Trend analysis of rainfall and temperature data for India

This article aims to review studies pertaining to trends in rainfall, rainy days and temperature over India. Sen's non-parametric estimator of slope has been frequently used to estimate the magnitude of trend, whose statistical significance was assessed by the Mann-Kendall test. Spatial units for trend analysis vary from station data to sub-division to sub-basin/river basins. There are differences in the results of the various studies, and a clear and consistent picture of rainfall trend has not emerged. Although the different units (sub-basins or sub-divisions) may have a non-zero slope value, few values are statistically significant. In a study on basin-wise trend analysis, 15 basins had decreasing trend in annual rainfall; only one basin showed significant decreasing trend at 95% confidence level. Among six basins showing increasing trend, one basin showed significant positive trend. Most of the basins had the same direction of trend in rainfall and rainy days at the annual and seasonal scale. Regarding trends in temperature, the mean maximum temperature series showed a rising trend at most of the stations; it showed a falling trend at some stations. The mean minimum temperature showed a rising as well as a falling trend. At most of the stations in the south, central and western parts of India a rising trend was found. Some stations located in the north and northeastern India showed a falling trend in annual mean temperature. Most of the data used in trend analysis pertained to the stations located in urban areas and these areas are sort of heat islands. This article also highlights the need of a network of baseline stations for climatic studies.