This chapter deals with the impact of meteorological drought on groundwater in a heterogeneous aquifer system located in the plain southeast of Xanthi, northeastern Greece, using fuzzy set theory. The research aims to investigate the linear relationship between meteorological drought and groundwater levels of shallow wells, as well as the key role of geology in drought propagation, in terms of time, to groundwater.
The study area is bounded to the east by the Lake Vistonida,
to the north by the River Kosynthos, to the west by the settlements of Vafeika
and Genisea, and to the south by the hill of Avdira and the settlement of Nea
Kessani. It is irrigated by a substantial number of wells (800 or more),
predominantly shallow. The area exhibits strong heterogeneity in soil
composition, consisting of coarse-grained fluvial deposits in the northwest and
fine-grained lake sediments in the southeast.
To achieve the study's objective, fuzzy regression analysis
based on Tanaka's approach is implemented. Tanaka's fuzzy linear regression
model is reduced to a linear programming problem with inclusion constraints,
ensuring that all observed data is included within the produced fuzzy band. The
Standardized Reconnaissance Drought Index (RDISt) and Standardized
Precipitation Index (SPI) serve as inputs (independent variables) of the
multiple fuzzy linear regression model. These drought indices are used to estimate
drought intensity and are calculated for several reference periods. Water table
serves the dependent variable, recorded by two water table loggers installed in
different geological formation areas. The multiple fuzzy linear regression
model produces a water table estimate for each time step with intervals of
values assigned, each associated with a membership degree (fuzzy output).
Hence, each fuzzy water table estimate is a fuzzy number characterized by its
left boundary, right boundary, and central value, thus, effectively
incorporating inherent uncertainty in estimation of groundwater level. To
address potential inconsistencies, a modification of Tanaka's fuzzy linear
regression model is suggested. It involves adding constraints to ensure that
the central values of the fuzzy outputs are equal to or greater than their
corresponding fuzzy semi-widths. In the evaluation process, the chapter employs
three suitability measures and a comparison measure for fuzzy numbers. These
measures assess the performance of the multiple fuzzy linear regression models
and provide insights into the relationship between meteorological drought
indices and groundwater levels.
The findings indicate a significant influence of annual
meteorological drought on groundwater. Moreover, groundwater that are hosted in
fine sediments, best related to annual drought indices, highlighting the
crucial role of geology in drought propagation time. Furthermore, the use of
RDISt indices enhances the results of multiple fuzzy linear regression models
in all cases, confirming the index's suitability for drought intensity
estimation in semi-arid regions. The proposed modification to Tanaka's fuzzy linear
regression model improves its applicability and reliability in the specific
study area, providing insights for groundwater fluctuation.
In summary, the study contributes to understanding the
complex interactions between meteorological drought, geology, and groundwater
response in the investigated aquifer system.
Author(s) Details:
Christopher A. Papadopoulos,
Democritus
University of Thrace, Greece.
Mike
Spiliotis,
Democritus
University of Thrace, Greece.
Basil Papadopoulos,
Democritus University of Thrace, Greece.
Fotios-Konstantinos Pliakas,
Democritus University of Thrace, Greece.
Please see the link here: https://stm.bookpi.org/RUMCS-V3/article/view/14040
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