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Net radiation is an essential forcing of climate in the lower layers of Earth's atmosphere. In this paper, radiation balance is measured in clay soil and green grass, and is compared with three urban materials. These materials: asphalt, concrete and white painted elastomeric polystyrene roofing sheet are widely used in Mexicali, Baja California, México. This study was carried out during August of 2011, the hottest time of the year. The 24-hour average values of net radiation found were: 137.2 W·m −2 for asphalt, 119.1 for concrete, 104.6 for clay soil, 152 for green grass and 29.2 for the polystyrene insulation. The latter two types of materials are likely to be the most effective in reducing urban heat island effects. This variation in the radiation balance has widespread implications for human living conditions, as land cover change tends to be towards surfaces that have higher levels of net radiation.

* Autor a quien debe ser dirigida la correspondencia.Recibido Abr. 26, 2013; Aceptado Jun. 17, 2013; Versión final recibida Ago. 16, 2013 Resumen El objetivo del estudio es aplicar, comparar y validar la técnica de modelado dinámico en la estimación de intensidad y hora en que ocurre la isla urbana de calor en Mexicali, México. Se analizaron diferencias térmicas horarias entre temperaturas urbanas y suburbanas de cuatro estaciones climatológicas durante el periodo 2002 a 2005. Mediante un algoritmo genético implementado con el software Stella se interpolaron temperaturas y se compararon con las calculadas por técnicas de interpolación elaboradas con un sistema de información geográfica. La validación se realizó mediante una prueba estadística de diferencia de medias. En tres estudios de caso se detectó el desarrollo de la isla urbana de calor con intensidades máximas promedio de 5.4°C, 5.2°C y 5.3°C. La validación evidenció que no existe diferencia significativa entre las interpolaciones realizadas con el modelo dinámico y con el sistema de información geográfica. Se concluye que el modelo dinámico es confiable y útil para el fin propuesto. Palabras clave: isla urbana de calor, modelación dinámica, algoritmo genético, interpolación de temperaturas. Detection of Urban Heat Island using Dynamic Modeling in Mexicali, B.C., Mexico AbstractThe aim of this study is to apply, compare and validate the dynamic modeling technique to estimate intensity and time of occurrence of the Urban Heat Island (UHI) in Mexicali, Mexico. Hourly temperature differences between urban and suburban air temperatures of four weather stations during the period 2002 to 2005 were analyzed. Using genetic algorithms developed with the software Stella, air temperatures were interpolated and compared to those calculated with interpolation techniques developed with a Geographic Information System. Their similarity was validated by a statistical test of mean difference. In three case studies, the development of the UHI, with average intensities of 5.4°C, 5.2°C and 5.3°C was detected. The validation showed that there is no significant difference between the interpolations done with the dynamic model and with the Geographic Information System. It is concluded that the dynamic model is reliable and useful for the intended purposes.

Autor a quien debe ser dirigida la correspondencia. ResumenSe evaluaron dos modelos de reducción de escala en la generación de escenarios de cambio climático en el Valle de Mexicali en México. Las técnicas comparadas son un Generador Estocástico de Tiempo Meteorológico (LARS-WG) y un método dinámico-estadístico (SDSM). Cada técnica se evaluó por su habilidad para reproducir algunas características estadísticas del clima observado en el período . Se elaboraron escenarios de cambio climático de temperatura y precipitación para los horizontes temporales 2020 y 2050. El LARS WG y el SDSM son técnicas sencillas que mostraron habilidades diferentes en la simulación de momentos estadísticos del clima observado, siendo ambos más eficientes para simular la temperatura que la precipitación. Para uno de los escenarios considerados se encontró diferencias de 0.1°C y 0.2°C para temperatura máxima y temperatura mínima y del 40.4% al 76.7% para precipitación. Palabras clave: reducción de escala, cambio climático, valle de Mexicali, LARS-WG, SDSM AbstractTwo downscaling models in the generation of climate change scenarios in the Mexicali valley in México were evaluated. The evaluated techniques were the stochastic weather generator (LARS-WG) and the dynamical-statistical model (SDSM). Each technique was evaluated for its ability to reproduce some statistical characteristics of the observed climate during the period 1961-1990. Climate change scenarios of temperature and precipitation for the period 2020 to 2050 were considered. LARS WG and SDSM are simple techniques that showed different abilities in simulating statistical moments of the observed climate, but both were more efficient for simulating temperature than precipitation. For one of evaluated scenarios differences of 0.1°C and 0.2°C for maximum and minimum temperature and 40.4% to 76.7% for precipitation.

In Mexico, open dumps that are maintained by the municipality but provide no covering of waste are not uncommon. Further, disposal at these sites is often performed by burning. The aim of this study was to determine the leachate plume from an open dump located in a depositional deltaic environment, with arid climate, low rainfall and where the water table is about 2 m below the surface. The methodology comprised analysis of groundwater monitoring wells and geophysical and geochemical prospecting techniques. The 3D geoelectric interpretation shows a typical area of these depositional environments with low resistive values (10-20 X-m) associated with the presence of sands and clays interbedded. However, there is a very low resistivity zone associated with the dump's impact which reaches values below 5 X-m, and it is located where the disposal and burning of wastes occurred. Another zone with values above 16 X-m appears as a limit for the advance of the saline. This is interpreted as a sandy lenses area. These sandy lenses with higher porosity transport aquifer's water. Thus the dump is in direct contact by this conduct with clean groundwater. Piper diagrams constructed with the chemical data analysis reveal that the groundwater in the area corresponds to the chlorinated and/or sulfated sodium type, showing the impact caused by the dump. The monitoring well (NP8, on-site) with the highest dissolved solids content behaves anomalously and belongs to the more conductive zone according to the geoelectric profiles. The subsoil geochemical behavior is influenced by the seasonal water table variations provoking the dissolution of burned and unburned wastes, but the effects of slow flows in the direction of the regional flow are not discarded. Although the most impacted area within the dump is characterized to a depth of 10 m, there is a slow flow in the direction of the regional flow that has been moving pollutants out of the dumpsite during its almost 20 years of operation. The results of this study provide valuable information for the authorities to carry out an appropriate restoration project.