El Niño has arrived, and its impacts will be felt at least until the end of the year. Once again, Southeast Asia is haunted by the threat of drought. However, a number of studies show that other factors are also at play.
Why does Southeast Asia need to stay alert?
“Southeast Asia’s agricultural sector is exceptionally vulnerable to a new El Niño shock, given that its two primary commodities, rice and palm oil, are highly concentrated and uniquely sensitive to climate anomalies,” Jason Lee, chair of the Global Heat Health Information Network’s Southeast Asia Hub, told Deutsche Welle. “This extreme exposure means that what begins as a localized, farm-level shock can rapidly spill over into a broader, systemic food-price and inflation crisis across the region.”
According to SEARCA (Southeast Asian Regional Center for Graduate Study and Research in Agriculture), in Southeast Asia, drought can appear in rice fields, upland farms, orchards, livestock areas, aquaculture ponds, and river deltas.
Historically, Southeast Asia has been quite vulnerable to drought. This was highlighted by a research team led by Tuyen V. Ha, a scientist at the German Remote Sensing Data Center, German Aerospace Center, Wessling.
“Mainland Southeast Asia is a major rainfed crop-producing area of the world, and this region is increasingly vulnerable to drought hazards,” Ha’s team stated in their study published in the International Journal of Applied Earth Observation and Geoinformation.
Droughts in this region, when they occur, pose a direct threat to at least 190–200 million people working in the agricultural sector across Southeast Asia. That figure does not include hundreds of millions of others who rely on the agricultural yield produced on those affected lands.
Ha’s team explained that drought is a recurring, slow-onset hazard with severe impacts on agricultural production and ecosystem health. “However, the monitoring and characterization of agricultural and vegetative droughts in this region remains understudied,” they explained.
To address this gap, the researchers analyzed 22 years (2000–2021) of satellite data (MODIS) to assess crop health and map drought patterns across Southeast Asia.
Their main finding was that drought patterns vary significantly by region.
Central Myanmar was the most frequently affected region (nearly 60% of the study period), though droughts there were typically short-lived. Meanwhile, in the Lower Mekong region, droughts were not only frequent but also lasted much longer. Cambodia has been the most severely impacted by drought in recent years, with its land progressively drying out.
Ha’s team noted that severe regional drought years occurred in 2000, 2004, 2005, 2010, 2016, 2019, and 2020—primarily affecting Central Myanmar, Thailand, and Cambodia.
Drought patterns have also shifted spatially. In the 2010s, severe droughts were concentrated in northern areas (such as Central Myanmar). More recently, the most impacted epicenter has shifted southward to the Lower Mekong region (Cambodia and surrounding areas).
Historically, drought episodes in Southeast Asia have correlated directly with El Niño. However, observing the findings of Ha’s team, this shift in Southeast Asian drought patterns appears to be influenced by other large-scale climate drivers.
Connection to extreme rainfall in Central Asia
In much of Asia, the impacts of climate change are felt through an increase in extreme weather events, particularly those related to water. In mainland Southeast Asia, droughts are becoming more common, while periods of extreme rainfall are on the rise in Central Asia.
Na Wang and Sylvia Dee from the Department of Earth, Environmental and Planetary Sciences at Rice University in Houston—along with two colleagues from other universities—were interested in understanding whether these two geographically distant weather extremes were linked. Their findings were published in Nature Geoscience.
“We wanted to know if the increase in both droughts and extreme precipitation were happening independent of one another, or if they were being driven by the same large-scale climate factors,” said Dee, an associate professor of Earth, environmental and planetary sciences and senior author on the study, as quoted by Rachel Leeson in a Rice University press release. “Understanding patterns in these climate extremes can help affected communities build climate resiliency and prepare for water-related disasters.”
To do so, the research team—which also included Jun Hu (College of Ocean and Earth Sciences, Xiamen University, Xiamen) and Kaustubh Thirumalai (Department of Geosciences, University of Arizona, Tucson)—needed to look far back into the region’s climate history, much further than recorded weather data could provide.
