Spatial Assessment of Indices for Characterizing the Erosive Force of Rainfall in El Salvador Republic

Soil erosion data in El Salvador Republic are scarce and there is no rainfall erosivity map for this region. Considering that rainfall erosivity is an important guide for planning soil erosion control practices, a spatial assessment of indices for characterizing the erosive force of rainfall in El Salvador Republic was carried out. Using pluviometric records from 25 weather stations, we applied two methods: erosivity index equation and the Fournier index. In all study area, the rainiest period is from May to November. Annual values of erosivity index ranged from 7,196 to 17,856 MJ mm ha(-1) h(-1) year(-1) and the Fournier index ranged from 52.9 to 110.0 mm. The erosivity map showed that the study area can be broadly divided into three major erosion risk zones, and the Fournier index map was divided into four zones. Both methods revealed that the erosive force is severe in all study area and presented significant spatial correlation with each other. The erosive force in the country is concentrated mainly from May to November.

Effects of rainfall on water quality in six sequentially disposed fishponds with continuous water flow

O estudo foi efetuado durante o período de chuva (dezembro-fevereiro) em seis viveiros de produção semi-intensiva de peixes, a fim de avaliar o efeito da chuva na qualidade da água de viveiros que apresentam fluxo contínuo de água, a qual é passada de um viveiro para outro sem tratamento prévio. Foram amostrados oito pontos de coleta nas saídas dos viveiros. O viveiro P1 (próximo à nascente) apresentou as menores concentrações físicas e químicas da água e as maiores no viveiro P4 (considerado um ponto crítico recebendo material alóctone proveniente de outros viveiros e do escoamento do setor de criação de rãs). A disposição seqüencial dos viveiros estudados promoveu aumento nas concentrações dos nutrientes, clorofila-a e condutividade. As chuvas características desta época do ano aumentaram o fluxo de água nos viveiros e conseqüentemente, carreando material particulado e dissolvido de um viveiro para outro e, promovendo um aumento das variáveis limnológicas em direção do P3 ao P6. Os resultados sugerem que a chuva no período de estudo afetou positivamente a qualidade da água dos viveiros estudados, porém, como os sistemas analisados estão dispostos em distribuição seqüencial e escoamento constante da água de viveiros e tanques paralelos sem tratamento prévio, cuidados devem ser averiguados para que o aumento do fluxo de água provocado pelas chuvas não tenha efeito adverso nos viveiros estudados.

Effect of temperature, leaf wetness, and rainfall on the production of Guignardia citricarpa ascospores and on back spot severity on sweet orange

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Growth regulator losses from cotton plants due to rainfall

Reguladores de crescimento aplicados às plantas de algodoeiro (Gossypium hirsutum L.) podem ser lavados em função da ocorrência de chuvas. Chuvas que ocorrem próximas à época de aplicação podem ocasionar elevada perda e necessidade de reaplicação dos produtos visando à taxa de crescimento desejada. Avaliou-se o efeito do intervalo de tempo entre a ocorrência de chuva simulada e a aplicação de cloreto de mepiquat e cloreto de chlormequat no algodoeiro no crescimento das plantas, além de estimar a necessidade de reaplicação dos reguladores. Plantas de algodão foram cultivadas em vasos de 12 L que permaneceram em casa de vegetação. Os reguladores de crescimento foram aplicados 40 dias após a emergência, quando 50% das plantas apresentavam botão floral. A chuva foi simulada 1, 2, 4, 6 e 24 horas após a aplicação dos reguladores. Determinou-se a altura das plantas antes da aplicação dos produtos e a cada 3 dias até o 30º dia. Na colheita, foi avaliado o número de ramos e estruturas reprodutivas, com posterior determinação da massa da matéria seca. Também foi determinado o crescimento acumulado e taxa de crescimento das plantas. Os dois reguladores reduziram a massa da matéria seca das plantas, independente do intervalo para ocorrência da chuva. O crescimento excessivo das plantas foi controlado, porém, com eficiência reduzida quanto menor o intervalo para simulação de chuva. em todos os períodos avaliados houve perda de produtos, com necessidade de reaplicação. A taxa de reaplicação de cloreto de mepiquat para os diferentes intervalos de chuva foi, em média, 17% maior.

Rainfall intensity and Mepiquat Chloride persistence in cotton

Em parte das regiões onde se encontram as maiores áreas de algodão no Brasil atualmente, o índice pluviométrico está ao redor de 2.000 mm anuais, existindo risco de ocorrer lavagem do Cloreto de Mepiquat (CM) das folhas do algodoeiro antes de ser absorvido pelas plantas. O objetivo deste trabalho foi avaliar a lavagem do CM aplicado no algodoeiro por diferentes laminas de chuva simulada. Os tratamentos constaram de três doses do regulador à base de cloreto de mepiquat: 0, 15.0 e 30.0 g ha-1 e quatro lâminas de chuva simulada: 5, 10, 20 e 40 mm, mais um tratamento sem chuva. Foram utilizados vasos de 12 litros de capacidade e a cultivar Delta Opal. Os parâmetros avaliados foram: altura de plantas, número de ramos reprodutivos, massa de matéria seca, retenção de estruturas reprodutivas e área foliar. Quanto maior a intensidade de chuva ocorrida após a aplicação do regulador maior foi o comprometimento da ação do produto, que repercutiu em interferência no crescimento das plantas. Chuvas de 5.0 mm, ocorridas 90 minutos após a aplicação do cloreto de mepiquat, já causaram prejuízo na ação do produto no crescimento do algodoeiro, sendo o efeito maior com o aumento da quantidade de chuva simulada.

