La importancia de la sequía sobre la agricultura de regadío es el fundamento de este artículo que analiza y evalúa el riesgo de escasez de agua sobre el resultado económico de este tipo de agricultura. El objetivo es controlar en tiempo real dicho riesgo. Se estiman diversos modelos de regresión que explican la productividad del regadío a través de un índice de precios ponderado para los principales cultivos, la tendencia y la disponibilidad de agua. Estos modelos, que se corrigen por auto-correlación, muestran una buena capacidad explicativa. En segundo lugar se llevan a cabo simulaciones ex-ante de la productividad del regadío empleando funciones ajustadas del balance de agua. Este marco metodológico proporciona la base para un sistema de gestión del riesgo de sequía en tiempo real a través de funciones de distribución de los resultados económicos esperados, que pueden ser revisadas de manera mensual antes del inicio de la campaña de riegos. Los resultados de la simulación demuestran que se pueden anticipar los efectos de las sequías, y por tanto, servir a los gestores del agua como complemento de los modelos hidrológicos para gestionar las reservas de agua en los años de escasez. Se identifican diferentes perfiles de riesgo. Por ejemplo en Genil-Cabra se comprueba la alta resiliencia del sistema después de eventos de sequía, mientras que en La Plana de Castellón el riesgo de abandono de tierras de regadío ha aumentado. En Genil-Cabra las pérdidas estimadas para la sequía de 2007 equivalen a 60 millones de euros. El modelo se aplica en algunas de las comunidades de regantes agrícolamente más relevantes de España. | The importance of water scarcity in irrigated agriculture in Spain provides the rationale for this paper, which analyses and evaluates the risk of water shortage on the economic result of this kind of agriculture. The main objective is to monitor this risk on a real-time basis. For this aim, we first estimated a number of regression models that explain irrigated agricultural productivity based on crop price indices, a time trend and water availability. These models, which correct for auto-correlation, yield good explanatory power. Second we carried out ex ante simulations of agricultural productivity using fitted distribution functions of water balance. The risk model framework provides the basis for a real time drought management system through a variety of distribution functions of expected economic results, which can be revised on a monthly basis before the beginning of the irrigation season. The results of the simulation show how this kind of risk model can be used to anticipate the effects of droughts and complement the hydrological models used to manage water storage in years of scarcity. Different risk profiles are identified. For example, in Genil-Cabra we found that the resilience of the system after a drought period is very high, whereas in La Plana de Castellón the risk of irrigation area abandonment is increasing year by year. In Genil-Cabra the estimated losses were 60 million euros in 2007. The models were applied to some of the most agriculturally relevant irrigation districts in Spain.

The rocket (Euruca sativa) is an important vegetable in human´s feed and one of the most nutritious, rich in minerals such as potassium, sulfur and iron, and vitamins A and C. Since the late 90’s the rocket is gaining more market, with an increase in quantity sold, and its area planted. The aim for this study is to assess the effect of potassium on the yield characteristics, SPAD reading and efficiency in water use by plants of rocket. The experiment was conducted in a greenhouse during May-June 2011. The experimental plot consisted of vase built by PET 2.5 liter bottle with a capacity of 1 dm-3 of soil, using a wool wick for irrigation by capillary. The experimental design was completely randomized and its treatments consisted of six doses ofK2O: 0; 50; 100; 150; 200 and 250 mg dm-3 and using as source KCl and six replications. The variables analyzed were SPAD readings, leaf number, fresh mass, dry mass, root dry mass and water use efficiency. The potassium fertilization increases the SPAD reading and water use efficiency by rocket plants in potassium doses of 156.4 and 200 mg dm-3, respectively. Variables fresh and dry mass of plants are influenced by potassium fertilization with adjust of linear regression model. Variables number of leaves and root dry weight are not influenced by potassium fertilization.ResumoA rúcula (Euruca sativa) é uma hortaliça relevante na alimentação humana sendo uma das mais nutritivas, ricas emminerais como potássio, enxofre e ferro, além das vitaminas A e C. Desde o final da década de 90 a rúcula vem conquistandomercado com um aumento na quantidade comercializada e na sua área de plantio. Objetivou-se pelo presente estudo avaliaro efeito de doses de potássio nas características produtivas, leitura SPAD e eficiência no uso da água por plantas de rúcula.O experimento foi realizado em casa de vegetação no período de maio a junho de 2011. A parcela experimental consistiu devaso construído por garrafa PET de 2,5 litros, com capacidade para 1 dm-3 de solo, utilizando-se pavio de lã para irrigação porcapilaridade. O delineamento experimental foi inteiramente casualizado cujos tratamentos consistiram de seis doses de K2O: 0;50; 100; 150; 200 e 250 mg dm-3 utilizando-se como fonte o KCl e seis repetições. As variáveis analisadas foram leitura SPAD,número de folhas, massa fresca e massa seca da parte aérea, massa seca da raiz e eficiência no uso da água. A adubação compotássio aumenta a leitura SPAD e a eficiência no uso de água por plantas de rúcula nas doses de potássio de 156,4 e 200 mg dm-3,respectivamente. As variáveis massas fresca e seca de plantas são influenciadas pela adubação potássica com ajuste a modelolinear de regressão. As variáveis número de folhas e massa seca de raiz não são influenciadas pela adubação potássica.

