4. Discussion
The hydrological or natural water cycle is a foundational concept for comprehending the circulation and dispersion of water on Earth. Over time, our comprehension of this cycle has progressed from the speculative philosophies of early scholars such as Plato and Aristotle to the development of comprehensive, contemporary scientific frameworks.
4.1. Western Ancient Philosophical Speculations
In ancient Greece, the earliest conceptions regarding the genesis of rivers centered on the hypothesis of immense subterranean caverns and reservoirs (Angelakis, 2012). These expansive underground passageways and reservoirs were thought to be the wellspring of the uninterrupted flow of rivers, even in times of drought. Such suppositions exerted significant influence during that era, as evidenced in the monumental works of Homer. He says, "There exists a colossal subterranean water vortex known as ’Oceanus,’ from which all rivers and oceans, all springs and unfathomable pools emanate" (Homer, 1991, p. 319).
During the 5th century BC, several prominent Greek philosophers contributed to the early study of natural water phenomena. Anaximenes (585–525 BC) extensively researched meteorological occurrences and proposed logical interpretations for the origins of wind, rainbows, cloud formation, rain, and snow (Kočandrle, 2019). During the same period, Hippon, a Pythagorean philosopher, postulated that the ultimate source of all water on Earth was the sea (Stewart & Howell, 2003). Concurrently, Anaxagoras (500-428 BC) and Plato (429-347 BC) speculated, drawing from Homer’s poetic perspectives, that river water emanated from vast subterranean caverns, a theory later proven incorrect (Furley, 1987). Plato, in his work Timaeus, also introduced the notion of water traveling from the sea into extensive subterranean channels beneath the earth termed "Tartarus," then returning to the sea, representing a rudimentary comprehension of the water cycle, albeit inaccurately characterized by modern standards (Bucaille, 2015).
Aristotle (384-323 BC) astutely postulated that rainwater is a result of the evaporation of seawater. He proposed that seawater evaporating into the air renders it ’sweet’, and when the vapor condenses, it does not revert to its salty state (Aristotle & Barnes, 2014). Aristotle was among the earliest to comprehend the imperative need for a continuous cycle to sustain river and sea water levels, preventing rivers from desiccation and seas from inundation. In his work "Meteorologica," Aristotle disputed the concept of a substantial reservoir within the Earth’s crust with a compelling argument:
If anyone can imagine a reservoir large enough to hold the water flowing every day and consider the volume of that water, it is clear that a container capable of holding all the water flowing in a year would be larger than the earth, or at least not much smaller.
(Aristotle & Barnes, 2014, p. 230)
Aristotle laid the foundation for understanding the hydrological cycle by observing natural phenomena, particularly the interplay of water, air, and solar influence. In his work Meteorologica, he articulated a conceptual framework in which water vapor, induced by solar heating, ascends from the earth’s surface, undergoes cooling and condensation processes, leading to precipitation, and eventually returns to the earth. Although lacking a comprehensive understanding of contemporary science, Aristotle’s insights represented a pivotal step toward systematically comprehending the natural water cycle (Koutsoyiannis & Mamassis, 2021).
Notwithstanding his often logical reasoning, Aristotle had difficulty accepting that rainfall alone was responsible for creating springs and rivers. He grappled with the mystery of how rivers could maintain their flow for prolonged periods, spanning weeks or even months, without rainfall. This riddle continued to perplex society during that time (Deming, 2005).
The philosopher Seneca (3 BC-65 AD) provided a succinct overview of the Roman era’s understanding and perspectives on the natural water cycle. He argued that rainfall alone was insufficient to replenish the various river sources and springs adequately. Seneca contended that while rain could cause torrents, it could not sustain a consistent river flow. He emphasized the significance of the evaporation process. He posited that the coexistence of air and water played a pivotal role in the emergence and course of water flowing out of the soil, giving rise to springs and rivers (Duffy, 2017).
