Modelling Hourly Variability of Meteorological Parameters Using FPCA in the Western Himalayas: Evidence from Srinagar (1972–1989 & 1991–2024)

In this work, Functional Principal Component Analysis (FPCA), first time is applied to study the variability in meteorological parameters over Western Himalayan Region (Srinagar), particularly hourly rainfall, during the two wet seasons: winter (December-January-February, DJF) and the southwest monsoon (June-July-August-September, JJAS). The analysis covers two periods: 1972-1989 (Pre-1990, henceforth) and 1991-2024 (Post-1990, henceforth). The analysis revealed that the DJF rainfall between 1972 and 1990 (pre-1990) was primarily characterized by synoptic-scale circulation patterns and associated cloud bands. However, between 1991 and 2024 (post-1990), it became more closely tied to cloud type & its formation, as well as relative humidity dynamics (moisture fields), with a limited dependence on wind fields over the Srinagar region. The pre-1990 summer monsoon (JJAS) rainfall pattern is found to be convective cloud-driven. However, a temperature-driven convective instability, the primary mechanism, dominated the post-1990 monsoonal rainfall activity over Srinagar. FPCA3 reveals a significant change in the structural behavior of MSLP variability, although the post-1990 period is marked by diminished midday peaks & modified morning patterns. The analysis suggested that post-1990 temperature variability during JJAS occurred more frequently but tended toward the weaker anomalies, accompanied by notable adjustments in both the timing (FPCA2) and the form (FPCA3) of the diurnal temperature cycle. Overall, these findings imply that winter temperature variability after 1990 became more frequent, less balanced, and structurally more intricate.