O período de centrifugação, necessário ao equilíbrio da umidade no solo, é fator determinante da precisão da curva de retenção de umidade. O objetivo deste trabalho foi avaliar o efeito do período de centrifugação na curva de retenção de umidade em cinco tipos de solo da região do Cerrado. As curvas de retenção foram ajustadas por meio de regressão não-linear, e a soma dos erros residuais do ajuste foi utilizada para avaliar as diferenças estatísticas entre elas, pelo teste da razão de verossimilhança. As curvas de retenção de umidade foram agrupadas em famílias de curvas, para cada tipo de solo, para facilitar a visualização das diferenças. Os resultados mostraram claramente que o período de centrifugação afeta a curva de retenção, promovendo, assim, nítida rotação nas curvas em torno do ponto de saturação. Utilizando-se a técnica da regressão inversa, foi possível estabelecer o período de centrifugação necessário ao equilíbrio da umidade, de cada tipo de solo, correspondente ao nível de significância de 5%, no intervalo de confiança de 90%. Para os solos estudados, o período de centrifugação necessário à extração da água, em cada rotação aplicada, pelo método tradicional da centrífuga, deve ser superior a 80 minutos.<br>The centrifugation time, necessary to the equilibrium of soil moisture, is a determinant factor for the precision of the soil-water retention curve. The objective of this work was to evaluate the effect of the centrifugation time on the soil-water retention curve of five soil-types from the Cerrado region. The retention curves were adjusted using non-linear regression, with the sum of minimum square errors being used to evaluate the statistical differences among them. For each soil type, the obtained retention curves were presented as a family of curves to facilitate the visualization of differences among them. The results showed clearly that the time of centrifugation affects the retention curve, imposing a visible rotation on the curves, centered at the saturation point. Using the technique of the inverse regression, it was possible to calculate the necessary time of centrifugation for each soil type, based on the 5% significance level and 90% confidence interval. For the studied soils, the time of centrifugation necessary for extracting water from the soil sample up to equilibrium, at each applied rotation, using the traditional method of soil-centrifugation for determining soil-water retention curve, has to be over 80 minutes.

