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Wageningen Universiteit Pays Bas (2007)

Development of an agricultural drought assessment system : integration of agrohydrological modelling, remote sensing and geographical information

Vazifedoust, M.

Titre : Development of an agricultural drought assessment system : integration of agrohydrological modelling, remote sensing and geographical information

Auteur : Vazifedoust, M. 

Université de soutenance : Wageningen Universiteit

Grade : PhD thesis 2007

Résumé partiel
Iran faces widespread droughts regularly, causing large economical and social damages. The agricultural sector is with 80-90 % by far the largest user of water in Iran and is often the first sector to be affected by drought. Unfortunately, water management in agriculture is also rather poor and hence water productivity of crops WP is far below potential. The growing water scarcity due to drought and the increasing water demands of industries, households and environment, are major threats to sustainable agricultural development in Iran. Therefore, the development of a reliable agricultural drought assessment system would be very beneficial for proper operational decision making on farms, for early warning, for identification of potential vulnerability of areas and for mitigation of drought impacts.

Given the current water scarcity, the limited available amount of water should be used as efficient as possible. To explore on-farm strategies which result in higher WP-values and thus economic gains, the physically based agrohydrological model Soil Water Atmosphere Plant (SWAP), was calibrated and validated using measured data at 8 selected farmer’s fields (wheat, fodder maize, sunflower and sugar beet) in the Borkhar irrigation district in Iran during the agricultural year 2004-05. Using the calibrated SWAP model, on-farm strategies i.e. deficit irrigation scheduling, optimal irrigation intervals and extent of cultivated area, were analyzed based on relations between WP- indicators and water consumption. The results showed a large potential of the improvement of water productivity under limited water supply in the Borkhar irrigation district.

Although agrohydrological models like SWAP offer the possibilities for predicting crop yield, such models may become inaccurate because of uncertainty of input parameters like irrigation scheduling, soil hydraulic parameters and planting dates. This holds especially true when applying distributed modelling at regional scale. Hence to reduce the uncertainty in application of SWAP at regional scales, remotely sensed data of leaf area index and evapotranspiration were used in combination with a geographical information system. The remotely sensed data were inserted into the distributed SWAP model using data assimilation techniques i.e. sequential updating.

Data of LAI were derived from Visible and Near Infrared (VNIR) spectral bands of remote sensing data with moderate to high spatial resolution. However, due to resolution limitations of existing remotely sensed data i.e. thermal bands, these data could not be used directly for routine ET estimation of individual fields. Therefore, a new disaggregation method based on linear disaggregation of ET components within each MODIS pixel, was developed and applied to the simulated MODIS data. The results of the proposed approach were further compared with two other disaggregation approaches being based on weighted ratios, as derived from dividing ET maps of high and low spatial resolution data.

Mots clés : drought / water deprivation / assessment / remote sensing / geographical information systems / mathematical models / irrigated farming / irrigated soils / crop yield / simulation models / agrohydrology / modeling

Présentation : Wageningen Dissertation

Texte intégral : Wageningen Dissertation

Page publiée le 27 mars 2008, mise à jour le 25 mai 2021