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The research work entitled “Geostatistical analysis of groundwater level in
Thiruvananthapuram district” was carried out at the College of Agriculture, Vellayani
during 2019-2021. The objective of the study was to analyze the spatiotemporal variations
in the groundwater level, identify the relationship between groundwater and climatic
factors (i.e., rainfall and temperature), and to prepare the thematic map for the location. To
characterize the spatiotemporal fluctuations in groundwater level within the research
region, various geostatistical approaches were used. The WRIS [Water Resource
Information System] website was used to collect groundwater level data for 29 different
locations within the study area for 10 years, from 2008 to 2017. The selection of data points
was based on the even spatial distribution such that all the locations in the district are
entirely covered. The NASA satellite website data was used to collect the rainfall and
temperature data for the 29 distinct sites throughout a ten-year period. The semivariogram
models were fitted to assess the spatial continuity of groundwater level. The nugget to sill
ratio is also identified for detecting the spatial dependency. In the research region, the
kriging interpolation approach was used to assess the spatiotemporal fluctuations in
groundwater levels. If the data sets are normally distributed, the kriging interpolation
technique will be more successful. Thus, the data points were subjected to exploratory data
analysis to test the normality of the data set.
The normality of the data sets is found out by Shapiro-Wilk’s normality test. The
results showed that the years 2010 and 2017 are not normally distributed as the null
hypothesis of the test is rejected. And also, in the case of temperature and rainfall, all the
data points were not normally distributed. Thus, for the proper analysis, the log
transformation was performed to the data sets which are not normally distributed and
proceeded to further steps.
The relationship of groundwater and climatic factors were accounted with the
correlation analysis. The results showed that the temperature is having more dependency
with the groundwater level fluctuation than the rainfall.
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The semivariogram fitting were done to the groundwater level drop for each
location, groundwater level over the years, and for the average groundwater level to
identify the spatial and temporal variations in the study area. The drop was found out for
each location by taking the difference between the groundwater levels of the years 2008
and 2017. The positive drop refers the depletion in the groundwater level and the negative
drop refers the increment in the groundwater level. The nugget to sill ratio explains that the
groundwater level drop is having a relatively strong spatial dependence. The three models,
Spherical, Exponential and Gaussian models were fitted to the groundwater level for each
year. The best fit model was selected by accounting the Adjusted R2 value.
The spatiotemporal variation was studied by kriging interpolation method. The
thematic maps were created to analyze the groundwater level variations. The maps were
created in the ArcGIS 10.4 software. By investigating the maps prepared, the groundwater
level depletion is observed severely in the Varkala region, and the Parassala region. The
groundwater level at the high ranges like Ponmudi, Bonacaud, and Neyyar regions are
maintaining a decent amount of groundwater level.
From the PCA biplots prepared, the study concluded that there is a gradual
groundwater depletion happening from 2008 to 2017. And from the biplot of years, the
temperature is relatively high in 2016, 2017 where the groundwater level is also high. And
the temperature is relatively low in 2008, 2009 where the groundwater level is also low.
Thus, it can be concluded that the groundwater is having some dependency with the
temperature variations which have been detected in the correlation analysis. From the
biplot of different locations, it can be analyzed that the Varkala, Sreekariyam, Pothencode,
Chengal, Neyyattinkara regions are having high groundwater depth. And Kattakkada,
Kallar, Palode, Ariyanadu, Maruthamoola, Peringamala regions are having low
groundwater depth.
From the research performed, it can be concluded that, most of the locations are
having a positive drop in the groundwater, which represents that the groundwater depletion
is happening in temporal structure in the study area. The highest depletion in the
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groundwater is seen in Pothencode, Chengal, Varkala, Neyyattinkara regions. The rate of
groundwater level drop is 1.49 meters, which is positive, and can be inferred that there is
depletion in the groundwater level. The nugget to sill ratio of the groundwater level drop
in the study area is 0.367, which refers that the depletion is moderately spatially dependent.
From the correlation analysis, it can be concluded that the temperature is a major factor
influencing the groundwater depletion than the rainfall, because there is a positive
significant correlation between groundwater and temperature. The groundwater depth of
Varkala, Pothencode, Sreekariyam, Neyyattinkara, Chenkal, Kulathoor is high, and at
Kattakkada, Palode, Kallar, Ariyanadu have low groundwater depth which can be
concluded from PCA biplot of different locations

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