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Tunis, Tunisia

Hanafi S.,Laboratoire Of Genie Rural | Frija A.,ICARDA | Jamin J.-Y.,CIRAD - Agricultural Research for Development | Zairi A.,Laboratoire Of Genie Rural | And 2 more authors.
Cahiers Agricultures | Year: 2015

Despite research efforts and the multiple interventions of States, the productivity of water, land, and capital resources is often low, particularly in Tunisia. This study provides a framework for analyzing the performance of irrigated farms and examines the level and the effective determinants of this performance. Technical and economic data were collected through detailed questionnaires and used to calculate technical efficiency (TE) and irrigation water use efficiency (IWUE) for each farm, with the data envelopment analysis (DEA) approach. These efficiencies were subjected to statistical analysis for a set of field variables. The results show that TE is satisfactory at 0.84 on average. However, IWUE is much lower, at 0.61 on average. There is therefore significant potential for improving it. The most important determinants of the efficiencies are access to water and access to credit, both of which are possible levers to improve TE and IWUE. Neither irrigation techniques nor the choice of crops nor the water distribution method influence the differences in the efficiencies. Livestock presence is significant for the differences in IWUE, showing that water is used more efficiently with forage crops for livestock. Current modernization projects in Tunisia to convert open canal systems to pressurized pipe systems should take these results into account. But converting the irrigation system alone is not enough to improve efficiency. Scenarios that do not require such large investment may thus be more worthwhile.

Amri R.,CNRS Center for the Study of the Biosphere from Space | Zribi M.,CNRS Center for the Study of the Biosphere from Space | Lili-Chabaane Z.,INAT | Duchemin B.,CNRS Center for the Study of the Biosphere from Space | And 2 more authors.
Remote Sensing | Year: 2011

The analysis of vegetation dynamics is essential in semi-arid regions, in particular because of the frequent occurrence of long periods of drought. In this paper, multi-temporal series of the Normalized Difference of Vegetation Index (NDVI), derived from SPOT-VEGETATION satellite data between September 1998 and June 2010, were used to analyze the vegetation dynamics over the semi-arid central region of Tunisia. A study of the persistence of three types of vegetation (pastures, annual agriculture and olive trees) is proposed using fractal analysis, in order to gain insight into the stability/instability of vegetation dynamics. In order to estimate the state of vegetation cover stress, we propose evaluating the properties of an index referred to as the Vegetation Anomaly Index (VAI). A positive VAI indicates high vegetation dynamics, whereas a negative VAI indicates the presence of vegetation stress. The VAI is tested for the above three types of vegetation, during the study period from 1998 to 2010, and is compared with other drought indices. The VAI is found to be strongly correlated with precipitation. © 2011 by the authors.

Sahli A.,INAT | Moyne C.,University of Lorraine | Stemmelen D.,University of Lorraine
Transport in Porous Media | Year: 2010

Boiling in a porous layer heated from below at constant heat flux and cooled at constant temperature from the upper permeable surface leads below the critical flux of appearance of a vapor zone at the bottom in the approximation of dominated reservoirs to two solutions: a liquid-dominated one and a vapor-dominated one. The stability of these two situations is analyzed. The approach allows to understand the respective roles played by the gravitational instability, natural convection in the liquid upper layer, and movement of the interface between the two regions. Taking into account the confinement allows the comparison of these theoretical results with experimental results obtained in the laboratory. © 2009 Springer Science+Business Media B.V.

Fontanelli G.,CNR Institute of Neuroscience | Paloscia S.,CNR Institute of Neuroscience | Zribi M.,CNRS Center for the Study of the Biosphere from Space | Chahbi A.,INAT
Remote Sensing Letters | Year: 2013

Remote sensing of vegetation by using active microwave sensors is important for the management of land and water resources. Microwave radiation at X-band penetrates only the upper part of the canopy; thus, radar backscattering comes mainly from the top vegetation layer, making the scattering from soil almost negligible. Fourteen in situ measurement campaigns were carried out during which sixteen SAR images of COSMO-SkyMed and TerraSAR-X were acquired on the test site of Merguellil Basin, in the centre of Tunisia, from March to May 2012. A clear sensitivity of the backscattering coefficient, measured by both sensors, to the leaf area index (LAI) of green plants of wheat and barley (at both HH and VV polarizations) was observed, and it did not seem to be greatly affected by the variations in soil moisture, even in HH polarization. As expected, the sensitivity to LAI of dry plants was, instead, almost negligible. The decreasing trend of backscattering as vegetation grows, which has already been observed in past investigations, also at lower frequencies, was confirmed. Due to the similar geometry and dimensions of the two crop types, none of the sensors succeeded in separating the two crop types. © 2013 Taylor and Francis.

Zribi M.,CNRS Center for the Study of the Biosphere from Space | Paris Anguela T.,LATMOS | Duchemin B.,CNRS Center for the Study of the Biosphere from Space | Lili Z.,INAT | And 3 more authors.
Water Resources Research | Year: 2010

The present paper proposes an empirical approach for the modeling of vegetation development, using moisture measurements only. The study is based simply on the use of two databases: one containing soil moisture products derived from ERS scatterometer data over the period 1991-2006 and the other containing normalized difference vegetation indices (NDVI) derived from advanced very high resolution radiometer over the period 1991-2000. The study is applied over the Kairouan plain, the central semiarid region of Tunisia (North Africa). Soil moisture products were first validated on the basis of comparisons with Global Soil Wetness Project, Phase 2 Data, outputs and rainfall events. The soil moisture distribution during the rainy period between October and May is described and is found to be correlated with the vegetation dynamics estimated using the NDVI products. Finally, a semiempirical model is proposed, based on satellite moisture and NDVI products, which allows the NDVI value to be estimated for a period of 1 month during the rainy season as a function of the moisture profile estimations obtained during the previous months. This approach could prove very useful and provide a simple tool for the modeling of vegetation dynamics during rainy seasons in semiarid regions. Copyright © 2010 by the American Geophysical Union.

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