Posted by: silvavpr | April 3, 2017

The Top 20 Papers

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The principle of maximum entropy can provide consistent basis to analyze water resources and geophysical processes in general. In this paper, we propose to assess the space-time variability of rainfall and streamflow in northeastern region of Brazil using the Shannon entropy. Mean values of marginal and relative entropies were computed for a 10-year period from 189 stations in the study area and entropy maps were then constructed for delineating annual and seasonal characteristics of rainfall and streamflow. The Mann–Kendall test was used to evaluate the long-term trend in marginal entropy as well as relative entropy for two sample stations. High degree of similarity was found between rainfall and streamflow, particularly during dry season. Both rainfall and streamflow variability can satisfactorily be obtained in terms of marginal entropy as a comprehensive measure of the regional uncertainty of these hydrological events. The Shannon entropy produced spatial patterns which led to a better understanding of rainfall and streamflow characteristics throughout the northeastern region of Brazil. The total relative entropy indicated that rainfall and streamflow carried the same information content at annual and rainy season time scales.

PAPER – 2016 – Science of the Total Environment

Freshwater scarcity has increased at an alarming rate worldwide; improved water management plays a vital role in increasing food production and security. This study aims to determine the water footprint of Brazil’s national food consumption, the virtual water flows associated with international trade in the main agricultural commodities, as well as water scarcity, water self-sufficiency and water dependency per Brazilian region. While previous country studies on water footprints and virtual water trade focused on virtual water importers or water-scarce countries, this is the first study to concentrate on a water-abundant virtual water-exporting country. Besides, it is the first study establishing international virtual water trade balances per state, which is relevant given the fact that water scarcity varies across states within the country, so the origin of virtual water exports matters. The results show that the average water footprint of Brazilian food consumption is 1619 m3/person/year. Beef contributes most (21%) to this total. We find a net virtual water export of 54.8 billion m3/year, mainly to Europe, which imports 41% of the gross amount of the virtual water exported from Brazil. The northeast, the region with the highest water scarcity, has a net import of virtual water. The southeast, next in terms of water scarcity, shows large virtual water exports, mainly related to the export of sugar. The north, which has the most water, does not show a high virtual water export rate.

PAPER – 2016 – WATER

Virtual water trade is often considered a solution for restricted water availability in many regions of the world. Brazil is the world leader in the production and export of various agricultural and livestock products. The country is either a strong net importer or a strong net exporter of these products. The objective of this study is to determine the volume of virtual water contained in agricultural and livestock products imported/exported by Brazil from 1997 to 2012, and to define the water self-sufficiency index of agricultural and livestock products in Brazil. The indexes of water scarcity (WSI), water dependency (WDI) and water self-sufficiency (WSSI) were calculated for each Brazilian state. These indexes and the virtual water balance were calculated following the methodology developed by Chapagain and Hoekstra (2008) and Hoekstra and Hung (2005). The total water exports and imports embedded in agricultural and livestock products were 5.28 _ 1010 and 1.22 _ 1010 Gm3 yr_1, respectively, which results in positive virtual water balance of 4.05 _ 1010 Gm3 yr_1. Brazil is either a strong net importer or a strong net exporter of agricultural and livestock products among the Mercosur countries. Brazil has a positive virtual water balance of 1.85 _ 1010 Gm3 yr_1. The indexes used in this study reveal that Brazil is self-sufficient in food production, except for a few products such as wheat and rice. Horticultural products (tomato, onion, potato, cassava and garlic) make up a unique product group with negative virtual water balance in Brazil.

PAPER – 2016 – Journal of Environmental Management

Using the Shannon entropy, the space-time variability of rainfall and streamflow was assessed for daily rainfall and streamflow data for a 10-year period from 189 stations in the northeastern region of Brazil. Mean values of marginal entropy were computed for all observation stations and entropy maps were then constructed for delineating annual and seasonal characteristics of rainfall and streamflow. The Mann-Kendall test was used to evaluate the long-term trend in marginal entropy as well as relative entropy for two sample stations. The marginal entropy values of rainfall and streamflow were higher for locations and periods with the highest amounts of rainfall. The entropy values were higher where rainfall was higher. This was because the probability distributions of rainfall and resulting streamflow were more uniform and less skewed. The Shannon entropy produced spatial patterns which led to a better understanding of rainfall and streamflow characteristics throughout the northeastern region of Brazil. The total relative entropy indicated that rainfall and streamflow carried the same information content at annual and rainy season time scales.

PAPER – 2015

A correct evaluation of water losses as evapotranspiration (ET) by crops is important for allocating irrigation water and improving water use efficiency. Field experiments were conducted throughout 2009/2010 (second ratoon) and 2010/2011 (third ratoon) in a sugarcane field of a commercial distillery located on the coastal area of Paraiba state, Brazil. The main objective of this study was to determine crop coefficient, water requirements and water use efficiency (WUE) of sugarcane grown in a tropical climate. The experimental design was by randomized block design with four irrigation treatments and three replications using two center pivots. Crop evapotranspiration (ET) was determined by field soil water balance and reference evapotranspiration (ETo) was obtained based on Penman–Monteith method (FAO/56), using data of air temperature, relative humidity, wind speed and solar radiation from Data Collection Platform, located next to the experimental site. The experimental area was cultivated with irrigation applied weekly by a center pivot system in addition to rainfall. The irrigation scheduling was based on four irrigation levels (T1 = 25%, T2 = 50%, T3 = 75% and T4 = 100% of ETo). Results showed that ET and WUE are strongly influenced by soil water availability. When averaged across two years, productivity increased according to increases in water level. Sugarcane ET ranged from 2.7 (rain-fed condition) to 4.2 mm day−1 (100% ETo irrigation treatment).

