FAQ: Climate change fuels rising heat and drought across India
Extreme weather events are becoming more common across the world, and India is feeling the heat—quite literally. Among the most concerning of these are concurrent droughts and heatwaves, which can have devastating effects on agriculture, water resources, and public health. When high temperatures and low rainfall happen at the same time, the impact on society is significantly worse than if they occurred separately. For example, wheat crop yields plummet when heat and drought coincide.
What are concurrent droughts and heatwaves?
Droughts and heatwaves on their own are bad enough, but when they strike together, the consequences can be even more severe. Droughts occur when there’s a prolonged shortage of rainfall, leading to water scarcity. Heatwaves, on the other hand, are periods of excessively high temperatures that can cause serious health risks and damage ecosystems. When these two events coincide and simultaneously create drought conditions across more than one region at a time, they are called concurrent droughts. With global temperatures rising, concurrent droughts and heatwaves are becoming more frequent and intense.
A study in Scientific Reports, Nature by Sharma and Majumdar analysed combined heat waves and droughts in India from May to October (1951-2010). They found, using a combined heat wave index, that 3-day heat waves increased in north-west, north-east, coastal, and South India but decreased in the Indo-Gangetic plains. Drought, measured by the Standardised Precipitation Index, expanded in Central India. The frequency of simultaneous heat waves and droughts rose between 1981 and 2010 compared to 1951-1980.
How do heat and drought interact to create more severe consequences?
The heightened concern surrounding concurrent heat and drought events stems from their synergistic impact, far exceeding the effects of individual extremes. Research indicates that the simultaneous occurrence of these conditions amplifies stress on multiple systems. For instance, agricultural yields, particularly of staple crops like wheat, experience substantial reductions due to the combined pressures of high temperatures and moisture deficit, disrupting food security.
Studies on compound climate extremes and agricultural impacts often feature these findings. Increased evapotranspiration rates driven by heat, coupled with diminished precipitation, lead to severe strain on water resources and potential shortages. Research (Manan Sharma et al) on hydrological impacts of compound events and climate change and water security highlights these issues.
Furthermore, public health is significantly compromised, with heightened risks of heatstroke and dehydration, particularly in vulnerable populations. Studies focusing on heat stress and public health and climate change and health impacts document these effects. The increased water scarcity can also elevate the risk of waterborne diseases, further compounding health challenges. Scientific investigations have shown that the interactive effects of heat and drought are not merely additive but often multiplicative, exacerbating each other's impacts and creating cascading consequences across ecological and socio-economic domains.
What are compound warm-dry spells, and why are they a concern for urban India?
Climate change is causing more frequent and widespread compound warm-dry spells, where extreme heat waves, low rainfall, and altered wind patterns occur together. Traditional risk assessments often focus on single factors like temperature or rainfall, missing the crucial interaction of these elements. A study by Ganguly examining meteorological records from 23 urban and peri-urban locations in India (1970-2018) reveals that compound warm-dry spells—simultaneous or successive occurrences of extreme heatwaves, low precipitation, and altered wind patterns—are increasing due to climate change.
This research shows that considering the combined effect of several factors dramatically increases the frequency of extreme events. What were previously considered 50-year severe heat events are now occurring every 5 to 17 years when the interdependence of temperature, precipitation, and wind is accounted for. This indicates a significant acceleration of warming-induced desiccation across India's urban areas.
While climate change and human activities have long been blamed for these extremes, recent research highlights another crucial factor: large-scale climate variability modes. These include El Niño Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), Indian Ocean Dipole (IOD), and North Atlantic Oscillation (NAO)—natural climate patterns that can set the stage for extreme weather events. Understanding how these systems work could help us improve early warning systems and better prepare for future crises.
But beyond the influence of climate change, researchers have found strong links between these extreme events and natural climate variability patterns. Understanding these relationships could help us forecast these events well in advance.
How do climate variability modes influence concurrent drought and heat waves?
To better predict and prepare for the amplified impacts of concurrent drought and heat waves in India, it is essential to examine how key climate variability modes, including ENSO, PDO, IOD, and NAO, individually and collectively influence the likelihood of these devastating events.
