Compound drought and heatwave events, known in the literature as CDHEs, occur when drought conditions and heatwave episodes overlap in the same place at the same time. Scientists regard these combined extremes as far more damaging than either hazard alone, because dry soils amplify surface heating while heat accelerates moisture loss from vegetation and waterways. The twin stresses have been linked to crop failures, forest dieback, elevated mortality among people with respiratory conditions, strains on water supplies, and increased wildfire risk. In a rapidly warming world, understanding where and how often these overlapping extremes will strike has become a central question for climate adaptation planning.

To answer that question for the eastern Baltic, researchers Laurynas Klimavičius and Egidijus Rimkus of Vilnius University turned to downscaled projections from five climate models participating in the Coupled Model Intercomparison Project Phase 6, or CMIP6. The team drew on the NASA NEX-GDDP-CMIP6 database, which provides statistically downscaled daily climate data at a fine enough resolution to capture regional and local patterns. They evaluated two Shared Socioeconomic Pathways: the moderate SSP2-4.5 scenario, in which emissions decline gradually over the coming decades, and the high-end SSP5-8.5 scenario, which assumes continued heavy reliance on fossil fuels throughout the century.

The study focused on the warm season from April through September, when both droughts and heatwaves exert their greatest impact on agriculture, forestry, and human health. Droughts were identified using the Standardised Precipitation Index, a widely adopted drought metric originally developed in the 1990s that compares precipitation totals against long-term climatological norms. Heatwaves were defined using a percentile-based threshold, with a heatwave day counted whenever daily maximum air temperature exceeded the 90th percentile of the historical distribution. This dual-index approach allowed the researchers to pinpoint the days on which both a drought, according to the SPI, and a heatwave, according to the temperature threshold, were recorded simultaneously across the study area.

The results reveal a striking asymmetry between the two components of the compound hazard. Although most of the models foresee an increase in the number of drought days across the region during the final decades of the century, running from 2081 to 2100, those changes are mostly not statistically significant. Precipitation patterns over the eastern Baltic are inherently variable, and projected shifts in rainfall are smaller relative to natural variability than projected shifts in temperature. Heatwave days, by contrast, are expected to increase significantly across the entire study area by the end of the 21st century under both scenarios, a consequence of the relentless rise in mean and extreme temperatures that virtually all climate models agree upon.

Because heatwaves are the more robustly projected element, it is the warming of the atmosphere that primarily drives the increase in compound events. As air temperatures rise and heatwaves become more frequent and more likely to coincide with existing dry spells, the recurrence of compound drought and heatwave events increases almost mechanically. By the end of the century, the study projects an additional 1 to 5 CDHE days per year under the moderate SSP2-4.5 pathway, but a far more alarming 6 to 18 additional days per year under the high-emissions SSP5-8.5 scenario. In practical terms, that means that in the worst case, more than two additional weeks of simultaneous drought and extreme heat each warm season compared with the recent past.

Perhaps even more consequential than the frequency increase is the finding that both the duration and the maximum spatial extent of compound events will also grow. Longer, more expansive CDHEs are particularly threatening because they strain emergency response systems, dry out entire landscapes rather than isolated pockets, and allow compounding damage to accumulate across successive weeks. The magnitude of these changes, the authors note, is ultimately determined by precipitation patterns, meaning that regions within the eastern Baltic that receive the most pronounced declines or reorganisations of summer rainfall will face the steepest increases in compound hazard.

The findings place the eastern Baltic within a broader global picture that has emerged over the past decade. Research across Europe, China, Australia, and North America has consistently shown that compound hot-dry extremes are intensifying faster than individual hazards, and that high-end warming pathways carry a disproportionately amplified risk. Some studies have warned that climate change will accelerate the high-end risk of these events globally, while European-scale analyses suggest that hot and dry summers will become more frequent and expand northward, bringing Mediterranean-style compound extremes into the mid-latitudes. The new study extends this evidence into a region where adaptation infrastructure for such hazards remains comparatively limited.

The authors are careful to acknowledge the uncertainties inherent in their projections. Results depend on the choice of climate models, the scenarios selected, the study period and index definitions, and other methodological factors. Only five models were used, and the statistical downscaled dataset, while high-resolution, carries its own biases. The weak statistical significance of drought trends in particular underscores how difficult it remains to pin down the future of regional precipitation, even as temperature projections grow increasingly confident. Nonetheless, the direction of change in compound events appears clear across the model ensemble, because the temperature-driven component dominates the overlap.

For policymakers and communities across Lithuania, Latvia, and neighboring territories, the study delivers a sobering planning signal. Agriculture, forestry, water management, and public health systems in the region will need to prepare for a warm season in which combined drought and heat stress becomes a routine rather than exceptional feature of the late-summer landscape. The gap between the two emissions scenarios is the study’s clearest message: the difference between a manageable rise of a few compound days per year and an 18-day escalation lies almost entirely in the emissions choices made over the coming decades.

