IB Geography A.1.1 the Drainage Basin as an Open System Notes

Components and Processes in Drainage Basins

1. Imagine you’re hiking in the mountains after a rainstorm.
2. As you look around, you notice water trickling down rocks, pooling in small depressions, and eventually joining a rushing stream.
3. Have you ever wondered how all these small flows connect to form rivers and, ultimately, reach the ocean?
4. This interconnected journey of water is orchestrated by the drainage basin system, a dynamic network of inputs, stores, flows, and outputs.

The Drainage Basin is An Open System

1. A drainage basin is like nature’s giant funnel, collecting precipitation from the land and channeling it into rivers that eventually flow to the sea.
2. What makes this system fascinating is its open nature: water enters (inputs), moves through various pathways (flows), is held temporarily (stores), and exits (outputs).
3. This continuous movement is a key part of the hydrological cycle.

Inputs: Precipitation as the Starting Point

1. The journey begins with precipitation, which transfers water from the atmosphere to the Earth's surface.
2. Precipitation can take many forms, rain, snow, hail, or sleet and its characteristics (type, intensity, and duration) significantly influence how water moves through the system.
   1. Rainfall intensity: During heavy rain, the soil’s infiltration capacity can be overwhelmed, leading to surface runoff.
   2. Snow and ice: Water stored in frozen forms (the cryosphere) is released gradually as it melts, providing a steady supply to rivers.
   3. Seasonal variation: In some regions, precipitation patterns shift with the seasons, affecting water availability and river flow.

Outputs: Water Leaving the System

Water exits the drainage basin through two main processes:

1. Evaporation

1. Evaporation transforms water from a liquid to a gas, returning it to the atmosphere.
2. Factors like temperature, wind speed, and surface characteristics influence evaporation rates.