WEEK 1 – INTRODUCTION TO HYDROLOGY &
THE HYDROLOGIC CYCLE
🔹 Practical Scope of Hydrologic Analysis

Hydrology is used to determine:
INTRODUCTION TO HYDROLOGY
o
The amount and flow rate of water
Water and its forms, movement, behavior and spatio-temporal
distribution has always been complex to which we still need to
give our attention to as it is undeniably our necessity. In the
following lectures, let us altogether process how the study of
hydrology, having been able to maximize ideologies, principles
and theories of understanding water and its system, started.
More profoundly, we will be able to realize basic terminologies
and definitions that guide us into further grasp of the study as
we proceed to the next lessons.
o
At a given location and time
o
Under natural conditions (without human
control)
🔹 Hydrology vs. Hydraulics

Example: You're an engineer studying a river in a
mountainous area.
You want to find out:
🔹 Definition of Hydrology

Hydrology is a multidisciplinary subject that deals
with:
o
Occurrences
o
Circulation
o
Storage
o
Distribution of surface and groundwater on
Earth.

Includes physical, chemical, and biological
reactions of water in both natural and man-made
environments.

Related closely to: meteorology, geology,
oceanography, and ecology due to complex
interrelations with the hydrologic cycle.
Derived from ancient Greek: “hydro” (water) + “logy”
(word/science/study).

Broadly means the science of water, but now
specifically refers to:

🔹 Hydrology vs. Other Disciplines


Hydrology focuses on continental water
processes, making it distinct from:
o
Meteorology (atmosphere)
o
Climatology
o
Oceanology (oceans)
o
Glaciology (ice masses)
However, hydrology also integrates with these
disciplines via the global water balance.
How much rainfall the area gets in a year

How much water will flow into the river during a
storm

How likely it is for the river to flood nearby
villages
Hydraulics: Water in controlled, human-made
systems (e.g., pipes, irrigation, pumping systems).
Example: Now, imagine you’re designing a pipe
system to bring water from that river to a nearby
town.
You calculate:
1. Continental water processes – involving
water in solid, liquid, and vapor states, and
biological processes that affect the water
cycle.
2. Global water balance – examining how
water moves and is stored between
atmosphere, oceans, and continents,
including residence times.

➡️ This is hydrology:
You're working with natural water processes, like
rainfall, runoff, infiltration, and river discharge without
controlling them.
🔹 Etymology and Modern Definition

Hydrology: Water in natural systems without human
control.

The diameter of the pipes

The pressure needed to pump water uphill

How fast the water will flow through valves and
channels
➡️ This is hydraulics:
You're working with controlled water flow, using
engineered systems like pipes, pumps, and tanks.
🔹 Hydrology and Hydroclimatology Focus

Studies water science with engineering
applications

Examines interaction of water in all its forms:
o

Evaporation, cloud formation, rain/snow,
stream flow, groundwater
Dynamic and cyclic nature of water is central
(hydrologic cycle).
🔹 Importance of Integrated Water Management

Due to high interaction of water with Earth’s
components, water management must be:
o
Sustainable
o
Integrated

Global attention is increasing on water as a vital
environmental element.

THE MAIN CHALLENGE: to understand the
principles and laws governing the formation and
movement of water in nature.
🔹 Need for System Approach

Studying hydrology and climate requires a
holistic/system approach:
A holistic/system approach means looking at all the parts of
the environment together as a connected system, instead of
studying them separately.
In the context of hydrology and climate, this approach
considers:



How rainfall, temperature, wind, and clouds affect each
other
How land, water, air, and even human activities interact
How these interactions influence the entire water cycle
So instead of focusing on just one factor (like rainfall), you
analyze how everything is linked — just like how a machine
works with many parts moving together.

o
Understanding system concepts
o
Considering all environmental components
and their relationships
The Earth’s environment is made of interconnected
systems:
o
A systems approach helps analyze global
and regional climatic events.
🔹 System Approach in Hydrology

Traditional variables studied:
o
Temperature, wind, humidity, clouds,
precipitation, runoff

However, these are not enough to define hydrologic
systems.

Other important factors:

o
Vertical atmospheric structure
o
Land and sea influence
o
Human (anthropogenic) activities
The hydrologic cycle is seen as a true model of a
holistic system, often cited in literature across art,
science, and engineering.
📚 References
1. Bedient, P., Huber, W & Vieux, B. (2012). Hydrology
and Floodplain Analysis. Pearson.
2. Brutsaert, W. (2005). Hydrology, an Introduction.
Cambridge University Press.
3. Karamouz, M., Nazif, S. & Falahi, M. (2013).
Hydrology and Hydroclimatology: Principles and
Applications. CRC Press.
END OF LECTURE 1
THE HYDROLOGIC CYCLE
One of the things we need to primarily comprehend is the
water cycle. During our pre- college days, our knowledge of
water cycle is just limited to Condensation, Precipitation and
Evaporation. But, it is actually a lot more than that. The
movement of water in its cycle is much more complex and it
undergoes several processes and moves along various strata
of layers.