Browsing by Author "Perez, Felipe"

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    Comparing Methods for the Regionalization of Intensity-Duration-Frequency (IDF) Curve Parameters in Sparsely-Gauged and Ungauged Areas of Central Chile
    (2023) Sanguesa, Claudia; Pizarro, Roberto; Ingram, Ben; Ibanez, Alfredo; Rivera, Diego; Garcia-Chevesich, Pablo; Pino, Juan; Perez, Felipe; Balocchi, Francisco; Pena, Francisco
    Estimating intensity-duration-frequency (IDF) curves requires local historical information of precipitation intensity. When such information is unavailable, as in areas without rain gauges, it is necessary to consider other methods to estimate curve parameters. In this study, three methods were explored to estimate IDF curves in ungauged areas: Kriging (KG), Inverse Distance Weighting (IDW), and Storm Index (SI). To test the viability of these methods, historical data collected from 31 rain gauges distributed in central Chile, 35 degrees S to 38 degrees S, are used. As a result of the reduced number of rain gauges to evaluate the performance of each method, we used LOOCV (Leaving One Out Cross Validation). The results indicate that KG was limited due to the sparse distribution of rain gauges in central Chile. SI (a linear scaling method) showed the smallest prediction error in all of the ungauged locations, and outperformed both KG and IDW. However, the SI method does not provide estimates of uncertainty, as is possible with KG. The simplicity of SI renders it a viable method for extrapolating IDF curves to locations without data in the central zone of Chile.
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    Establishment of Monterrey Pine (Pinus radiata) Plantations and Their Effects on Seasonal Sediment Yield in Central Chile
    (2023) Pizarro, Roberto; Garcia-Chevesich, Pablo; Ingram, Ben; Sanguesa, Claudia; Pino, Juan; Ibanez, Alfredo; Mendoza, Romina; Vallejos, Carlos; Perez, Felipe; Flores, Juan Pablo; Vera, Mauricio; Balocchi, Francisco; Bustamante-Ortega, Ramon; Martinez, Gisella
    Sediment production and transport in a basin are generally a function of the degree of soil protection, normally represented by plant cover. In this study, two basins located at similar latitudes but with different hydrological regimens and plant covers were studied, one with a pluvial regimen and forest plantations (Purapel) and another one with the pluvio-nival regimen and native forest (Nuble). For this purpose, sediment yield was analyzed in both drainage areas using the Mann-Kendall statistical test. Both basins showed larger amounts of sediment production during winter months. In addition, sediment yield trends did not show significant variation in the case of the Nuble, most likely due to non-relevant changes in plant cover over time. However, there is a sustained decrease in annual sediment release at Purapel, coinciding with the afforestation in the basin, so it is logical to attribute the referred reduction to this process. For the first time, the behavior of two watersheds is contrasted, one covered with native forest and the other one with forest plantations, appreciating that the basin covered with plantations presents a reduction in sediment production over time, which means that forest plantations are efficient in sediment retention, even in contrast to native forest. However, both basins have different types of soil, topography, etc., meaning that more studies are needed to support this theory.
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    Millimagnitude photometry for transiting extrasolar planetary candidates.: II. transits of OGLE-TR-113-B in the optical and near-ir
    (2007) Diaz, Rodrigo F.; Ramirez, Sebastían; Fernandez, José Miguel; Gallardo, José; Gieren, Wolfgang; Ivanov, Valentin D.; Mauas, Pablo; Minniti, Dante; Pietrzynski, Grzegorz; Perez, Felipe; Ruiz, Maria Teresa; Udalski, Andrzej; Zoccali, Manuela
    We present precise V-and K-s-band transit photometry for the planetary host star OGLE-TR-113. Using the Ks-band photometry, we confirm the dwarf nature of OGLE-TR-113 and obtain new estimates for its effective temperature, distance, and reddening. We employ the V-band photometry to obtain planetary and orbit parameters from the transit fit, alpha = 0.0232 +/- 0: 0038 AU, orbital period P = 1.4324752 +/- 0.0000015 day, i = 86.7-90, and R-p 1.09 +/- 0.09 R-J. These values are in excellent agreement with previous works. Assuming a mass M-p 1.32 +/- 0.19 M-J for the planet, we obtain its mean density p = 1.26 +/- 0.50 g cm(-3), also in agreement with previous works. The transit observed in the K-s-band has a larger scatter, and we find its amplitude to be consistent with that in the V band. In this way, we find an independent confirmation of the planetary nature of OGLE-TR-113b.
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    Streamflow Trends in Central Chile
    (2023) Sanguesa, Claudia; Pizarro, Roberto; Ingram, Ben; Balocchi, Francisco; Garcia-Chevesich, Pablo; Pino, Juan; Ibanez, Alfredo; Vallejos, Carlos; Mendoza, Romina; Bernal, Alejandra; Valdes-Pineda, Rodrigo; Perez, Felipe
    The availability of water in Chile has shown signs of decline in recent decades. This is problematic because Chile's economy depends on mining, forestry, and agricultural activities, all limited by the availability of water resources. In this study, daily, monthly and annual flows in 31 basins located in the arid-semiarid zones (29 & DEG;12 & PRIME; S-33 & DEG;58 & PRIME; S) and in the humid-subhumid zones (34 & DEG;43 & PRIME; S-38 & DEG;30 & PRIME; S) of Chile were evaluated using the Mann-Kendall trend test and the quantile-Kendall procedure during three periods: 1984-2021 (31 stations), 1975-2021 (20 stations), and 1969-2021 (18 stations). Results showed that, at the annual level, trends were predominantly negative in both climatic zones and over the three periods analyzed. In the arid-semiarid zone, a higher frequency of annual significant negative trends was found in maximum flows in 1969-2021 and 1975-2021, compared to the last period under study. The humid-subhumid zone showed significant annual negative trends in all series analyzed. At the monthly level, on the other hand, the arid-semiarid zone showed a decrease in significant negative trends as the number of years analyzed increased, for all flow types. The humid-subhumid zone did not indicate a similar defined pattern. Likewise, the quantile-Kendall procedure showed a reduction in the significant trends as the length of the time series was increased in the arid-semiarid zone, but no such pattern was observed in the humid-subhumid zone. Furthermore, a relationship was observed for the PDO and the summer month flows for both zones. Consequently, it is concluded that the flow trends are generally negative, and their statistical significance depends on the period studied.