Francisco J. Meza

Estimation of mean monthly solar global radiation as a function of temperature

Solar radiation is the primary energy source for all physical and biochemical processes that take place on earth. Energy balances are a key feature of processes such as temperature changes, snow melt, carbon fixation through photosynthesis in plants, evaporation, wind intensity and other biophysical processes. Solar radiation level is sometimes recorded, but generally it needs to be estimated by empirical models based on frequently available meteorological records such as hours of sunshine or temperature. This paper evaluates the behavior of two empirical models based on the difference between maximum and minimum temperatures and compares results with a model based on sunshine hours. This work concludes that empirical models based on temperature have a larger coefficient of determination than the model based on cloud cover for the normal conditions of Chile. These models are easy to use in any location if the parameters are correctly adjusted. In addition, probability distribution functions and confidence intervals for solar radiation estimates using stochastic modeling of temperature differences were calculated. ©2000 Published by Elsevier Science B.V. All rights reserved.

Water security and adaptive management in the Arid Americas

Societal use of freshwater, ecosystems’ dependence on water, and hydroclimatic processes interact dynamically. Changes in any of these subsystems can cause unpredictable feedback, resulting in water insecurity for humans and ecosystems. By drawing on resilience theory, we extend current productive–destructive framings of water security to better address societal–ecosystem–hydroclimatic (SEH) interactions, dynamics, and uncertainties that drive insecurity but also offer response opportunities. Strengthening water security in this sense requires strategies that (1) conceptually and practically interlink SEH subsystems; (2) recognize extreme conditions and thresholds; and (3) plan for water security via structured exchanges between researchers and decision makers in ways that account for institutions and governance frameworks. Through scrutiny of case evidence from water-scarce regions in western North America and the Central Andes, we assert that ensuring water security requires adaptive management (interactive planning that accounts for uncertainties, initiates responses, and iteratively assesses outcomes). Researchers and stakeholders from these regions are pursuing a multiyear series of workshops that promote science-based decision making while factoring in the political implications of water planning. This study briefly reviews an emerging water security initiative for the arid Americas that aims to enhance understanding of adaptive approaches to strengthen water security. Finally, by synthesizing efforts in the arid Americas, we offer insights for other water-insecure regions.

Impacts of Climate Change on Irrigated Agriculture in the Maipo Basin, Chile: Reliability of Water Rights and Changes in the Demand for Irrigation

AbstractAgricultural 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°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 ...

Value of perfect forecasts of sea surface temperature anomalies for selected rain-fed agricultural locations of Chile

This study evaluates the value of perfect forecasts of El Nino phases for selected rain-fed agricultural locations of Chile. The analysis framework incorporates a soil–crop-atmosphere system model and employs an expected utility decision algorithm that reflects a wide range of possible risk attitudes. The value of perfect forecasts is generally greater than zero indicating that real El Nino forecasts could potentially have economic value. Forecast value depends upon crop and location. The value of forecasts increases as the agricultural system becomes more susceptible to climatic variability. Among the regions under study, Temuco (38.5 ◦ S) and Valdivia (39.4 ◦ S) are likely to see the largest gains from long-term sea surface temperature forecasts.

Value of operational forecasts of seasonal average sea surface temperature anomalies for selected rain-fed agricultural locations of Chile

This study investigates the economic value of several simple forecasts of 3-month average eastern tropical Pacific sea surface temperature anomalies (SSTA). Two Chilean agricultural regions were selected and the value of information for the main crops is obtained using an integrated model. The value of perfect forecasts is computed along with several simply formulated imperfect seasonal forecasts using a classification of the sea surface temperature anomalies in the equatorial Pacific. The main relationships between the accuracy of the forecasts and the economic benefits that can be obtained by using sea surface temperature forecasts are presented.

Nitrogen Application in Irrigated Rice Grown in Mediterranean Conditions: Effects on Grain Yield, Dry Matter Production, Nitrogen Uptake, and Nitrogen Use Efficiency

ABSTRACT Field experiments were conducted in the major rice growing area of Chile to evaluate the effects of nitrogen (N) fertilization and site on grain yield and some yield components, dry matter production, N uptake, and N use efficiency in rice cultivar ‘Diamante’. Two sites (indicated as sites 1 and 2) and six N rates (0, 50, 100, 150, 200, and 300 kg N ha−1) were compared. Nitrogen fertilization increased yield, panicle density, spikelet sterility, dry matter production, and N uptake at maturity. 90% of maximum yield was obtained with 200 kg N ha−1 in site 1 (12,810 kg ha−1) and with 100 kg N ha−1 in site 2 (8,000 kg ha−1). These differences were explained by lower panicle density, and the resulting lower dry matter production and N uptake in site 2. Nitrogen use efficiency for biomass and grain production, and grain yield per unit of grain N decreased with N fertilization. While, agronomic N use efficiency and N harvest index were not affected. All N use efficiency indices were significantly higher in site 1, except grain yield per unit of grain N. The observed variation in N use efficiency indices between sites would reflect site-specific differences in temperature and solar radiation, which in turn, determined yield potentials of each site. On the basis of these results, cultivar ‘Diamante’ would correspond to a high-N use efficiency genotype for grain yield.

