Groundwater Drought Analysis under Data Scarcity: The Case of the Salento Aquifer (Italy)

Salento is a regional coastal karst aquifer located in Southern Italy with a highly complex geological, geomorphological, and hydrogeological structure. High and unruly exploitation of groundwater from licensed and unlicensed wells for irrigation and drinking purposes affects groundwater, with consequent degradation of its qualitative and quantitative status. The increased frequency of meteorological droughts and rising temperatures may only worsen the already compromised situation. The absence of complete and enduring monitoring of groundwater levels prevents the application of some methodologies, which require long time series. The analysis of climate indexes to describe the groundwater level variation is a possible approach under data scarcity. However, this approach may not be obvious for complex aquifers (in terms of scale, intrinsic properties, and boundary conditions) where the response of the groundwater to precipitation is not necessarily linear. Thus, the proposed research deals with the assessment of the response of the Salento aquifer to precipitation variability based on correlations between the Standardized Precipitation Index (SPI) and Standardized Precipitation and Evapotranspiration Index (SPEI) and groundwater levels for nine monitoring wells from July 2007 to December 2011. The study aims at evaluating the ability of the above indicators to explain the behavior of groundwater on complex aquifers. Moreover, it has the general aim to verify their more general reliable application. Results of three different correlation factors outline direct and statistically significant correlations between the time series. They describe the Salento aquifer as a slow filter, with a notable inertial behavior in response to meteorological events. The SPI 18-months demonstrates to be a viable candidate to predict the groundwater response to precipitation variability for the Salento aquifer.

Hydrometeorological Consequences on the Water Balance in the Ganga River System Under Changing Climatic Conditions using Land Surface Model

United Nations Sustainable Development Goal (SDG) ensures adequately accessible water and management for all. Due to the rapid increase in population and industries along the Ganga river, it is necessary to estimate the water budget for fulfilling the demand for water in the future. The M-K test conducted on the Noah-Land Surface Model data for 72 years results in maximum declining trend of water budget in the Yamuna Lower (Q=-3.82BCM/year), and minimum in the Damodar sub-basin (Q=-0.10BCM/year). All the sub-basins show increase in groundwater level (mbgl) except the Kali Sindh, which shows decreasing trend (Q=-0.07 m/year). The extreme severe groundwater drought were estimated using Standard Groundwater Level Index (SGWLI), of the values for the Ram Ganga Confluence (SGWLI=2.44;2005), Upper stream of Gomti (SGWLI=2.06;2014), Ghaghra (SGWLI=2.22;2005), Ram Ganga (SGWLI=2.28;2005), Yamuna Lower (SGWLI=2.13;2007), Kali Sindh (SGWLI=2.30,2.67;2002,2003), Chambal Upper (SGWLI=2.30,2.20;2001,2003), Son (SGWLI=2.02;2010), Gandak (SGWLI=2.37;2010),Kosi (SGWLI=2.08;2012), Damodar (SGWLI=2.72;2010), and Bhagirathi (SGWLI=2.06;2014) were obtained for a period of 1996 to 2016 using a total of 62,050 observed well data.The obtained in-situ point data are converted into the surface raster using geostatistical technique. Our results show declining trend in the water budget of all the 19 sub-basin of the Ganga basin, and also the groundwater drought in several parts. Policy makers will benefit from our findings as they can use them to further UN Sustainable Development Goals such as ending poverty (SDG-1), hunger eradication (SDG-2), clean water & sanitation (SDG-6), socioeconomic development (SDG-8) and climate action (SDG-13) all of which must be accomplished before 2030.

Economic tradeoff between domestic well impact and reduced agricultural production with groundwater drought management: Tulare County, California (USA), case study

Formal policy analysis can aid resource management where groundwater is used intensively. Approaches for developing equitable and effective pumping allocations for drought are evaluated in the context of the 2012–2016 drought in Tulare County, California, USA. Potential economic impacts of policy alternatives on two user groups with conflicting interests are considered. Tradeoffs between losses of agricultural profit and response costs for domestic wells that run dry are estimated for various maximum groundwater depth policies. A welfare maximizing approach for identifying policies that limit depth to groundwater is evaluated and found to be ineffective because agricultural opportunity costs are much larger than domestic well costs. Adding a fee for additional drought groundwater pumping is proposed as a more impactful and balanced management policy approach. For the case study presented, a fee range of $300 to $600/acre-foot ($300–$600/1,233 m3) yielded an effective groundwater management policy for reducing domestic well impacts from drought and balancing agricultural impacts of drought with the need to replenish additional drought pumping in wetter years. Recent management policies enacted in the study area agree with this finding. These results may provide a useful perspective for analytically examining and developing groundwater management policies near the study area and elsewhere.

