Spatio-Temporal Variability of Pre-monsoon Convective Events and Associated Rainfall over the State of Odisha (India) in the Recent Decade

The state of Odisha is situated on the eastern coast of India and is highly vulnerable to massive convective activity in the pre-monsoon season (PM), i.e., from March to May; however, there is a scarcity of studies in this context using long-term datasets. Therefore, an in-depth investigation of the variability in convective events and associated rainfall during PM over the state of Odisha has been carried out for the period 2009-2018 using the European Centre for Medium-Range Weather Forecasts (ECMWF) fifth-generation reanalysis (ERA5) datasets. The convective events (severe and moderate) identified using two sets of threshold values of three different convective indices, i.e., convective available potential energy (CAPE), the K Index, and the Total Totals Index, show an increasing trend in recent years, with South Coastal Odisha (SCO) and North Coastal Odisha (NCO) showing the highest increase. Subsequently, the spatial distribution of rainfall suggests that the maximum convective precipitation (CP) is experienced over NCO and adjacent eastern districts of North Interior Odisha (NIO). The spatial distribution of the 2 m temperature suggests that there exists a strong temperature gradient between the western and eastern portions of the state. However, the gradient weakens for the years associated with the anomalous distribution of CP. The distinct tropospheric temperature difference between the lower levels (LL) and upper levels (UL) clearly suggests that the warming (cooling) of LL is associated with high (low) CP over the region. This is further established by the coherent signature of specific humidity. The frozen hydrometeors (cloud ice and snow) are the major facilitators for the occurrence of CP over the study region. The moisture transport (MT) is associated primarily with the anomalous distribution of spatial rainfall. The years with suppressed convective activity have a distinct signature of a negative MT anomaly along with anomalous north-easterly winds (as against the typical south-westerly flow). It is also demonstrated that the anomalous MT scenario is highly modulated by the land-sea temperature contrast over the region.