Performance evaluation of the Bhakra Irrigation System, India, using remote sensing and GIS techniques

Irrigation systems / Irrigation canals / Irrigation scheduling / Performance evaluation / Remote sensing / GIS / Irrigated farming / Satellite surveys / Sustainable agriculture / Productivity / Groundwater / Salinity / Crop yield / Wheat / Surface irrigation / India / Bhakra Irrigation System

Evaporation Estimation of Rift Valley Lakes: Comparison of Models

Evapotranspiration (ET) accounts for a substantial amount of the water flux in the arid and semi-arid regions of the World. Accurate estimation of ET has been a challenge for hydrologists, mainly because of the spatiotemporal variability of the environmental and physical parameters governing the latent heat flux. In addition, most available ET models depend on intensive meteorological information for ET estimation. Such data are not available at the desired spatial and temporal scales in less developed and remote parts of the world. This limitation has necessitated the development of simple models that are less data intensive and provide ET estimates with acceptable level of accuracy. Remote sensing approach can also be applied to large areas where meteorological data are not available and field scale data collection is costly, time consuming and difficult. In areas like the Rift Valley regions of Ethiopia, the applicability of the Simple Method (Abtew Method) of lake evaporation estimation and surface energy balance approach using remote sensing was studied. The Simple Method and a remote sensing-based lake evaporation estimates were compared to the Penman, Energy balance, Pan, Radiation and Complementary Relationship Lake Evaporation (CRLE) methods applied in the region. Results indicate a good correspondence of the models outputs to that of the above methods. Comparison of the 1986 and 2000 monthly lake ET from the Landsat images to the Simple and Penman Methods show that the remote sensing and surface energy balance approach is promising for large scale applications to understand the spatial variation of the latent heat flux

Regionalization of surface flux densities and moisture indicators in composite terrain : a remote sensing approach under clear skies in Mediterranean climates

The growing concern about environment has increased the number of land surface processes studies. Computer simulation models of land surface processes have been developed for a range of scales and with different levels of physical complexity. Because the interactions between soil, vegetation and atmosphere vary both spatially and temporally, regional evaporation in heterogeneous natural landscapes is difficult to predict by means of computer simulation models. Remote sensing measurements of land surface radiative properties offer however a means to indirectly measure land surface state conditions at a range of scales. A straightforward estimation of evaporation from radiative properties of the land surface is hampered by the fact that only a very few parameters of the classical flux-profile relationships can be estimated directly from remote sensing measurements. Moreover, the accuracy of surface temperature measurements necessary to solve flux-profile relationships is still poor. Inclusion of ground measurements is a possible solution, but the absence of such data on large scales and for heterogeneous land surfaces where these parameters are not measured, forms an immediate obstacle for the implementation of remote sensing algorithms.A Surface Energy Balance Algorithm for Land (SEBAL) has been developed in a way that the need for collateral measurements is partly eliminated, a very accurate surface temperature map is no longer required (although it should be as good as possible) and a land use classification to relate surface temperature to evaporation is not needed. Each pixel is characterized by a surface hemisherical reflectance, surface temperature and a vegetation index. The methodology composes of multiple flux-profile relationships for small sub-areas. Although the concept has a physical basis, the parameters are estimated by empirical relationships, for instance a relationship between near-surface vertical air temperature difference and surface temperature forms an essential component in the estimation of the sensible heat flux density.The absolute surface energy balance terms are estimated on an instantaneous time basis. Temporal integration of instantaneous surface flux densities is feasible using the evaporative fraction (latent heat flux density/net available energy): The evaporative fraction remains fairly constant during daytime hours for both homogeneous and heterogeneous areas. A physical explanation for this is given. A bulk surface resistance of a heterogeneous landscape has been related analytically to canopy and bare soil evaporation resistances. Measurements in central Spain have shown that the evaporative fraction and bulk surface resistance are suitable indicators to describe areal patterns of near-surface soil water content. Although the bulk surface resistance has a distinct diurnal variation, it is much less affected by changes in net available energy and therefore preferred to describe the energy partitioning for longer time series (weeks, months).SEBAL has been validated with data available from regional evaporation projects in Egypt and Spain. The error of high resolution evaporative fraction estimations decreases from 20% to 10% at a scale of 1 km to 5 km respectively, The error of low resolution evaporative fraction images at a scale of 100 km is approximately 1 to 5 %. Hence, the error averages out if a larger set of pixels is considered. It is concluded that the uncertainty of evaporation in regional water balances and model studies can be substantially reduced by estimating evaporation with remote sensing measurements using the proposed SEBAL technique

Calibração e validação do modelo SEBAL para as condições semi-áridas do Nordeste brasileiro.

A precisão na determinação da evapotranspiração atual(ET)reduz significativamente incertezas no balanço hídrico de uma bacia hidrográfica. Medidasde ET em áreas de parreirais, pomar de manga e vegetação natural (caatinga) foram feitas no sub médio São Francisco. Métodos micro meteorológicos foram usados que fornecem valores pontuais para locais específicos (Teixeiraetal.,2007,2008a,b) .As extrapolações diretas de dados pontuais para escala regional podem conduzir erros nas estimativas de ET,porque medidas locais defluxos não podem fornecer uma amostragem precisa para um aárea maior(Wylieetal.,2003). Um dos algoritmos usados para estimativa daETem escala regional por sensoriamento remoto é o Surface Energy Balance Algorithm for Land SEBAL (Bastiaanssen,1995).Embora este algoritmo tenha sido elaborado para calcularos componentes do balanço de energiaem escala regional usando um mínimo de dados de campo,aparametrização local das equações pode melhorar a precisão da sequações(Ducheminetal.,2006). Este trabalho atualcombina dados do satélite Land sate medições de campo para rever as equações empíricas do algoritmo SEBAL.assim como a validação final do evapotranspiração regional em escala diária. As equações relevantes foram adaptadas para as condições semi áridas do sub médio São Francisco,e aplicadas então a cada imagem individual do satélite Landsat

Uso do sensoriamento remoto para a determinação da produtividade de água no Submédio São Francisco.

O objetivo deste trabalho foi determinar a contabilidade hídrica no Submédio São Francisco através de imagens de satélite, dados agrometeorológicos e informações estatísticas e se estas retiradas estão sendo produtivas, analisando-se a PAC das principais culturas comercia nesta sub bacia hidrográfica