Jala Vijnana (जलविज्ञानम्)

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Jala vijnana (Samskrit: जलविज्ञानम्) is the science of water, referred to as Hydrology in modern parlance. Ancient samskrit literature contains the most valuable and highly advanced scientific discourses on hydroscience, sadly unexplored to a great extent.

In vedas one can find references to the concept of loosely bound water molecules; Puranas mention that water is not created or destroyed and it undergoes a change of state through the various phases of water cycle. Earliest references to the process of raindrop formation, rainfall patterns, astronomical factors that affect rains, the chemical aspects such as evaporation, condensation, cloud formation, precipitation are all found interspersed in ancient texts, showcasing the technological advancement of Bharatavarsha.

Effects of Yajnas (in causing rains), forests, reservoirs, classification of clouds, their color, rainfall capacity etc, forecasting of rainfall on the basis of natural phenomena like color of the sky, clouds; wind direction, lightening, and the activities of animals was well developed in ancient days. Varshamapana yantra (rain guage) a contrivance to measure rainfall was referred in Arthashastra of Kautilya and Ashtadhyayi of Panini. The modern hydrology evaluations are based on the ancient technology used in such yantras differing in the weight measure (of Drona and Pala) instead of the modern linear measurement of rainfall. The quantity of rainfall in various parts of Bharat was also predicted by Kautilya.

Brhat samhita discusses the ground water development and water quality methods. Driven by sound concepts, people of ancient Bharat could locate groundwater, analyze its distribution and had knowledge of reaching these water-tables to irrigate fields.

Water Formations

Hydrology involves the study of flowing water bodies, change of water states and other elements of hydrology and water resources as follows

• Hydrologic or Water Cycle
• Precipitation, cloud formation, measurement etc.
• Interception and Infiltration
• Stream flow and Geomorphology
• Ground Water
• Evapotranspiration
• Water Quality
• Water use and conservation.

A few of these topics are discussed below.

Water Cycle

The Hydrological or Water Cycle is an important concept in hydroscience. It is the chain of events describing the movement of water involving the total earth system comprising of the atmosphere (the gaseous envelop), the hydrosphere (surface and subsurface water), lithosphere (soils & rocks), and the biosphere (plants & animals). In one of the three phases (solid, liquid, and vapour) the water passes through these four parts of the earth system.

A number of mantras in the Rigveda support the fact that our ancient rshis and maharshis have thorough knowledge of the water cycle and processes involved.

• आदह स्वधामनु पुनर्गर्भत्वमेरिरे। दधाना नाम यज्ञियम्॥४॥ (Rig. Veda. 1.6.4) Water which gets divided in minute particles due to the heat of the sun is carried by wind and after the conversion into cloud it rains again and again. Rigveda (1.19.7) also reiterates the transfer of water from earth to the atmosphere by the wind.
• इन्द्रो दीर्घाय चक्षस आ सूर्यं रोहयद् दिवि। वि गोभिरद्रिमैरयत्॥३॥ (Rig. Veda. 1.7.3) Just as the sun is created and placed such as to illuminate the whole universe, so also as a rule of universe, it extracts water continuously to convert it to cloud and ultimately discharge as rain. Rig veda (1.23.17) also supports this concept.

Yajurveda also discusses the water cycle as follows, the movement of water from from clouds to earth and its flow through channels and storage into oceans and further evaporation.

प्र पर्वतस्य वृषभस्य पृष्ठान्नावश्चरन्ति स्वसिचज्ञयानाः । ता आववृत्रन्नधरागुदक्ता अहिं बुध्न्यमनु रीयमाणाः । विष्णोर्विकर्मणम् असि । विष्णोर्विक्रान्तम् असि । विष्णोः क्रान्तम् असि ॥ (Shuk. Yaju. Veda. 10.19)

Water cycle is described in the Vaiseshika Sutras. Watery vapors closer to the earth in combination with sun's rays ascend upwards into the sky forming clouds. The Vaiseshika Sutras by Kanada clearly mention the interactions of these particles as follows

नाड्या वायुसंयोगादारोहणम् । वैशेषिक-५,२.५ । नोदनापीडनात् संयुक्तसंयोगाच्च । वैशेषिक-५,२.६ । वृक्षाभिसर्पणमित्यदृष्टकारितम् । वैशेषिक-५,२.७ । (Vais. Sutr. 5.2.5-7)

Further to the rising of water vapour, cloud formation, lightning and thunder are explained in the Vaiseshika sutras and bhashya as follows

अपां सङ्घातो विलयनं च तेजः संयोगात् । वैशेषिक-५,२.८ । तत्र विस्फूर्जतुर्लिङ्गम् । वैशेषिक-५,२.९ । वायुसंयुक्तास्सूर्यरश्मयः अपः भूमिष्ठास्तावदन्तरिक्षमारोहयन्ति ।। (Vais. Sutr. 5.2.8-10)

अन्तरिक्षमारूढाः खल्वापः धूमेन ज्योतिषा वायुना च संसृज्यमानाः मेघभावमापद्यन्ते (Form clouds) |

Water rising (in the form of vapor) by combining with the smoke, heat (of the sun's rays) and winds (in the upper strata) form the Clouds.

जले दिव्यज्योतिस्संयोगे सति विद्युत्प्रकाशः (Lightning) ततो विस्फूर्जथुः (Thunder) |

Kalidasa also poetically mentions the formation of clouds in his Meghadoota.

धूमज्योतिस्सलिलमरुता सन्निपातः क्व मेघः । (Megh. 5)

Varahamihira's Brhad Samhita extensively discusses about hydrometrology comprising of Pregnancy of clouds (Adhyaya 21), Pregnancy of air (Adhyaya 22) and quantity of rainfall (Adhyaya 23).