Msellem et al. (2026) Variability and Trends in Evaporation and Water Balance over Tanzania

Identification

• Journal: Journal of Geoscience and Environment Protection
• Year: 2026
• Date: 2026-01-01
• Authors: Moh’d Abdalla Msellem, Yuanshu Jing, Innocent Junior John
• DOI: 10.4236/gep.2026.143003

Research Groups

• Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters (CIC-FEMD), Nanjing University of Information Science and Technology, Nanjing, China.
• Jiangsu Key Laboratory of Agricultural and Ecological Meteorology, Nanjing University of Information Science and Technology, Nanjing, China.
• Geography and Economic Department, Faculty of Humanities and Social Sciences, Dar es Salaam University College of Education, Dar es Salaam, Tanzania.

Short Summary

This study investigates the spatiotemporal variability and long-term trends of evaporation and the precipitation-evaporation balance (P-E) over Tanzania from 1995 to 2025 using ERA5-Land reanalysis data, revealing significant seasonal and spatial heterogeneity and a general decline in evaporation, impacting regional water availability.

Objective

• To investigate the spatiotemporal variability and long-term trends of evaporation and the precipitation-evaporation balance (P-E) over Tanzania, focusing on seasonal cycles, long-term changes, and the coupling between evaporation, precipitation, and temperature.

Study Configuration

• Spatial Scale: Tanzania (approximately 945,000 km²), between latitudes 1°S and 12°S and longitudes 29°E and 41°E, at a spatial resolution of 0.1° × 0.1°.
• Temporal Scale: 1995-2025 (30-year period), analyzed using monthly and annual averages.

Methodology and Data

• Models used: No specific models were run by the authors for simulation; analysis was performed on ERA5-Land reanalysis data, which is generated by a physically based land-surface model coupled with atmospheric reanalysis.
• Data sources: ERA5-Land reanalysis dataset from the European Centre for Medium-Range Weather Forecasts (ECMWF), providing hourly estimates of land-surface variables including evaporation, precipitation, and near-surface air temperature.

Main Results

• Evaporation exhibits strong seasonal and spatial heterogeneity across Tanzania. It peaks during the wet season (November-May) under energy-limited conditions and weakens in the dry season (June-October) under moisture-limited constraints.
• The precipitation-evaporation (P-E) balance shows seasonal surpluses during rainy periods (March-May and November-December) and deficits during dry months, most pronounced in the semi-arid central plateau.
• Evaporation is positively correlated with temperature across most months, particularly during the dry season.
• The relationship between evaporation and precipitation shifts seasonally: positive correlations dominate during wet months (January-April), while negative correlations are widespread during the dry season (June-September), reflecting soil moisture memory effects.
• Trend analysis (1995-2025) reveals a significant decline in evaporation across most months, particularly June-October, with the strongest negative trend in November (approximately −6.2 mm/month). March shows a consistent increase in evaporation.
• The observed declining evaporative rates, combined with shifting precipitation patterns, suggest a tightening regional water balance with implications for agriculture, surface water availability, and drought resilience.

Contributions

• Provides a comprehensive national-scale assessment of evaporation variability, trends, and water balance over Tanzania, addressing a gap in previous localized studies.
• Links national-scale evaporation dynamics to both local soil-moisture processes and large-scale climate drivers.
• Offers a diagnostic framework for evaluating climate model performance and improving water resource management and agricultural decision-making under increasing climate variability in East Africa.

Funding

Not explicitly stated in the paper.

Citation

@article{Msellem2026Variability,
  author = {Msellem, Moh’d Abdalla and Jing, Yuanshu and John, Innocent Junior},
  title = {Variability and Trends in Evaporation and Water Balance over Tanzania},
  journal = {Journal of Geoscience and Environment Protection},
  year = {2026},
  doi = {10.4236/gep.2026.143003},
  url = {https://doi.org/10.4236/gep.2026.143003}
}