In his treatise De Architectura, Marcus Vitruvius, a prominent Roman author, scientist, and engineer of the 1st century BC, provided comprehensive insights into the phenomenon of rainfall and the factors contributing to the formation of mountain springs. He attributed these mechanisms primarily to evaporation and topographical influences. Vitruvius’ explanations resemble the contemporary understanding of the hydrological cycle as acknowledged in current literature (Karterakis et al., 2007).
4.2. Contributions of the Medieval Period
During the Medieval Period, spanning from the first century AD to the 17th century AD, the field of science was characterized by a lack of significant progress, often referred to as a "dark age". The hydrological cycle received limited attention during this time, with prevalent adherence to ancient theories, such as the concept of giant underground water reservoirs from the Greek and Roman eras. The dominant influence on scientific thought during this period stemmed from Christian church teachings, with the Bible serving as the primary reference for scholars, shaping their observations and scientific studies. A notable reference from the book of Ecclesiastes in the Bible describes the sea as the source of all rivers and springs: “All the rivers run into the sea, yet the sea is not full; unto the place from whence the rivers come, thither they return” (Bible.com, 2024).
The interpretation of this verse by contemporary church scholars and followers of the era suggested that water from the sea would flow back to the rivers, potentially through channels or openings beneath the sea floor. While this conceptualization was consistent with the modern hydrological cycle, it mistakenly implied that the process involved openings in the sea floor (Adams, 1954). This implies that the Biblical interpretation aligned with outdated intellectual concepts that deviated from absolute truth. Given that most intellectuals during that era were associated with the church, this perspective gained traction and prevailed throughout the medieval period.
During the medieval period, Athanasius Kircher (1602-1680), a prominent German priest, contributed significantly to the field of hydrology with his 1664 publication Mundus Subterraneus. Kircher posited the theory of the hydrological cycle, proposing that the Earth’s subsurface contained various conduits that transported water to extensive reservoirs within mountains, subsequently releasing it to the surface through springs. He likened this mechanism to the human body’s blood circulation, though this analogy was widely disregarded then. Mundus Subterraneus sheds light on the challenges faced by medieval society in comprehending the relationship between rainfall and river flow, especially considering that rain was not acknowledged as the primary source of river water during this era (Angelakis, 2012).
The challenge that confronted Kircher was akin to that of Aristotle: how to account for the continuous flow of rivers in the absence of rainfall? As a clergyman, Kircher’s perspective was influenced by Ecclesiastes, which posited that seawater returned to rivers and land to sustain a cycle. This raised a secondary question: How does saline seawater transform into freshwater in springs and terrestrial rivers?
Based on the analysis, Kircher did not answer the first query satisfactorily. However, he attempted to tackle the second question by suggesting that seawater seeped into the earth’s subsurface and underwent a distillation process facilitated by the earth’s internal heat (Rosbjerg & Rodda, 2019).
An alternative hypothesis, similar to Kircher’s, posited for the hydrological cycle was proposed by the Alembic theory, initially presented in the book "Chemisches Laboratorium" by J. J. Becher (1635-1682). According to Becher’s theory, the Earth resembled a vast distillation apparatus. When seawater seeped through the ocean floor and entered the Earth, it was heated by subterranean heat and vaporized. As the vapor descended, it permeated the cavernous interiors of mountains. The vapor condensed and turned into water upon encountering colder temperatures and snow on the mountains. This water gave rise to springs that cascaded down the mountainsides, eventually returning to the sea (Koutsoyiannis & Mamassis, 2021).
The concept comprises two significant incongruities:
- (a)
The assertion that water flows from sea level to mountain peaks contradicts fundamental laws of nature, as water predominantly descends from higher to lower elevations rather than the opposite.
- (b)
The linkage between the sea and the mountains would give rise to a notable inconsistency due to the disparity in salinity between seawater and freshwater from rivers and springs.
Efforts to reconcile these discrepancies were rooted in a combination of conjecture and Christian religious doctrines, which typically lacked robust scientific underpinnings and empirical substantiation. For instance, unconventional ideas emerged during that era, proposing that the ocean surface was elevated compared to the land, ostensibly accounting for the possibility of water flowing toward mountains. Alternatively, specific hypotheses proposed that water movement from lower to higher elevations was orchestrated by divine intervention, as documented by Karterakis et al. (2007).
