Mapping the Unequal Distribution of Global Precipitation

On average, nearly one meter (39 inches) of rain or snow falls on the Earth in a year. However, differences in latitude, winds, changes in the Earth’s surface, and the planet’s tilt, make for an unequal distribution of global precipitation.

Cartographer Perrin Remonté uses data from Chelsea Climate to visualize this by splitting the world in two. One half, in blue, receives more than one meter of rain (or snow) in a year, the other half receives less.

What Affects Global Precipitation Patterns?

From the water cycle we know that precipitation starts with evaporation. However, moist air needs to cool and then condense to come down as rain (or snow). Below we list some major factors influencing precipitation.

• Proximity to water: Oceans and lakes provide a constant source of moisture.
• Lower latitudes: Areas at, or close to the equator, are hotter and this can increase evaporation from nearby water bodies.
• Topography: Mountain ranges, especially along coasts, force warm air to rise and cool, resulting in rain or snow on the windward side and dry rain shadows on the lee side.
• Trade winds: Persistent, easterly surface winds blow from subtropical high-pressure areas toward the equator, carrying moist air from the ocean to the land.

So, how do these factors interact to form the global precipitation map visualized above?

Ranked: Countries Which Receive Highest Rain or Snow

A quick look at the map reveals some obvious insights. For one, most of the Earth that receives above average rainfall is covered by oceans. After all, oceans are 71% of the Earth’s surface, but, crucially, they provide the moisture for precipitation to occur.

Over landmasses, we see more complex interaction between earlier listed factors. Here’s the average rainfall received by each country in 2020, sourced from the World Bank.

At the top of the list Colombia experienced 3,240 millimeters (125.8 inches) of rain in 2020. This is due to its equatorial location, proximity to the Intertropical Convergence Zone (where trade winds from both hemispheres meet), two coastlines, and the presence of the Andes mountain range.

In fact, the next 22 ranks are countries that lie at or near the equator or have significant coastlines that lead to higher than average rainfall.

Bhutan, ranked 24th with 2,200 mm (86.6 inches) of rain is the first completely landlocked country in the dataset. Despite this, the country is on the path of the southwest monsoon (a seasonal wind laden with moisture) originating in the Indian Ocean, which encounters the windward side of Himalayas, causing rainfall.

In many countries like India, China, and the U.S., the coasts receive above average rainfall compared to the landlocked regions inside the countries.

However, countries in North Africa, like Egypt and Libya, are arid despite their coasts. High-pressure weather systems prevent moist air from rising, mountains cause rain shadows, and cold ocean currents reduce the chance of steady evaporation. Additionally, the region is in the 30 degree latitude band around the equator where atmospheric conditions cause drier conditions, leading to deserts.

What Does Mapping Global Precipitation Tell Us?

Knowing rain and snow patterns is critical for scientists studying the Earth’s climate system, as it reveals the impact of factors like geography, topography, and ocean currents on local climes.

It also aids in short-term weather forecasting, predicting when and where rain or snow may occur.

Practically, this data helps in water management, monitoring drought and flood conditions, enabling quick responses to extreme weather events.

This article was published as a part of Visual Capitalist's Creator Program, which features data-driven visuals from some of our favorite Creators around the world.