PAPER – 2013 – SUGARCANE

Abstract

The database from the National Center for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) re-analysis project available for the period from 1948 to 2009 was used for obtaining long-term solar radiation for northeastern Brazil. Measurements of global solar radiation (Rs) from data collection platform (DCP) for four climatic zones of northeastern Brazil were compared to the re-analysis data. Applying cluster analysis to Rs from database, homogeneous sub-regions in northeastern Brazil were determined. Long times series of Rs and sunshine duration measurements data for two sites, Petrolina (09°09′S, 40°22′W) and Juazeiro (09°24′S, 40°26′W), exceeding 30 years, were analyzed. In order to exclude the decadal variations which are linked to the Pacific Decadal Oscillation, high-frequency cycles in the solar radiation and sunshine duration time series were eliminated by using a 14-year moving average, and the Mann–Kendall test was employed to assess the long-term variability of re-analysis and measured solar radiation. This study provides an overview of the decrease in solar radiation in a large area, which can be attributed to the global dimming effect. The global solar radiation obtained from the NCEP/NCAR re-analysis data overestimate that obtained from DCP measurements by 1.6% to 18.6%. Results show that there is a notable symmetry between Rsfrom the re-analysis data and sunshine duration measurements.

Keywords: Global dimming; Mann–Kendall test; Net radiation; Pacific Decadal Oscillation

2010 – PAPER – SOLAR ENERGY – ROBERTA

 

Abstract

This study attempted to assess a bioclimate index and the occurrence of an urban heat island in the city of Campina Grande, northeastern Brazil, using data taken from mobile measurements and Automatic Weather Stations (AWS). The climate data were obtained during two representative months, one for the dry season (November 2005) and one for the rainy season (June 2006) at seven points in an urban area. Tenminute air temperatures recorded by an AWS installed in urban areas were compared to those from a similar station located in a suburban area to assess the urban heat island (UHI). The data were collected using a 23X data logger (Campbell Scientific, Inc.) programmed for collecting data every second. The thermal discomfort level was analyzed by Thom’s discomfort index (DI), and an analysis of variance was applied for assessing if there was any statistically significant difference at the 1% and 5% significance level of thermal comfort among points. Mann–Kendall statistical test was used for identifying possibly significant trends in a time series for air temperature, relative humidity, and class A pan evaporation for the city of Campina Grande. The present study found UHI intensities of 1.48ºC and −0.7ºC for the months taken as representative of the dry and rainy seasons, respectively. Summer in the city has partially comfortable conditions while the winter is fully comfortable. There are significant changes in DI hourly values between seasons. Only during the rainy season did all points of the city have a comfortable condition until 8:19 h, at which time they become partially comfortable for the rest of the day. Results indicated that there was a 1.5ºC increase in air temperature and a 7.2% reduction in relative humidity throughout the analyzed time series. The DI also showed a statistically significant increasing trend (Mann–Kendall test, p <0.01) for the dry and rainy seasons and annual period of approximately 1ºC in the last 41 years in the city of Campina Grande.

Keywords: Discomfort index; Climatic variables; Heat island; Mann–Kendal test; Urban area

Abstract

This study evaluated the effects of climate change on cowpea bean crop grown in northeastern Brazil based on the reports of the Intergovernmental Panel on Climate Change (IPCC). The water balance model combined with Geographic Information System techniques was used to identify regional areas where the cowpea bean crop will suffer yield reduction due to climate changes. Model input variables were: rainfall, crop coefficients, potential evapotranspiration and duration of the crop cycle. A limit value of 0.5 was adopted for the water requirement satisfaction index (WRSI), being the ratio of actual to maximum evapotranspiration. The acceptable seeding date was defined as the date at which the water balance simulation presented a WRSI value greater than the limit value, with a frequency of at least 80%. An increase in air temperature will cause a significant reduction in the areas currently favorable to cowpea bean crop growth in northeastern Brazil, and it is recommended that bean varieties better suited to high-temperature conditions should be planted.

Keywords: Climate change; Crop modeling; Rainfall; Water balance model

2010 – PAPER – AWAT

Abstract

Knowledge of evapotranspiration (ET) and water-use efficiency (WUE) is essential in cropsmanagement mainly in arid and semiarid regions where water resources are scarce for irrigation. Field experiments were conducted at a commercial farm to obtain the WUE and ET of mango orchard growth in a semiarid environment of northeastern region of Brazil. Measurements were performed within a randomly selected experimental plot with the spacing of 10 m _ 5 m between rows and plants. Soil water balance method was used to obtain the mango orchard evapotranspiration while the Penman–Monteithmethod (FAO/56) was used for determination reference evapotranspiration (ETo). Soil water content was determined by six tensiometer sets installed at 0.20 m layer intervals from the soil surface down to 1.20 m soil depth. The experimental plot was irrigated with a sprinkler irrigation system based on four irrigation levels (T1 = 70%, T2 = 80%, T3 = 90% and T4 = 100% of ETo. Results showed that ET and WUE are strongly influenced by soil water availability. Mango yield varied from a minimum value of 28.06 ton/ha in treatment T4 to a maximum value of 31.06 ton/ha in treatment T3. Such difference was found to be statistically significant (P < 0.05) by Tukey’s test. Results also indicated that WUE values based on irrigation and evapotranspiration were maximum and minimum for low (treatment T1) and high (treatment T4) water levels, respectively.

Keywords: Mangifera indica L.; Mango yield; Water requirements

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