Trend assessment of rainfall, temperature and relative humidity using non-parametric tests in the national capital region, Delhi

Understanding rainfall and temperature’s spatio-temporal variations at the local, regional, and global scale is vital for planning soil and water conservation structures and making irrigation decisions. The present investigation attempts to observe the rainfall and temperature variability and trend over 31 years (1990-2020) in the National Capital Region (NCR), Delhi, India, obtained from IARI meteorological station, Pusa, New Delhi. The statistical trend analyses Mann-Kendall (MK) test followed by Theil Sen slope estimator test was used for annual and monthly analysis to assess the trend direction and magnitude of the change over time. Pettitt's test detected the inflection point in the variable time series. The annual Tmax, Tmin, and rainfall showed no trend in the time series data. However, Tmax indicated a statistically significant decreasing trend in January and December. This implies a dip in the temperature during the winter months of January and December. Similarly, Tmin revealed a statistically significant decreasing trend in January and December. But a statistically increasing trend for Tmin was observed in April, which may cause a harsh environment for cultivating the Zaid season crops due to increased warming. The Pettitt test showed no change point in the time series trend in the annual Tmax and Tmin data series. For January Tmax data, the trend change point occurred in 1998. However, it was observed that Tmin in April showed a change point in the time series trend in 1999. The change point in the annual average rainfall data was marked in 2012. A didactic implication of these changes on hydrologic design and crop irrigation decisions was discussed in this paper.