Application and comparison of different statistical methods for the analysis of groundwater levels over time: Response to rainfall and resource evolution in the Piedmont Plain (NW Italy)

Analyzing post-2000 groundwater level and rainfall changes in Rajasthan, India, using well observations and GRACE data

Research on groundwater and water resources is essential for preserving viable environments. Although the arid area has been identified as a significant hotspot for groundwater depletion, the Indian desert region was not included in the initial analysis. This study intends to evaluate Rajasthan's groundwater level (GWL) and rainfall trends from 2000 to 2021 and how variations in GWLs are related to long-term rainfall. Annual GWL and rainfall data time series were collected from 921 monitoring stations for 33 districts of Rajasthan. The GWL trends and rainfall were identified using non-parametric modified Mann-Kendall test and Spearman rho techniques. Pearson's, Kendall's (tau b), and Spearman's analyses were used to determine the correlation between GWL and rainfall. The results from the modified Mann-Kendall and Spearman rho methods reveal that GWL has a significant declining trend in 38 % of districts, where 13 % have no trend, and the rest of 49 % have a rising trend. The yearly rainfall trend at 70 % and 30 % of the districts are rising and stable, respectively. A negative correlation between GWL depth and rainfall was discovered in each district, where 15 % are firm, 58 % are moderate, and 27 % are weak negative correlations. Also, the regression analysis estimates the effect of rainfall on GWL, which was observed: rainfall negatively influenced the depth of GWL at 58 % of the districts, had a positive impact at 33 %, and others had no effect. GRACE TWS anomaly shows a decreasing trend of -1.22 cm/yr, and GRACE and GWL anomalies have a positive relationship (r = 0.471). Results conclude that rainfall is the primary influencer on GWL in this semi-arid region vulnerable to drought.

Insights into long-term changes of groundwater levels in the typical region of Zhangjiakou City, China

Little information is available on the long-term changes of groundwater levels and their associated influencing factors. Zhangjiakou City was chosen as a case to reveal the temporal and spatial dynamics of groundwater level and its driving factors in the long term. Herein, the observation data of groundwater level from 56 wells was investigated from 1981 to 2015, including the collected meteorological data, socio-economic data, and groundwater resource exploitation situation. Results showed that the groundwater level in Zhangjiakou City tended to be decreased, and the decrease rate was gradually accelerated. In the past 35 years, the groundwater level of Bashang Plateau has decreased by 3.59 m < 3.6 m in Yuyang Basin < 7.17 m in Zhuohuai Basin < 20.41 m in Chaixuan Basin. The dynamic changes of groundwater level in four geomorphic units in Zhangjiakou City were significant correlation between the total population and other socio-economic factors, including primary industry production value; common cultivated land area; effective irrigation area; total grain yield; total vegetable yield; total production of pork, beef, and mutton; secondary industry production value; tertiary industry production value; and year-end total population. Furthermore, the principal component analysis of groundwater level variation in Zhangjiakou city showed that the variance contribution rates of the first principal component in the characteristic indicators of the Bashang Plateau, Chaixuan Basin, Zhuohuai Basin, and Yuyang Basin were 75.7%, 83.9%, 66.1%, and 77.8%, respectively, which mainly reflect the information of socio-economic factors. This indicated that socio-economic factors were the main driving factor influencing the continuous decline of groundwater levels in Zhangjiakou City. The obtained findings can provide new insights into the sustainable development of social economy and the rational utilization and allocation of regional water resources.