recharge (−0.042 m y−1) and in the overpressured discharge zone (0.009 m y−1), and insignificant in the rest of the area (−0.005 m yr−1). The present results concur with previous findings from the area but provide a statistically sound and reproducible delineation of the regime areas on a much finer scale than before. With the determination of the different climatic processes driving the semicentennial trends prevailing in the shallow groundwater, the high vulnerability of the recharge zone is underlined, while the outlined overpressured flow system seems to act independently from semicentennial precipitation trends. This study provides a more in-depth picture of the long-term changes in shallow groundwater and its drivers in of one of the most important agricultural areas in Hungary. It outlines, in a generally applicable way, the most vulnerable subareas for irrigation relaying on shallow groundwater extraction. In addition, the results can help adaptation-strategy decision makers to initiate a more effective and area-focused intervention in the case of the predicted negative trends for vulnerable recharge areas under various climate change scenarios.

Does Crop Rotation Enhance Groundwater Health? A Review of the Winter Wheat Fallow Policy in the North China Plain

Agricultural water management is a vital component of realizing the United Nation’s Sustainable Development Goals because of water shortages worldwide leading to a severe threat to ecological environments and global food security. As an agro-intensified irrigation area, the North China Plain (NCP) is the most important grain basket in China, which produces 30%–40% of the maize and 60%–80% of the wheat for China. However, this area has already been one of the largest groundwater funnels in the world due to long-term over-exploitation of groundwater. Due to the low precipitation during the growing period, winter wheat requires a large amount of groundwater to be pumped for irrigation, which consumes 70% of the groundwater irrigation. To alleviate the overexploitation of groundwater, the Chinese government implemented the Winter Wheat Fallow Policy (WWFP) in 2014. The evaluation and summarization of the WWFP will be beneficial for improving the groundwater overexploitation areas under high-intensity irrigation over all the world. So far, there have been few attempts at estimating the effectiveness of this policy. To fill this gap, we assessed the planting area of field crops and calculated the evapotranspiration of crops based on remote-sensed and meteorological data in the key area—Hengshui. We compared the agricultural water consumption before and after the implementation of this policy, and we analyzed the relationship between changes in crop planting structure and groundwater variations based on geographically weighted regression. Our results showed the overall classification accuracies for 2013 and 2015 were 85.56% and 82.22%, respectively. The planting area of winter wheat, as the most reduced crop, decreased from 35.71% (314,053 ha) in 2013 to 32.98% (289,986 ha) in 2015. The actual reduction in area of winter wheat reached 84% of the target (26 thousand ha) of the WWFP. The water consumption of major crops decreased from 2.98 billion m3 of water in 2013 to 2.83 billion m3 in 2015, a total reduction of 146 million m3, and 88.43% of reduced target of the WWFP (166 million m3). The planting changes of winter wheat did not directly affect the change of shallow groundwater level, but ET was positively related to shallow groundwater level and precipitation was negatively related to shallow groundwater levels. This study can provide a basis for the WWFP’s improvement and the development of sustainable agriculture in high-intensity irrigation areas.

Spatial variability of shallow groundwater level in the Northern Kathmandu Valley

Groundwater is the water which is present in pore spaces and in the fractures of the geological materials beneath earth surface. Water is incompressible substance and presence of small amount of water in geological material modifies the behavior of geological material under stresses. Determination of engineering behavior of the geological material is almost impossible skipping the role of water. The objective of this study was to map and evaluate shallow groundwater level of the northern Kathmandu Valley covering main rivers such as the Bagmati River, Bishnumati River, Dhobi Khola and the Manahara Khola. These rivers flow from the North to the South across the sand rich sediment zone. Static groundwater levels of 239 wells were measured from different locations of the study area in April/March 2017 (Dry Season) and in August 2017 (Wet Season). Shallow groundwater level was measured from soil surface to water level using well water depth logger (Qin and Li, 1998). The result showed that groundwater level ranged from 0.6 m to 12.5 m in dry season and 0.1 m to 13 m in wet season. The groundwater level increased by average of 34.68% (n = 235) as compared to that in dry season. Increase in the groundwater level suggests recharge of groundwater in wet season of the study area. The flow pattern of groundwater levels from the study shows flow of shallow groundwater towards the major rivers of that particular river watershed. As a consequence, seepage flow and piping erosion is likely along the riverbank slopes. Increase in recharge of groundwater during wet season exhibits that the northern region of the Kathmandu Valley is potential for groundwater recharge and can be used to manage water for the dry period.