Ground Water and Ecosystem Sustainability

Until now, groundwater—a critical water resource around the globe, especially in dry regions—has been largely unstudied in its importance and role in sustaining ecosystems. “A vast majority of our planets freshwater is groundwater, but we don’t acknowledge or manage it sustainably, resulting in serious consequences for humans and natural ecosystems.” “Groundwater is critical for many ecosystems, but water agencies and conservationists rarely account for their water requirements. “Groundwater-dependent ecosystems such as wetlands, floodplains, and riparian zones have very outsized importance on biodiversity. Upwards of 80 to 90 percent of species in a general region may be dependent on these ecosystems in some form or another.” It was discovered that during drought events, groundwater-dependent vegetation that maintains a connection to groundwater could serve as critical drought refugia for associated species, such as riparian birds or fish. However, when groundwater levels deepen beyond plants’ rooting zones during drought, these safe havens can be lost. “Globally, there are increasing efforts to manage groundwater resources for multiple purposes, not only to support drinking water needs or high-value agriculture.
Climate change will impact every aspect of biophysical systems and society. However, unlike other components of the climate system, the impact of climate change on the groundwater system has only recently received attention. This focus is due to the realization that groundwater is a vital freshwater resource crucial to global food and water security, and is essential in sustaining ecosystems and human adaptation to climate variability and change. Also, we appraise the use of coupled groundwater-climate and land surface models in groundwater hydrology as a means of improving existing knowledge of climate change-groundwater interaction, finding that most models anticipate decreases in groundwater recharge, storage and levels, particularly in the arid/semi-arid tropics. Reducing uncertainties in future climate projections and improving our understanding of the physical processes underlying models to improve their simulation of real-world conditions remain a priority for climate and Earth scientists. Despite the enormous progress made, there are still few and inadequate local and regional aquifer studies, especially in less developed regions.
Groundwater plays a vital role in sustaining ecosystems and ensuring human adaptation to extreme and unexpected global environmental changes, particularly as surface water systems become increasingly unsustainable in the face of rapid population growth and climate change. Groundwater is an important component of the climate system, but many potential impacts of climate change remain largely unknown, because the climate system is intricate, characterized by a web of complex interactions and feedbacks. In general, most studies envisage an intensification of the hydrological cycle; higher temperatures are expected to drive increases in evaporation and evapotranspiration Er but a simultaneous increase in humidity and CO2 could counteract the effect of temperature, and leave ET unchanged in a warming climate. Precipitation is projected to increase in amount and intensity in many places while other places are projected to experience drought. Also, the portion of precipitation falling as snow is likely to decrease. This lesser amount of snow will melt more quickly, leading to higher average annual surface runoff, especially in temperate climates.
Most prior studies on the potential impact of the changing climate on the hydrological cycle have focused on the surface and visible portion of the cycle—precipitation, atmospheric water vapor, ET, stream flow, snow cover and so on. This bias is mainly due to their visibility and accessibility— qualities which make for relative ease of observation, measurement, and investigation of its component characteristics and interaction. Until recently, there have been fewer studies on climate change-groundwater relationships. The difficulties involved in probing the nature and characteristics of water below the Earth surface, in part, account for this deficiency in understanding groundwater response to climate change forcing. Also, groundwater is relatively insensitive to seasonal and even decadal climate variability. Providing a complete picture of groundwater response to the changing climate is even more challenging given that the impacts of climate change are often modified by human and indirect agents such as land-use change and over-exploitation of groundwater.
However, given that groundwater accounts for almost 96% of the Earth’s unfrozen freshwater and 33% of total water withdrawals worldwide, there is growing concern, focus, and research on the impact of climate change on groundwater resources. Climate change is no longer a hypothesis. There is a global consensus among climatologists and other Earth scientists that the global climate is changing. Since the instrumentation period began, the Earth’s climate has undergone unprecedented changes, and these changes have been projected to continue well into this century. For instance, the last four years are the warmest years on record and the ten warmest years are all in the 21st century. The global average temperature has risen almost 1 °C since records began, and atmospheric CO2 is currently at an all-time high of 416 ppm as of April 2020. Today, climate change has remained on the front burner of world-leading studies in environmental science and climatology, and it remains topical at national and international levels because of its influence on policy and decision making in socioeconomic domains. It is seen as a multidisciplinary subject matter and has attained a universal presence in the academic arena because its impact pervades all of Earth’s systems. There is less agreement, however, about how much warming will occur in future and what effect it would have on various life forms.
Increasing temperatures have led to the melting and receding of glaciers and ice-sheets—reinforced by the Arctic amplification and the cryospheric positive feedback mechanism. This melting of ice, combined with thermal expansion of the oceans cause average sea level to rise. Other parts of the climate system (such as the hydrological cycle) respond to climate change forcing through numerous—often intractable—feedbacks .In all, scientific knowledge of climate processes has improved. Climate models now produce realistic simulations of past and future climate change. However, many uncertainties still exist in our knowledge about specific microphysical processes and complex interactions that govern the climate system. Future projections of climate change and alterations to groundwater due to climate change will require sophisticated theoretical models to be more reliable.
Most naturally dry regions with very little precipitation have seasonally or year-round surface and groundwater depletion; however, even more rainy regions, such as the Indian sub-continent and the Great Plains of the US, show significant depletion. These latter areas indicate places of intense industrial and agricultural water use. Countries with large RPGw tend to be located in dry, hot climates where the little precipitation is consumed by ET and groundwater recharge is severely limited. Most of the Middle East and North Africa fall into this class, and watersheds in this region suffer seasonal and dry-year surface and groundwater depletion.
The rapid growth in world population and the associated increase in water demand do not proffer a complete explanation for the massive depletion of groundwater storage. Many studies have established correlations between climate perturbations and groundwater levels. As global warming and climate change drives more intense and frequent climate extremes, precipitation, evaporation, and surface water will become more variable, making groundwater a threatened and yet critical resource in sustaining ecosystems. Indeed, increasing groundwater demand will characterize future scenarios for water resource management and food security, as it is the only viable means of meeting the water needs of rural areas and arid regions.
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