Crop insurance demand in wheat production: focusing on yield gaps and asymmetric information

Analysis of yield gaps were conducted in the context of crop insurance and used to build an indicator of asymmetric information. The possible influence of asymmetric information in the decision of Spanish wheat producers to contract insurance was additionally evaluated. The analysis includes simulated yield using a validated crop model, CERES-Wheat previously selected among others, whose suitability to estimate actual risk when no historical data are available was assessed. Results suggest that the accuracy in setting the insured yield is decisive in farmers’ willingness to contract crop insurance under the wider coverage. Historical insurance data, when available, provide a more robust technical basis to evaluate and calibrate insurance parameters than simulated data, using crop models. Nevertheless, the use of crop models might be useful in designing new insurance packages when no historical data is available or to evaluate scenarios of expected changes. In that case, it is suggested that yield gaps be estimated and considered when using simulated attainable yields

Thresholding Soil Surface Images

Soil erosion is a complex phenomenon involving the detachment and transport of soil particles, storage and runoff of rainwater, and infiltration. The relative magnitude and importance of these processes depends on several factors being one of them surface micro-topography, usually quanti[U+FB01]ed trough soil surface roughness (SSR). SSR greatly affects surface sealing and runoff generation, yet little information is available about the effect of roughness on the spatial distribution of runoff and on flow concentration. The methods commonly used to measure SSR involve measuring point elevation using a pin roughness meter or laser, both of which are labor intensive and expensive. Lately a simple and inexpensive technique based on percentage of shadow in soil surface image has been developed to determine SSR in the field in order to obtain measurement for wide spread application. One of the first steps in this technique is image de-noising and thresholding to estimate the percentage of black pixels in the studied area. In this work, a series of soil surface images have been analyzed applying several de-noising wavelet analysis and thresholding algorithms to study the variation in percentage of shadows and the shadows size distributio

Robust regression applied to fractal/multifractal analysis.

Fractal and multifractal are concepts that have grown increasingly popular in recent years in the soil analysis, along with the development of fractal models. One of the common steps is to calculate the slope of a linear fit commonly using least squares method. This shouldn?t be a special problem, however, in many situations using experimental data the researcher has to select the range of scales at which is going to work neglecting the rest of points to achieve the best linearity that in this type of analysis is necessary. Robust regression is a form of regression analysis designed to circumvent some limitations of traditional parametric and non-parametric methods. In this method we don?t have to assume that the outlier point is simply an extreme observation drawn from the tail of a normal distribution not compromising the validity of the regression results. In this work we have evaluated the capacity of robust regression to select the points in the experimental data used trying to avoid subjective choices. Based on this analysis we have developed a new work methodology that implies two basic steps: ? Evaluation of the improvement of linear fitting when consecutive points are eliminated based on R pvalue. In this way we consider the implications of reducing the number of points. ? Evaluation of the significance of slope difference between fitting with the two extremes points and fitted with the available points. We compare the results applying this methodology and the common used least squares one. The data selected for these comparisons are coming from experimental soil roughness transect and simulated based on middle point displacement method adding tendencies and noise. The results are discussed indicating the advantages and disadvantages of each methodology

Utilización de los sistemas de información geográfica para la estimación automática de la escorrentía directa