So, the researchers turned to paleoclimate records, datasets created by natural resources such as tree rings, sediment, and ice cores that preserve evidence of past weather patterns. For instance, variations in tree-ring width can reveal which years in a tree’s life were drier or wetter.
Sediment layers, extracted from places like lake beds or salt marshes, provide other clues: darker layers indicate wetter periods, while lighter layers point to dry spells.
Spanning two millennia
By carefully analyzing and integrating these various natural records, scientists were able to reconstruct weather patterns going back thousands of years.
“We used paleoclimate records gathered together for the region to reconstruct historic moisture patterns in mainland Southeast and Central Asia going back thousands of years,” said Wang, a Rice alumnus and lead author of the study.
“Then we used climate model simulations to look at the mechanisms driving simultaneous precipitation and drought extremes, investigating potential physical pathways that could be linking them,” Wang added.
The models showed that concurrent droughts and extreme rainfall events have occurred across mainland Southeast Asia and Central Asia over the last two thousand years. This means, Wang explained, that even though drought and extreme rainfall are diametrically opposed events, they are linked to one another by large-scale climate patterns.
The research team then compared modern periods of drought and high rainfall with historical records. While periods of drought and heavy precipitation have always been a regular feature of the region’s climate, the researchers found that the frequency of these events has increased significantly in recent times.
“If we look at the recent drought record in mainland Southeast Asia, what stands out is not only that these are among the most extreme droughts of the past millennium, but also that droughts are occurring much more frequently,” Wang said. “We also now know that this high drought frequency is linked to increased periods of precipitation in Central Asia.”
An evolving system
According to Wang, model projections indicate that under future warming scenarios, the relationship between these hydroclimate extremes in both regions will not only persist, but the frequency of short-term extreme events is expected to increase.
Extreme hydroclimate events, such as droughts or heavy rainfall periods, often have the greatest impact on surrounding ecosystems and communities. An increased frequency of these events, regardless of their severity, can have drastic impacts.
“These results highlight the importance of understanding extreme weather and climate change as an evolving system, rather than focusing on isolated events,” Dee said. “In order to understand, respond to and predict climate change, we have to first understand the climate system’s baseline state using its past as prologue for future risks.”
Physical drivers and future risks
Scientists have recently shifted paradigms, moving from a simple deterministic approach to a complex systemic one. Another research team demonstrated that the above findings hold true: drought in Southeast Asia does not depend on just one or two variables.
“Conventional wisdom suggests that tropical droughts in Southeast Asia are closely linked to natural climate variability like El Niño. However, the extreme 2014 drought occurred independently of El Niño, suggesting other dynamic forcings at play,” noted a team led by Shuping Ma (Department of Civil and Environmental Engineering, National University of Singapore, Singapore) in their study published in Earth’s Future.
In early 2014, Southeast Asia experienced extreme drought. In response, Ma’s team explored the complex interplay between dynamic and thermodynamic processes in drought formation.
Using a different lens and methodology from Wang and Dee, Ma’s team demonstrated that El Niño—often viewed as the primary “specter” behind Southeast Asian droughts—is not the sole factor. Extreme droughts (such as in 2014) can occur even in the absence of El Niño.
“We find that the 2014 drought primarily resulted from air subsidence due to anticyclone-driven mid-troposphere divergence, leading to significant precipitation deficits, which are further intensified by reduced marine moisture inflow from the West Pacific,” they wrote.
Ma’s team explained that by incorporating dynamic and thermodynamic drivers into a bivariate probabilistic framework, they found that the likelihood of a 2014-like drought will increase by 25% and 43% under stabilization and business-as-usual scenarios, respectively, by mid-century (2030–2064).
According to their findings, this increased drought risk is dominated by changes in dynamic processes triggered by climate change, specifically reduced mid-tropospheric vertical motion.
Meanwhile, the role of thermodynamic processes and their dependence structure was less significant.
However, Ma’s team highlighted that “significant inter-model inconsistence in attributing the relative importance of these factors highlights the challenges of using current climate models for robust risk assessment.”