Influence of soil properties in different management systems: Estimating soybean water changes in the agro-IBIS model

The water balance in agricultural cropping systems is dependent on the physical and hydraulic characteristics of the soil and the type of farming, both of which are sensitive to the soil management. Most models that describe the interaction between the surface and the atmosphere do not efficiently represent the physical differences across different soil management areas. In this study, the authors analyzed the dynamics of the water exchange in the agricultural version of the Integrated Biosphere Simulator (IBIS) model (Agro-IBIS) in the presence of different physical soil properties because of the different long-term soil management systems. The experimental soil properties were obtained from two management systems, no tillage (NT) and conventional tillage (CT) in a long-term experiment in southern Brazil in the soybean growing season of 2009/10. To simulate NT management, this study modified the top soil layer in the model to represent the residual layer. Moreover, a mathematical adjustment to the computation of leaf area index (LAI) is suggested to obtain a better representation of the grain fill to the physiological maturity period. The water exchange dynamics simulated using Agro-IBIS were compared against experimental data collected from both tillage systems. The results show that the model well represented the water dynamics in the soil and the evapotranspiration (ET) in both management systems, in particular during the wet periods. Better results were found for the conventional tillage management system for the water balance. However, with the incorporation of a residual layer and soil properties in NT, the model improved the estimation of evapotranspiration by 6%. The ability of the Agro-IBIS model to estimate ET indicates its potential application in future climate scenarios. © 2018 American Meteorological Society

Climate Change and Intense Irrigation Growth in Western Bahia, Brazil: The Urgent Need for Hydroclimatic Monitoring

In Western Bahia, one of the most active agricultural frontiers of the world, cropland area and irrigated area are increasing at fast rates, and water conflicts have been happening at least since 2010. This study makes a hydroclimatic analysis of the water resources in Western Bahia, from both supply and demand viewpoints. Time series of precipitation for the period 1980–2015 and river discharge for the period 1978–2015 are analyzed, indicating a significant reduction of up to 12% in rainfall since the 1980s, and a reduction in river discharge in all stations studied, in both the rainy season and the dry season. Combined with that, irrigated area has increased over 150-fold in 30 years, and in the most irrigated regions, has increased by 90% in the last eight years only. Seven regions in Western Bahia have been identified where the potential for water use conflicts is critical. Moreover, the combination of reduced availability and increased demand of water resources indicates that, if current trends are maintained, conflicts over water may become more frequent in the next years or decades. A short-term alternative to avoid such conflicts is to largely avoid irrigation during the months with low discharge. However, a monitoring system in which the availability and demand of water resources for irrigation are actually measured and monitored, is the safest path to provide water security to this region

Variabilidade das chuvas e disponibilidade dos recursos hídricos nos últimos 40 anos no Oeste da Bahia, Brasil

