Pre- and post-1975 scaling relationships of monsoon and non-monsoon hourly precipitation extremes with coincident temperature across urban India

Abstract

• Scaling relationship of hourly precipitation extremes with air temperature and DPT. • Scaling coefficients during monsoon are negative and have dropped post 1975. • Scaling coefficients during non-monsoon are close to CC scaling rate. • Super-CC scaling rates for some locations using DPT as the scaling variable. • Probability of monsoon extremes is higher when conditioned on higher temperatures. This study presents a scaling analysis of extremes in hourly precipitation with coincident temperature in 14 urban locations across India for monsoon as well as non-monsoon seasons, and examines the probabilistic association through bivariate copula. Using gridded hourly rainfall and dew point temperature (DPT) datasets from ERA5 Reanalysis and daily maximum temperature from the India Meteorology Department (IMD), it examines how far the scaling relationships of sub-daily precipitation extremes with temperature deviate from the Clausius-Clapeyron (CC) scaling across different climatic regimes in India. Pre- and post-1975 analyses were conducted to evaluate if the scaling relationships have altered in line with the global climate shift of the 1970s. Findings from the study indicate that during the monsoon, the scaling relationship was negative in all the cities except Pune (PNQ) during the post-1975 period. In fact, in most of the locations (e.g., Bhopal (BHO), Jaipur (JAI) and Mumbai (BOM)), the scaling coefficient for monsoon rainfall extremes decreased after the 1975 global climate shift. During the non-monsoon season, the scaling coefficient was slightly positive almost everywhere and approximately equal to the CC scaling rate, both pre- and post-1975; the only exception being in PNQ, where a negative scaling was observed. The joint probabilistic distributions for BOM showed that the non-exceedance probability of extreme rainfall was higher when conditioned on higher temperatures in the monsoon season; however, the opposite was observed in the non-monsoon season pre-1975. A similar distinct seasonal feature was noticed in a few other locations including New Delhi (DEL). Using DPT as the scaling variable, Chennai (MAA), Guwahati (GAU) and Tiruchirappalli (TRZ) showed positive scaling in both pre- and post-1975 in both monsoon and non-monsoon seasons. Unlike with maximum air temperature, super-CC scaling was observed with DPT in the monsoon season for TRZ (pre-and post-1975) and for MAA and GAU (pre-1975) and also in the non-monsoon season for MAA (pre-and post-1975) and for GAU and BOM (post-1975). This analysis is expected to provide useful insights into the regional and seasonal distribution of hydrological extremes for a subsequent assessment of their impacts on the design of urban infrastructure.