El Niño Southern Oscillation (ENSO): You’ve probably heard of El Niño, the warming phase of ENSO, which disrupts weather patterns around the world. In India, El Niño is notorious for weakening monsoons, leading to drought conditions. The study found that concurrent drought and heat waves are far more likely when El Niño precedes summer, particularly in northwestern, central, and southeastern India. On the other hand, La Niña, the cooler counterpart of El Niño, typically brings heavier rainfall, reducing the likelihood of concurrent drought and heat waves.
Pacific Decadal Oscillation (PDO): Unlike ENSO, which operates on short timescales, PDO is a long-term climate pattern influencing sea surface temperatures in the North Pacific Ocean. The research suggests that during the positive phase of PDO (when North Pacific waters are warmer), India experiences more drought-like conditions. While PDO doesn’t directly drive heatwaves, its impact on monsoon rainfall could make droughts more severe, increasing the potential for CDHWs.
Indian Ocean Dipole (IOD): IOD reflects temperature differences between the western and eastern Indian Ocean. A positive IOD tends to enhance monsoon rains, while a negative IOD leads to drier conditions. The study found that when a positive IOD occurs, concurrent drought and heat wave events become more frequent, particularly in western and northern India. This suggests that while positive IODs might bring some rain, they can also trigger erratic temperature fluctuations, contributing to heatwave formation.
North Atlantic Oscillation (NAO): While NAO primarily influences winter weather in Europe and North America, it also has an effect on India’s climate. A positive NAO phase, which strengthens westerly winds over the Atlantic, can lead to drier conditions in India before the monsoon, increasing the risk of concurrent drought and heat waves. The study found that this effect is particularly noticeable in the Himalayan region.
What did the study find?
To connect concurrent drought and heat waves with climate variability, researchers used wavelet coherence analysis and composite analysis based on climate data from 1951 to 2018. They measured drought severity using the standardised precipitation index (SPI) and tracked heat waves using the standardised heat index (SHI). The study also introduced an attribution table framework, a novel way to quantify the probability of concurrent drought and heat wave events based on preceding climate patterns.
Key findings
Strong relationship between climate variability and concurrent drought and heat waves - The study found a statistically significant correlation between concurrent drought and heat wave occurrences and climate variability modes. Among these, El Niño had the most significant impact, increasing the likelihood of concurrent drought and heat waves across multiple regions in India.
El Niño as a major driver — concurrent drought and heat wave events were most frequently observed following El Niño events, especially in northwestern, central, and southeastern India. The weakened monsoon and dry conditions caused by El Niño create ideal conditions for both drought and extreme heat to develop simultaneously.
Influence of other climate modes – While El Niño had the strongest effect, positive IOD and positive NAO phases also increased the probability of concurrent drought and heat waves. The study found that these climate patterns tend to create persistent dry and hot conditions across different regions of India, although their impacts varied spatially.
Lagged effects and seasonality – The research suggested that the timing of climate variability modes plays a critical role; concurrent drought and heat wave events were more likely to occur when these patterns were active in the preceding months, highlighting the importance of early detection and forecasting.
What does this mean for India?
Better early warning systems: At the moment, India doesn’t have a dedicated early warning system for concurrent drought and heat waves. Given the clear connection between concurrent drought and heat waves and climate variability modes, meteorologists and policymakers could use seasonal forecasts to anticipate extreme events and prepare accordingly.
Smarter agricultural and water management: Concurrent drought and heat waves are disastrous for agriculture and water resources. Farmers and policymakers must prioritise drought-resistant crops, improved irrigation techniques, and water conservation efforts to reduce their vulnerability to extreme weather.
More research needed: While this study makes important connections, some questions remain. For instance, the lag effects between droughts and heatwaves weren’t fully explored, and more research is needed to refine multi-variable climate models. Additionally, researchers should investigate how different climate indices interact, as some events may be driven by multiple overlapping factors.
Conclusion
India is on the front lines of compound extreme events, with concurrent droughts and heatwaves becoming more frequent and severe. This research provides valuable insights into how natural climate variability modes contribute to these extremes. Most importantly, it highlights the potential for using climate variability indices to improve seasonal forecasts and disaster preparedness.
As climate extremes intensify, integrating scientific research into policy decisions will be critical for building resilience. Understanding the role of natural climate cycles can help us develop better early warning systems, mitigate the impacts of concurrent drought and heat waves, and protect communities from the worst effects of extreme weather.