Rain­fall for agri­cul­ture 

Rain is agriculture’s most impor­tant source of water. This info­graphic presents surprising facts about precip­i­ta­tion and its impor­tance for crops and soils.

October 2026

Text: Annina Werths
Illustration: Gernot Walter, Emese Györffy
Photos: Adobe Stock / Great Brut Here

It’s getting wet

The Earth’s total annual precip­i­ta­tion is equiv­a­lent to approx­i­mately 

circa

0

cubic kilo­me­tres

of water falling across all oceans and land areas.

That is around

0

quadrillion litres of water 


This water is contin­u­ally redis­trib­uted through evap­o­ra­tion, precip­i­ta­tion and runoff.

Source: USGS – The Water Cycle

Where does the water fall?

Most water falls into the sea, but the sea also supplies rain.

Rain falls on the

conti­nents

Rain falls into the

oceans

Around

86%

of global evap­o­ra­tion occurs over the oceans. Some of this water vapour is trans­ported over land through the atmos­phere, where it falls as precip­i­ta­tion. 

Source: USGS – The Water Cycle

How much is 1mm of rain?

1mm of rain
=

1 litre of water 
per square metre. 

1,000,000 litres of water 
over 100ha. 

Gaseus

Water vapour remains for up to   

0 days

in the atmos­phere before turning into rain.

Source: NASA Earth Obser­va­tory – The Water Cycle

A rain­drop is a giant among cloud droplets

While a typical cloud droplet is only around 20 microme­tres in diam­eter, rain­drops can reach several millime­tres. For the tiny, suspended droplets to become rain, they must grow within the cloud and merge through colli­sions.

A long way down

500m

from rain clouds

15km

from thun­der­clouds

Before a rain­drop reaches a field, it has fallen at least 500m and not more than 15km

Source: World Mete­o­ro­log­ical Oraniza­tion (WMO)

Speed

approx 30km/h

is the falling speed.

That is

8–10m

per second, meaning that from a height of 2,000m, the fall takes around four minutes. 

Source: NASA Mission Measuring Rain­fall

Shape

In reality, a rain­drop does not look like a teardrop. As it falls, air resis­tance flat­tens its under­side – almost like a tiny bread roll. A large rain­drop in heavy rain can resemble a para­chute.

1–2mm

drizzle

2–5mm

light to moderate rain

5–7mm

heavy rain

7–9mm

very heavy rain

Steady rain

Slow, steady rain is consid­ered partic­u­larly valu­able in agri­cul­ture because the water can seep deep into the soil instead of running off at the surface. This provides a lasting supply of water for plants, soil life and ground­water.

Soil cover

Cover crops and crop residues inter­cept rain­drops before they strike the soil with full force. This protects soil aggre­gates from breaking down and reduces erosion and surface crusting. The protec­tive cover also slows evap­o­ra­tion.

Source: NRCS – Soil Health

Soil

Soil is a natural water reser­voir. Every soil has a sequence of layers that store water to varying degrees. 

Topsoil

Depth: 5–40cm
humus and minerals 

Subsoil

Depth: 50–150cm
weath­ered rock and substances leached from the topsoil

Ground­water

Some rain­drops seep only a few metres into the ground, while others travel through soil layers for decades before being stored as ground­water.

The right amount for every crop

When rain fails, fields suffer from drought. When it is too heavy, it washes away nutri­ents and damages soil struc­ture. The ideal amount of rain­fall depends on the crop, its growth stage, the soil type, temper­a­ture, evap­o­ra­tion and the time of year. 

From water-effi­cient to water-inten­sive crops

Onions

Seasonal water require­ment:

500–700mm

Char­ac­ter­is­tics:

Their water require­ment is surpris­ingly low, although their shallow root system makes onions sensi­tive to water short­ages and means they need a consis­tent water supply.

Sorghum / millet

Seasonal water require­ment:

450–650mm

Char­ac­ter­is­tics:

Highly drought-tolerant.

Pota­toes

Seasonal water require­ment:

500–700mm

Char­ac­ter­is­tics:

Partic­u­larly sensi­tive to water short­ages during tuber forma­tion and growth.

Maize

Seasonal water require­ment:

500–800mm

Char­ac­ter­is­tics:

The crit­ical period is around flow­ering and grain forma­tion. Drought stress at this stage can have a partic­u­larly severe impact on yield.

Sugar cane

Seasonal water require­ment:

1,500–1,700mm

Char­ac­ter­is­tics:

The long growing season and enor­mous biomass produc­tion result in a corre­spond­ingly high water require­ment.

Source: FAO-Daten­bank Crop Water Infor­ma­tion

Which are the wettest and driest places in the world? 

Wettest place

Driest place

Mawsynram in India

11,870mm

rain­fall per year

In Mawsynram, the long-term average rain­fall is around 11,870 litres per square metre.  

This is due to its loca­tion: Moist monsoon air from the Bay of Bengal meets the Khasi Hills, rises, cools and releases its mois­ture as rain. 

Atacama Desert in Chile

1–3mm

rain­fall per year

In parts of the Atacama Desert, long-term average annual rain­fall is between 1 and 3mm. 

Source: NASA Earth Obser­va­tory