Science-Policy Dialogues for Water Security: Addressing Vulnerability and Adaptation to Global Change in the Arid Americas

www.EnvironmEntmagazinE.org voLUmE 54 nUmBEr 3 Climate change and watersupply uncertainty coupled with mounting human demands for water are straining the availability and quality of freshwater in much of the world. These twin forces cause a palpable rise in societal vulnerability, here considered as susceptibility to adverse effects of global environmental change.1 The vulnerability of water supplies (or, water vulnerability) places human communities at risk for exposure,2 or change,3 and thereby creates huge adaptation challenges. The actions being taken to reduce risks and capitalize on opportunities are considered adaptation or adaptive strategies.4 The most sensitive and vulnerable communities are those that face the greatest exposure and are most limited in their capacity to adapt. Rapidly growing and ever wealthier urban populations, expanding agribusinesses, diverse industries, extensive mining, power generation, and tourism often deprive water from or degrade its quality for use by marginalized populations of smallholder farmers and the urban poor, as well as for ecosystems along streams, lakes, and coasts recognized as biodiversity hotspots in the arid landscape. The arid5 Americas—as characterized by the southwestern United States, northwestern Mexico, north-central Chile and Argentina, and northeastern Brazil—manifest the just-described challenges especially well.6 This article focuses on two areas where our research team has been developing science-policy adaptation strategies: (1) the Sonora-Arizona drylands shared by Mexico and the United States (See map at right), and (2) the drylands east and west of the Central Andes in Chile and Argentina (see map, page 32). In these areas water remains acutely limited even as drought and flood extremes increase, ecosystems are under growing pressure, and economic globalization drives water demand. These global-change conditions threaten the security of access to water. Yet the foregoing conditions prevail—with little regard for constraints to supply, insufficient understanding of vulnerability, and inadequate attention to adaptive measures.7 To the extent that such problems are attributable to human agency,8 there is evidence that effective policies and actions can alleviate some of the harm.9 Our article describes two interactive Science-Policy Dialogues for Water Security:

Application of water quality indices and analysis of the surface water quality monitoring network in semiarid North-Central Chile

Surface water quality has increasing importance worldwide and is particularly relevant in the semiarid North-Central Chile, where agriculture and mining activities are imposing heavy pressure on limited water resources. The current study presents the application of a water quality index in four watersheds of the 29°–33°S realm for the period 1999–2008, based on the Canadian Council of Ministers for the Environment approach and the Chilean regulation for irrigation water quality. In addition, two modifications to the index are tested and a comprehensive characterization of the existing monitoring network is performed through cluster analysis. The basins studied show fairly good water quality in the overall, specially the Limarí basin. On the other hand, the lower index values were obtained for the headwaters of Elqui, associated with the El Indio mining district. The first modification of the indicator (i.e., to consider parameters differentially according to their effect on human health or the environment) did not produce major differences with respect to the original index, given the generally good water quality. The second modification (i.e., to consider as threshold values the more restrictive figures derived from a set of regulations) yielded important differences in the indicator values. Finally, an adequate characterization of the monitoring network was obtained. The results presented spatial coherence and the information can be used as a basis for the optimization of the monitoring network if required.

Using a Gridded Global Dataset to Characterize Regional Hydroclimate in Central Chile

AbstractCentral Chile is facing dramatic projections of climate change, with a consensus for declining precipitation, negatively affecting hydropower generation and irrigated agriculture. Rising from sea level to 6000 m within a distance of 200 km, precipitation characterization is difficult because of a lack of long-term observations, especially at higher elevations. For understanding current mean and extreme conditions and recent hydroclimatological change, as well as to provide a baseline for downscaling climate model projections, a temporally and spatially complete dataset of daily meteorology is essential. The authors use a gridded global daily meteorological dataset at 0.25° resolution for the period 1948–2008, adjusted by monthly precipitation observations interpolated to the same grid using a cokriging method with elevation as a covariate. For validation, daily statistics of the adjusted gridded precipitation are compared to station observations. For further validation, a hydrology model is driven...

Irrigation infrastructure development in the Limarí Basin in Central Chile: implications for adaptation to climate variability and climate change

One option to deal with climate variability in agriculture is to build irrigation infrastructure, although this may lead to the overdevelopment of water resources, leading to ‘basin closure’. The Limarí Basin, in central north Chile, has relied on irrigation infrastructure over the last 30 years to increase water supply reliability and extend irrigated acreage, especially for permanent crops. This situation has reduced adaptation opportunities in the basin, which is currently experiencing a severe drought that, according to climate change projections, is expected to persist in the future, with important consequences for the sustainability of agriculture production.