Alladi Ramakrishnan Hall

Role of the Himalaya in defining Indian Weather and Climate

A.P. Dimri

JNU, New Delhi

The western Himalayas (WH) is characterized by heterogeneous land surface
characteristics and topography. During winter (December, January, and February
– DJF), eastward moving low-pressure synoptic weather systems, called Western
Disturbances (WDs) in Indian parlance, cause the majority of the precipitation
mostly in the form of snow. The interplay between land surface/topography and
WDs greatly controls precipitation distribution over the region. This study
seeks to evaluate this using a mosaic-type parameterization of subgrid-scale
topography and landuse (subBATS) for regional climate simulation with a
regional climate model (RegCM3). The model coarse grid cell size in the control
simulation is 60 km while the subgrid cell size is 10 km. The present study
compares two 22-yr simulations (1980-2001) during winter (DJF). The first
simulation is without (CONT) and the second is with (SUB) the fine scale
subgrid scheme. Representing the fine scale processes using the subgrid scheme
SUB experiment simulates reduced precipitation by ~2 mm d-1 with comparison to
CONT experiment. This estimation of reduced and closer to the corresponding
observed precipitation is important for regional water budget over the WH which
is primarily governed by topographic and land surface disaggregation.
Validation with corresponding observations over similar elevations shows that
SUB displays an improvement over CONT experiment. This relevant decrease of
precipitation in SUB using disaggregation- reaggregation methodology for
initial model input fields in subBATS scheme is due to better representation of
the WH topography. In case of temperature, SUB experiment displays colder bias
(~2-4oC) than the CONT over the Himalayas. This preliminary finding is
important for studying regional water balance, snow melt accumulation in
following summer period.