Near-surface water vapor dynamics and its response to condensation events in arid regions

Near-surface water vapor condensation is one of the most crucial steps to fully utilize atmospheric water sources in ecological agriculture. It is often required to clarify the dynamic relationship between near-surface water vapor and condensation. This study aims to investigate near-surface water vapor dynamics and their response to condensation events in arid regions. Three geographical conditions of northwest China were selected to capture the meteorological parameters, including the southeast margin of the Tengger Desert (TD), the arid belt of the center in Ningxia Hui Autonomous Region (CANX), and the semi-arid region in Ningxia Hui Autonomous Region (SANX). The hydrostatic integration was employed to calculate water vapor flux and content within a 100 m range above ground at each observation point, based on the evolution patterns of meteorological factors with hight at the Yinchuan radiosonde station. The leaf wetness sensor of PHYTOS31 was used to calculate the condensation water amount at 5 cm above ground. A correlation analysis was performed on the water vapor, condensation water, and meteorological parameters. The results indicate that there were significant differences in annual total condensation water at TD, CANX, and SANX sites (P<0.05), with annual averages of 13.35, 22.68, and 32.80 mm, respectively, during the observation period. Spatiotemporal variations in water vapor flux and content were significant (P <0.05) at all three stations, thus peaking in summer and declining in winter. Minimum monthly water vapor flux at TD, CANX, and SANX were 1.9, 2.3, and 1.8 kg/(m·s), respectively, while minimum monthly water vapor content was 1.30, 1.45, and 1.60 mm, respectively. Peak water vapor flux and content occurred in July at SANX, and in August at TD and CANX. Water vapor flux was markedly higher at the southeast margin of the Tengger Desert and arid region than that in the semi-arid regions, with 21.2, 19.4, and 13.9 kg/(m·s) for the maximum TD, CANX, and SANX, respectively. The monthly average water vapor content was highest at the SANX site (13.69 mm), while those were 11.35 and 11.23 mm, respectively, at the TD and CANX sites. The primary wind direction ranges influencing water vapor flux and content at the three stations were: TD with 0°–60° and 150°–210°, CANX with 180°–240°, and SANX with 0°–30°, 120°–240°, and 300°–359°. In terms of a single condensation event, both water vapor flux and content decreased during the condensation accumulation phase, whereas there was an increase when the condensation dissipated. Condensation content showed a significant negative correlation with water vapor content (P<0.05). The correlation coefficients for TD, CANX, and SANX were −0.652, −0.751, and −0.722, respectively. Water vapor flux first decreased and then increased during the diurnal cycle without condensation, due to the absence of water vapor phase change. While water vapor content shared an increasing trend. Water vapor flux and content exhibited a significant negative correlation (P<0.05) during the process. These findings can also provide valuable insights to characterize near-surface water vapor dynamics under diverse geographical conditions.