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Titre : Atmospheric Effects of Irrigation in Monsoon Climate : The Indian Subcontinent
Nom du conférencier : Obbe Tuinenburg
Son affiliation : LMD
Laboratoire organisateur : LMD
Date et heure : 06-06-2013 10h30
Lieu : Salle de réunion du LMD/Jussieu (UPMC - Tour 45-55 3e étage, salle 315)
Résumé :

This PhD research studies the atmospheric effects of large scale irrigation in India from three perspectives : (1) the local effects of a moister land-surface on the triggering of precipitation, (2) the atmospheric fate of evaporation due to irrigation, i.e. where does the evaporation lead to (down-wind) precipitation?, and (3) What are the effects of a moister land-surface on the land scale (monsoon) moisture transport patterns? In the first part, several land-atmosphere indicators are tested globally (60S-60N). This confirms the presence of a land-atmosphere coupling hot-spot in the Indian peninsula, proposed by previous studies (Koster et al.(2004)). Moreover, the CTP-HIlow framework of Findell et al (2003) performs well globally and over the Indian region. Secondly, the CTP-HIlow framework is tested in India, using a slab model combined with atmospheric soundings. A small adaptation of the framework improved the performance in predicting the influence of the land surface on precipitation triggering. During the periods two months before the monsoon onset and after the monsoon retreat, precipitation triggering was found to be sensitive to land surface wetness. The third part studied the atmospheric moisture budget for the Ganges basin, using a three-dimensional atmospheric moisture tracing model, combined with ERA-interim reanalysis. The fraction of evaporation that recycles within the Ganges basin was found to be up to 60%. In the last part of the study, four atmospheric models were run with and without irrigation to test the large scale effects of irrigation on the Ganges basin atmospheric water budget. The local effects on precipitation were minimal and not uniform across the models.

The Ganges river basin evaporation increased, as well as the amount of evaporation recycled within the river basin. However, the large scale wind patterns showed an uniform change across the models. Due to an increased flow in the direction of north-west India, the precipitation in east-India decreased while it increased in north-west India and Pakistan. Therefore, the Ganges basin precipitation decreased slightly.

The conclusion of the work is that:

(1) India is one of the global locations where the land surface is important in modulating precipitation, especially in the period before and after the monsoon season.

(2) Large fractions of the evaporation recycle within the Ganges river basin, so a significant part of any increase in evaporation due to irrigation can potentially be reused within the basin.

(3) However, if the extent of irrigation becomes too large, the large scale wind patterns shift and the Ganges river basin precipitation will decrease.

Contact :

MP Lefebvre (0144272799)