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## Hydrology (水文学)

Mount Usu / Sarobetsu post-mined peatland
From left: Crater basin in 1986 and 2006. Cottongrass / Daylily

 The science which deals with the water of the earth, their occurrence, circulation and distribution on the planet, their physical and chemical properties and their interactions with the physical and biological environment, including their responses to human activity (UNESCO 1964) 索引

### Water cycle (水循環)

 Water in the earth is always in movement, and the natural water cycle, also known as the hydrologic cycle, describes the continuous movement of water on, above, and below the surface of the Earth. Water is always changing states between liquid, vapor, and ice, with these processes happening in the blink of an eye and over millions of years. H and O tracers of the hydrologic cycle

### Hydrological balance (水収支)

= water economy, and water balance
General equation
ΔS = P - R - G - E - T

ΔS: storage
P: precipitation
R: to runoff
G: to groundwater
E: to evaporation
T: to transpiration

E = P - R - G - T - ΔS

= P - (b - a)

a: amount of remaining water for dt or Δt
b: known amount of water

= P - ΔS

if ΔS = b - a

##### Water balance in stream
Ideal
P = R + E + T + G
Practical
P = R + E + T + G + ΔS

ΔS: changes (increase or decrease) in water storage at a given time unit for the observation of runoff and/or precipitation in a watershed

ΔS ≈ 0: possibly approximate when the unit of period is a year for treating the data

G ≈ 0: possibly apporximate for small watershed

P = R + (E + T)

## Continuum dynamics (連続体力学)

### Fluid dynamics (流体力学)

 Foundation to understand climatology and hydrology Magnus effect (マグナス効果): Magnus, Heinrich G (1802-1870) an observable phenomenon commonly associated with a spinning object moving through a fluid, including air applied to ball sports Def. Magnus force, FA = Δp·A = cA·ρ/2(u12 - u22)·A cA: a scalar dependent on the rotating object u: the speed of the fluid relative to each surface, 1 and 2 ρ: fluid density