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The Role of Land Surface Processes in the Indian Summer Monsoon: A High-Resolution GCM Study

The Role of Land Surface Processes in the Indian Summer Monsoon: A High-Resolution GCM Study

Marie-Estelle Demory*, Pier Luigi Vidale* and Malcolm Roberts**
* NCAS-Climate, University of Reading, UK
** Met Office Hadley Centre, Exeter, UK

The Indian summer monsoon is a vital climate process, affecting the lives of many millions of people. A better understanding of the underlying mechanisms is important for prediction.

In this study, we investigate the impact of land surface processes on the Indian monsoon. In fact, previous studies(e.g. Becker et al. 2001) have investigated the importance of snow cover in Eurasia for the onset of the monsoon, which may be linked by a modification of the positioning of the subtropical jet and thus circulation. Moreover, other studies (e.g. Ferranti et al. 1999) indicated the existence of a positive feedback between soil moisture and precipitation, which may have an impact on the maintenance of the summer Indian monsoon.

For the purpose of investigating these two mechanisms, we use the high-resolution (60km) atmospheric version of the Hadley Centre's general circulation model HadGEM1 (NUGAM, developed as part of the UK-Japan Climate Collaboration). We show that lower resolution versions of HadGEM1 have poor skill at representing the monsoon; NUGAM performs better, probably due to the fact that mesoscale mountains are resolved, affecting both Himalaya snow cover and local circulation. However the soil remains too dry in India during the summer and precipitation too little. As further sensitivity tests for this study, soil physical parameters as well as the treatment of snow-melt infiltration have been modified.

Results from the first experiment indeed show an improvement in the development of the Indian monsoon, which still needs further investigation. The land surface climate of other regions of the world is also better represented, with the reduction of a significant warm bias over land, present in HadGEM1 at all resolutions.