Drought and Groundwater Development

Groundwater is an important freshwater source that satisfies the needs of a significant portion of the world’s population, industries, and ecosystems. It is estimated that the total amount of groundwater in the world is approximately four trillion cubic meters [1]. Particularly, in the Middle East Asian and African regions, surface water sources are scarce and polluted, and people rely heavily on groundwater [2] Due to climate change and increased evapotranspiration, the depth of groundwater production is becoming deeper. Recently, unusual droughts have occurred not only in these regions but also in mid-latitude regions, leading to water scarcity. Therefore, various technologies are being developed and applied to secure water resources.

Groundwater exists in aquifers, the world’s largest water reservoir, and plays an important role in maintaining ecosystems. Particularly, in an era of climate change, groundwater plays a crucial role in helping humans adapt proactively to climate variability. The importance of groundwater has increased even more in recent years as it plays a crucial role in regulating the quantity of soil and surface water to cope with extreme climate events, such as droughts and floods, and it is a key factor affecting food productivity. Thus, deciding how to utilize groundwater resources as a means of coping with climate change on a global scale has become a critical issue [3].

Drought is a costly natural disaster that has a widespread impact on agriculture, ecosystems, water resources, social economy, and politics. Although drought is a common phenomenon that occurs in a hydrological cycle, its frequency and magnitude have been increasing in recent years because of climate change [4] When drought occurs, it has serious impacts on various sectors and sometimes leads to the over-exploitation of groundwater, which is an alternative water source. Moreover, the demand for agricultural and domestic water continues to increase worldwide as economic growth and living standards are improved. In water-scarce countries with inadequate water supply systems, surface water is vulnerable to weather changes, such as drought; therefore, alternative water sources, such as groundwater, are considered as a systematic means of water supply.

Artificial recharge is a technique that increases the total water amount by artificially injecting surface water, rainfall, reused water, or other water sources into underground aquifers. This involves the installation of artificial structures, such as artificial recharge basins, wetlands, canals, underground dams, and infiltration facilities, or changing the ground conditions to inject water artificially [5]. This technology is becoming more widely used in areas affected by climate change, such as major drought-prone regions in Africa and India. The biggest advantage of artificial recharge is that surplus water can be infiltrated into the ground for later usage during dry periods. It allows a larger amount of water to be stored in the subsurface compared to natural conditions and takes advantage of the natural purification capacity of aquifers during storage [6] The methods of artificial recharge vary greatly and include injection wells, bank filtration, ditches, recharge basins, in-channel modification, and others.

In the United States, injection and infiltration technologies using wells have a long history, and aquifer storage and recovery (ASR) is one of the most widely used methods for storing and recovering groundwater. The main purpose of artificial recharge is to secure water for drinking water supply. It is stored underground to alleviate seasonal imbalances in water demand and is used when needed. In Europe, in particular Germany, the bank filtration technique, which is a form of artificial recharge, is widely used to secure water supply [7]. To design and investigate artificial recharge facilities for groundwater, various factors need to be analyzed, including terrain-related and meteorological characteristics, permeability and storage capacity of aquifers, clogging characteristics of soil, water supply for artificial recharge, and depth of groundwater level. In addition, the demand and supply of water and the specifications of the artificial recharge and extraction facilities used must be determined.

Groundwater helps alleviate droughts by providing underground flow to maintain stream flow during dry periods. The increased quantity of water resulting from artificial recharge not only contributes to increasing stream flow during drought periods, but it also slows down the rate of discharge in basins, thus contributing further to stream flow during such periods. Thus, artificial groundwater recharge can delay drought propagation and provide an efficient means of water supply during droughts. High technical challenges in the process of artificial recharge need to be addressed to increase the efficiency of artificial recharge facilities. The main cause of efficiency reduction is clogging, and various technologies have been developed over the past decades to evaluate and solve clogging, although current solutions are still inadequate. Land use and land cover (LU/LC) in a country are also important factors that influence groundwater recharge and surface runoff, and decision makers should consider LU/LC to increase natural groundwater recharge in the country’s development [8].

This Special Issue focuses on various technologies to resolve water scarcity and contamination caused by abnormal droughts in Asia and Africa. It includes research on the utilization of groundwater level and precipitation data; drought prediction and diagnosis; and evaluation technologies for securing water resources [3,9,10]. In general, in an upstream watershed, water is quickly discharged, so drought damage appears there first. Then, the scope of the drought gradually widens, resulting in an increase in the scale of its damage. Generally, for widespread droughts, central governments show interest and quickly pursue various policies; however, for localized droughts that occur in upstream areas of a watershed, passive measures are mostly taken. In terms of water welfare, fundamental policies for drought relief and securing water resources should be pursued for these upstream areas that are marginalized [11]. Some of the technologies covered in this Special Issue are applicable to such water-welfare blind spots [12].

We conclude this Special Issue with the expectation that the research results presented here will contribute to solving water problems in various countries, particularly as solutions during periods of drought when surface water is limited.