The study, led by Deepti Tandel with Mani Kant Verma and M.K. Verma, set out to quantify how large-scale ocean-atmosphere interactions shape regional monsoon variability at a scale that matters for farmers and water managers. Climate change is increasingly altering rainfall patterns, and understanding the fingerprints of ENSO and the IOD on district-level rainfall, monsoon onset, and wet-dry conditions provides a scientific basis for drought monitoring and agricultural planning. The team assembled daily rainfall data for the monsoon season across the full 65-year record, then applied a battery of statistical tools designed to detect trends, classify drought severity, and test associations with ocean indices.

Methodologically, the researchers used the Modified Mann-Kendall test, which corrects for autocorrelation in time series, together with Sen’s slope estimator to quantify the magnitude of trends in rainfall. To characterise drought and wetness, they computed the Standardised Precipitation Index (SPI), a widely used metric that expresses rainfall anomalies in units of standard deviation, with values below zero indicating drier-than-normal conditions and values above zero indicating wetter-than-normal ones. Associations with ocean conditions were tested using both Pearson and Spearman correlation analyses, while differences among groups were evaluated with the Kruskal-Wallis test and Dunn’s post-hoc comparisons. This combination of non-parametric and correlation-based techniques allowed the team to assess trends and teleconnections robustly across districts with differing rainfall regimes.

The results paint a picture of substantial spatial variability. District-level SPI values ranged from approximately −2.5 to +3.0, spanning severe drought to pronounced wetness within a single state. The analysis identified 15 major drought years: 1965, 1966, 1968, 1974, 1979, 1982, 1986, 1991, 1997, 2002, 2009, 2013, 2015, 2017, and 2023. In contrast, seven years stood out as major wet years: 1961, 1980, 1981, 1994, 2001, 2003, and 2025. During the major drought years, the mean SPI across districts ranged from −1.733 to −0.505, confirming that these events were widespread rather than localised, yet the spread of values also underscored how unevenly drought stress is distributed across the state.

Monsoon onset, a critical variable for sowing decisions in rainfed agriculture, varied considerably across the state, from 14 June in the earliest districts to 2 July in the latest. This three-week spread means that neighbouring districts can face very different planting windows in the same season, complicating one-size-fits-all agricultural advisories. The timing of onset was found to be significantly influenced by conditions in the preceding months: the March-April-May Oceanic Niño Index (MAM ONI), a measure of Pacific sea surface temperature anomalies, and the state of the IOD both had significant effects on rainfall variability and on when the monsoon actually arrived over individual districts.

The statistical link between the Pacific and Chhattisgarh’s rains was quantified directly. The association between ONI and monsoon rainfall was significant in both correlation frameworks, with Pearson’s r = 0.401 (p = 0.001) and Spearman’s ρ = 0.416 (p = 0.006). These moderate but highly significant coefficients indicate that a substantial fraction of year-to-year monsoon variability in the state is traceable to the phase of ENSO, a finding consistent with the broader literature on how Pacific sea surface temperature anomalies modulate the Indian summer monsoon through large-scale atmospheric circulation changes.

Perhaps the most striking result is the spatial pattern of emerging aridity. The districts of Mungeli, Kabirdham, Bilaspur, Balodabazar, and Surajpur experienced moderate to extremely dry conditions, while Bastar, Bijapur, Narayanpur, and Sukma, in the forested south of the state, showed a transition from extremely wet to moderately wet conditions. This shift indicates an emerging tendency toward dryness even in historically wetter districts, suggesting that the drying signal is not confined to the already arid margins but is creeping into areas whose farming systems and ecosystems were built around more abundant rainfall.

The authors attribute this increasing tendency toward aridity to the combined influence of ENSO, the IOD, and regional hydroclimatic processes. The IOD, a seesaw of sea surface temperatures between the western and eastern Indian Ocean, can reinforce or offset ENSO’s influence on Indian rainfall depending on the relative phases of the two modes. When both act in concert, their combined effect on monsoon circulation can be amplified, and the Chhattisgarh analysis suggests that such interactions leave detectable imprints on district-scale rainfall, onset timing, and drought severity across the 65-year record.

