A study of changes in rainfall and temperature patterns at four cities and corresponding meteorological subdivisions over coastal regions of India

Changes in the surface air temperature and rainfall, extreme events and their future projections at four Indian cities and corresponding meteorological subdivisions and homogeneous zones have been analyzed in this study based on observed gridded datasets from the India Meteorological Department (IMD) and climate projections from nine IPCC models. The cities include Howrah, Vishakhapatnam, Madurai and Kochi. Their corresponding meteorological subdivisions are Gangetic West Bengal, Coastal Andhra Pradesh, Tamil Nadu & Pondicherry and Kerala. When one considers the larger spatial scale, these cities and meteorological subdivisions are situated in the temperature homogeneous zones of North East, East Coast and West Coast. Similarly, North East and Peninsular India are the rainfall homogeneous zones where these four cities are situated. In this study, indication of change in any climate parameter is assumed to be strong if the same is found in a city and also in its meteorological subdivision and homogeneous zone. When the indications are of the same nature in a city and either in its meteorological subdivision or homogeneous zone, it is termed as weak. Comparison shows that the values of annual mean temperature and summer monsoon precipitation simulated by MIROC 3.2 (medres) and NCAR_CCSM3 models are close to the corresponding observed values at each of the four cities. Analysis shows similar trends in the annual mean observed temperature and monsoon precipitation in the selected four cities and their corresponding meteorological subdivisions and homogeneous zones. Based on IMD gridded datasets, the rise in annual mean temperature at 1% significant level during 1969-2005 in Kochi and its subdivision and homogeneous zone is a strong indication of warming. At Madurai such warming is weak. Whereas, at Howrah and Vishakhapatnam, there are no strong indications of warming based on the available IMD gridded data. So far as the future is concerned, the results show that in the coming 30 years, the projections of mean temperature rise at Vishakhapatnam, Madurai and Kochi at 1% significance are strong, whereas at Howrah it is weak. Extreme temperature events such as warm days & nights and cold days & nights have also been examined. There is strong projection of the decrease in the moderately cold events (T05p) at 1% significance at Madurai. At the same place, the projection of moderately warm events (T95p) is weak. At Kochi the projections of increase in low (T90p) and moderate (T95p) warm events at 1% significance are weak. There are no strong projections of increase/decrease of warm/cold events in Howrah and Vishakhapatnam.