Planetary boundary layer plays a critical role in the monsoon circulation studies at regional scales through exchange of land surface fluxes (heat and moisture) with atmosphere. The objective of the present study is to identify the spatial variability of long-term seasonal trends of planetary boundary layer height (PBLH) over Indian subcontinent and its association with atmospheri parameters. Monthly atmospheric boundary layer height data obtained from European centre for medium range weather forecast ERA-5 reanalysis has been used for the study during 1980–2018. Statistically robust non-parametric Mann Kendall test is used to investigate the significance of trend at 95% confidence interval. From the results it has been observed that decreasing trend for PBLH is noticed during pre-monsoon and monsoon seasons over Indian region. PBLH over central and north-west India is deeper (1600–1800 m) during pre-monsoon season whereas PBLH is shallow during other seasons. Seasonal variation of PBLH shows a strong negative association with the relative humidity (r more than −0.8) whereas it shows strong positive association with surface temperature (r > 0.7) and surface zonal winds (r > 0.5) over Indian subcontinent. Evaporative fraction which acts as a dominant controlling factor for the variation in PBLH is positively associated (r > 0.7) with the PBLH during monsoon season. Decreasing trend of PBLH during monsoon season may be attributed to the decrease in latent heat flux and increase in relative humidity that results in entrap of moisture at lower levels and may enhance the formation of extreme events. Inter annual variability of PBLH over Indian subcontinent demonstrates in-phase relationship with the deficit and excess monsoon years. Further to this, PBLH is found to be strongly negatively correlated with PM2.5 (r more than −0.5) during pre-monsoon and monsoon seasons suggesting an opposite phase relationship between the two parameters.

行星边界层通过地表通量（热量和水分）与大气的交换，在区域尺度的季风环流研究中发挥着关键作用。本研究的目的是确定印度次大陆上行星边界层高度 (PBLH) 长期季节性趋势的空间变异性及其与大气参数的关联。从欧洲中期天气预报中心 ERA-5 再分析获得的每月大气边界层高度数据已用于 1980-2018 年的研究。统计上稳健的非参数 Mann Kendall 检验用于研究 95% 置信区间的趋势显着性。从结果可以看出，在印度地区的季风前和季风季节期间注意到 PBLH 的下降趋势。在季风前季节，印度中部和西北部的 PBLH 较深（1600-1800 m），而其他季节的 PBLH 较浅。PBLH的季节性变化与相对湿度（r大于-0.8）呈强烈负相关，而与地表温度呈强烈正相关（r  > 0.7) 和 印度次大陆上空的地表纬向风 ( r > 0.5)。作为 PBLH 变化的主要控制因素的蒸发分数呈正相关（r > 0.7) 与季风季节的 PBLH。季风季节 PBLH 的下降趋势可能是由于潜热通量的减少和相对湿度的增加导致较低水平的水分滞留，并可能促进极端事件的形成。印度次大陆 PBLH 的年际变化表明与季风季赤字和过剩年有同相关系。此外，在季风前和季风季节，发现 PBLH 与 PM2.5（r 大于 -0.5）呈强烈负相关，表明这两个参数之间存在相反的相位关系。