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2.3 A tour of precipitation

Beginning in the 17th century, centers of wealth and power emerged in a narrow band of northern latitudes where mild weather put minimal stress on urban and industrial infrastructure. These societies were able to grow their local populations faster than the rest of the world and expand their reach, often by exploiting other lands and people.

By the 1950s, there were 2.5 billion people on Earth, and most lived in moderate climates. Since then, however, the distribution of the world’s population has shifted. We will pass 8 billion people in 2023, and the majority will live in places with more challenging climates. Climate change is reshaping both local precipitation patterns and the global water system—and everyone on Earth will be affected.

Stability and power.

Narrated by
  • Devika Bakshi

From the early 19th century to the early 20th century, the capital city of the small island nation of England reigned as the center of global power. Although it rained often and consistently in London, the volume of rain was minimal—just 5cm (2in) of rain per month. An umbrella and a trench coat, useful in a wet but ultimately mild climate, kept Londoners comfortably dry.

London, England

Climate Zone
Temperate No Dry Season Warm Summer
Coordinates
51.5°N
0.1°W
Population
8,961,989

London headed a formal colonial empire that stretched beyond the isle’s borders and an informal one that was even broader. The British navy, banks, and insurance companies dominated waterways, financial flows, and insurance markets around the world. The trench coats associated with British life became an expression of wealth and control.

Change in frequency of historic “1-in-100-year” storm

London, England

This chart depicts changes in the expected frequency of the historical “1-in-100-year” one-day precipitation event (1% probability of occurring in any given year) as the atmosphere warms. Circles indicate averages, and bars indicate a range of estimates from different models. For example, at 1.5°C of warming, climate models project that the historic 1% storm will occur 2.5 times more frequently, on average. The bar at 3°C indicates a range of potential frequencies from less than 3 times as frequent to more than 11 times as frequent.

Our warming climate is beginning to upset the predictability of British life. Erratic summers and unexpected storms are inundating towns along rivers and coasts, creating flooding risks that didn’t exist before. Insurance companies typically offer policies to compensate people who suffer a 1-in-100-year storm, but frequent intrusions of water into buildings are dismissed by the industry as uninsurable “nuisance flooding.” It’s unlikely that residents who have had to evacuate their ground floor apartments, or constantly de-mold their basements, consider it simply a “nuisance.” In the increasingly flood-prone capital of insurance, few homes or businesses have policies, and many who now want them are turned down, forcing people to question what once felt like easy assumptions of predictability.

Living with the monsoon.

In the Indian state of Punjab, the extreme but historically predictable patterns of the summer monsoon shape local life and are essential to the region’s agricultural practices, dropping about 79% of the state’s annual rainfall between June and September.Although it has never been easy for farmers to cope with the power of the monsoon’s heavy seasonal rains, over centuries, farmers figured out what, how, and when to plant based on the monsoon’s patterns. They were so successful that Punjab is known as the “breadbasket of India.”

Punjab, India

Climate Zone
Arid Steppe Hot
Temperate Dry Winter Hot Summer
Coordinates
29.5°N to 32.5°N
73.9°E to 76.8°E
Population
27 million (2011)

However, as the climate warms, both the monsoon and the dry seasons are changing. In Punjab monsoon rainfall has declined over the last two decades, and a longer and hotter dry season parches crops and dries out the irrigation canals that make agriculture possible in the region. While canals run dry in Punjab, regions like coastal Maharashtra have experienced more intense monsoon rainfall, breaking daily records in the summer of 2021 with increases of up to 900% above the long-term average. In Punjab’s neighboring state of Rajasthan, monsoon rains have both decreased and increased on a district-by-district basis within the single state.

Opposing trends in such closely neighboring regions show what climate science has already projected: the monsoon will become less consistent and predictable across India. Half of all Indian workers are in agriculture, and rainfall problems often fall on desperate farmers who have little in the way of support. This country was already dominated by an extreme climate, but it was previously more consistent. What will this uncertainty bring for a now-massive population fighting to feed itself?

Punjab average monthly rainfall (mm), 1981-2009

Ludhiana airport

The above chart shows average monthly rainfall recorded between 1981 and 2009 at the Ludhiana airport in Punjab, India. The summer monsoon season created the spike in rainfall quantities seen between June and September.

Perhaps most concerning is not the amount of monsoon rainfall but its timing. The monsoon now often starts later, is interrupted by dry spells, and can continue into what used to be the dry season. Temporal uncertainty is likely to increase, making crop cycles of planting, germination, maturation, and harvest even harder to plan. These challenges come with great consequence in a country already home to 189 million people who are undernourished, or 14% of India’s total population. As in other parts of the world, the distress of crop failures in Punjab has caused people to migrate into already-crowded cities, seeking work, food, and government assistance.

