Warming Highlands, Shrinking Seasons: Climate Shifts Squeeze Ethiopia’s Bread Wheat Harvests

In the central highlands of Ethiopia, where bread wheat has anchored smallholder farming for generations, the growing season is quietly being rewritten. A new study published in Discover Sustainability by Sakatu Hunduma of Hawassa University and colleagues documents how rainfall and temperature patterns have shifted between 1989 and 2020, and how those shifts are translating directly into lost wheat productivity. Drawing on more than three decades of daily meteorological records from the Ethiopian Meteorological Institute, the researchers combined classical climate statistics with crop-calendar analysis to produce one of the most detailed portraits yet of how a warming, increasingly erratic climate is reshaping agriculture in this critical wheat belt.

The team’s starting point was deceptively simple: measure how variable the climate actually is, and whether its long-term trends are statistically real. To do this, they deployed a suite of well-established indices. The Coefficient of Variation captured how much rainfall swings from year to year relative to its average, while the Precipitation Concentration Index revealed whether rain arrives in destructive bursts or spreads evenly across the season. The Standardized Anomaly Index placed each individual year in context, flagging those that fell far above or below the long-term norm. For trend detection, they used the Mann–Kendall test, a non-parametric method that identifies monotonic trends without assuming the data follow a normal distribution, paired with Sen’s slope estimator, which quantifies the magnitude of change per year while remaining robust to outliers.

The rainfall findings are sobering. Precipitation in the study area proved highly variable both in space and in time, and in 58 percent of the years examined, rainfall fell below the long-term mean. That means for more than half of the past three decades, farmers in the central highlands have been farming under rainfall deficits, planning their planting and fertilizing around water that never arrived in expected quantities. High values of the Precipitation Concentration Index in certain years pointed to rainfall arriving in concentrated, intense episodes rather than gentle, sustained showers, a pattern that simultaneously raises erosion risk and reduces the fraction of water that actually infiltrates the soil profile where wheat roots can reach it.

Temperature told an unambiguous story. Both daily maximum and daily minimum temperatures rose significantly across all study locations between 1989 and 2020, with the researchers reporting statistical significance at the p < 0.01 level. Maximum temperatures climbed by 0.043 to 0.081 degrees Celsius per year, while minimum temperatures increased by 0.034 to 0.094 degrees Celsius per year. Compounded over the 31-year record, those rates translate into warming on the order of 1.3 to 2.5 degrees Celsius, a substantial shift for a highland ecosystem where wheat is already grown near the upper edge of its thermal tolerance in many locations. Rising minimum temperatures are particularly consequential for wheat, because warmer nights accelerate phenological development, shorten the grain-filling period, and increase respiratory losses that erode final yield.

Perhaps the most striking result concerns the growing season itself. Using INSTAT+ 3.37 statistical software, a tool specifically designed for agrometeorological analysis, the researchers characterized when the rainy season actually begins and ends, and how long the window for crop production lasts. They found that the start of the rainy season now ranges from June 13, corresponding to day 165 of the year, to as late as July 6, day 188. The end of the season ranges from October 10, day 284, to November 2, day 307. The length of the growing period consequently spans a wide band, from just 96 days to as many as 136 days. That 40-day spread is not an academic curiosity; it is the difference between a crop that completes grain fill before the rains vanish and one that fails mid-season.

This shifting crop calendar has direct, cascading consequences for bread wheat, a staple that supplies a large share of calories for Ethiopian households and dominates the highland farming systems of the study region. When the rains arrive late, farmers who plant on traditional dates sow into drying soil, and germination suffers. When the season ends early, wheat planted even a few weeks behind schedule encounters terminal moisture stress during flowering and grain filling, the growth stages most sensitive to water deficit. The study’s authors note that these climate shifts disrupt farming calendars, trigger crop failures, and threaten food security, a chain of impacts that begins with a few weeks of rainfall timing and ends on the household plate.

To quantify how much of the yield story climate can explain, the team turned to combined multiple regression analysis, modeling wheat yield as a function of the assessed climate variables across the selected study sites. The results revealed a striking spatial gradient in climate sensitivity: the climate variables explained between 17 and 83 percent of the change in wheat yield depending on the site. At the high end of that range, more than four-fifths of year-to-year yield variation is attributable to climatic factors alone, before accounting for soil quality, fertilizer use, variety choice, or pest pressure. The wide range itself is informative, suggesting that some locations buffer climate stress better than others, whether through deeper soils, higher elevations, or more favorable rainfall regimes, while others sit squarely on the climate knife-edge.

The implications extend well beyond the central highlands. Ethiopia is the largest wheat producer in sub-Saharan Africa, and wheat is a national priority crop in ambitious government self-sufficiency programs. Yet the study’s findings suggest that the biophysical foundation of that production is moving. A growing season that once reliably spanned four months can now contract to barely three, and nighttime temperatures that once supported slow, steady grain development are rising faster in some locations than daytime maxima. For a crop whose yield potential is set by the interaction of temperature, radiation, and water availability during a finite window, every day shaved off that window is a day of lost photosynthesis and lost grain.

The researchers are explicit about the adaptation pathway. Farmers in the affected highlands, they argue, must switch to early-maturing, drought-tolerant crop varieties and implement soil moisture conservation practices. Early-maturing wheat cultivars can complete their life cycle within the shortened and increasingly unpredictable growing window, escaping terminal drought that longer-season varieties cannot. Drought-tolerant genetics, meanwhile, maintain yield under the moisture deficits that 58 percent below-average rainfall years make routine rather than exceptional. Soil moisture conservation, including practices such as mulching, tied ridging, and improved infiltration management, addresses the other side of the water balance, capturing the intense, concentrated rainfall episodes that the Precipitation Concentration Index revealed and holding that water in the root zone for the crop to use.

What makes this study valuable is its methodological transparency and its grounding in three decades of station data rather than coarse gridded products. By combining the Mann–Kendall and Sen’s slope tests for trend, multiple variability indices for character, and regression for impact, the researchers built a chain of evidence that runs unbroken from the rain gauge to the wheat field. The picture that emerges is of a farming system under compound stress: rainfall that is late, concentrated, and frequently below normal; temperatures rising on both daily extremes; growing seasons that contract and shift; and yields that in some places swing almost entirely with the weather. For the millions of smallholders who depend on bread wheat in the Ethiopian highlands, the study is less a forecast than a description of the present, and its central message is that adaptation choices, in variety, in planting strategy, and in soil management, will determine whether the region’s most important staple can keep pace with its changing climate.

Subject of Research: Climate variability and its impact on bread wheat productivity in the central highlands of Ethiopia

Article Title: Analysis of climate trend, variability and its implications on bread wheat (Triticum aestivum L.) productivity in central highlands of Ethiopia

Article References: Hunduma, S., Meseret, A., Edao, A. L., & Yoseph, T. (2026). Analysis of climate trend, variability and its implications on bread wheat (Triticum aestivum L.) productivity in central highlands of Ethiopia. Discover Sustainability. https://doi.org/10.1007/s43621-026-04710-8

Image Credits: AI Generated

DOI: 10.1007/s43621-026-04710-8

Keywords: climate variability, bread wheat, Ethiopia, rainfall trends, temperature trends, growing season, Mann-Kendall test, food security, agrometeorology, crop adaptation, highlands, drought