Browsing by Author "Meza, Francisco J."

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    Assessments CO2 assimilation on a per-leaf-area basis are related to total leaf area
    (AMER SOC HORTICULTURAL SCIENCE, 2007) Righetti, Timothy L.; Vasconcelos, Carmo; Sandrock, David R.; Ortega Farias, Samuel; Moreno, Yerko; Meza, Francisco J.
    Net photosynthetic rates often are dependent on leaf size when expressed on a leaf-area basis (CO2 assimilation as ULMOI(.)m(-2.)s(-1)). Therefore, distinguishing between leaf-size-related and other causes of differences in net photosynthetic rate cannot be determined when data are presented on a leaf-area basis. From a theoretical perspective, CO2 assimilation expressed on a leaf-area basis (mu mol(.)m(2.)s(1)) will be independent of leaf area only when total net CO(2)assimilation (leaf CO(2)assimilation as mu mol(.)s(-1)) is linearly related to leaf area and the function describing this relationship has a nonzero y intercept. This situation was not encountered in the data sets we evaluated; therefore, ratio-based estimates Of CO2 assimilation were often misleading. When CO2 assimilation data are expressed on a per-leaf-area basis (the standard procedure in the photosynthesis literature), it is difficult to determine how photosynthetic efficiency changes as leaves or plants mature and difficult to compare the efficiency of treatments or cultivars when leaf size or total plant leaf area varies.
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    Climate change impacts on irrigated maize in Mediterranean climates: Evaluation of double cropping as an emerging adaptation alternative
    (ELSEVIER SCI LTD, 2008) Meza, Francisco J.; Silva, Daniel; Vigil, Hernan
    Because its relevance for the sustenance and livelihood of human systems, the assessment of the impacts that future climatic conditions may have on agricultural productivity becomes a key piece of information for agricultural scientists and policy makers.
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    Economic value of seasonal climate forecasts for agriculture: Review of ex-ante assessments and recommendations for future research
    (AMER METEOROLOGICAL SOC, 2008) Meza, Francisco J.; Hansen, James W.; Osgood, Daniel
    Advanced information in the form of seasonal climate forecasts has the potential to improve farmers' decision making, leading to increases in farm profits. Interdisciplinary initiatives seeking to understand and exploit the potential benefits of seasonal forecasts for agriculture have produced a number of quantitative ex-ante assessments of the economic value of seasonal climate forecasts. The realism, robustness, and credibility of such assessments become increasingly important as efforts shift from basic research toward applied research and implementation. This paper surveys published evidence about the economic value of seasonal climate forecasts for agriculture, characterizing the agricultural systems, approaches followed, and scales of analysis. The climate forecast valuation literature has contributed insights into the influence of forecast characteristics, risk attitudes, insurance, policy, and the scale of adoption on the value of forecasts. Key innovations in the more recent literature include explicit treatment of the uncertainty of forecast value estimates, incorporation of elicited management responses into bioeconomic modeling, and treatment of environmental impacts, in addition to financial outcomes of forecast response. It is argued that the picture of the value of seasonal forecasts for agriculture is still incomplete and often biased, in part because of significant gaps in published valuation research. Key gaps include sampling of a narrow range of farming systems and locations, incorporation of an overly restricted set of potential management responses, failure to consider forecast responses that could lead to "regime shifts," and failure to incorporate state-of-the-art developments in seasonal forecasting. This paper concludes with six recommendations to enhance the realism, robustness, and credibility of ex-ante valuation of seasonal climate forecasts.
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    Estimating reference evapotranspiration (ETo) using numerical weather forecast data in central Chile
    (ELSEVIER, 2010) Silva, Daniel; Meza, Francisco J.; Varas, Eduardo
    Water demand at a basin level is influenced by many factors such meteorological variables. soil moisture, vegetation type and irrigation system Among them, climate is the major driver, because weather conditions determine energy balances and vapor pressure deficits that affect the magnitudes of vapor flux from surface to atmosphere.
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    Impacts of Climate Change on Irrigated Agriculture in the Maipo Basin, Chile: Reliability of Water Rights and Changes in the Demand for Irrigation
    (ASCE-AMER SOC CIVIL ENGINEERS, 2012) Meza, Francisco J.; Wilks, Daniel S.; Gurovich, Luis; Bambach, Nicolas
    Agricultural regions located in snowmelt-dominated Mediterranean climate basins have been identified as being highly vulnerable to the impacts of climate change. The Maipo basin in central Chile is one such region. Projections of future climate conditions suggest major challenges for this basin. Precipitation levels are projected to decrease by the end of the century, and temperature levels in the mountains are expected to increase by around 3-4 degrees C. Such changes would affect both river discharge and irrigation water demand. This paper illustrates potential climate change impacts on the hydroclimatological regime of the Maipo basin, focusing on irrigated agriculture and its demands on water use rights. The impact assessment was carried out by combining a multisite stochastic weather generator with a disaggregation technique for historical monthly flows of the Maipo river at El Manzano. Demand for irrigation was simulated with a daily water budget model. Data showed that water demands from irrigated agriculture tend to increase as a consequence of the simulated changes in temperature and precipitation. The magnitudes of these changes depend on crop types and their prevalence in the region. It was concluded that the reliability of water allocations under the current water rights system may be strongly negatively affected. In particular, projected hydrological impacts for the climate change scenario considered indicate that the 15th percentile currently used as the basis for water rights may become the 40th or 50th percentile in the future, suggesting that present water allocations will become overcommitted. DOI: 10.1061/(ASCE)WR.1943-5452.0000216. (C) 2012 American Society of Civil Engineers.
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    Obtaining daily precipitation parameters from meteorological yearbooks
    (ELSEVIER SCIENCE BV, 2006) Meza, Francisco J.
    This study compares the performance of two different methods, one based on the method of moments and the other based on maximum likelihood, in their assessment of the main statistical features of daily precipitation using censored information found in meteorological yearbooks. A Monte Carlo simulation was performed to generate series of daily rainfall and summarize them in the same format meteorological yearbooks report precipitation. While the method of moments for censored data (c-Mo) is a good alternative for the estimation of the parameters of precipitation occurrence due to its simplicity, the method of maximum likelihood for censored data (c-MLE) shows better results in estimating the parameters and quantiles of daily precipitation intensities. The c-MLE method is a good alternative even in situations in which the wrong candidate distribution is fit. The precision of the estimates obtained using both methods is increased when larger sample sizes are used, however c-MLE shows better results than c-Mo method for small sample sizes. (c) 2006 Elsevier B.V. All rights reserved.