The historical understanding posited that the earth’s internal heat caused subterranean water to evaporate and emerge at the earth’s surface, including high-altitude mountain peaks (Bucaille, 2015). Contemporary scientific inquiry has since invalidated these beliefs.
4.3. Renaissance and Enlightenment
During the Renaissance era in Europe, there was a notable resurgence in scientific research, driven by a renewed interest in empirical observation and experimentation. Notably, Leonardo da Vinci (1452–1519) conducted detailed observations of cloud formation, rainfall, and river systems, emphasizing the interconnections among these natural elements. Da Vinci was the first to propose the existence of permeable, porous hydrogeological structures, particularly in sloped and hilly regions. He suggested rain and melting snow from mountain peaks could infiltrate these permeable layers, traveling deep underground before resurfacing as springs or flowing back to the sea (Rosbjerg & Rodda, 2019).
In his book Admirable Discourses (Kirsop, 1961), Bernard Palissy (1510–1590), a prominent figure of the Renaissance and Enlightenment, diverged from the prevailing belief of his time regarding the origins of rivers and streams. He posited that rainwater, rather than water from the sea, was the primary source of these water bodies. Palissy, a French Protestant known for his opposition to the limitations imposed by the church, presented a comprehensive scientific explanation of the hydrological cycle. In 1580, Palissy’s work provided a definitive clarification, asserting that rivers and springs are exclusively derived from precipitation and snowmelt. His scholarly investigation of natural springs led him to conclude that their origins were tied solely to precipitation and snow. This departure from the established belief of the time significantly contributed to advancing scientific understanding of hydrology.
In his work, Palissy refuted the notion of seawater migrating to land through hidden subterranean passages to create springs. He contended that if springs stemmed from seawater infiltrating inland, they would carry a salty composition. Palissy also showcased astute observation by posing a fundamental query: If springs were indeed a result of seawater, why would they desiccate during the summer? (Palissy, 1957).
Another exciting thing about Palissy’s work was that he correctly explained the time lag between rain and water flow, a perplexing issue for scholars from Aristotle to Kircher:
Rainwater that falls on land, mountains, and any other inclined surface in the direction of rivers or springs does not rapidly reach them. It would cause every spring to shrivel up during the summer. Nevertheless, the water that precipitates on the ground during the winter months is unable to move swiftly; rather, it seeps gradually until it encounters an obstruction; upon encountering granite, it proceeds in the direction of the rivers. Based on this, it can be deduced that beneath these rivers are numerous continuous springs that flow only slowly and alternate between winters.
(Palissy, 1957, pp. 67-68)
The renowned ceramic artist Palissy met his demise in prison after being apprehended by royal forces and steadfastly refusing to renounce his Protestant faith in favor of Catholicism, which held sway in France during that era (Deming, 2005).
The research conducted by Edme Mariotte (1620–1684) and Pierre Perrault (1611-1680) in France and several modern scientists further substantiated and extended his findings. Their extensive quantitative studies of rainfall and river flow provided empirical evidence that contributed to the developing understanding of the hydrological cycle. Their emphasis on the significance of measurement and observation laid the groundwork for contemporary hydrology.
4.4. Scientific Understanding in the Modern Era
In the following years, with the progress of scientific knowledge into the contemporary era, numerous researchers conducted thorough studies on this subject. Pierre Perrault illustrated his empirical efforts to measure the hydrological cycle in 1674. In his publication, "De l’Origine des Fontaines," he designated a specific area for rainwater accumulation, calculated average precipitation using a rain gauge, and subsequently quantified the volume of water passing through a particular canal. His research revealed a rainfall-to-river flow ratio of 6 to 1, indicating that the quantity of rainfall exceeded the amount required to supply water to springs and rivers. Furthermore, an excess of water had not yet completed the hydrological cycle, suggesting that some water remained underground (Nace, 1974).
