Ethiopia’s South Region Faces Hotter Nights, Longer Droughts and Shortening Return Periods of Extremes

A sweeping 38-year analysis of weather records from across Ethiopia’s South Ethiopia Region has found that the region’s climate is not simply warming on average but is becoming markedly more extreme, with hot days, hot nights, dry spells and heavy rainfall events all trending upward at the majority of monitoring stations. The study, published in BMC Environmental Science, examined daily temperature and precipitation observations from 36 stations spanning 1981 to 2018 and is among the first to combine long-term trend detection with return-period analysis for this part of the country, which was carved out as one of four new regional states in 2024 from the former Southern Nations, Nationalities, and Peoples’ Region.

The research team, Tefera Ashine Teyso and Ebrahim Esa of Ethiopian Civil Service University, drew on an internationally standardized toolkit to make their findings comparable with studies worldwide. They selected ten extreme climate indices from the 27 recommended by the Expert Team for Climate Change Detection Indices, or ETCCDI, a framework developed under World Meteorological Organization auspices to track events that follow different statistical laws than averages. Trend analysis was performed station by station using the RClimDex package in the R statistical environment, which applies the nonparametric Mann-Kendall test for significance and Sen’s slope estimator to quantify the magnitude of change. The base period for percentile-based thresholds was set to 1981 through 2010.

The temperature results are unambiguous. Warm nights, defined as nights exceeding the 90th percentile threshold, increased at 75 percent of the stations, and roughly 55 percent of those stations showed statistically significant increases at the p = 0.001 level, including Bedesa, Yirgachefe, Bule, Chencha, Sawla and Hana. Warm days rose at approximately 83 percent of stations, with about two-thirds of those trends statistically significant, at sites such as Nechsar, Dilla, Fisihagenet, Chencha, Sawla and Hana. Mirroring that pattern, cool nights declined at 75 percent of stations and cool days at about 80.5 percent, with many of those decreases also statistically significant. The region is not only heating up; its coldest nights and days are disappearing.

Spell-duration indices reinforce the picture of sustained warming. The warm spell duration indicator, which counts runs of at least six consecutive days above the 90th percentile threshold, increased at 83 percent of stations, with 16 stations showing significant upward trends. The corresponding cold spell duration indicator decreased at 61 percent of stations, six of them significantly. Together, these measures indicate that heat episodes are lasting longer while cold episodes are contracting, a signature consistent with warming reported elsewhere in Ethiopia, including semiarid western Tigray and the Borena zone, though the authors note that some regions outside Ethiopia, such as Solapur district in western Maharashtra, India, have shown opposite trends in cool extremes, underscoring how geography shapes the character of climate change.

Precipitation extremes tell a more complicated but equally troubling story. Consecutive dry days, the longest run of days with less than one millimeter of rain, increased at 77 percent of stations, with nine stations reaching statistical significance at p = 0.05. At the same time, more than half of the stations recorded increases in very wet days, defined as total precipitation above the 95th percentile, and extremely wet days above the 99th percentile, as well as in the number of days with at least 20 millimeters of rain. Stations such as Nechsar, Chencha, Omorate, Turmi, Humbo, Bako Gazer, Boditi, Sawla and Hana registered significant trends in one or more of these heavy-rainfall indices. The region, in other words, is experiencing both longer droughts and more intense downpours, sometimes at the same stations.

Beyond trends, the study broke new ground for the region by estimating how the magnitude of extremes has changed across recurrence intervals of 2, 5, 10, 25, 50 and 100 years, comparing the periods 1981 to 1999 and 2000 to 2018. The authors used CumFreq software, which fits a wide family of probability distributions, including Gumbel, Fréchet, Weibull, Pareto and composite forms, and selects the best model by minimizing the mean absolute difference between observed and calculated cumulative frequencies. Extreme values were extracted using a peak-over-threshold approach with fixed 90th and 10th percentile cutoffs, and 90 percent confidence intervals were estimated from binomial principles to quantify uncertainty in the return-level estimates.

The return-period analysis revealed that extremes once expected only rarely are now arriving with greater force. Values above the 90th percentile of daily maximum temperature increased across all six recurrence intervals at roughly 64 percent of stations with 90 percent confidence, with the largest positive changes at Areka, Bako Gazer, Dimitu, Dilla, Gubire, Kemba and Keyafer. Minimum temperature extremes below the 10th percentile rose at more than 80 percent of stations. Precipitation showed sharp spatial contrasts: Yirgachefe saw increases of 358 and 869 millimeters per month for the 50- and 100-year return periods, while Bulki recorded decreases of 348 and 600 millimeters over the same intervals, and Kemba and Bako Gazer also declined. This variability reflects Ethiopia’s complex topography, which previous national studies have linked to strong spatial differences in extreme rainfall behavior.

Perhaps the most consequential finding is the shortening of recurrence intervals for both high-temperature and heavy-precipitation events. A recurrence interval, or return period, is the average time between events of a given size or larger; when that interval shrinks, a flood or heat wave once expected once a century becomes a more routine hazard. For communities that depend on rain-fed agriculture, the practical meaning is stark: less time to recover between shocks, less reliable planting calendars, and greater exposure of crops, livestock and water supplies. The region’s bi-modal rainfall, driven by the seasonal migration of the Intertropical Convergence Zone and peaking in April and October, already leaves water availability uneven across agroecological zones ranging from humid highlands receiving up to 2,000 millimeters annually to lowlands that often receive less than 900 millimeters.

The stakes are amplified by the region’s human geography. South Ethiopia covers roughly 49,239 square kilometers and is home to an estimated 8.4 million people, nearly 79 percent of whom live in rural areas. Its fertile midlands support some of the densest rural populations in Ethiopia, with places like Wenago in the Gedeo Zone reaching up to 600 people per square kilometer, and enset, coffee, cereals and livestock anchoring household economies. The authors argue that the observed intensification of extremes threatens agriculture, water access, health systems and overall community resilience, and they call for adaptation strategies tailored to the region’s distinct ecological and socioeconomic conditions, including disaster risk reduction, sustainable land management and the expansion of climate-smart practices such as agroforestry and integrated soil fertility management that have already shown promise among smallholder farmers.

Scientifically, the study fills a gap that has left southern Ethiopia underrepresented in the literature on climate extremes, which has historically focused on national averages, large river basins such as the Nile, or better-studied regions of central and northern Ethiopia. Because extreme events are rare and statistically distinct from mean climate shifts, they require dedicated indices and frequency analysis that most subnational studies have not attempted. By pairing station-level trend detection with probabilistic return-level estimation across a dense network of 36 stations, the research provides the kind of spatially resolved, long-term evidence base that policymakers in agriculture, water resources and infrastructure need. The message it delivers is urgent: climate change is already amplifying hazards across South Ethiopia, and without targeted intervention, the risks documented over these four decades are likely to escalate further.

Subject of Research: Trends and recurrence intervals of temperature and precipitation extremes in the South Ethiopia Region

Article Title: Climate extremes: trends and magnitudes for different recurrence intervals in the South Ethiopia region

Article References: Teyso, T. A., & Esa, E. (2026). Climate extremes: trends and magnitudes for different recurrence intervals in the South Ethiopia region. BMC Environmental Science, 3(1), Article 1. https://doi.org/10.1186/s44329-025-00042-6

Image Credits: AI Generated

DOI: 10.1186/s44329-025-00042-6

Keywords: climate extremes, South Ethiopia, ETCCDI indices, RClimDex, CumFreq, return periods, warm spells, consecutive dry days, heavy precipitation, Mann-Kendall test, climate adaptation, Ethiopian Meteorological Institute