Rainfall Variability in Multi-Source Observations and Simulation over the Uttarakhand Himalaya,India

Abstract:

The distribution of monsoon rainfall has a large variability and therefore it is always a challenging task for the Himalayan region. The Central Himalayan region which covers Uttarakhand state is a hot spot in the global climate system in terms of its unique geographical features. Thus the study of spatial and temporal distribution of rainfall in the central Himalaya has great relevance for the planning of policy formulation especially in the context of global warming. However, very little is known about the details of weather and climatic variability over this region. At the same time, conclusions derived over other locations may not be applicable over the Himalayan region. Thus information about the long term climate is important to understand the nature of different climatic systems over any region.

In the present study, spatial trend of rainfall over Uttarakhand region is analysed using the multi-source data . Firstly from NCEP reanalysis, it is found that the region receives rain of 4 mm/day over the Uttarakhand region during annual and monsoon season. In order to see the rainfall variability at small scale, the very high resolution data from APHRODITE and IMD data are being used, and this analysis shows a clear variation at spatial scale with in the region. It is observed that highest rainfall with value up to 14mm/day in east part of Uttarakhand. If we analyse the spatial pattern of linear trend (expressed as % of respective SD) of annual and monsoon rainfall from 1951 to 2003, there is increasing trend in annual rainfall in east and north part of the Uttarakhand. Middle part is showing decreasing trend in annual and monsoon rainfall.

Comparison of 24-year (1980-2003) daily climatology of the seasonal (June-September) cycles of monsoon rainfall averaged over whole Uttarakhand from ensemble of two observations (i.e. IMD gridded and APHRODITE) and ensemble of simulation using a variable resolution GCM has been carried out. The analysis shows that the daily rainfall climatology is well captured by the ensemble simulation throughout the monsoon season. But in last 15 days of monsoon season the simulated rainfall is higher than the observed rainfall climatology. Over the season as whole the observed and simulated rainfall over the Uttarakhand region are strongly correlated (CC=0.43) at 99% confidence level.