01
Surface water
rivers · lakes · wetlands · reservoirs
Fast-moving and highly visible stores that integrate runoff from across a watershed.
Reservoirs · fluxes · watersheds · groundwater
Hydrology
Hydrology follows water through connected reservoirs and pathways. Rain and snow become infiltration, runoff, soil moisture, groundwater, streamflow, evaporation, transpiration, ice, and stored water, all constrained by landscape, climate, geology, and time.
Hydrologic system
The water cycle is really a map of reservoirs connected by fluxes.
The familiar evaporation–condensation–precipitation loop is only the atmospheric slice. Hydrology asks where water is stored, how quickly it moves, what controls its path, and how one part of the watershed affects another.
02
Groundwater
aquifers · pore water · springs
Subsurface storage moving through connected pores and fractures, often on slower timescales than surface flow.
03
Snow & ice
snowpack · glaciers · seasonal ice
Frozen storage delays the release of water and strongly shapes seasonal runoff in many regions.
04
Soil & biosphere
soil moisture · plants · organisms
A thin but active reservoir where infiltration, root uptake, evaporation, and transpiration meet.
Watershed budget lab
Track water by balancing inputs, outputs, and storage.
For a chosen watershed and time interval, precipitation enters the budget. Evapotranspiration and runoff leave it. The remainder changes storage in soil, groundwater, lakes, snow, or other reservoirs.
Budget equation
P = ET + Q + ΔS
This simplified form hides many sub-fluxes, but the accounting principle is the backbone of hydrology.
Precipitation (P)
10040160
Evapotranspiration (ET)
4810100
Runoff / discharge (Q)
325100
Derived storage change
+20
storage increases
depletionbalancerecharge
Interpretation
A positive ΔS can mean aquifer recharge, wetter soil, rising lake levels, or accumulating snow. A negative ΔS means stored water is being drawn down. Which reservoir changes depends on the watershed and season.
Flow pathways · reference
Water can take many routes from precipitation to discharge.
Which pathway dominates depends on soil, slope, vegetation, geology, rainfall intensity, antecedent moisture, snow and ice, land use, and the scale at which the watershed is observed.
Infiltration
Water crosses the land surface and enters soil or porous material.
Percolation
Water moves deeper through soil and rock toward groundwater storage.
Runoff
Water moves across the land surface or through shallow subsurface pathways toward channels.
Streamflow
Channels integrate upstream water and transport it through the drainage network.
Evapotranspiration
Evaporation plus plant transpiration returns water to the atmosphere.
Recharge & discharge
Groundwater enters or leaves storage as water crosses the water table or emerges to springs, streams, wetlands, and coasts.