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Accueil du site → Doctorat → Pays-Bas → 2013 → Atmospheric effects of irrigation in monsoon climate : the Indian subcontinent

Wageningen University (2013)

Atmospheric effects of irrigation in monsoon climate : the Indian subcontinent

Tuinenburg, O.A.

Titre : Atmospheric effects of irrigation in monsoon climate : the Indian subcontinent

Auteur : Tuinenburg, O.A.

Université de soutenance : Wageningen University

Grade : PhD thesis 2013

During the 20th century, an increasing population increased the demand for food. As a consequence, agricultural activity has expanded and become more intense. A part of this intensification is the use of irrigation systems to water crops. Due to this irrigation, dams and channeling systems, water can be made available for agriculture in places or during seasons with limited precipitation. In monsoon climates, such as India, the majority of the precipitation falls in one season. During the rest of the year, water that is stored in dammed reservoirs can be made available to spread the water availability more evenly over the year. Previous studies with large scale hydrological models have shown that as a consequence of human influences (such as dams and irrigation systems), the river flow decreases during the wet monsoon months, but the evaporation of water into the atmosphere increases during the dry months. However, these large scale hydrological models did not take into account the atmospheric effects of a changed land surface. This PhD research studies these atmospheric effects of large scale irrigation in India. Three perspectives are taken to determined the influence of irrigation : (1) the local effects of a moister land-surface on the triggering of precipitation (i.e. does the change in land surface wetness lead to a different amount of precipitation ?), (2) the atmospheric fate of evaporation due to irrigation (i.e. where does the evaporation lead to (down-wind) precipitation ?), and (3) the effects of a moister land-surface on the large scale (monsoon) moisture transport patterns (i.e. do the monsoon flows change significantly due to large scale irrigation ?) In the first part (the first perspective), several land-atmosphere diagnostics are tested globally. The goal of these diagnostics is to determine the influence of the land surface on precipitation, based on surface and atmospheric conditions. Of these diagnostics, the CTP-HIlow framework (Convective Triggering Potential and Humidity Index of the LOWer atmosphere) of Findell and Eltahir (2003a) performed well globally and over the Indian region. The summertime atmospheric conditions were diagnosed using this framework and the presence of a land-atmosphere coupling hot-spot in the Indian peninsula, proposed by previous studies (Koster et al. (2004)), is confirmed. Secondly, the local perspective is taken in the Indian subcontinent. The CTP- HIlow framework is tested in India, using an atmospheric slab model (a simple, one- dimensional model of the atmosphere) combined with atmospheric soundings (balloon measurements of temperature and moisture of an atmospheric profile of up to 30 km). This model is run twice ; once with a wet land surface and once with a dry land surface. The results of these model runs can have two outcomes ; the land surface does not have an influence on precipitation or it does have an influence. The CTP-HIlow framework proves to be useful to classify the potential influence of the land surface. When the atmosphere is very wet (low values of HIlow ), precipitation will occur regardless of the land surface, when the atmosphere is very dry (high HIlow values) no precipitation will occur, regardless of the land surface. However, for intermediate HIlow values, the effect of the land surface depends on the stability or the amount of convective energy (CTP) in the atmosphere. The stability of the atmosphere is related to how fast a particle will ascend in the atmosphere, which depends mostly on the temperature profile

Mots clés : irrigation / atmosphere / monsoon / evaporation / water budget / india


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