Tantravahi Venkata Ramana Rao

Trends of precipitation indices in Ceará State.

The principal objective of this work is to provide new information on the trends in the total precipitation and extreme events of precipitation in the State of Ceara, making an analysis of different indices of detection of climatic changes, based on data of daily precipitation. Precipitation data of 18 stations were used, in the period from 1935 to 2006, representing all the microregions of the State; the software used in the processing and quality control of the data was RClimdex 1.9.0. The results show local changes in the precipitation and a visible increase in the humidity conditions in Ceara.

Assessment of daily actual evapotranspiration with SEBAL and S-SEBI algorithms in cotton crop

The main objective of this study is to assess the daily ET accuracy obtained by remote sensing algorithms in comparison with measurements in situ. The experiment was conducted in the State of Ceara, Brazil, in a cotton experimental field of EMBRAPA using Bowen ratio measurements to obtain the energy balance components. SEBAL and S-SEBI algorithms were used with four TM Landsat – 5 images of 2005, in order to determine the actual evapotranspiration of cotton crop. The comparison between the estimated values by remote sensing algorithms and the measured values in situ showed that the methods (SEBAL and S-SEBI) presented satisfactory results. The S-SEBI algorithm is an important tool to be applied in ET analysis of semi-arid regions, due its practicability to solve the energy balance and its processing is simpler than SEBAL algorithm which needs the solution of an iterative process.

Estimation of soil moisture in the root-zone from remote sensing data

Field-based soil moisture measurements are cumbersome. Thus, remote sensing techniques are needed because allows field and landscape-scale mapping of soil moisture depth-averaged through the root zone of existing vegetation. The objective of the study was to evaluate the accuracy of an empirical relationship to calculate soil moisture from remote sensing data of irrigated soils of the Apodi Plateau, in the Brazilian semiarid region. The empirical relationship had previously been tested for irrigated soils in Mexico, Egypt, and Pakistan, with promising results. In this study, the relationship was evaluated from experimental data collected from a cotton field. The experiment was carried out in an area of 5 ha with irrigated cotton. The energy balance and evaporative fraction (Λ) were measured by the Bowen ratio method. Soil moisture (θ) data were collected using a PR2 - Profile Probe (Delta-T Devices Ltd). The empirical relationship was tested using experimentally collected Λ and θ values and was applied using the Λ values obtained from the Surface Energy Balance Algorithm for Land (SEBAL) and three TM - Landsat 5 images. There was a close correlation between measured and estimated θ values (p<0.05, R2 = 0.84) and there were no significant differences according to the Student t-test (p<0.01). The statistical analyses showed that the empirical relationship can be applied to estimate the root-zone soil moisture of irrigated soils, i.e. when the evaporative fraction is greater than 0.45.

DOWNWARD LONGWAVE RADIATION ESTIMATES FOR CLEAR-SKY CONDITIONS OVER NORTHEAST BRAZIL

The main objective of this paper is to assess the performance of nine downward longwave radiation equations for clear-sky condition and develop a locally adjusted equation using the observed vapor pressure and air temperature data. The radiation and atmospheric parameters were measured during the months of October 2005 to June 2006 at a micrometeorological tower installed at the experimental site in a banana orchard in the semiarid region of Northeast Brazil. The comparative statistics for the performance of the downward longwave radiation calculation models during daytime and nighttime compared to measured data have shown that the parameterizations with more physical foundations have the best results. The locally adjusted equation and Sugita and Brutsaert model developed in 1993 showed errors less than 1.0% in comparison with measured values. Downward longwave radiation is one of the most expensive and difficult component of the radiation budget to be monitored in micrometeorological studies. Hence, the locally adjusted equation can be used to estimate downward longwave energy, needed as input to some agricultural and hydrological models, in semi-arid regions of the Northeast Brazil, where this component is not monitored.

Avaliação de métodos para estimativa de coeficientes da cultura de amendoim

The peanut crop with its low water requirement, short growing period and a higher demand, which is not attended by the regional markets, is an important alternative crop to be grown in the irrigated areas of the Brazilian Northeast, especially in the sandy soils. This paper is concerned with the evaluation of different methods, which determine the water requirements of a peanut crop. The crop water consumption is determined from two evapotranspirometers with constant water table. The reference evapotranspiration is obtained by using different methods. The peanut crop water requirement is in the order of 650 mm and the crop coefficient obtained from the methods of Class A Pan evaporimeter, Hargreaves and Thornthwaite, is more adequate for efficient management of irrigation.

Analysis of the evaporative fraction using eddy covariance and remote sensing techniques

The main objective of this study was to demonstrate the ability of the instantaneous measurements of the evaporative fraction (EF) to estimate the average daily EF and apply the remote sensing algorithm (SEBAL - Surface Energy Balance Algorithms for Land) to obtain the regional distribution of the instantaneous EF in the Semi-arid region of Brazil. The results show that cloudiness is not related to stability of EF and that the correlation between the diurnal stability of EF and the meteorological parameters have shown weak correlation on cloudy days, and strong correlation with the vapor pressure deficit (VPD) on cloud free days. The EF derived from remote sensing data were compared with the field measurements and presented absolute percent difference less than 12%, evidencing the agreement between the SEBAL algorithm results and measured data, and showing that it is a promising tool to provide estimates of the EF to obtain the evapotranspiration.

TRENDS IN TEMPERATURE AND GROWING SEASON LENGTH IN IDAHO-USA DURING THE PAST FEW DECADES

This study attempts to provide new information on seasonal and annual trends, on a regional scale, using records of daily air temperature over Idaho, USA, through the analysis of the Growing Season Length (GSL), and maximum and minimum air temperature data from multiple stations in the region, as well as, to obtain the temporal correlation between the daily air temperature and Sea Surface Temperature (SST) indices. The analyses were conducted using long-term and high quality data sets for 35 meteorological stations for the period between 1970 and 2006. The results suggest that both daily maximum and minimum temperatures had increasing trends, but the minimum air temperature is increasing faster than the maximum air temperature. On average, the GSL has increased by 7.5 days/decade during the period 1970-2006, associated with increasing temperatures. Trends in regional air temperature and their indication of climate change are of interest to Idaho and the rest of the world. The trends obtained herein corroborate with the general idea that during the last century the globe has warmed.

TEMPORAL VARIABILITY OF EXTREME TEMPERATURE INDICES IN UTAH DURING THE PAST FEW DECADES

The main objective of this study was to analyze the trends in five annual extreme indices of temperature for Utah, USA. The analyses were conducted for 28 meteorological stations, during the period from 1970 to 2006, characterized by high quality data set. The analyses of extreme temperature indices have identified an increase in the maximum and minimum air temperatures in Utah. Predominantly, the minimum air temperature is increasing in the studied region. Most of Utah has shown a decrease in the diurnal temperature range, which indicates that the minimum temperature is increasing faster than the maximum temperature.