The practical implications are considerable. Chhattisgarh’s economy is heavily dependent on rainfed agriculture, and previous work by the same group has documented how dry and wet spells affect crop productivity in the state. By demonstrating that pre-monsoon ocean conditions carry usable information about subsequent rainfall variability and onset timing, the study provides a scientific foundation for district-level drought monitoring, seasonal agricultural planning, and water-resource management. The identification of specific drought-prone and wet-to-dry transition districts offers a spatially targeted basis for climate-resilient strategies, from crop choice and irrigation investment to contingency planning for delayed monsoons.

As climate change continues to reshape global precipitation patterns, studies of this kind highlight how global ocean oscillations and regional processes interact to determine the fate of individual farming districts. For Chhattisgarh, the message from six and a half decades of data is clear: the monsoon is becoming more uneven, drought years are a recurring feature of the record, and even the wettest corners of the state are drifting toward drier conditions. Translating that statistical evidence into early-warning systems and adaptive water management may prove essential for the millions of people whose livelihoods depend on the timing and abundance of the Southwest monsoon rains.

Subject of Research: Influence of ENSO and the Indian Ocean Dipole on Southwest monsoon rainfall variability and drought across Chhattisgarh, India

Article Title: Spatiotemporal variability of Southwest monsoon rainfall and drought in Chhattisgarh: associations with ENSO and IOD

Article References: Tandel, D., Verma, M. K., & Verma, M. (2026). Spatiotemporal variability of Southwest monsoon rainfall and drought in Chhattisgarh: associations with ENSO and IOD. Theoretical and Applied Climatology, 157(11), Article 728. https://doi.org/10.1007/s00704-026-06662-5

Image Credits: AI Generated

DOI: 10.1007/s00704-026-06662-5

Keywords: monsoon, Chhattisgarh, ENSO, Indian Ocean Dipole, drought, Standardised Precipitation Index, rainfall variability, monsoon onset, climate change, trend analysis, India, agriculture

The research, led by Malaguièhèwa Grâce Pekeyi of the Federal University of Technology Minna in Nigeria, together with Appollonia Aimiosino Okhimamhe, Tayo Iyanda Yahaya and Isaiah Sule, analysed 45 years of climate data spanning 1981 to 2025 across three agroecological zones of northern and north-central Togo. The team combined records from three synoptic weather stations with two independent gridded datasets: NASA POWER reanalysis data and the CHIRPS satellite-based precipitation archive. This multi-source approach matters in a region where ground-based weather networks are sparse and patchy, a limitation the authors document explicitly in their appendix on missing station data.

Methodologically, the study is a tour de force of classical climate diagnostics. The researchers applied the Hamed-Rao modified Mann-Kendall test, a non-parametric trend test corrected for autocorrelation, alongside Sen’s slope estimator to quantify the magnitude of change. To detect abrupt shifts in climate records, they deployed three independent change-point tests: the Pettitt test, the Buishand test and the Standard Normal Homogeneity Test. All analyses were run at annual, seasonal and monthly timescales, giving the team a finely resolved view of when and where the climate system has shifted.

The headline result is striking for what it does not show. No statistically significant precipitation trends were detected at any station, at any timescale. In a region often assumed to be sliding steadily into drought, total rainfall has remained remarkably stable over the 45-year window. This finding aligns with a broader pattern across the Sahel and Sudanian zones of West Africa, where the catastrophic rainfall declines of the 1970s and 1980s have partially recovered, even as rainfall variability and extreme events have intensified.

But temperature tells a different story. All stations showed significant warming of between +0.27 and +0.34 degrees Celsius per decade, a rate consistent with regional and global warming trends. In a rain-fed agricultural system, this warming is far from benign. Higher temperatures increase atmospheric evaporative demand, meaning that even unchanged rainfall delivers progressively less effective moisture to soils and crops. It is precisely this mechanism that the study’s drought indices were designed to capture.

The researchers computed three complementary drought metrics: the Standardised Precipitation Index (SPI), which reflects rainfall anomalies alone; the Standardised Precipitation-Evapotranspiration Index (SPEI), which subtracts the moisture demand imposed by temperature; and the Willmott-Feddema Moisture Index, a ratio-based measure of climatic water balance. The comparison proved revealing. While SPI and SPEI tracked each other closely in the decades before 2000, they diverged significantly after that point, with the divergence strongest at Sokodé, the station in the wettest of the three zones. Because SPEI accounts for warming-driven evapotranspiration while SPI does not, this post-2000 split is a statistical fingerprint of temperature stress emerging on top of stable rainfall.

