Critical soil moisture thresholds for evapotranspiration in rainfed semi-arid maize in Kenya
Journal
Agricultural and Forest Meteorology
Journal Volume
385
Start Page
111219
ISSN
0168-1923
Date Issued
2026-06
Author(s)
Räsänen, Matti
Omondi, Julius
Odongo, Vincent
Abera, Temesgen
Tuure, Juuso
Heiskanen, Janne
Alakukku, Laura
Merbold, Lutz
Pellikka, Petri
Vesala, Timo
Abstract
Understanding how maize (Zea mays L.) evapotranspiration (ET) and its drivers vary under rainfed semi-arid conditions remains limited, despite general estimates across growth stages. This study aimed to quantify growth stage–specific ET in rainfed maize, characterize its soil and atmospheric controls, and evaluate seasonal and interannual variability using the Surface Energy Balance System (SEBS) model. ET was measured using the eddy covariance method over two long rainy seasons. Crop growth stages were identified using the normalized difference vegetation index (NDVI) from Sentinel-2, and ERA5 reanalysis data were used as inputs for the SEBS model. The measured growing‐season ET ranged from 221 to 269 mm season⁻¹ for the two wet years. However, long‐term SEBS estimates (2014–2022) revealed rainfall control on soil moisture and ET, with seasonal ET spanning 94–408 mm season⁻¹. Results show that the critical soil moisture threshold (θcrit) separating non-stressed and water-stressed ET conditions is not a fixed soil property but varies with crop growth stage and soil depth. Growth-stage-specific θcrit at 0.1 m depth ranged from 0.05 to 0.07, while growing-season θcrit derived from ETSEBS varied from 0.04 to 0.09 across years. The ET–soil matric potential relationship exhibited stage-specific hydraulic thresholds (–1.5 MPa during early vegetative and –1.3 MPa during reproductive stages), reflecting shifts in soil–plant hydraulic functioning across the season. Together, these stage‐specific moisture and stress thresholds clarify ET responses to soil and rainfall dynamics, enhancing crop‐model parameterization and informing water‐management strategies in rainfed semi‐arid maize systems.
Subjects
ERA5
Maize growth stages
SEBS
Soil matric potential
Soil moisture content
Publisher
Elsevier BV
Type
journal article