Long-term trend in clouds and precipitation over an urban city Ahmedabad in the Western-Indian region

Abstract

This study analyzes the cloud base height (CBH) and precipitation patterns over Ahmedabad, a semi-arid urban city in the Western-Indian region, over the period 2000 to 2021. The study compares ERA5 precipitation product with GSMaP_ISRO precipitation data during the Indian Summer Monsoon (ISM) period and examines trends in cloud frequency across different altitude levels over the Ahmedabad region. Results indicate that the ERA5 is able to represent the monthly rainfall patterns over the study region. The findings reveal that clouds accounting for significant rainfall during ISM typically have a cloud base height (CBH) below 1 km, with the highest frequency observed between 200 m and 250 m. A notable increasing trend in the frequency of rainy clouds (rain > 0.5 mm/hour) is observed during September (withdrawal monsoon) with an increase of (0.49 ± 0.23) % per year. Also, a significant increase in low (0–2 km) and mid-level (2–6 km) cloud frequency is observed during September, which correlates with an annual rise in September rainfall by approximately 5.37 ± 3.52 mm from 2000 to 2021. These changes are linked to alterations in lower and upper tropospheric temperatures, influenced by aerosols, reflecting the impact of anthropogenic activities on cloud properties and precipitation patterns.