Water transparency is one of the main indicators of seasonal changes from the water level in lacustrine systems, but other environmental spatial and temporal variables can act jointly on water transparency. The diagnosis of interactions among physical-chemical variables and water transparency can be made by fitting statistical models based on multiple regression analysis. The objective of this study is to evaluate the set of limnologic variables that best predict the seasonal variation in water transparency in lakes of the western Amazon. These data were collected in both the drought and flood seasons in 78 lakes of the Mamirauá Reserve for Sustainable Development (RDSM). The delineation of the sampling followed the choice of variables, the analysis of premises imposed by the linear regression model and the validation of the model. The variables that best fitted the model were: water level, bottom temperature, conductivity, and pH for both seasons analyzed (R2 = 0.64). The resulting model suggests that the physical-chemical variables influence the re-suspension process and sedimentation of particulate material together with the seasonal variation of the water level at the lake system of RDSM.<br><br>A transparência da água é um dos principais indicadores das flutuações sazonais do nível d’água em sistemas lacustres, porém outras variáveis ambientais espaço-temporais podem, conjuntamente, atuar sobre a transparência da água. O diagnóstico das interações entre variáveis físico-químicas e a transparência da água pode ser delineado pelo ajuste de modelos estatísticos fundamentados em análise de regressão múltipla. O presente estudo teve como objetivo avaliar o conjunto de variáveis limnológicas que melhor prediz a variação sazonal da transparência da água em lagos na Amazônia Ocidental. Os dados foram coletados durante os períodos de seca e cheia em 78 lagos da Reserva de Desenvolvimento Sustentável Mamirauá (RDSM). O delineamento seguiu a escolha das variáveis, análise das premissas impostas pelo modelo de regressão linear e validação do modelo. As variáveis que melhor se ajustaram ao modelo foram: nível da água, temperatura de fundo, condutividade e pH para ambos os períodos de análise (R2 = 0,64). O modelo resultante sugere que o processo de ressuspensão e sedimentação do material particulado influenciam as variáveis físicas e químicas juntamente à variação sazonal no nível da água nos sistemas de lagos da RDSM.

O período de centrifugação, necessário ao equilíbrio da umidade no solo, é fator determinante da precisão da curva de retenção de umidade. O objetivo deste trabalho foi avaliar o efeito do período de centrifugação na curva de retenção de umidade em cinco tipos de solo da região do Cerrado. As curvas de retenção foram ajustadas por meio de regressão não-linear, e a soma dos erros residuais do ajuste foi utilizada para avaliar as diferenças estatísticas entre elas, pelo teste da razão de verossimilhança. As curvas de retenção de umidade foram agrupadas em famílias de curvas, para cada tipo de solo, para facilitar a visualização das diferenças. Os resultados mostraram claramente que o período de centrifugação afeta a curva de retenção, promovendo, assim, nítida rotação nas curvas em torno do ponto de saturação. Utilizando-se a técnica da regressão inversa, foi possível estabelecer o período de centrifugação necessário ao equilíbrio da umidade, de cada tipo de solo, correspondente ao nível de significância de 5%, no intervalo de confiança de 90%. Para os solos estudados, o período de centrifugação necessário à extração da água, em cada rotação aplicada, pelo método tradicional da centrífuga, deve ser superior a 80 minutos. | The centrifugation time, necessary to the equilibrium of soil moisture, is a determinant factor for the precision of the soil-water retention curve. The objective of this work was to evaluate the effect of the centrifugation time on the soil-water retention curve of five soil-types from the Cerrado region. The retention curves were adjusted using non-linear regression, with the sum of minimum square errors being used to evaluate the statistical differences among them. For each soil type, the obtained retention curves were presented as a family of curves to facilitate the visualization of differences among them. The results showed clearly that the time of centrifugation affects the retention curve, imposing a visible rotation on the curves, centered at the saturation point. Using the technique of the inverse regression, it was possible to calculate the necessary time of centrifugation for each soil type, based on the 5% significance level and 90% confidence interval. For the studied soils, the time of centrifugation necessary for extracting water from the soil sample up to equilibrium, at each applied rotation, using the traditional method of soil-centrifugation for determining soil-water retention curve, has to be over 80 minutes.

Dynamic variation in the saltwater–freshwater transition zone below a seafront beach in South Korea was investigated with long-term monitoring of the groundwater in relation to the precipitation, wave height, and tide. Correlation, spectral analysis, and regression analysis of monitoring data were performed to deduce the relationships between these factors. The general shape of the transition zone was affected by the seasonal groundwater levels, but temporary fluctuations were predominantly affected by local rising-groundwater-level events. The distinct increases in the groundwater level were closely related to the wave height. Different patterns of electrical conductivity (EC) change were detected in the shallow and deep zones, and these differences indicated that the transition zone was highly dynamic. The EC values at shallow depths were temporarily increased by the wave setup and tidal fluctuations during the rising-groundwater events, but the EC at greater depths was reduced by the seaward or downward movement of the relative freshwater. In exceptional cases, during extreme increases in the groundwater level resulting from seawater flooding, the rapid downward flow of the flooding saltwater through the well bore caused synchronous EC fluctuations at all depths.