In recent decades, the increased demand for food, both nationally and internationally has driven agricultural expansion in Brazil. Biophysical, social, and economic factors have made Brazilian Cerrado one of the biomes with the greatest capacity to occupy its territory with crops. This expansion has started in the 1970s, and currently, the Brazilian Cerrado accounts for 40% of the national agricultural production. Western Bahia is one of the most active agricultural frontiers globally in this biome, with a rapid increase in agricultural and irrigated areas. This study aims to make a hydrological, climatic, and water availability analysis and the impacts that this growth can caused in the last 40 years, from 1980 to 2020. First, considering the period 1980-2015, a climate analysis showed a significant reduction in rainfall of up to 12% since the 1980s, and a reduction in river flows, both for dry and rainy seasons. Seven sub-regions in Western Bahia were identified with a potential risk of conflicts over water use. These regions experienced a 150-fold increase in the irrigated area since 1990s and 90% from 2010 to 2018. In recent years, these conflicts have become more frequent due to a combination of factors: climate variability, increased demand for water resources, and continued trends of decreasing precipitation. Second, in a complementary analysis, extending the analysis period to 2020, it was investigated how the interaction of large-scale (represented by Atlantic Multidecadal Oscillation – AMO) and mesoscale (topography) processes can affect the region’s climate variability. Precipitation and river discharge data indicate a continued reduction. Precipitation has decreased by 11.5% since 1980s. The rainiest bimester, December and January (DJ), indicated a significant negative correlation with AMO (R = -0.62, α = 0.01), showing that precipitation decreases in DJ when the AMO index is positive. Within these 40 years, the five rainiest and driest DJs were selected. The rainiest ones showed that large-scale mechanisms interact with the local topography, promoting a stronger convection and high rainfall rates over the region. There is a regional suppression of convection for this driest DJ bimesters, including over the topographic gradient, shifting the convection center further west, and decreasing rainfall in Western Bahia. The climate variability in the region and the intense growth of irrigation have made the potential of conflicts over water use more frequent. Furthermore, with the continuous increase in North Atlantic temperatures, it is unlikely that the wet climatic conditions existing before the early 1990s will return. Thus, precipitation in the region will be affected, putting pressure on water availability and directly impacting economic activities dependent on climate. Keywords: Climate change. Water security. Hydroclimatic analysis.Nas últimas décadas, o aumento da demanda por alimentos tanto nacional quanto internacionalmente impulsionou a expansão agrícola no Brasil. Fatores biofísicos, sociais e econômicos fizeram do Cerrado brasileiro um dos biomas com maior capacidade de ocupação de seu território com cultivos agrícolas. Essa expansão teve início na década de 1970 e, atualmente, o Cerrado brasileiro responde por 40% da produção agrícola nacional. O Oeste da Bahia é uma das fronteiras agrícolas mais ativas do mundo neste bioma, com rápido aumento de áreas agrícolas e irrigadas. Este estudo tem como objetivo fazer uma análise hidrológica, climática, de disponibilidade hídrica e dos impactos que esse crescimento causou nos últimos 40 anos, de 1980 a 2020. Primeiramente, considerando o período 1980-2015, uma análise climática mostrou uma redução significativa nas chuvas de até 12% desde a década de 1980 e redução das vazões dos rios, tanto na estação seca quanto na chuvosa. Sete sub-regiões do Oeste da Bahia foram identificadas com risco potencial de conflitos pelo uso da água. Essas regiões tiveram um aumento de 150 vezes na área irrigada desde 1990 e 90% de 2010 a 2018. Nos últimos anos, esses conflitos se tornaram mais frequentes devido a uma combinação de fatores: variabilidade climática, aumento da demanda por recursos hídricos e continuidade das tendências de diminuição da precipitação. Em segundo lugar, em uma análise complementar, considerando o período 1980-2020, investigou-se como a interação de processos de grande escala (representada pela Oscilação Multidecadal do Atlântico – AMO) e de mesoescala (topografia) podem afetar a variabilidade climática da região. Os dados de precipitação e descarga fluvial indicam uma redução contínua. A precipitação diminuiu 11,5% desde a década de 1980. O bimestre mais chuvoso, dezembro e janeiro (DJ), indicou uma correlação negativa significativa com a AMO (R = -0,62, α = 0,01), mostrando que a precipitação diminuiu em DJ quando o índice AMO é positivo. Nesses 40 anos, foram selecionados os cinco DJs mais chuvosos e secos. Os mais chuvosos mostraram que mecanismos de grande escala interagem com a topografia local, promovendo convecção mais forte e altas taxas de chuva sobre a região. Há uma supressão regional da convecção para os bimestres DJ mais secos, inclusive sobre o gradiente topográfico, deslocando o centro de convecção mais para oeste e diminuindo as chuvas no Oeste da Bahia. A variabilidade climática da região e o intenso crescimento da irrigação tornaram mais frequente o potencial de conflitos pelo uso da água. Além disso, com o aumento contínuo das temperaturas do Atlântico Norte, é improvável que as condições climáticas úmidas existentes antes do início da década de 1990 retornem. Assim, a precipitação na região será afetada, pressionando a disponibilidade hídrica e impactando diretamente as atividades econômicas dependentes do clima. Palavras-chave: Mudanças climáticas. Segurança hídrica. Análises hidroclimáticas.Coordenação de Aperfeiçoamento de Pessoal de Nível Superio

