Determination and Analysis of Weather over Administrative Regions of India: 1951 to 2021

Non-availability of official, single-source, reliable and easy to access weather data at administrative regions such as states and districts poses significant challenges for Indian social science research community interested in climate impact research and policy. This paper provides a brief summary of evolution of access to weather data in the public domain over the past three decades in India. Gridded datasets being the standard for making available the official weather information, the paper discusses the concepts and procedures involved in using such data products to arrive at weather information at various administrative scales. A transparent approach to spatially interpolate the gridded weather data (supplied by IMD) on temperature and rainfall to determine state and district level estimates of weather over the period 1951 to 2021 is presented. The paper further analyzes the long-term trends and changes in the distribution of annual and intra-annual temperature and rainfall at the All India level and at one sub-national state (Tamil Nadu) level across multiple time-scales (i.e., 1951-1980, 1981-2010, and 2011-2021) using traditional methods such as Mann-Kendall tests and Sen’s Slope estimates. The paper further reports the climate trends across Tamil Nadu districts over the period 1951 to 2021 using the visually appealing Innovative Polygon Trend Analysis.