Precipitation Types and Measurement Methods

Precipitation

According to the process leading to their formation:

Orographic Precipitation

Terrain features, such as mountains and ridges, act as fixed screens and barriers. These force moist, warm air masses to rise. Consequently, this results in an adiabatic process that culminates in condensation and precipitation.

Convective Precipitation

Convective precipitation results from the warming of soil or water and the air in contact with it. This warm, moist air rises because its density is less than that of the upper layers. In doing so, it undergoes an adiabatic process that leads to condensation and rain.

Cyclonic Precipitation

A cyclone is an enormous mass of air that spins at very high speeds around a vortex. It is formed by strong temperature differences between atmospheric layers, giving rise to significant changes in the position of air masses.

Average Precipitation Over a Watershed

To determine the average precipitation over a watershed or a specific area, records from rainfall stations are used.

Averaging Method

This method consists of determining the average rainfall as the arithmetic mean of the records from stations within a watershed. This method is suitable if the rainfall recording stations are evenly distributed in space.

Method of Isohyets

With the precipitation records from the basin, isohyets (lines of equal precipitation) are drawn. The isohyets divide the total catchment area "A" into sub-areas Ai. Each area can be assigned a precipitation value (pi) equal to the average of the isohyets bounding it.

Thiessen Polygon Method

Lines are drawn between the stations, forming triangles. Each vertex of a triangle must have a station.

To divide the basin area into areas of influence for each station, the bisectors of the triangle sides are used. This divides the basin area into "n" areas, corresponding to the "n" stations that affect the watershed.

Artificial Rain

Creating artificial rain at one point on land would increase evaporation proportionally at another point, followed by a redistribution process to maintain balance.

• Initial Nuclei Contribution

  This involves incorporating basic nuclei into the clouds. These nuclei cause the integration of smaller droplets to form larger ones.

• Artificial Nucleation

  This method involves spreading substances among the clouds that cause the formation of nuclei by cooling the environment, resulting in ice crystals. These substances can be silver iodide or carbon dioxide (dry ice).

• Droplet Integration

  This method adds water to the clouds to increase their mass (q), causing them to fall due to gravity. This is achieved by dispersing water into the clouds from aircraft, often called "cloud seeding."