Modeling soybean yield in biophysical and agroeconomic models

Modelos biofísicos de crescimento de cultura consideram os fatores naturais de crescimento e produtividade das culturas agrícolas, mas negligenciam a influência de fatores econômicos no processo. Por outro lado, modelos estatísticos de natureza agroeconômica são utilizados para simular a produção de culturas sob a influência de variáveis econômicas, porém ignorando eventos biofísicos, como por exemplo a influência de uma seca. Este trabalho acopla um modelo agroeconômico a um modelo biofísico de crescimento da cultura de soja. Este trabalho fez simulações espacialmente distribuídas da produtividade de soja no território nacional para o período de 1994 a 2012, utilizando três tipos de modelos: um modelo puramente biofísico (INLAND – Integrated Land Surface Model); um modelo puramente agroeconômico (modelo de regressão linear) e um híbrido biofísico-econômico (INLAND/linear). Para o modelo agroeconômico e híbrido foram utilizados como parâmetros econômicos o custo de transporte, o tamanho médio da fazenda e o preço da soja. Utilizando um algoritmo genético (NSGA-II/Optis) foi realizada uma calibração da produtividade de soja em dois níveis hierárquicos. Foram realizadas oito simulações com configurações diferentes destes modelos. Os melhores resultados foram obtidos com os modelos que consideraram variáveis econômicas e climáticas. O modelo empírico, contemplando variáveis econômicas e climáticas, apresentou o melhor resultado entre todas as simulações, contemplando variáveis econômicas e climáticas, chegando a uma correlação de 0,72. O modelo biofísico com a inserção das variáveis econômicas, ou seja, com limitantes econômicos na produtividade de soja, teve a produtividade potencial simulada reduzida a uma produtividade real simulada próxima da observada, com viés médio no período 1994-2012 de -0,01 ton ha -1 . A correlação entre os dados simulados e observados aumentou de 0,12 usando o modelo puramente biofísico para 0,55 usando o modelo hibrido. O modelo puramente biofísico, quando testado xnacionalmente no Brasil, apresentou resultados de produtividade potencial próximos aos campeões de concursos de produtividade de soja.Crop models consider the environmental factors influencing the growth and yield of agricultural crops, but neglect the influence of economic factors on the process. On the other hand, statistical agroeconomic models are used to simulate crop yields under the influence of economic variables, however neglecting biophysical events, such as the influence of a drought. This work couples an agroeconomic model with a soybean crop model. This work simulated spatially distributed soybean yield in Brazil for the period 1994-2012, using three types of models: a purely biophysical model (INLAND – Integrated Land Surface Model); a purely agroeconomic model (linear regression model) and a hybrid biophysical- economic model. For the agroeconomic and hybrid models, the economic parameters used are the cost of transportation, average farm size and the soybean price. Using a genetic algorithm (NSGA-II/Optis) a calibration of the soybean yield was performed at two hierarchical levels. Eight simulations were performed with distinct settings of these models. The best results were obtained with the models that considered purely economic and climate variables. The empirical model, contemplating economic and climate variables, presented the best result among all the simulations reaching a correlation of 0.72. The biophysical model with economic variables introduced economic constraints on the soybean yield, had the simulated potential yield reduced to a simulated real yield close to the observed, with a mean bias of -0.01 ton/ha in the 1994-2012 period. The correlation between simulated and observed data increased from 0.12 using the purely biophysical model to 0.55 using the hybrid model. The purely biophysical model, when tested nationally in Brazil, showed results of potential yield close to the soybean yield contest championsConselho Nacional de Desenvolvimento Científico e Tecnológic

Climate Change and Intense Irrigation Growth in Western Bahia, Brazil: The Urgent Need for Hydroclimatic Monitoring

In Western Bahia, one of the most active agricultural frontiers of the world, cropland area and irrigated area are increasing at fast rates, and water conflicts have been happening at least since 2010. This study makes a hydroclimatic analysis of the water resources in Western Bahia, from both supply and demand viewpoints. Time series of precipitation for the period 1980−2015 and river discharge for the period 1978−2015 are analyzed, indicating a significant reduction of up to 12% in rainfall since the 1980s, and a reduction in river discharge in all stations studied, in both the rainy season and the dry season. Combined with that, irrigated area has increased over 150-fold in 30 years, and in the most irrigated regions, has increased by 90% in the last eight years only. Seven regions in Western Bahia have been identified where the potential for water use conflicts is critical. Moreover, the combination of reduced availability and increased demand of water resources indicates that, if current trends are maintained, conflicts over water may become more frequent in the next years or decades. A short-term alternative to avoid such conflicts is to largely avoid irrigation during the months with low discharge. However, a monitoring system in which the availability and demand of water resources for irrigation are actually measured and monitored, is the safest path to provide water security to this region