Subsequently, a French physicist and clergyman, Edme Mariotte (1620-1684) conducted a similar experiment, yielding a heightened ratio of approximately 8 to 1 (Deming, 2017).
Italian naturalist and medical scientist Antonio Vallisnieri (1661-1730) made a significant contribution by conducting an extensive study in the Alps on the natural formation of springs and rivers. A key finding of his research was the concept of infiltration. Vallisnieri observed that despite the extensive Monte S. Pellegrino snowfield, the narrow rivers near Modena had low discharge. Detailed observations revealed that the water from the snowmelt atop the mountain traveled through imperceptible subterranean pathways for a considerable distance from Modena to Bologna, passing through small porous permeable strata. This discovery confirmed that subterranean routes, discussed in the Middle Ages, transported water naturally from mountain summits to depths rather than from oceans to mountains (Luzzini, 2014). This development led to humans’ near-complete understanding of the hydrological cycle around 1715.
Recent findings in contemporary hydrology have elucidated that the hydrological cycle, also known as the natural water cycle, is an ongoing process encompassing the movement of groundwater, terrestrial water, and atmospheric water on Earth. Primarily driven by solar radiation, this cycle initiates with the conversion of liquid water from the Earth’s seas, lakes, and rivers into gaseous water vapor. Additionally, plants contribute to this process through transpiration, releasing water vapor into the atmosphere. The water vapor ascends and cools, undergoing condensation to form clouds, resulting in precipitation in various forms, such as rain, snow, hail, or sleet. This natural process replenishes the Earth’s surface water reservoir and concurrently seeps into the soil, augmenting groundwater reserves (Oki & Kanae, 2006).
Precipitation in rain and snow can lead to surface runoff, where water flows over the land and enters rivers, lakes, and, eventually, the oceans. Some of this water infiltrates the ground, replenishing aquifers and natural groundwater reservoirs, which can resurface through springs. Surface water supports human, plant, and animal life (Ibrahim & Ibrahim, 2024). The continuous movement of water is essential for sustaining life, regulating the climate, and preserving the natural balance of ecosystems (Yang et al., 2021). The hydrological cycle is directly responsible for ensuring the consistent distribution and availability of freshwater worldwide.
4.5. The Quran and the Hydrological Cycle
The Quran, revealed in the 7th century, contains verses that intricately depict the water cycle, aligning with modern scientific knowledge. Within various surahs (chapters) of the Quran, these descriptions eloquently portray fundamental processes of the natural water cycle, including evaporation, condensation, and the precise movements of water.
Have you not seen that Allah sent down water from the sky, then made it penetrate into the earth (and gush forth) in the form of springs? Then He brings forth with it crops of different colors, and afterwards they wither, and you see them turned yellow, then He makes them chaff. Surely in that there is a lesson for the people of understanding.
(The Noble Quran, Translation by T. Usmani, 2024, 39:21)
The mentioned verse alludes to rain descending from the sky and permeating the earth, ultimately giving rise to springs. During the 7th century, when the Quran was revealed in the Arabian Peninsula, the global understanding of the natural water cycle was in its infancy, leading to the proposal of various unconventional theories. These included the existence of vast subterranean reservoirs and the notion that seawater was being forced inland through specific underground channels, thereby creating springs on the earth’s surface and even atop mountain peaks. In contrast, the Quran succinctly expounded that terrestrial springs originate from rain, which has since garnered scientific validation (Kresic & Stevanovic, 2009).
Do you not realize that Allah drives the clouds, then joins them together, then turns them into a heap? Then you see the rain coming out from their midst. He sends down from the sky mountains (of clouds) having hail in them, then He afflicts with it whomsoever He wills and turns it away from whomsoever He wills. The flash of its lightning seems to snatch away the eyes
(The Noble Quran, Translation by T. Usmani, 2024, 24:43)
The passage delineates clouds’ motion, aggregation, and stratification, elucidating the subsequent occurrence of precipitation, including hail. Additionally, it expounds on the generation of lightning as an offshoot of cloud movement, which has been empirically substantiated (National Geographic, 2009).
