Formulation of a tropical town energy budget (t-TEB) scheme

This work describes the tropical town energy budget (t-TEB) scheme addressed to simulate the diurnal occurrence of the urban heat island (UHI) as observed in the Metropolitan Area of Rio de Janeiro (MARJ; -22A degrees S; -44A degrees W) in Brazil. Reasoning about the tropical urban climate have guided the scheme implementation, starting from the original equations from Masson (Bound-Lay Meteorol 94:357-397, 2000). The modifications include (a) local scaling approaches for obtaining flux-gradient relationships in the roughness sub-layer, (b) the Monin-Obukhov similarity framework in the inertial sub-layer, (c) increasing aerodynamic conductance toward more unstable conditions, and (d) a modified urban subsurface drainage system to transfer the intercepted rainwater by roofs to the roads. Simulations along 2007 for the MARJ are obtained and compared with the climatology. The t-TEB simulation is consistent with the observations, suggesting that the timing and dynamics of the UHI in tropical cities could vary significantly from the familiar patterns observed in mid-latitude cities-with the peak heat island intensity occurring in the morning than at night. The simulations are suggesting that the thermal phase shift of this tropical diurnal UHI is a response of the surface energy budget to the large amount of solar radiation, intense evapotranspiration, and thermal response of the vegetated surfaces over a very humid soil layer.

Non-stationary frequency analysis of extreme daily rainfall in Sao Paulo, Brazil

This work is an assessment of frequency of extreme values (EVs) of daily rainfall in the city of Sao Paulo. Brazil, over the period 1933-2005, based on the peaks-over-threshold (POT) and Generalized Pareto Distribution (GPD) approach. Usually. a GPD model is fitted to a sample of POT Values Selected With a constant threshold. However. in this work we use time-dependent thresholds, composed of relatively large p quantities (for example p of 0.97) of daily rainfall amounts computed from all available data. Samples of POT values were extracted with several Values of p. Four different GPD models (GPD-1, GPD-2, GPD-3. and GDP-4) were fitted to each one of these samples by the maximum likelihood (ML) method. The shape parameter was assumed constant for the four models, but time-varying covariates were incorporated into scale parameter of GPD-2. GPD-3, and GPD-4, describing annual cycle in GPD-2. linear trend in GPD-3, and both annual cycle and linear trend in GPD-4. The GPD-1 with constant scale and shape parameters is the simplest model. For identification of the best model among the four models WC used rescaled Akaike Information Criterion (AIC) with second-order bias correction. This criterion isolates GPD-3 as the best model, i.e. the one with positive linear trend in the scale parameter. The slope of this trend is significant compared to the null hypothesis of no trend, for about 98% confidence level. The non-parametric Mann-Kendall test also showed presence of positive trend in the annual frequency of excess over high thresholds. with p-value being virtually zero. Therefore. there is strong evidence that high quantiles of daily rainfall in the city of Sao Paulo have been increasing in magnitude and frequency over time. For example. 0.99 quantiles of daily rainfall amount have increased by about 40 mm between 1933 and 2005. Copyright (C) 2008 Royal Meteorological Society

Modeling study of the aspect ratio influence on urban canopy energy fluxes with a modified wall-canyon energy budget scheme

The influence of the aspect ratio (building height/street canyon width) and the mean building height of cities on local energy fluxes and temperatures is studied by means of an Urban Canopy Model (UCM) coupled with a one-dimensional second-order turbulence closure model. The UCM presented is similar to the Town Energy Balance (TEB) model in most of its features but differs in a few important aspects. In particular, the street canyon walls are treated separately which leads to a different budget of radiation within the street canyon walls. The UCM has been calibrated using observations of incoming global and diffuse solar radiation, incoming long-wave radiation and air temperature at a site in So Paulo, Brazil. Sensitivity studies with various aspect ratios have been performed to assess their impact on urban temperatures and energy fluxes at the top of the canopy layer. In these simulations, it is assumed that the anthropogenic heat flux and latent heat fluxes are negligible. Results show that the simulated net radiation and sensible heat fluxes at the top of the canopy decrease and the stored heat increases as the aspect ratio increases. The simulated air temperature follows the behavior of the sensible heat flux. (C) 2010 Elsevier Ltd. All rights reserved.

