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<p>Reliable soil water balance models are needed for sugarcane water management under rainfed and non-standard field conditions. This study optimized crop coefficients and assessed the Thornthwaite and Mather Crop (ThM) and FAO-56 dual-Kc models for estimating daily and 10-day soil water content (θ) and actual evapotranspiration (ET<sub>a</sub>) in rainfed sugarcane in Alagoas State, Brazil. Field θ was measured with a reflectometry probe, and ET<sub>a</sub> was determined using the Bowen ratio-energy balance method. The Metropolis-Hastings algorithm implemented in OpenModel was used to optimize the mid-season crop coefficient (K<sub>c_mid</sub>) for ThM, and the mid-season basal crop coefficient (K<sub>cb_mid</sub>) and soil water depletion fraction (p) for dual-Kc, using measured ET<sub>a</sub> or θ as the optimization reference. The ET<sub>a</sub>-based optimized K<sub>c</sub> and K<sub>cb</sub> values were 0.89–0.90, lower than the FAO-56 tabulated values and close to the experimental K<sub>c</sub> (0.79 ± 0.11), whereas θ-based optimization resulted in a K<sub>cb</sub> of 1.04, and a very low K<sub>c</sub> (0.38), suggesting parameter compensation. Daily ET<sub>a</sub> estimates improved mainly under soil water recharge (P – ET<sub>c</sub> ≥ 0), whereas both models performed poorly under soil water extraction (P – ET<sub>c</sub> &lt; 0), indicating limitations in representing water stress and short-term soil water redistribution. Soil water content was simulated more consistently than ET<sub>a</sub>, especially after optimization. Aggregation to 10-day intervals improved model robustness, with dual-Kc performing better for ET<sub>a</sub> and ThM providing the best soil water estimates. Thus, the optimized models are useful for medium-term water balance assessment and irrigation scheduling but should be used cautiously for daily ET<sub>a</sub> estimation under water-stress conditions.</p>

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Inverse Modeling for Crop Coefficient Optimization in Thornthwaiteand Mather and FAO-56 Dual-Kc Models for Daily and 10-day Estimation of Actual Evapotranspiration and Soil Water Content in Rainfed Sugarcane

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年7月17日

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  • Jéssica Mota Pimenta,
  • Adolpho Emanuel Quintela da Rocha,
  • Marcos Alex dos Santos,
  • Guilherme Bastos Lyra,
  • Ricardo Araújo Ferreira Júnior,
  • Mariana de Oliveira Pereira,
  • Daniel Silveira Pinto Nassif,
  • José Leonaldo de Souza,
  • Fábio Freitas Ferreira,
  • Gustavo Bastos Lyra

摘要

Reliable soil water balance models are needed for sugarcane water management under rainfed and non-standard field conditions. This study optimized crop coefficients and assessed the Thornthwaite and Mather Crop (ThM) and FAO-56 dual-Kc models for estimating daily and 10-day soil water content (θ) and actual evapotranspiration (ETa) in rainfed sugarcane in Alagoas State, Brazil. Field θ was measured with a reflectometry probe, and ETa was determined using the Bowen ratio-energy balance method. The Metropolis-Hastings algorithm implemented in OpenModel was used to optimize the mid-season crop coefficient (Kc_mid) for ThM, and the mid-season basal crop coefficient (Kcb_mid) and soil water depletion fraction (p) for dual-Kc, using measured ETa or θ as the optimization reference. The ETa-based optimized Kc and Kcb values were 0.89–0.90, lower than the FAO-56 tabulated values and close to the experimental Kc (0.79 ± 0.11), whereas θ-based optimization resulted in a Kcb of 1.04, and a very low Kc (0.38), suggesting parameter compensation. Daily ETa estimates improved mainly under soil water recharge (P – ETc ≥ 0), whereas both models performed poorly under soil water extraction (P – ETc < 0), indicating limitations in representing water stress and short-term soil water redistribution. Soil water content was simulated more consistently than ETa, especially after optimization. Aggregation to 10-day intervals improved model robustness, with dual-Kc performing better for ETa and ThM providing the best soil water estimates. Thus, the optimized models are useful for medium-term water balance assessment and irrigation scheduling but should be used cautiously for daily ETa estimation under water-stress conditions.