[ES] En este trabajo se utilizan los Sistemas de Información Geográfica SIG como herramienta en la modelización hidrológica. La automatización del proceso de modelado permite la rápida ejecución y actualización; ofreciendo una objetivación en el tratamiento de los datos, a la vez que introduce la posibilidad, una vez creada la base de datos, de calibrar el modelo. El objetivo del presente artículo es la generación de un programa informático compatible con un SIG en formato raster IDRISI (para Windows, versión 2.1) con el fin de desarrollar un modelo distribuido que permita definir la variabilidad espacial y temporal del volumen de escorrentía de una cuenca, mediante la simulación del sentido de desplazamiento del flujo de escorrentía directa en combinación con su velocidad. El programa se ha aplicado en un área situada en el noroeste de la Comunidad de Madrid que coincide con la cuenca vertiente a la estación de aforo 03002. La utilización de los SIG para la estimación automática de la escorrentía directa hace posible una rápida y eficaz calibración de los parámetros de la modelización hidrológica para su evaluación, a la vez que permite la caracterización de una cuenca y la estimación de caudales máximos. El programa, que se ha denominado HIDROGIS, supone una alternativa en el desarrollo de modelos distribuidos espacio-temporales.Este trabajo se ha realizado en el marco del proyecto financiado por la Universidad Politécnica de Madrid Modelización de sistemas hidrológicos en pequeñas cuencas vertientes mediante sistemas de información geográfica (A9701) de la OTT-UPM. También quisieramos agradecer al CEDEX,y a la Confederación Hidrográfica del Tajo (Ministerio de Medio Ambiente) su atención y amabilidad al aportar los datos aplicados.Almorox Alonso, J.; Hontoria Fernández, C.; Saa Requejo, A. (2001). Utilización de los sistemas de información geográfica para la estimación automática de la escorrentía directa. Ingeniería del Agua. 8(3):295-304. https://doi.org/10.4995/ia.2001.2868SWORD29530483Barnes, H.H. (1967). Roughness Characteristics of Natural Channels. U.S. Geological Survey Water Supply Paper 1899.Barredo, J.I. y Bosque, J. (1996): Delimitación de unidades homogéneas del relieve a partir de un modelo digital de elevaciones. Estudios Geográficos. LVII, nº 225. Madrid.Eastman, J.R., Kyem, P.A.K., Toledano, J. y Jin, W. (1993). GIS and Decision Making. UNITAR. Explorations in Geographic Information Systems Technology. Volume 4. UNITAR European Office. Suiza.Eastman, J.R. (1997). IDRISI for Windows. Version 2.0. Clark Labs for Cartographic Technology and Geographic Analysis. Clark University. Worcester. EE.UU.Engman, E.T. (1986). Roughness coefficients for routing surface runoff. Journal of Irrigation and Drainage Engineering 112 (1). p. 39-53.ESRI (1989). PC-ARC/INFO. Environmental Systems Research Institute. Inc. EEUU.Ferrer, M.; Rodriguez, J. y Estrela, T. 1995. Generación Automática del Número de Curva con Sistemas de Información Geográfica. Ingeniería del Agua. Vol. 2. Nº 4. p. 43-58.Francés, F. y Benito, J. 1995. La Modelación Distribuida con Pocos Parámetros de la Crecidas. Ingeniería del Agua. Vol. 2. Nº 4. p. 7-24.Llamas, J. (1993). Hidrología General. Principios y Aplicaciones. Servicio Editorial del País Vasco.Meijerink, A.M.J.; Brouwer, H.A.M.; Mannaerts, C.M. y Valenzuela, C.R. 1994. Introduction to the use of Geographic Information System for practical hydrology. UNESCO-International Hydrological Program y International Institute for Aerospace Survey and Earth Sciences (ITC). Publicación Nº. 23. Holanda.Pilgrim, D.H., y Cordery, I. (1993). Flood Runoff. In Handbook of hydrology. D.R. Maidment, ed., McGraw-Hill, Inc.Ponce, V.M. y Hawkins, R.H. (1996). Runoff curve number: has it reached maturity?. Journal of hydrologic engineering. 1 (1). 11-19.Robredo, J.C. y Mintegui, J.A. 1994. Diseño de un modelo distribuido elemental para el análisis del comportamiento hidrológico de una cuenca vertiente. Ingeniería del Agua. Vol. 1. Nº 4. p. 79-100.SCS. Soil Conservation Service. (1984). Engineering Field Manual for Conservation Practices. Fourth Printing. Chapter 2. Estimating Runoff

Shadow Analysis of Soil Surface Roughness Compared to the Chain Set Method and Direct Measurement of Micro-relief.

Erosion potential and the effects of tillage can be evaluated from quantitative descriptions of soil surface roughness. The present study therefore aimed to fill the need for a reliable, low-cost and convenient method to measure that parameter. Based on the interpretation of micro-topographic shadows, this new procedure is primarily designed for use in the field after tillage. The principle underlying shadow analysis is the direct relationship between soil surface roughness and the shadows cast by soil structures under fixed sunlight conditions. The results obtained with this method were compared to the statistical indexes used to interpret field readings recorded by a pin meter. The tests were conducted on 4-m2 sandy loam and sandy clay loam plots divided into 1-m2 subplots tilled with three different tools: chisel, tiller and roller. The highly significant correlation between the statistical indexes and shadow analysis results obtained in the laboratory as well as in the field for all the soil?tool combinations proved that both variability (CV) and dispersion (SD) are accommodated by the new method. This procedure simplifies the interpretation of soil surface roughness and shortens the time involved in field operations by a factor ranging from 12 to 20

Climate Change and Temporal and Spatial Evolution of the Multifractal Universal Parameters in Ebro River Basin

Multifractal techniques are applied to the study of rainfall daily time series over 14 stations from Ebro river Basin over the second half of XX century. The aim is to determine how climate change affects the evolution of the probability distribution of daily precipitation, through the values of universal multifractal parameters: C1; ; H y s for different periods of time. These will offer direct explanations of the shape of the distribution, especially about the extreme events: C1 is the mean intermittency codimension. When C1 increases the precipitation becoming less continuous and more sporadic in time. Therefore there is an increase of extremes. ; is a mesure of multifratility so an increase of it corresponds to a larger variation of the range of precipitation intensity, and thus also of extremes. H is the degree of non-conservation of the field, which measures the scale dependency of the average field. s; the maximal probable singularity that can be observed on a unique sample. It’s directly related to the ratio of the range and the mean of field. From the data collected, we perceive a decline in average rainfall, from 1980. But how is affected the global parameters in this situation?. Results vary according to different rainfall stations

Frequency and Intensity of drought events over Ebro River basin.