Allah is the One who sends the winds, so they stir up a cloud, then He spreads it in the sky however He wills, and makes it (split) into pieces. Then you see the rain coming out from its midst. So, once He makes it reach those whom He wills from His slaves, they start rejoicing,
(The Noble Quran, Translation by T. Usmani, 2024, 30:48)
The passage delineates the pivotal role of wind in orchestrating cloud movement and precipitation, along with the rain descending upon those deemed worthy by Allah. In contemporary society, technological advancements have provided the means to stimulate rainfall from previously non-responsive clouds through a method known as cloud seeding. Nevertheless, as expounded by French meteorologist M.A. Facy in the Encyclopedia Universalis within the section dedicated to precipitation.
"It will never be possible to make rain fall from clouds that do not have the characteristics of rain clouds or have not reached the appropriate stage of evolution (maturity). Therefore, humans cannot accelerate the process of rain through technical means when the natural conditions for it do not exist. If humans could truly control rain, droughts would end—which clearly, they have not. Thus, having control over rain and good weather remains a dream."
(M.A. Facy, as quoted in Bucaille, 2015, p. 177)
The observation mentioned validates the enduring relevance of the Quranic verse. It highlights the influence of natural factors, such as wind and other meteorological conditions, in dictating the distribution and occurrence of rainfall beyond human control.
And We sent down water from the sky in due measure, then We lodged it in the earth, and of course, We are able to take it away.
(The Noble Quran, Translation by T. Usmani, 2024, 23:18)
The following verse asserts that the quantity of rain and stored water on earth is predetermined. According to modern hydrological research, the total amount of water in the atmosphere and soil remains constant (Linton, 2008; Van der Ent & Tuinenburg, 2017). While the forms of water in circulation may vary, such as snow, dew, rain, or groundwater, the overall quantity of water within the hydrological cycle remains consistent (Jacob, 2001).
At any given time, the Earth’s atmosphere contains approximately 12,900 cubic kilometers (km³) of water particles. This quantity remains relatively stable, contributing to the overall balance of water on the Earth’s surface. Should all the water particles in the atmosphere precipitate simultaneously, it would result in a global submersion of the Earth’s surface by about one inch or approximately 2.5 cm (Schneider et al., 2011).
The verse highlights the constancy of water stored within the earth. Rainwater is typically absorbed into the ground through permeable layers and small pores in the soil. However, rapid urban development has led to ground surfaces being covered with impermeable materials such as cement and concrete, impeding rainwater from infiltrating the ground (Cheng et al., 2022).
The consistent quantity of water stored underground means that the hindrance of water infiltration disrupts the natural balance established by a higher power. Consequently, this disturbance contributes to frequent urban flash floods and sudden flooding. Human actions must align with the principles outlined in these Quranic verses. This requires modifications to urban constructions, which can enable rainwater to readily permeate the ground, thus mitigating the reoccurrence of flood disasters
How well We poured water, then how nicely We split the earth, then We grew in it grain, and grapes and greens, and olive and date-palms, and gardens, full of thick trees, and fruits and fodder, as a benefit for you and your cattle.
(The Noble Quran, Translation by T. Usmani, 2024, 80:25-32)
The verse under scrutiny underscores the manifestation of rain on earth and Allah’s precise division of the earth. Islamic exegetes such as Ibn Kathir have expounded upon this verse, interpreting it as indicative of Allah’s placement of water within the earth, allowing it to permeate layers and percolate into the stored seeds, which subsequently germinate into lofty, rooted trees on the earth’s surface (Kathir, 2021). Furthermore, the initial segment of the Quranic verse can be construed to signify that rainwater descending to the earth permeates the earth’s crevices through porous spaces and fine apertures in the soil, facilitating subterranean storage of water (MyIslam.org, 2024; Islamic Foundation UK, 2024). This serves as an attestation to the veracity of the Quranic verses.