Perhaps the most technically intriguing result concerns what that divergence does and does not mean. The team tested an independent Penman-Monteith formulation of potential evapotranspiration, the physically rigorous standard that accounts for radiation, wind and humidity as well as temperature. Intriguingly, Penman-Monteith PET itself showed no comparable warming-driven increase, yet the SPI-SPEI divergence persisted even under this alternative formulation. The authors interpret this carefully: the divergence reflects a broader shift in the surface energy and moisture balance rather than temperature alone, a conclusion that guards against the common criticism that SPEI simply exaggerates warming effects when computed with temperature-based evapotranspiration estimates.

Change-point analysis added a further layer of nuance. All three tests pointed to a common shift year at exactly 2003, a remarkable coincidence across independent statistical methods. Yet the authors report that this change point was not statistically clear-cut, meaning the evidence for an abrupt regime shift falls short of conventional significance thresholds. The honest reading is that the early 2000s marked a gradual transition rather than a sharp break, with the moisture balance drifting into a new regime over several years rather than snapping at a single moment.

The Willmott-Feddema Moisture Index delivered the study’s most sobering spatial message. All stations recorded predominantly negative MI values across the study period, indicating a persistent climatic moisture deficit: on average, atmospheric demand for water exceeds supply across the entire region. Yet when the team mapped trends across the gridded datasets, they found predominantly positive, wetting trends, with significant drying confined to fewer than 8 percent of grid cells. The region, in other words, is simultaneously water-limited on average and not systematically getting drier in space, a paradox that underscores why single-metric drought assessments so often mislead.

For Togo, the practical implications are immediate. The country’s northern regions have faced acute drinking water shortages, prompting government responses as recently as late 2025, and the study’s authors explicitly frame their work as relevant to early-warning systems and water-resource management. Because the SPI-SPEI divergence shows that rainfall-only drought indices now systematically understate moisture stress, the researchers argue that temperature-sensitive indices should anchor drought monitoring in the region. For the rain-fed cereal systems that dominate northern Togo’s agriculture, where previous work has linked rainfall variability directly to yield outcomes, the message is that the enemy is no longer declining rainfall but rising evaporative demand, a quieter and harder-to-see threat that demands equally vigilant measurement.

Subject of Research: Hydroclimatic variability and drought characterisation in northern and north-central Togo from 1981 to 2025

Article Title: Hydroclimatic variability and drought characterisation in Northern and North-Central Togo, 1981–2025

Article References: Pekeyi, M. G., Okhimamhe, A. A., Yahaya, T. I., & Sule, I. (2026). Hydroclimatic variability and drought characterisation in Northern and North-Central Togo, 1981–2025. Theoretical and Applied Climatology, 157(11), Article 701. https://doi.org/10.1007/s00704-026-06621-0

Image Credits: AI Generated

DOI: 10.1007/s00704-026-06621-0

Keywords: drought, Togo, West Africa, climate change, Standardised Precipitation Index, SPEI, evapotranspiration, rain-fed agriculture, CHIRPS, NASA POWER, trend analysis, water resources

The team assembled daily rainfall data spanning 123 years, from 1901 to 2024, and subjected it to a battery of statistical tests designed to separate genuine long-term trends from natural variability. They applied the Mann-Kendall test and its modified variant, which corrects for autocorrelation in the time series, alongside Sen’s slope estimator to quantify the magnitude of change. To probe extremes, they used the Peak Over Threshold method, which counts and sizes rainfall events exceeding a defined limit. Drought behaviour was tracked with the Standardised Precipitation Index and the Aridity Index, while low-flow analysis captured how streamflow during dry periods has evolved. The result is a multi-layered diagnosis of a water system under stress from every direction.

The headline finding is deceptively small: an annual decrease in rainfall of 8.4 millimetres per year. That figure alone would not raise alarms, but the monthly breakdown reveals where the damage concentrates. March rainfall is declining at 0.578 millimetres per year, April at 1.419 millimetres per year, July at 1.593 millimetres per year and August at 1.84 millimetres per year, the last being the heart of the monsoon. December, by contrast, shows a marginal increase of 0.005 millimetres per year, statistically negligible in practical terms. The pattern matters because losses in the pre-monsoon months erode the soil moisture and spring recharge that communities depend on before the monsoon arrives, while losses in July and August shrink the total volume available for storage.