Lately, several researchers have pointed out that climate change is expected to increase temperatures and lower rainfall in Mediterranean regions, simultaneously increasing the intensity of extreme rainfall events. These changes could have consequences regarding rainfall regime, erosion, sediment transport and water quality, soil management, and new designs in diversion ditches. Climate change is expected to result in increasingly unpredictable and variable rainfall, in amount and timing, changing seasonal patterns and increasing the frequency of extreme weather events. Consequently, the evolution of frequency and intensity of drought periods is of most important as in agro-ecosystems many processes will be affected by them. Realising the complex and important consequences of an increasing frequency of extreme droughts at the Ebro River basin, our aim is to study the evolution of drought events at this site statistically, with emphasis on the occurrence and intensity of them. For this purpose, fourteen meteorological stations were selected based on the length of the rainfall series and the climatic classification to obtain a representative untreated dataset from the river basin. Daily rainfall series from 1957 to 2002 were obtained from each meteorological station and no-rain period frequency as the consecutive numbers of days were extracted. Based on this data, we study changes in the probability distribution in several sub-periods. Moreover we used the Standardized Precipitation Index (SPI) for identification of drought events in a year scale and then we use this index to fit log-linear models to the contingency tables between the SPI index and the sub-periods, this adjusted is carried out with the help of ANOVA inference

Change of extreme rainfall indexes at Ebro River Basin

The purpose of this work is to provide a description of the heavy rainfall phenomenon on statistical tools from a Spanish region. We want to quantify the effect of the climate change to verify the rapidity of its evolution across the variation of the probability distributions. Our conclusions have special interest for the agrarian insurances, which may make estimates of costs more realistically. In this work, the analysis mainly focuses on: The distribution of consecutive days without rain for each gauge stations and season. We estimate density Kernel functions and Generalized Pareto Distribution (GPD) for a network of station from the Ebro River basin until a threshold value u. We can establish a relation between distributional parameters and regional characteristics. Moreover we analyze especially the tail of the probability distribution. These tails are governed by law of power means that the number of events n can be expressed as the power of another quantity x : n(x) = x? . ? can be estimated as the slope of log-log plot the number of events and the size. The most convenient way to analyze n(x) is using the empirical probability distribution. Pr(X mayor que x) ? x-?. The distribution of rainfall over percentile of order 0.95 from wet days at the seasonal scale and in a yearly scale with the same treatment of tails than in the previous section

Soil fragmentation study applying different tillage systems

Runoff generation depends on rainfall, infiltration, interception, and surface depressional storage. Surface depressional storage depends on surface microtopography, usually quantified trough soil surface roughness (SSR). SSR is subject to spatial and temporal changes that create a high variability. In an agricultural environment, tillage operations produce abrupt changes in roughness. Subsequent rainfall gradually decreases roughness. Beside it, local variation in soil properties and hydrology cause its SSR to vary spatially at different scales. The methods commonly used to measure it involve collecting point elevations in regular grids using laser profilers or scanners, digital close range stereo-photogrammetry and terrestrial laser scanning or LIDAR systems. In this case, a laser-scanning instrument was used to obtain representative digital elevation models (DEMs) at a grid resolution of 7.2x7.2mm that cover an area of 0.9x0.9m. The DEMs were obtained from two study sites with different soils. The first study site was an experimental field on which five conventional tillage methods were applied. The second study site was a large olive orchard with trees planted at 7.5x5.0m and bare soils between rows. Here, three tillage treatments were applied. In this work we have evaluated the spatial variability of SSR at several scales studying differences in height calculated from points separated by incremental distances h were raised to power values q (from 0 to 4 in steps of 0.1). The q = 2 data were studied as a semivariogram model. The logarithm of average differences plotted vs. log h were characterized by their slope, ?(q). Structure functions [?(q) vs. q] were fitted showing that data had nonlinear structure functions typical of multiscale phenomena. Comparisson of the two types of soil in their respective structure functions are shown

Universal Multifractal description applied to precipitation pattern in the Ebro River Basin

Water supplies in the Ebro River Basin are increasingly stressed, especially during the summer season. The year-to-year fluctuations in rainfall over this area exert vital influence on the regional hydrology, agriculture and several related industries in the region. Repeated anomalous rainfall in recent decades has had a devastating impact on this region, both socially and economically. We characterised the change in the rainfall variability pattern in the Ebro River Basin using universal multifractal (UM) analysis, which estimates the concentration of the data around the precipitation average (C1, codimension average), the degree of multiscaling behaviour in time (α index) and the maximum probable singularity in the rainfall distribution (γs ). Fourteen meteorological stations were selected based on the length of rainfall series and the climatic classification to obtain a representative untreated data set from the river basin. Daily rainfall series from 1957 to 2002 were obtained from each meteorological station and subdivided (1957–1980 and 1981–2002) to analyse the difference between the 2 periods. The general scenario observed in this study, through the UM parameters, can be summarised as follows: the range of variation of precipitation amounts was spatially more homogenous in 1980–2002 than in 1957–1979; at the same time, there is higher frequency of dry periods at different scales in 1980–2002; and in almost all of the stations, the range of precipitation over the years has been decreasing at a lower rate than the rainfall average. We then analysed the evolution of the UM parameters from 1957 to 2002. Continuous variations in C1 and α were found for 2 of the stations, indicating that a precipitation regime change has begun in the last few decades and should be considered in the agricultural development of the region