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

Abstract

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.

A New Approach in Determining the Decadal Common Trends in the Groundwater Table of the Watershed of Lake “Neusiedlersee”

“…Results concur with general knowledge that, at the level of interannual variability, changes in SGW levels are driven primarily by evapotranspiration and the interannual distribution of precipitation [73]. Therefore, finding significant correlations between precipitation and SGW level variations can help assess aquifer vulnerability [17,74].…”

“…A knowledge of these factors is crucial to a better understanding of the hydrogeological processes that characterize the water table, something which is crucial to the development of an appropriate water resource management strategy for the area. The excess knowledge provided by the present study could serve as a benchmark for further preparation for the severe negative effects likely to come about as a result of climate change in the area [17,79,80…”

“…The combined application of the used data analysis methods (DFA, HCA, LDA) to the SGW data and additional explanatory environmental parameters have proven to be sufficient to provide an extensive overview of their relationship with the regional meteorological conditions and topography as determining their primary characteristics; while the different behavior of the clusters of the SGW wells provides the foundation to delineate the different flow regimes (recharge and discharge areas) [17].…”

“…These factors should all be considered in determining groundwater vulnerability, since, with recharge water, pollutants enter the subsurface water bodies and can travel laterally within the aquifer or vertically to the water table [11], rendering higher risks to higher recharge rates [10].The SGW table plays an important role in groundwaterdependent ecosystems [12], and has an effect on surface vegetation and yield of agricultural crops [13,14]. Consequently, a decline in the water table can reduce well yield and increase pumping costs, having serious economic impact on areas where groundwater is used as the major source of irrigation [15][16][17]. While in temperate climates diurnal fluctuations in the groundwater table are driven in large measure by the water consumption of vegetation [18], it can also be affected by other factors, such as the depth of the water table, soil moisture, and so on.…”

The Role of Environmental Background Processes in Determining Groundwater Level Variability—An Investigation of a Record Flood Event Using Dynamic Factor Analysis

“…On the basis of the results, it can be assumed that the three determined CTs did indeed prove CT 1 was identified with the integrated evapotranspiration as a background factor, which is in close linear relation with CT 1 (r = −0.896), even without temporal displacement. A similar approach has been successfully applied in other studies [54][55][56][57][58][59] in which the integrated evapotranspiration played a significant role in the fluctuation of water levels. No major increase in the strength of the relationship was observed, not even when the CT 1 was displaced temporally-the correlation coefficient did not change significantly with a 4-day displacement either (Q1: −0.913, Q3: −0.905).…”