Correct understanding of groundwater/surface-water (GW–SW) interaction in karst systems is of greatest importance for managing the water resources. A typical karst region, Fangshan in northern China, was selected as a case study. Groundwater levels and hydrochemistry analyses, together with isotope data based on hydrogeological field investigations, were used to assess the GW–SW interaction. Chemistry data reveal that water type and the concentration of cations in the groundwater are consistent with those of the surface water. Stable isotope ratios of all samples are close to the local meteoric water line, and the ³H concentrations of surface water and groundwater samples are close to that of rainfall, so isotopes also confirm that karst groundwater is recharged by rainfall. Cross-correlation analysis reveals that rainfall leads to a rise in groundwater level with a lag time of 2 months and groundwater exploitation leads to a fall within 1 month. Spectral analysis also reveals that groundwater level, groundwater exploitation and rainfall have significantly similar response periods, indicating their possible inter-relationship. Furthermore, a multiple nonlinear regression model indicates that groundwater level can be negatively correlated with groundwater exploitation, and positively correlated with rainfall. The overall results revealed that groundwater level has a close correlation with groundwater exploitation and rainfall, and they are indicative of a close hydraulic connection and interaction between surface water and groundwater in this karst system.

A stochastic study of long-term forecasts of seawater intrusion with an application to the Korba aquifer (Tunisia) is presented. Firstly, a geostatistical model of the exploitation rates was constructed, based on a multi-linear regression model combining incomplete direct data and exhaustive secondary information. Then, a new method was designed and used to construct a geostatistical model of the hydraulic conductivity field by combining lithological information and data from hydraulic tests. Secondly, the effects of the uncertainties associated with the pumping rates and the hydraulic conductivity field on the 3D density-dependent transient model were analysed separately and then jointly. The forecasts of the impacts of two different management scenarios on seawater intrusion in the year 2048 were performed by means of Monte Carlo simulations, accounting for uncertainties in the input parameters as well as possible changes of the boundary conditions. Combining primary and secondary data allowed maps of pumping rates and the hydraulic conductivity field to be constructed, despite a lack of direct data. The results of the stochastic long-term forecasts showed that, most probably, the Korba aquifer will be subject to important losses in terms of regional groundwater resources.

Freshwater scarcity is an ever-increasing problem throughout the arid and semi-arid countries, and it often results in poverty. Thus, it is necessary to enhance understanding of freshwater resources availability, particularly for groundwater, and to be able to implement functional water resources plans. This study introduces a novel statistical approach combined with a data-mining ensemble model, through implementing evidential belief function and boosted regression tree (EBF-BRT) algorithms for groundwater potential mapping of the Lordegan aquifer in central Iran. To do so, spring locations are determined and partitioned into two groups for training and validating the individual and ensemble methods. In the next step, 12 groundwater-conditioning factors (GCFs), including topographical and hydrogeological factors, are prepared for the modeling process. The mentioned factors are employed in the application of the EBF model. Then, the EBF values of the GCFs are implemented as input to the BRT algorithm. The results of the modeling process are plotted to produce spring (groundwater) potential maps. To verify the results, the receiver operating characteristics (ROC) test is applied to the model’s output. The findings of the test indicated that the areas under the ROC curves are 75 and 82% for the EBF and EBF-BRT models, respectively. Therefore, it can be inferred that the combination of the two techniques could increase the efficacy of these methods in groundwater potential mapping.

A method of evaluating the risk of floor water inrush using principal component logistic regression analysis (PCLRA) and an improved analytic hierarchy process (IAHP) is presented. The approach was validated by a case study at the Yangcheng coal mine in Shandong Province, China. First, the risk assessment index of floor water inrush was determined based on geological and hydrogeological conditions of the study area. Then, a comprehensive evaluation model (CEM), combining PCLRA with IAHP, was constructed to determine the comprehensive weight of each water-inrush evaluation index. Finally, water-inrush risk zoning was determined with GIS. The results show that the CEM, compared with the water-inrush coefficient method (WICM) traditionally and commonly used in China, has higher fitting accuracy and more detailed division of water-inrush risk areas. This method not only follows the observations in reality, but also fully considers the relative importance of water-inrush evaluation indices. The results can provide a theoretical basis for the safe mining of coal seams above confined groundwater.