Subject of Research: Future projections of compound drought and heatwave events in the eastern Baltic Sea region using CMIP6 climate models

Article Title: Future projections of compound drought and heatwave events in the eastern part of the Baltic Sea region

Article References: Future projections of compound drought and heatwave events in the eastern part of the Baltic Sea region. (n.d.). https://doi.org/10.1007/s00704-026-06563-7

Image Credits: AI Generated

DOI: 10.1007/s00704-026-06563-7

Keywords: compound drought and heatwave events, Baltic Sea region, CMIP6, SSP2-4.5, SSP5-8.5, Standardised Precipitation Index, heatwaves, drought, climate change, NEX-GDDP, extreme weather, climate projections

Conducting a multi-faceted assessment, the researchers delve into a large transboundary river basin, which serves as a crucial lifeline for millions. By utilizing a range of bias-corrected simulations from the Coupled Model Intercomparison Project Phase 6 (CMIP6), they aim to project potential alterations in extreme hydro-climatic events. This robust methodological approach is necessary, given the elevated stakes surrounding water resources, agricultural productivity, and regional livelihoods that are intricately tied to climate variations.

The significance of this work cannot be overstated. The transboundary nature of the river basin in question means that any changes in hydro-climatic patterns have wide-reaching implications that cross political and geographic boundaries. The study not only assesses potential risks but also highlights the necessity for collaborative strategies among nations that share the river for effective resource management in the face of climate uncertainties. This exploration is timely, given the rising tensions over water scarcity and allocation exacerbated by climatic shifts.

In the context of increasing frequency and intensity of extreme weather events, understanding hydro-climatic extremes becomes essential. The research reveals a spectrum of scenarios under which these extremes might manifest, including intense flooding and droughts, both driven by changes in precipitation patterns and temperature rises. The correlation between these trends offers critical insights into how communities can prepare and adapt in anticipation of such events.

One of the noteworthy aspects of the study is its use of bias correction techniques. These techniques are vital for ensuring that the projections are realistic and relevant, especially when applied to local contexts. By correcting for systematic biases present in climate model outputs, the authors have enhanced the reliability of their projections, providing a clearer picture of what the future may hold for this vital water resource. This sophistication in methodology sets a precedent for future research in hydro-climatic studies.

Hydro-climatic extremes do not only pose immediate threats; they also have cascading effects on ecosystems and biodiversity. The study underscores the potential disruptions to aquatic habitats, with implications for fish populations and other wildlife dependent on stable hydrological conditions. As climate change continues to influence these patterns, understanding the interconnectedness of water resources and biodiversity becomes paramount for conservation efforts.

The projected changes highlighted in the paper are alarming. Increases in both the intensity and frequency of heavy precipitation events are expected to lead to greater flooding risks. Conversely, periods of severe drought are anticipated to become more common, affecting not only drinking water supplies but also irrigation systems crucial for agricultural production. This dual threat emphasizes the urgent need for adaptive water management strategies that can withstand the increasing unpredictability of climate events.

Furthermore, the findings on temperature variations present another layer of complexity. Rising temperatures are expected to exacerbate evaporation rates, worsening the impacts of droughts and raising the stakes for agricultural viability. The implications for food security cannot be overlooked, as regions may face simultaneous threats from both floods and droughts, challenging the resilience of food systems and rural livelihoods.

This research also poses critical questions regarding policy implications. As nations grapple with climate change, the study calls for regional cooperation and integrated management of transboundary water resources. Such collaborative efforts could play a crucial role in fostering resilience and ensuring sustainable development. Policymakers must take heed of these findings and engage in dialogues that prioritize shared learning and resource allocation strategies.

In a rapidly changing climate landscape, this study serves as a compelling reminder of the importance of proactive planning. The intricate interplay of climate factors can create compounded risks, making it essential for communities to adopt innovative adaptation strategies. From implementing green infrastructure solutions to enhancing water conservation practices, there are numerous pathways to mitigate the impacts of hydro-climatic extremes.

What is particularly compelling about the research is its assertion that the trajectory of climate impacts is not set in stone. By adopting robust climate action initiatives, it is possible to influence outcomes positively. This notion of agency amidst existential threats is encouraging, illustrating that communities can take steps toward resilience and sustainability through informed action.

In summation, Rahaman, Saiduzzaman, and Islam’s research sheds light on the urgent challenges posed by hydro-climatic extremes in large transboundary river basins. Their findings underscore the necessity for an integrated approach that spans scientific research, policy formulation, and community engagement. As we move forward in addressing climate change, such interdisciplinary efforts will be key to ensuring that vulnerable regions can thrive in an uncertain future.

The implications of this study extend beyond academia and into the realms of policy, conservation, and community resilience. By understanding the shifts in hydro-climatic extremes, stakeholders can better position themselves to respond to future challenges. As the global community continues to grapple with the realities of climate change, it is research like this that will guide action and inspire hope for sustainable futures.

Through a continued focus on empirical evidence and collaborative solutions, we can begin to chart a course through ambiguity toward a more resilient and harmonious coexistence with our planet’s changing climate.

Subject of Research: Hydro-climatic extremes in transboundary river basins

Article Title: Future changes in hydro-climatic extremes of a large transboundary river basin using multi-model bias-corrected CMIP6 projections.

Article References:

Rahaman, K., Saiduzzaman, M., Islam, A. et al. Future changes in hydro-climatic extremes of a large transboundary river basin using multi-model bias-corrected CMIP6 projections.
Environ Sci Pollut Res 32, 18709–18731 (2025). https://doi.org/10.1007/s11356-025-36754-0

Image Credits: AI Generated

DOI: https://doi.org/10.1007/s11356-025-36754-0

Keywords: Hydro-climatic extremes, CMIP6 projections, transboundary river basins, climate change, water resources, biodiversity, adaptive management, policy implications.