Assessing climate change effects on Turkish tea farming through a dual approach using MMQR and machine learning – Scientific Reports

Turkey’s tea heartland along the Eastern Black Sea is feeling the pressure of a changing climate. New analysis of two decades of data across the key producing provinces—Artvin, Giresun, Ordu, Rize, and Trabzon—shows how shifting temperature, rainfall, and humidity are reshaping productivity, with implications for livelihoods, food security, and the regional economy. By combining a distribution-sensitive statistical method with modern machine learning, the study offers a sharper picture of what helps or hinders tea yields—and what policymakers can do next.

Why tea is at stake

Tea cultivation anchors rural life in the Eastern Black Sea region, where steep slopes, abundant rainfall, and mild temperatures have long favored the crop. These same conditions, however, make plantations sensitive to climatic swings. Warmer seasons, altered rainfall patterns, and persistently high humidity can affect leaf flushes, disease pressure, and overall plant health. Understanding which variables matter most—across good and poor harvest years alike—is crucial for adapting practices and protecting incomes.

A dual lens on climate and productivity

The analysis covers 2004 to 2022 and evaluates tea productivity in the five provinces where the crop is concentrated. Two complementary methods are used:

• Method of moments quantile regression (MMQR), which assesses how climate variables influence productivity across the full distribution of outcomes—not just the average—capturing effects in both low- and high-yield years.
• Machine learning models that rank the relative importance of factors shaping yields, highlighting which variables most strongly drive changes on the ground.

This combined approach builds a more resilient understanding of climate impacts by pairing statistically rigorous estimates with data-driven variable importance, reducing the risk of overlooking subtle but consequential relationships.

What the data reveal

• Humidity depresses productivity: Across many points in the productivity distribution, higher humidity is associated with lower yields. Persistently moist conditions can favor leaf diseases, reduce air movement within dense canopies, and limit transpiration—factors that collectively constrain plant performance.
• Temperature supports yields within the observed range: Warmer conditions, as recorded over the study period, are linked to higher productivity. In this cool, maritime climate, modest warming likely lengthens the effective growing window and accelerates growth, provided heat does not cross stress thresholds.
• Precipitation boosts productivity: Adequate rainfall remains a key ally for tea, which is a water-demanding crop. Within the observed range, more precipitation correlates with better yields, underscoring the crop’s reliance on consistent moisture, especially during peak growth periods.
• Tea farming area is the dominant driver in machine learning results: Among all variables evaluated, the extent of tea cultivation emerges as the most influential, while humidity ranks as the least influential in that particular framework. The prominence of cultivated area points to the combined effects of land availability, management intensity, and structural factors such as plantation age and replanting cycles.

Taken together, these findings emphasize that while rainfall and moderate warming can be beneficial in this setting, excessive humidity undermines productivity. Management strategies that reduce stagnant moisture around plants could unlock gains even as the climate shifts.

Policy and practice: where to focus

• Moisture management: Improve canopy airflow through pruning and optimized plant spacing; encourage rapid post-rain drainage; expand disease surveillance and integrated pest management to counter humidity-related pressures.
• Soil fertility: Invest in soil testing and balanced nutrient plans; increase organic matter with composts and mulches to stabilize moisture and bolster root health.
• Erosion control: Scale up terracing, contour planting, living groundcovers, and hedgerows to keep soils in place on steep slopes and maintain long-term productivity.
• Irrigation infrastructure for dry spells: Develop small-scale, efficient systems and storage solutions to buffer short rainfall deficits, with scheduling aligned to tea phenology.
• Land-use planning: Protect and rehabilitate productive tea areas to avoid fragmentation, support renewal of aging stands, and ensure that expansion aligns with sustainable slope and soil criteria.
• Climate services and extension: Provide localized forecasts and early warnings; train growers in adaptive practices that target humidity control, soil stewardship, and water efficiency.

Beyond averages: why method matters

By looking across the full spectrum of harvest outcomes, MMQR reveals relationships that might be obscured by averages—such as humidity’s drag on yields in both weak and strong years. Meanwhile, machine learning’s ranking of variable importance helps decision-makers prioritize interventions with the greatest leverage, such as land and plantation management, while still addressing climate-sensitive risks like excessive humidity.

What’s next for resilient tea

Future analyses can extend this framework to capture the influence of extreme events—heatwaves, floods, and landslides—that are becoming more frequent and can wipe out gains from favorable averages. Pairing these models with higher-resolution weather and soil data, as well as information on plant age, cultivar choice, and management practices, would further refine local adaptation strategies. Regional programs that encourage varietal improvement, targeted replanting, and precision water management can turn climate findings into practical, farm-level benefits.

The takeaway

In the Eastern Black Sea, climate change is not a distant threat—it is already reshaping tea productivity. Evidence from two decades of data indicates that managing humidity, maintaining soil and slope integrity, and investing in smart water infrastructure will be central to sustaining yields. With informed, region-specific policies and field-level support, Turkey’s tea sector can adapt to the climate realities ahead while safeguarding rural livelihoods.