Drought is defined by how exceptional it is: For a dry period to be classified as a drought, it must be drier than the norm for a given place. Drought can result from a low supply of precipitation (less rain and snow) as well as high demand for moisture like high evaporation due to high temperatures. 

A year-plus drought (12 or more months) is an extended dry period, long enough to affect surface water flows and groundwater in most places. A longer drought is harder to recover from than a shorter drought: It takes more time for the region to exit the drought and return to the local norm. Because water sources are more heavily impacted by year-plus drought conditions, this drought length carries greater implications for growing seasons for crops, ecosystems, and soil moisture. 
Drought patterns are changing in Chiapas, Mexico, where rain-fed agriculture supports over half the population.

Chiapas at 0.5°C of warming

Climate zone: tropical and temperate

Population: 5.5 million (2020)

Risk factors: drought, heat, wildfire

The 74,000 square kilometer southernmost state in Mexico borders Guatemala to the south and the Pacific Ocean to the southwest. Chiapas contains distinct geography: plains, mountains, valleys, highlands, and coastal lands.

Weather in Chiapas was generally humid and mild with consistent precipitation. In the north of the state, rain was plentiful, with slightly drier conditions closer to the ocean. Across the whole state, rainfall was predictable enough that a large part of the population in Chiapas came to rely on rain-fed crops like corn, beans, bananas, coffee, and cacao for economic subsistence. Today, Chiapas supplies 30% of Mexico’s water needs through rainfall and surface waters.

At 0.5°C of warming, year-plus drought likelihood across Chiapas varied between 21% and 25% in the average year. Drought occurred, at most, about once in four years.

Today, 96% of agricultural fields in Chiapas rely only on rainfall for cultivation, and over half the state’s population is employed in agriculture, livestock, forestry, and fishing. Over one million of Chiapas’s large indigenous population continue to live as subsistence farmers. The agriculture that defines and supports this region relies on steady precipitation. 

As the climate warms, the frequency of droughts, including long droughts, is increasing, even in places accustomed to regular rainfall like Chiapas. 

Chiapas at 1°C and beyond

Between 1971 and 2000, Earth’s global average temperature was 0.5°C above the pre industrial average. More recently, we’ve moved past 1°C, so we use 1°C of warming as a proxy for the weather that we’re used to—the recent past. 

From 0.5°C to 1°C of warming a new trend appeared in Chiapas: The grid cell colors show that the mountainous highland region running parallel to the coast transitioned from experiencing 11-33% likelihood of year-plus drought to experiencing 34-50% likelihood. The most severe risk of year-plus drought in Chiapas was in this highland region, where likelihood reached as high as 41%. The rest of Chiapas was mostly still experiencing between a 20% and 30% likelihood of year-plus drought (about once in four years).

The next warming threshold, 1.5°C, is impending (and the closest to the climate in 2024.) 2°C of warming is a potential future scenario. 

At 1.5°C, almost all of Chiapas experiences a 34-50% likelihood of year-plus drought. In the central highlands, one selected grid cell shows an annual likelihood of year-plus drought of 48%, while another has transitioned into a new bracket of likelihood at 52%. In this warming scenario, year-plus drought happens about half the time in and around the selected cells, or about once in two years.

At 2°C, a selected grid cell in the central highlands can anticipate a 55% annual likelihood of year-plus drought. The whole highland mountainous region is still experiencing higher drought likelihood than the rest of the state, as high as 59% in some places. This suggests that in this area at 2°C of warming, year-plus drought is more likely than not. For the rest of Chiapas, the likelihood still sits in the 34-50% range.

2.5°C and 3°C of warming are potential but avoidable, depending on the pace and scale of human greenhouse gas emissions. 

2.5°C and 3°C of warming are potential but avoidable, depending on the pace and scale of human greenhouse gas emissions.

At 2.5°C of warming, grid cells in the central highland region show likelihood of year-plus drought as high as 68%. Coastal Chiapas still contains grid cells with a likelihood of year-plus drought between 30% and 40%, but the rest of the state experiences drought about half the time or more. 

At 3°C of warming, annual likelihood of year-plus drought in the central highland region can be as high as 75% (about once every 18 months)— a tremendous jump from the approximately 25% likelihood seen across the state in a historic climate. At 3°C, Chiapas is projected to be in year-plus drought most of the time. Almost all grid cells contain likelihoods approaching or surpassing 50%, and some can only expect a drought-free year a quarter of the time. These numbers seem staggering, especially compared with the recent past or even present-day conditions. With drought likelihood this high, it’s probable that Chiapas as a region will undergo aridification—the long-term transition into permanent dryness.  

Because 2.5°C and 3°C are more distant thresholds of warming, these projections give us an impression of what we need to avoid. Data like this can be as much a tool for anticipating risk as motivation to avoid harmful outcomes by slowing and stopping warming. 

What could a year-plus drought mean for Chiapas? 

Chiapas’s unique geography and economy are important to assessing year-plus drought risk. Thinking about drought likelihood in combination with Chiapas’s vulnerabilities is the first step to understanding its risks and making informed decisions about the future. 

Here are a few guiding questions to start considering drought risk in Chiapas:  

• 96% of agricultural fields in Chiapas are rain-fed, and over half the population works in agriculture, livestock, fishing or forestry. What preparations do stakeholders in these industries need to make to prepare local systems for a future in which a year of drought is more likely than not?
• Some crops grown in Chiapas, like coffee and cacao, demand large amounts of water to grow and cultivate. What techniques could local farmers use to help make their crops and fields more drought-resistant?
• Drought’s impact on agriculture includes reduced regional production and economic income, increased food prices, increased unemployment, and subsequent migration. In the region containing Chiapas, lower crop yields and higher food insecurity were identified as drivers of migration. What might happen to economic opportunity and migration trends when year-plus drought likelihood increases?
• An estimated 14% of global rain-fed cropland was affected by drought between March and August 2022, representing $6 billion of production value. What might the national and international impact be if a breadbasket region like Chiapas experiences regular, extended drought in the future?
• Beyond its borders, Chiapas supplies 30% of Mexico’s water needs through rainfall and surface waters. What knock-on effects of drought in Chiapas might be felt throughout the country?

Examining the range of possible outcomes for a climate impact in a place, putting that data in context, and looking for vulnerabilities is a framework you can apply to any place with any Probable Futures map. We offer maps of 30+ climate variables at warming scenarios ranging from 0.5 to 3°C of warming. We invite you to explore and think about what climate impacts could mean in the places you care about.