Blood rain, a term that conjures up images of fairy tales and legends, is actually a fascinating and entirely natural meteorological phenomenon. Contrary to what its name might suggest, it has nothing to do with actual blood, but refers to precipitation that takes on a red, ochre or orange hue. This effect is the result of the presence of dust or sand particles in the atmosphere, which, when mixed with the rain, alter its usual colouring.

Scientific basis of blood rain

Blood rain is an impressive example of the natural phenomena that occur on Earth. Far from being an ominous omen, it represents a manifestation of complex atmospheric processes and the interaction between different components of the Earth system. Understanding these events not only enriches our scientific knowledge but also allows us to appreciate the majesty of nature around us.

“THE ORIGIN OF THE BLOOD RAIN IS FOUND IN THE LIFTING OF DUST AND SAND PARTICLES BY THE ACTION OF WINDS”.

These particles can be transported through the atmosphere over long distances, from desert regions to areas where precipitation develops. When rain falls, it carries these particles with it to the ground, resulting in rain with reddish hues.

The transport of these particles is influenced by advection, i.e. the horizontal movement of air, and is closely linked to global atmospheric circulation patterns. The main components of these particles are iron oxides, which give the characteristic colouring to this type of rain.

Do “red rain” and “red snow” have the same origin?

As explained above, blood rain occurs when dust and sand particles are lifted by winds from surfaces such as deserts and transported through the atmosphere over long distances. When these particles mix with raindrops, they can give the precipitation a reddish, ochre, or orange colouration. The specific colouration depends on the mineral composition of the particles, with iron oxides being a common contributor to the reddish colour.

Red snow, on the other hand, is a type of snow that can be caused by similar reasons to blood rain, such as the presence of reddish dust and sand in the snow. However, a distinctive and frequent phenomenon behind red snow is the proliferation of specific algae, such as Chlamydomonas nivalis. These algae are unique adaptations to the cold environment and can bloom on snow under certain conditions, such as the presence of sunlight and relatively moderate temperatures within the cold range. The algae contain carotenoids, which give them a red or pink colouring, and when they multiply on the surface of the snow, they give it a characteristic reddish hue.

“IN BOTH CASES THE ALTERATION OF THE COLOUR IS DUE TO THE ADDITION OF EXTERNAL MATERIALS TO THE NATURAL PRECIPITATION”.

The relationship between these phenomena lies in the colouring mechanism of the precipitation, although the sources of the particles causing the colouring differ. In both cases, the alteration of the colour is due to the addition of external materials to the natural precipitation, be it windblown inorganic particles in the case of blood rain, or the proliferation of living organisms in the case of red snow.

In addition, both phenomena highlight the interaction between biological and geological systems and how environmental factors, such as wind, temperature and sunlight, can influence natural cycles and the occurrence of unusual natural events. These events also serve as indicators of ongoing ecological and climatic processes, offering unique insights into the dynamics of the Earth and the impact of environmental conditions on natural ecosystems.

Historical and recent examples

Blood rain has historically fascinated and puzzled observers around the world. This phenomenon, which results from the mixing of dust and sand particles in the atmosphere with rain, has been documented at various times and places, demonstrating its global reach and the diversity of its causes. The following are historical and recent examples that illustrate the occurrence of this phenomenon:

Kerala, India (1896): One of the first scientifically documented records of blood rain occurred in Kerala, India. This event intrigued scientists at the time, who initially could not explain the red colouring of the rainfall. Later studies suggested that the cause was the transport of dust particles from the desert.

But we also have recent examples that have stained different areas of the planet red in the 20th and 21st centuries, such as in Spain, the United Kingdom, Italy and Australia.

  • Europe (1901): In the early 20th century, several countries in Europe experienced reddish rainfall due to the presence of Saharan dust in the atmosphere. This event helped to better understand patterns of air mass movement and long-range particle transport.
  • Spain (2014): Spain has witnessed several episodes of blood rain, notably in 2014, when a significant amount of Saharan dust was transported towards Europe, staining rainfall red in several regions of the country.
  • Wales, United Kingdom (2016): In 2016, parts of Wales experienced blood rain, a phenomenon that surprised residents. Meteorological research linked this event to sandstorms in the Sahara, whose dust particles were blown northwards across the Atlantic.
  • Italy (2020): In March 2020, some regions of Italy witnessed orange-reddish rainfall due to a combination of precipitation and Saharan dust. This phenomenon not only changed the colour of the rain but also left dust deposits on vehicles, windows and streets.
  • Australia (2021): Australia, although far from the Sahara, has experienced similar phenomena, especially in areas prone to dust storms. In 2021, a combination of local drought and dust storms resulted in blood rain in several parts of the south-eastern part of the country.

These examples underscore the global nature of the blood rain phenomenon and highlight the importance of atmospheric and geographic conditions in its occurrence. Blood rain serves as a reminder of the complex natural processes that can have striking visual effects and of the interconnectivity of weather and climate systems on a planetary scale.

What is “blood rain” also called?

Blood rain” is also known under several other terms and is related to similar atmospheric phenomena involving the alteration of the natural colour of rain or visual phenomena in the sky. These terms and situations reflect the diversity of causes and visual effects related to particular atmospheric conditions. Some of these terms and phenomena include:

  • Red Rain: A more descriptive term that refers directly to the colour observed in precipitation.
  • Coloured Rain: A generic expression that can encompass not only red but also other unusual rain colourations.
  • Dust Precipitation: Although this term does not specify colour, it is closely related to the phenomenon in describing precipitation mixed with dust or sand particles.

Other atmospheric phenomena similar to blood rain

In addition to natural phenomena such as dust storms and volcanic eruptions, human activities such as fossil fuel burning, forest fires and industry can contribute to the occurrence of unusually coloured precipitation. The scattering of light by particles of different sizes and compositions can alter the perception of atmospheric colour and associated visual phenomena.

  • Yellow or Golden Rain: Sometimes dust particles present in the atmosphere can give rain a yellow or golden hue, especially when the dust comes from arid regions with a high concentration of minerals of this colour.
  • Coloured Mists: Fine particles in the atmosphere can also cause the formation of mists with unusual hues, such as reds, yellows or oranges, especially during sunrise or sunset, when sunlight is scattered differently.
  • Volcanic Ash in Rain: Erupting volcanoes can release large amounts of ash into the atmosphere, which, when mixed with rain, can result in greyish or black precipitation. This phenomenon is similar to blood rain in terms of the mixing of solid particles with precipitation.
  • Black Rain: Specifically associated with falling precipitation mixed with soot, ash from forest fires or industrial pollutants, resulting in a dark coloured rain.

These terms and phenomena underline the complexity of the interaction between the Earth’s atmosphere and the various natural and anthropogenic factors that can influence the appearance of rain and other atmospheric events. The observation and study of these events are not only of interest to meteorology and atmospheric science but also have implications for the understanding of global environmental and climate change.