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    Estimation of Yield Response Factor for Each Growth Stage under Local Conditions Using AquaCrop-OS
    (2020)
    Mathias Kuschel-Otárola
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    Niels Schütze
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    Eduardo Holzapfel
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    ;
    Oleksandr Mialyk
    We propose a methodology to estimate the yield response factor (i.e., the slope of the water-yield function) under local conditions for a given crop, weather, sowing date, and management at each growth stage using AquaCrop-OS. The methodology was applied to three crops (maize, sugar beet, and wheat) and four soil types (clay loam, loam, silty clay loam, and silty loam), considering three levels of bulk density: low, medium, and high. Yields are estimated for different weather and management scenarios using a problem-specific algorithm for optimal irrigation scheduling with limited water supply (GET-OPTIS). Our results show a good agreement between benchmarking (mathematical approach) and benchmark (estimated by AquaCrop-OS) using the Normalised Root Mean Square Error (NRMSE), allowing us to estimate reliable yield response factors ( K y ) under local conditions and to dispose of the typical simple mathematical approach, which estimates the yield reduction as a result of water scarcity at each growth stage.
      1Scopus© Citations 12
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    Decadal Variability of Dry Days in Central Chile
    (2024)
    Daniela Latoja
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    Mario Lillo-Saavedra
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    Consuelo Gonzalo-Martin
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    Marcelo Somos-Valenzuela
    Dry days are crucial in precipitation variability and water scarcity, particularly in Mediterranean regions facing increasing aridity. Despite their importance, most research focuses on precipitation amounts and temporal dynamics. This study addresses this gap by analyzing dry days’ temporal and spatial variability in central Chile (32–40 S), a region experiencing prolonged drought. We examined dry day patterns from 1960 to 2021 using high-resolution gridded precipitation data, defining dry days with five precipitation thresholds (0.10, 1, 2.5, 5, and 10 mm/day). Principal component and trend analyses were employed to characterize spatial and temporal variability. Results reveal a spatial pattern of dry days closely following precipitation patterns, with more dry days in northern and coastal areas. The first principal component explains 70–80% of the variance, and clustering methods allowed the definition of five homogeneous regions with distinct monthly dry-day characteristics. Long-term trends show a significant increase in annual dry days south of 38°S, while trends are weaker and non-significant further north. Notably, trend direction is highly sensitive to the analysis period, with some regions showing opposing trends before and after 1982. The 2010–2019 megadrought is detectable in decadal anomalies. We found links between dry day anomalies and large-scale climate patterns, suggesting modulation by changes in subtropical and extratropical atmospheric circulation. This comprehensive characterization of dry day climatology and variability provides crucial insights for water resource management and climate change adaptation in central Chile and similar Mediterranean regions worldwide. Our findings highlight the importance of considering dry day frequency in drought assessment and water planning, contributing to a more nuanced understanding of precipitation patterns in Mediterranean climates.
      8Scopus© Citations 6
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    Shifting dry spells in Central Chile: Implications for agricultural water planning
    (Wiley, 2025-10-22)
    Daniela Latoja
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    ;
    Mario Lillo
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    <jats:sec> <jats:title>Abstract</jats:title> <jats:p>Chile's agricultural production occurs in a highly variable Mediterranean climate and faces declining annual precipitation trends as well as growing competition from other uses. Water availability for agriculture depends on winter precipitation; however, a more even distribution of precipitation throughout the year would better support agricultural planning and management. We examine the occurrence, frequency, and trends of dry spells in Central Chile (32°–40° S) as a proxy for changes in the timing of dry‐wet seasons, using a gridded daily precipitation dataset spanning the period from 1960 to 2021. Our results indicate a significant increase in dry spells (+1 event/decade), but shorter (−2 days/event), and a significant decrease in precipitation per wet spell (−2 mm/event/decade). Findings suggest that changes in dry spells should also be considered in planning and policy, as some regions may be experiencing water shortages due to shifts in timing and access, rather than simply having less water.</jats:p> </jats:sec> <jats:sec> <jats:title>Core Ideas</jats:title> <jats:p> <jats:list list-type="bullet"> <jats:list-item> <jats:p>Changes in the length and timing of dry and wet spells impact seasonal precipitation.</jats:p> </jats:list-item> <jats:list-item> <jats:p>Changes in dry spells introduce more uncertainty to agricultural planning in Central Chile.</jats:p> </jats:list-item> <jats:list-item> <jats:p>Dry spells analysis complements other annual precipitation deficit indices.</jats:p> </jats:list-item> </jats:list> </jats:p> </jats:sec>
      1Scopus© Citations 2
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    Early Estimation of Tomato Yield by Decision Tree Ensembles
    (2022)
    Mario Lillo-Saavedra
    ;
    Alberto Espinoza-Salgado
    ;
    Angel García-Pedrero
    ;
    Camilo Souto
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    Eduardo Holzapfel
    Crop yield forecasting allows farmers to make decisions in advance to improve farm management and logistics during and after harvest. In this sense, crop yield potential maps are an asset for farmers making decisions about farm management and planning. Although scientific efforts have been made to determine crop yields from in situ information and through remote sensing, most studies are limited to evaluating data from a single date just before harvest. This has a direct negative impact on the quality and predictability of these estimates, especially for logistics. This study proposes a methodology for the early prediction of tomato yield using decision tree ensembles, vegetation spectral indices, and shape factors from images captured by multispectral sensors on board an unmanned aerial vehicle (UAV) during different phenological stages of crop development. With the predictive model developed and based on the collection of training characteristics for 6 weeks before harvest, the tomato yield was estimated for a 0.4 ha plot, obtaining an error rate of 9.28%.
      1  1Scopus© Citations 10
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    Force Measurement with a Strain Gauge Subjected to Pure Bending in the Fluid–Wall Interaction of Open Water Channels
    (2022)
    Luis Santana
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    ;
    Eric Forcael
    An experimental method to measure forces of small magnitude with a strain gauge as a force sensor in the fluid–wall interaction of open water channels is presented. Six uniaxial strain gauges were employed for this purpose, which were embedded across the entire sensing area and subjected to pure bending, employing two-point bending tests. Sixteen two-point bending tests were performed to determine the existence of a direct relationship between the load and the instrument signal. Furthermore, a regression analysis was used to estimate the parameters of the model. A data acquisition system was developed to register the behavior of the strain gauge relative to the lateral displacement induced by the loading nose of the universal testing machine. The results showed a significant linear relationship between the load and the instrumental signal, provided that the strain gauge was embedded between 30% and 45% of the central axis in the sensing area of the sensor (R2 &gt; 0.99). Thus, the proposed sensor can be employed to measure forces of small magnitude. Additionally, the linear relationship between the load and the instrumental signal can be used as a calibration equation, provided that the strain gauge is embedded close to the central axis of the sensing area.
      1  2Scopus© Citations 5