Compared to rain, dew is an important supplementary source of water for the survival of certain plants and animals in drylands. However, the hydrology of dew has not yet been fully investigated due to difficulties in measuring the amount and duration of it. In this study, a 3-year in-situ monitoring experiment was conducted from 2014 to 2016 in the semi-arid Sanyuan County, Shaanxi Province of China, using a leaf wetness sensor (LWS) and four associated meteorological instruments. Results showed that the average annual total dewfall was 32.8 mm with a daily maximum of 0.88 mm. The majority of daily dew occurred in the night from 18:00 to 8:00 with the maximum condensation rate occurring at around 4:00. The maximum dew residence time was about 18 h/day on the dew days in all seasons. However, the actual dew production period was about 14 h in spring (March–May), autumn (September–November), and winter (December–February), and only 11 h in summer (June–August). The maximum intensity and amount of dew always occurred in autumn (with an average amount of 12.2 mm or 37% of the annual total), followed closely by spring (11.4 mm, 35%), with much less in summer (6.6 mm, 20%) and winter (2.6 mm, 8%). The annual dew distribution by months showed a double crest variation, with two peaks in April–May and October–November, and two valleys in January–February and July. Comparatively, annual dewfall is only about 1/18th of the rainfall in this region, but the number of dew days (224 days, or 61% of year) is 2.6 times that of rain days (87 days, 24%), making dew a critical supplementary source of water for mitigating dry periods and supporting native plants and animals. Rain and dew are highly complementary as dew occurs in cloudless nights while the rain occurs in different and on much fewer occasions in the region. The dew amount was highly and positively correlated to the relative humidity of the air above the threshold of 81% (r = 0.78, p < 0.01), negatively correlated to the difference between air temperature T_a and dewpoint T_d, when (T_a − T_d) is less than 4 °C (r = −0.66, p < 0.01), and weakly correlated to wind speed (0.2 to 2 m·s⁻¹), wind direction, surface soil moisture, and temperature. In the Sanyuan region, two general wind directions, 30°–90°and 210°–270°, were more favorable for the formation of dew.

To elucidate the condensation characteristics and ecological effects of dew in semi-humid regions, this study took Yangzhuang Town of Tengzhou in the semi-humid zone of southwestern Shandong as the research area. Field observations of dew yield and environmental factors were carried out at four near-surface heights (0.2 m, 0.6 m, 1 m, and 2 m) from June to November 2025. The condensation patterns and driving factors of dew were analyzed, a ridge regression model was developed for dew yield simulation, and the ecological effects of dew were systematically expounded. The results indicate that dew exhibits a unimodal pattern characterized by nocturnal accumulation and diurnal dissipation. Both dew duration and dew yield are higher in autumn (September–November) than in summer (June–August), with the maximum dew yield observed at 1 m height. Dew yield shows a significantly positive correlation with relative air humidity (p < 0.05), and significantly negative correlations with vapor pressure deficit, dew point temperature, and air–dew point temperature difference (p < 0.05). It also presents a nonlinear relationship with wind speed, and the wind speed for dew condensation in this area ranges from 0.1 to 0.6 m/s, whereas cloud cover has no significant effect. The established ridge regression model performs satisfactorily in dew yield simulation. In addition, dew may provide continuous minor water supply during dry periods and potentially alleviate mild drought stress in plants. The results provide a scientific reference for the sustainable development and exploitation of dew water resources, the improvement in non-rainfall water theories, and the mitigation of drought.

Horizontal well air sparging (HAS) technology provides a promising approach for pollution remediation. In this study, a model experiment assessed the airflow distribution characteristics of HAS under varying air sparging (AS) pressure, tube burial depth, and groundwater flow conditions, while evaluating the retardation effects of HAS on dissolved groundwater contaminants. The results indicated that airflow velocity and diffusion range increased markedly with elevated AS pressure. Deeper AS tube burial depths resulted in more uniform airflow distribution and broader coverage. Groundwater flow significantly affected airflow distribution, as greater water head differences induced a downstream shift in the airflow pattern, resulting in an asymmetric diffusion range. Regarding pollutant retardation, airflow created a physical barrier by reducing permeability and interfacial resistance, effectively hindering pollutant diffusion. Airflow from the AS tube aligned parallel to the flow direction reduced Rhodamine B concentration by 53.1% over 300 min, preventing deeper pollutant migration into the sand layer. Conversely, airflow from the AS tube oriented perpendicular to the flow direction reduced Rhodamine B concentration by 84.38% over the same period, demonstrating superior effectiveness in limiting horizontal pollutant diffusion. These findings provide valuable theoretical insights and practical guidance for implementing HAS technology in groundwater pollution management.