Paradoxically, even as total rainfall declines, the extremes are intensifying. The Peak Over Threshold analysis shows that both the frequency and the intensity of extreme rainfall events have been increasing, with a daily deluge of 580 millimetres now assigned a return period of 100 years. This combination, fewer moderate rains and more violent downpours, is a signature increasingly reported across a warming Indian subcontinent, and it is uniquely hostile to water storage. Intense rainfall on degraded or steep terrain runs off rapidly rather than percolating into aquifers, so the water arrives as flood hazard instead of replenishing springs and wells. The study’s findings align with broader evidence that Indian rainfall extremes have grown more spatially variable and more intense even as seasonal totals stagnate or fall.

The hydrological story beneath the surface is equally troubling. By interlinking river stage records, groundwater levels and the region’s geology with the rainfall record, the researchers pieced together a picture of chronically low storage. The Shillong Plateau’s terrain and geology offer limited capacity to hold the enormous volumes that cascade through it during the monsoon, and the low-flow analysis confirms the consequence: streamflow during dry periods is reducing by 0.80 days per year, meaning the rivers run low ever earlier and stay low ever longer. The Aridity Index for July, August and September is decreasing by 0.003 millimetres per year, and the Standardised Precipitation Index reinforces the same conclusion, pointing to intensifying water scarcity through the winter and summer seasons.

What elevates the study beyond a statistical exercise is its socio-hydrological dimension. The researchers combined the secondary data analysis with a community assessment in Nongkya village, using participatory rural appraisal methods to capture how residents experience the scarcity that the numbers describe. The survey found that 61 percent of households experience water scarcity, a figure that independently corroborates the hydro-climatic indicators. This convergence between measured trends and lived experience is precisely what the socio-hydro-climatic framework is designed to achieve: water security is not a function of rainfall alone but of how climate, geology, infrastructure and human demand interact across the year.

The seasonal swing the region endures is extraordinary. The study characterises Cherrapunji’s annual hydro-climatic variability as ranging from hyper-arid and extremely dry conditions to humid and extremely wet ones, a range that few places on Earth experience within a single year. Managing water under such volatility demands infrastructure that can capture monsoon surpluses and carry them through a dry season that is lengthening year by year. Instead, the region’s storages remain low, its springs and streams falter earlier each dry season, and households increasingly face the classic paradox of the wet desert, a term that has been applied to Cherrapunji for nearly two decades as deforestation and land degradation compounded the climatic pressures.

Against this backdrop, the authors propose a set of adaptation strategies grounded in the specific hydrology of the plateau. Micro rainwater harvesting, small-scale capture systems distributed across households and slopes, would intercept some of the intense runoff before it escapes the landscape. Soil and land management aimed at enhancing percolation would help convert violent monsoon downpours into groundwater recharge, addressing the storage deficit at its source. Perhaps most significantly, the researchers argue for integrating traditional knowledge with technological approaches, recognising that Khasi communities have managed this landscape for centuries and that engineered solutions imposed without local insight have historically underperformed. The recommendation echoes a growing consensus in water security research that community-driven, participatory approaches outperform purely top-down interventions.

The implications extend well beyond a single town. Cherrapunji functions as a natural laboratory for the water security challenges that climate change is amplifying across South Asia, where the monsoon is becoming more erratic, extremes more severe, and dry-season stress more acute. The study’s methodological toolkit, combining modified trend tests, extreme-value analysis, drought indices, low-flow assessment and community perception surveys, offers a replicable template for other regions navigating the same transition from predictable seasonality to volatile hydro-climatic whiplash. As the authors make clear, the question for Cherrapunji is no longer whether the rain will fall, but whether anything can be done to keep it from vanishing the moment it does.

Subject of Research: Socio-hydro-climatic analysis of water security and rainfall trends in Cherrapunji, semi-arid India

Article Title: Socio-hydro-climatic analysis for water security in semi-arid India: a case of Cherrapunji, India

Article References: Paul, N., Pushpalatha, R., Roshni, T., Nair, A., Dutta, D., Singh, P. P., & P., A. (2026). Socio-hydro-climatic analysis for water security in semi-arid India: a case of Cherrapunji, India. Regional Environmental Change, 26(4), Article 211. https://doi.org/10.1007/s10113-026-02701-z

Image Credits: AI Generated

DOI: 10.1007/s10113-026-02701-z

Keywords: Cherrapunji, water security, rainfall trends, Mann-Kendall test, Standardised Precipitation Index, aridity index, low flow, groundwater, extreme rainfall, water scarcity, Meghalaya, climate change

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