Characteristics of Boundary Layer Height Variations in Global Arid Regions and Their Sensitivity to Influencing Energy Factors

Global warming has intensified the negative impacts of drought across most arid regions worldwide, leading to significant changes in the spatial pattern of surface energy, which in turn affects the structure and development of the upper atmospheric boundary layer ( ABL ) in these regions. Based on monthly mean ERA‐Interim reanalysis data from 1979 to 2018, this study examines the spatial distribution and variation trends of boundary layer height ( BLH ) over different arid regions of the global land, and quantitatively evaluates the sensitivity of BLH in seven typical arid regions to the two dominant energy terms required for ABL development‐namely, surface heating ( SHF ) and ABL ‐top entrainment ( H e )‐during the annual, warm‐season and cold‐season periods. The results show that the long‐term annual mean BLH over the global arid regions is approximately 841.8 m, nearly 200 m higher than that over more humid regions, with substantial regional differences. Specifically, in the driest and hottest regions‐West and South Asia (WSA) and North Africa (NAF)‐ BLH is relatively high, at approximately 951.2 and 932.1 m, respectively, while in South America (SAM), a relatively cold and humid region, BLH is the lowest at only 728.0 m. The differences in BLH among arid regions are influenced not only by the partitioning of surface energy but also by atmospheric dry‐wet conditions, low cloud fraction (low cloud amount/total cloud amount), and altitude. Over the past 40 years, BLH in most global arid regions (except for South Africa, SAF) has exhibited an upward trend, which is to some extent associated with the increase in sensible heat flux ( SHF ) and the decrease in latent heat flux ( LHF ) induced by the “dry gets drier” mechanism under global warming. In contrast, SAF is the only arid region worldwide that has become significantly wetter; the substantial wetting has shifted surface energy partitioning from sensible‐heat dominance toward latent‐heat competition (decreased SHF and increased LHF ), weakening the surface thermal forcing and leading to a downward trend in BLH . Comparative analysis reveals that the combined changes in surface SHF and ABL ‐top entrainment heat flux ( H e ) account for approximately 80% of the BLH variation in most global arid regions (and even over 90% in some regions). Both factors exert predominantly positive effects on BLH , with only the cold‐season H e effect in SAM being negative. Although BLH shows a consistently strong positive sensitivity to SHF changes across different periods in all arid regions, a higher SHF does not necessarily imply greater sensitivity; This is jointly regulated by the proportion of SHF in surface effective energy and atmospheric dry‐wet conditions. In addition, in the high‐elevation Pan‐Central Asia (PCA) region, characterized by high elevations, the heating efficiency of SHF is particularly prominent due to multiple factors. While the sensitivity of BLH to H e is considerably lower than that to SHF , it still plays an non‐negligible role in shaping the structural differences in BLH among arid regions. In regions with drier and hotter climates or higher elevations, the response of BLH to H e is more pronounced, which is associated with stronger entrainment in these regions. Notably, in the SAM region, the negative change in BLH induced by changes in H e during the cold season may be related to the presence of a thick inversion layer and a stable atmospheric structure with cold air below and warm air above in this region during this period.