Drought Assessment in the São Francisco River Basin Using Satellite-Based and Ground-Based Indices

The São Francisco River Basin (SFRB) plays a key role for the agricultural and hydropower sectors in Northeast Brazil (NEB). Historically, in the low part of the SFRB, people have to cope with strong periods of drought. However, there are incipient signs of increasing drought conditions in the upper and middle parts of the SFRB, where its main reservoirs (i.e., Três Marias, Sobradinho, and Luiz Gonzaga) and croplands are located. Therefore, the assessment of the impacts of extreme drought events in the SFRB is of vital importance to develop appropriate drought mitigation strategies. These events are characterized by widespread and persistent dry conditions with long-term impacts on water resources and rain-fed agriculture. The purpose of this study is to provide a comprehensive evaluation of extreme drought events in terms of occurrence, persistence, spatial extent, severity, and impacts on streamflow and soil moisture over different time windows between 1980 and 2020. The Standardized Precipitation-Evapotranspiration Index (SPEI) and Standardized Streamflow Index (SSI) at 3- and 12-month time scales derived from ground data were used as benchmark drought indices. The self-calibrating Palmer Drought Severity Index (scPDSI) and the Soil Moisture and Ocean Salinity-based Soil Water Deficit Index (SWDIS) were used to assess the agricultural drought. The Water Storage Deficit Index (WSDI) and the Groundwater Drought Index (GGDI) both derived from the Gravity Recovery and Climate Experiment (GRACE) were used to assess the hydrological drought. The SWDISa and WSDI showed the best performance in assessing agricultural and hydrological droughts across the whole SFRB. A drying trend at an annual time scale in the middle and south regions of the SFRB was evidenced. An expansion of the area under drought conditions was observed only during the southern hemisphere winter months (i.e., JJA). A marked depletion of groundwater levels concurrent with an increase in soil moisture content was observed during the most severe drought conditions, indicating an intensification of groundwater abstraction for irrigation. These results could be useful to guide social, economic, and water resource policy decision-making processes.

Groundwater Drought and Cycles in Xuchang City, China

The urban groundwater system is complex and affected by the interaction of natural and human factors. Groundwater scarcity can no longer reflect this complex situation, and the concept of groundwater drought can better interpret this situation. The groundwater drought cycle is the time interval in which groundwater droughts occur repeatedly and twice in a row. The study of the groundwater drought cycle can more comprehensively grasp the development characteristics of the groundwater drought, which is of great importance for the development, utilization, and protection of groundwater. This study used monthly observation data from seven groundwater wells in Xuchang, China, in the period 1980–2018. We applied the Kolmogorov–Smirnov test to select the best fitting distribution function and constructed a Standardized Groundwater Index (SGI). We analyzed groundwater drought at different time scales and used Morlet’s continuous complex wavelet transform to analyze the groundwater drought cycles. The following results were obtained: 1) the maximum intensity of groundwater drought in the seven observation wells ranged from 104.40 to 187.10. Well-3# has the most severe groundwater drought; 2) the drought years of well-5# were concentrated in 1984–1987 and 2003–2012 and those in the other wells in 1994–1999 and 2014–2018; and 3) the groundwater drought cycles in the seven observation wells were 97–120 months, and the average period is about 110 months. The cycle length had the following order: well-7# > well-4# > well-5# > well-2# > well-1# > well-3# > well-6. Therefore, Morlet wavelet transform analysis can be used to study the groundwater drought cycles and can be more intuitive in understanding the development of regional groundwater droughts. In addition, through the study of the Xuchang groundwater drought and its cycle, the groundwater drought in Xuchang city has been revealed, which can help local relevant departments to provide technical support and a scientific basis for the development, utilization, and protection of groundwater in the region.

Temporal and Spatial Dynamics of Drought in Central Asia during 2002-2017 Based on Grace Data

With the influences of climate change and human activities, the resources and environment of “One Belt and One Road” are facing severe problems and challenges. This study aims to analyze the temporal and spatial dynamics of the drought environment and the response of vegetation cover to the drought by using drought indicators. Gravity Recovery and Climate Experiment (GRACE) drought severity index (GRACE-DSI) and GRACE water storage deficit index (GRACE-WSDI), were calculated to present hydrological drought. Moreover, based on GRACE, Water-Global Assessment and Prognosis (WaterGAP) model, and Global Land Data Assimilation System (GLDAS) data, the groundwater in Central Asia was retrieved to calculate the groundwater drought index called the GRACE Standardized Groundwater Level Index (GRACE-SGI). The results show that the annual precipitation in Central Asia increased slightly at a rate of 0.39 mm/year (p = 0.82) since 2000, while the temperature increased slightly at a rate of 0.05 ℃/year (p = 0.10). The water storage decreased significantly at -0.59 mm/year (p <0.01) and experienced a decrease-increase-decrease process. During the study period, the arid situation in Central Asia deteriorated, especially in the eastern coast of the Caspian Sea and the Aral Sea basin. From 2007 to 2015, the Central Asian environment was generally arid and suffered from different du-rations and degrees of hydrological and groundwater droughts. The drought indicators (i.e., GRACE-DSI, GRACE-WSDI) and the NDVI showed a significantly positive correlation during the growing season. However, the NDVI of cultivated land and grassland distribution areas in Central Asia showed a strong negative correlation with GRACE-SGI. It is concluded that the drought environment in Central Asia affected the growth of vegetation. The continued deterioration of the arid situation may further stress the ecological system in Central Asia.