Anthropogenic heat in the city of So Paulo, Brazil

The main goal of this work is to describe the anthropogenic energy flux (Q (F)) in the city of So Paulo, Brazil. The hourly, monthly, and annual values of the anthropogenic energy flux are estimated using the inventory method, and the contributions of vehicular, stationary, and human metabolism sources from 2004 to 2007 are considered. The vehicular and stationary sources are evaluated using the primary consumption of energy based on fossil fuel, bio fuel, and electricity usage by the population. The diurnal evolution of the anthropogenic energy flux shows three relative maxima, with the largest maxima occurring early in the morning (similar to 19.9 Wm(-2)) and in the late afternoon (similar to 20.3 Wm(-2)). The relative maximum that occurs around noontime (similar to 19.6 Wm(-2)) reflects the diurnal pattern of vehicle traffic that seems to be specific to So Paulo. With respect to diurnal evolution, the energy flux released by vehicular sources (Q (FV)) contributes approximately 50% of the total anthropogenic energy flux. Stationary sources (Q (FS)) and human metabolism (Q (FM)) represent about 41% and 9% of the anthropogenic energy flux, respectively. For 2007, the monthly values of Q (FV), Q (FS), Q (FM), and Q (F) are, respectively, 16.8 +/- 0.25, 14.3 +/- 0.16, 3.5 +/- 0.03, and 34.6 +/- 0.41 MJ m(-2) month(-1). The seasonal evolution monthly values of Q (FV), Q (FS), Q (FM), and Q (F) show a relative minimum during the summer and winter vacations and a systematic and progressive increase associated with the seasonal evolution of the economic activity in So Paulo. The annual evolution of Q (F) indicates that the city of So Paulo released 355.2 MJ m(-2) year(-1) in 2004 and 415.5 MJ m(-2) year(-1) in 2007 in association with an annual rate of increase of 19.6 MJ m(-2) year(-1) (from 2004 to 2006) and 30.5 MJ m(-2) year(-1) (from 2006 to 2007). The anthropogenic energy flux corresponds to about 9% of the net radiation at the surface in the summer and 15% in the winter. The amplitude of seasonal variation of the maximum hourly value of the diurnal variation increases exponentially with latitude.

Atmosphere and hydrological controls of the evapotranspiration over a floodplain forest in the Bananal Island region, Amazonia

This article discusses seasonal and interannual variations of the evapotranspiration (ET) rates in Bananal Island floodplain, Brazil. Measurements included ET and sensible heat flux using the eddy covariance method, atmospheric forcings (net radiation, Rn, vapor pressure deficit, VPD, wind speed and air temperature), soil moisture profiles, groundwater level and flood height, taken from November 2003 to December 2006. For the hydrological years (October-September) of 2003/2004, 2004/2005 and 2005/2006, the accumulated precipitation was 1692, 1471, 1914 mm and the accumulated ET was 1361, 1318 and 1317 mm, respectively. Seasonal analyses indicated that ET decreased in the dry season (average 3.7 mm day(-1)), despite the simultaneous increase in Rn, air temperature and VPD. The increase of ET in the wet season and particularly in the flood period (average 4.1 mm day(-1)) showed that the free water surface evaporation strongly influenced the energy exchange. Soil moisture, which was substantially depleted during the dry season, and adaptative vegetation mechanisms such as leaf senescence contributed to limit the dry season ET. Strong drainage within permeable sandy soils helped to explain the soil moisture depletion. These results suggest that the Bananal flooding area shows a different pattern in relation to the upland Amazon forests, being more similar to the savanna strictu senso areas in central Brazil. For example, seasonal ET variation was not in phase with Rn; the wet season ET was higher than the dry season ET; and the system stored only a tiny memory of the flooding period, being sensitive to extended drought periods.