Megacities in challenging climates.

On the banks of the Congo River, southwest of the rainforest, lies Kinshasa, the capital of the Democratic Republic of Congo (DRC). Kinshasa sits in what is classified by scientists as a Tropical Wet and Dry climate, which has distinct rainy and dry seasons. The city typically receives little rainfall in June, July, and August, but is soaked with rain the rest of the year.

Kinshasa, Democratic Republic of Congo

Climate Zone
Tropical Wet and Dry
Coordinates
4.3°S,
15.3°E
Population
17.07 Million

In the last 50 years, places like these have changed significantly. What were once exclusively rural settings are now home to some of the world’s largest cities.

Giant metropolises in hot climates with extremes of precipitation are a new phenomenon unique to the 20th and 21st centuries. Residents are increasingly concentrated, often in fragile and insecure dwellings, as those found in slums, which face great peril when rainfall increases in frequency or severity.Millions of Kinshasans were already living precariously, but as increasingly heavy rains wash out entire neighborhoods and overwhelm sanitation systems, they are at greater risk of becoming homeless and affected by the spread of infection and disease.

Change in precipitation “1-in-100-year” storm

Change in precipitation (mm)
  • < -1
  • -1 - +11
  • +12 - +24
  • +25 - +50
  • > +50

This map of Kinshasa depicts how precipitation amounts from the “1-in-100-year” one-day precipitation event (i.e., 1% chance storm annually) will change in a warming world. Both the 1°C and 3°C warming scenario maps show change in precipitation amounts relative to the historical 0.5°C baseline.

Natural cycles and industrial farming.

Some of the most valuable farmland in the world is in the center of the United States. The state of Iowa, named for the indigeneous Ioway people who thrived on this land, is now a nearly continuous field of gridded farmland.

Iowa, United States

Climate Zone
Temperate Dry Winter Hot Summer
Coordinates
40.4° N to 43.5° N
90.1° W to 96.6°W
Population
3.2 Million

Year after year, cold winters gradually yielded to spring showers. The melting of winter snow and April rainfall would moisten the soil in time for planting. May rains would help germination. June was typically the wettest month with about 13cm (5in) of rainfall, after which rain clouds gradually gave way to sunshine. Corn and soybean plants spread their leaves and the summer grew hot. Iowan farmers did not need to develop irrigation, as the skies tended to deliver the water they needed. Capitalizing on the precision of this weather, corporate agriculture transformed the landscape with industrial farming methods into a massive, factory-like agricultural complex.

Recently, Iowa’s natural water schedule has started to lose its reliability, suffering from long dry spells and flooding events, with consequences both in Iowa and far away. Unusually warm springs rapidly melt snow that feeds the Des Moines, Cedar, and Mississippi Rivers which race through the state. These spring waters are frequently joined by “unseasonable” local rainfall. Later in the summer and fall, big storms increasingly contain far more water than in the past.

This results in deluges that are flooding large areas that have little drainage, in some years leaving thousands of square kilometers of farms and towns underwater for weeks or months at a time. Floods also carry vast quantities of fertilizer, pesticides, topsoil, and farm animal waste down the Mississippi River, contributing to fish and waterfowl die-offs in the Mississippi River system and a growing dead zone in the Gulf of Mexico.

Water in a warming world

Changes in the global water system are fundamentally caused by a warming atmosphere. Think of the earth’s warming trajectory like a freight train that, with great effort on our part, can be slowed. We know it is headed in one direction. In many ways, we laid the track. The farther that train travels, the more unpredictable our water patterns become.

The patterns that served as the bedrock of human civilization are already beginning to change, giving us a preview of what could be our future. Historically mild places like England and Western Europe are experiencing unprecedented bouts of dangerous heat and deadly flooding. In poorer countries with historically challenging climates, these changes are “threat multipliers,” straining already weak physical and social systems.In the face of untenable conditions, how many of us will have to abandon the town, city, country, or continent we’ve called home? Do our societies have the necessary structures to cope with this kind of disruption?

To prepare for the future, we’re going to have to challenge ourselves to think differently about society, its borders, its institutions, and its assumptions. We invite you to explore our maps of precipitation and imagine.

Explore our maps of precipitation

1

It is best to examine the impacts of climate change at increasing levels 
of warming, not by forecasting specific dates. Our maps offer “warming scenarios.”

2

With these warming scenarios, you can compare past, recent, impending, and potential climates.

3

Use your imagination, and what you already know about the world, to envision human, natural, and economic responses in each warming scenario.