1 Water Cycle: Fluxes and Storage

1.1 How much water is there? Where?

1.2 The natural water cycle (2019)

1.3 The new water cycle (2022)

Interactive chart: Pools and fluxes in the water cycle

1.4 Global water distribution

Source: Water Science School (2018). **(Percents are rounded, so will not add to 100)**
Water source	Volume (km^3)	% of freshwater	% of total water
Oceans, Seas, & Bays	1,338,000,000	–	96.54
Ice caps, Glaciers, & Permanent Snow	24,064,000	68.7	1.74
Groundwater	23,400,000	–	1.69
\quadFresh	10,530,000	30.1	0.76
\quadSaline	12,870,000	–	0.93
Soil Moisture	16,500	0.05	0.001
Ground Ice & Permafrost	300,000	0.86	0.022
Lakes	176,400	–	0.013
\quadFresh	91,000	0.26	0.007
\quadSaline	85,400	–	0.006
Atmosphere	12,900	0.04	0.001
Swamp Water	11,470	0.03	0.0008
Rivers	2,120	0.006	0.0002
Biological Water	1,120	0.003	0.0001

1.5 Energy drives the hydrologic cycle

From Margulis (2019)

A key aspect of the hydrologic cycle is the fact that it is driven by energy inputs (primarily from the sun). At the global scale, the system is essentially closed with respect to water; negligible water is entering or leaving the system. In other words, there is no external forcing in terms of a water flux. Systems with no external forcing will generally eventually come to an equilibrium state. So what makes the hydrologic cycle so dynamic? The solar radiative energy input, which is external to the system, drives the hydrologic cycle. Averaged over the globe, 342 W m^{-2} of solar radiative energy is being continuously input to the system at the top of the atmosphere. This energy input must be dissipated, and this is done, to a large extent, via the hydrologic cycle. Due to this fact, the study of hydrology is not isolated to the study of water storage and movement, but also must often include study of energy storage and movements.

1.6 Components of the water cycle

1.6.1 Water storage in oceans

1.6.2 Evaporation / Sublimation

Evaporation \longrightarrow cooling

Source: http://www.hk-phy.org/contextual/heat/cha/evapo02_e.html

Source: https://courses.lumenlearning.com/cheminter/chapter/evaporation/

Source: https://engineeringinsider.org/cooling-tower-types/

Source: https://slideplayer.com/slide/7418126/

1.6.3 Evapotranspiration

Source: http://www.eschooltoday.com/water-cycle/what-is-transpiration-and-evapotranspiration.html

1.6.4 Water storage in the atmosphere

Cumulonimbus cloud over Africa Source: https://commons.wikimedia.org/wiki/File:Cumulonimbus_Cloud_over_Africa_%28color%29.jpg

Picture of cumulonimbus taken from the International Space Station, over western Africa near the Senegal-Mali border.

If all of the water in the atmosphere rained down at once, it would only cover the globe to a depth of 2.5 centimeters. \begin{split} \text{amount of water in the atmosphere} & \qquad V = 12\, 900\, \text{km}^3 \\ \text{surface of Earth} & \qquad S = 4 \pi R^2;\quad R=6371\,\text{km}\\ & \qquad V = S \times h \\ \text{height} & \qquad h = \frac{V}{S} \simeq 2.5\,\text{cm} \end{split}

Try to calculate this yourself, and click on the button below to check how to do it.

Show/hide the code

# amount of water in the atmosphere
V = 12900 # km^3
# Earth's radius
R = 6371 # km
# surface of Earth = 4 pi Rˆ2
S = 4 * 3.141592 * R**2
# Volume: V = S * h, therefore
# height
h = V / S # in km
h_cm = h * 1e5 # in cm
print(f"The height would be ~ {h_cm:.1f} cm")

The height would be ~ 2.5 cm

1.6.5 Condensation

1.6.6 Precipitation

Source: Water Science School (2019e)
	Intensity (cm/h)	Median diameter (mm)	Velocity of fall (m/s)	Drops s^{-1} m^{-2}
Fog	0.013	0.01	0.003	67,425,000
Mist	0.005	0.1	0.21	27,000
Drizzle	0.025	0.96	4.1	151
Light rain	0.10	1.24	4.8	280
Moderate rain	0.38	1.60	5.7	495
Heavy rain	1.52	2.05	6.7	495
Excessive rain	4.06	2.40	7.3	818
Cloudburst	10.2	2.85	7.9	1,220