Leaching of nitrate and ammonium from cover crop straws as affected by rainfall

Nitrogen (N) mineralization dynamics in no-till systems is affected, among other factors, by N amount and quality in the mulch and by climatic conditions. Leaching of NO3-N and NH4-N from six plant species used as soil cover crops in tropical environments were evaluated when the straw was submitted to rainfall after chemical desiccation. Millet (Pennisetum glaucum), guinea sorghum (Sorghum vulgare), black oat (Avena strigosa), triticale (Triticum secale), Indian hemp (Crotalaria juncea), and brachiaria (Brachiaria decumbens) were grown in a greenhouse, in Botucatu-SP, Brazil. Forty-five days after emergence, the plants were cut at the root collar, oven-dried, and submitted to simulated rainfalls of 4.4, 8.7, 17.04, 34.9, and 69.8 mm, considering an amount of straw equivalent to 8 t ha(-1) of dry matter. The amounts of N-NO3- extracted from the straw by rainwater were very small. However, accumulated rainfall around 70 mm caused ammonium leaching ranging from 2.5 to 9.5kg ha(-1), depending on the species. Plant residues of triticale and black oat (grasses) and Indian hemp (legume) showed high N leaching intensity with the first rains after chemical desiccation. The amount of N leached from straw was highly correlated with N tissue content.

An intelligent system to real time rainfall prediction using radar data

This work presents a new approach for rainfall measurements making use of weather radar data for real time application to the radar systems operated by institute of Meteorological Research (IPMET) - UNESP - Bauru - SP-Brazil. Several real time adjustment techniques has been presented being most of them based on surface rain-gauge network. However, some of these methods do not regard the effect of the integration area, time integration and distance rainfall-radar. In this paper, artificial neural networks have been applied for generate a radar reflectivity-rain relationships which regard all effects described above. To evaluate prediction procedure, cross validation was performed using data from IPMET weather Doppler radar and rain-gauge network under the radar umbrella. The preliminary results were acceptable for rainfalls prediction. The small errors observed result from the spatial density and the time resolution of the rain-gauges networks used to calibrate the radar.

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

This work is an assessment of frequency of extreme values (EVs) of daily rainfall in the city of São 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 São 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

Effect of atypical rainfall on lotic zooplankton: comparing downstream of a reservoir and tributaries with free stretches

To contribute to the knowledge of lotic zooplankton from dammed and free stretches, we tested the hypothesis that the ecological attributes are different between these environments, which are subjected to several effects caused by different hydrological conditions. The study was carried out in the low Iguacu river, a large hydrographic basin in the south of Brasil. Two samplings were performed, one in the dry period (April/04) and the other in the atypical rainy period (July/04), in five stations downstream a large reservoir, and other 12 stations in four tributaries representing the upper, intermediate and low regions of each river. The observations suggest a clear spatial distribution of zooplankton in lotic stretches subjected or not to damming, mainly due to the effects of physical, chemical and biological variables. Furthermore, the atypical rainfall promoted alterations in community structure when compared to the dry period.

Probability distribution models for daily rainfall data for an interior station of Brazil

Two stochastic models have been fitted to daily rainfall data for an interior station of Brazil. Of these two models, the results show a better fit to describe the data, by truncated negative probability model in comparison with Markov chain probability model. Kolmogorov-Smirnov test is applied for significance for these models. © 1983 Springer-Verlag.

Potassium leaching from millet straw as affected by rainfall and potassium rates

Pearl millet (Penisetum glaucum) is an interesting species to be used as cover crop in tropical areas, showing a high ability in potassium uptake. Potassium (K) is not linked to organic compounds in the plant, and can easily be released from decaying straw becoming available for subsequent crops. This experiment evaluated K leaching from millet straw grown under potassium rates (0, 100, 200, and 300 mg dm-3), and submitted to five levels of simulated rain (5, 10, 20, 40, and 80 mm). Plants were grown in soil filled pots in a greenhouse. On the 50th day after emergence, the plants were desiccated with glyphosate. Artificial rain was applied over the straw. Potassium deficiency speeds up millet dehydration after herbicide application and increases lightly rain water retention in the straw. The amount of K leached right after plant desiccation is correlated with the residue nutrient content and can be as high as 64 kg ha-1 considering a mulch of 8 t ha -1. Although well-nourished millet plants release considerable amounts of K with the first rains, a large percentage of the nutrient is still retained in the straw. Copyright © Taylor & Francis, Inc.

Rainfall representativeness at TRMM & GPM PR resolution

Precipitation radar on board the TRMM satellite was a milestone in the rainfall observation capability in the large scale. Stemming from TRMM the new mission GPM (Global Precipitation Measurement) is to overcome some TRMM shortcomings like the high level of the PR MDZ. However, for major problems like the PR horizontal resolution, significant improvements are not foreseeable. This papers investigates the impact of TRMM PR resolution on the structure of tropical rainfall. The issue is approached by both gradient analysis and texture verification. Results indicate that the impact maybe significant, affecting important applications like in NWP. © 2005 IEEE.

Evaluation of the Tropical Rainfall Measuring Mission 3B43 product over an inland area in Brazil and the effects of satellite boost on rainfall estimates

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Feeding, body condition and reproductive investment of Astyanax intermedius (Characiformes, Characidae) in relation to rainfall and temperature in a Brazilian Atlantic Forest stream

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)