Forest carbon exchange is affected by various environmental variables, among which photosynthetically active radiation, temperature, saturated water vapor pressure deficit, and soil moisture content dominate. The global atmospheric temperature has risen significantly in recent decades, and the saturated water vapor pressure deficit has also increased, which has had a widespread and lasting impact on terrestrial carbon sinks. Here, using flux data from Mazongling in Jinzhai County from July 2020 to June 2023, the relationship between saturated water vapor pressure deficit and forest carbon flux was investigated on the basis of carbon flux changes in the forest ecosystem in response to environmental factors. Results revealed that vapor pressure deficit (VPD) and net ecosystem productivity (NEP) exhibited a quadratic relationship at the daily and monthly scales. When the VPD was greater than 1.2 kPa at the monthly scale, the NEP of the fir forest ecosystem decreased with increasing VPD. At the daily scale, the impact of the VPD on NEP was studied by month and season. The results revealed that the threshold value at which the VPD affected NEP differed across different months and seasons. Therefore, the VPD is an important factor in forest ecosystems and should be considered in the assessment of ecosystem carbon sinks. It also has far-reaching significance in the carbon cycle and ecological sustainable development.

Harvest-disrupting rain events (HDREs) are prolonged cloudy–rainy spells during winter wheat maturity that impede harvesting and drying, induce pre-harvest sprouting and grain mould, and threaten food security in the Huang–Huai–Hai Plain (HHHP), China’s core winter wheat region. Using daily meteorological records (1960–2019), remote sensing-derived land-use data and topography, we develop a hazard–exposure–vulnerability framework to quantify HDRE risk and its drivers at 1 km resolution. Results show that HDRE risk has increased markedly over the past six decades, with the area of medium-to-high risk rising from 26.9% to 73.1%. The spatial pattern evolved from a “high-south–low-north” structure to a concentrated high-risk belt in the central–northern HHHP, and the risk centroid migrated from Fuyang (Anhui) to Heze (Shandong), with an overall displacement of 124.57 km toward the north–northwest. GeoDetector analysis reveals a shift from a “humidity–temperature dominated” mechanism to a “sunshine–humidity–precipitation co-driven” mechanism; sunshine duration remains the leading factor (q > 0.8), and its interaction with relative humidity shows strong nonlinear enhancement (q = 0.91). High-risk hot spots coincide with low-lying plains and river valleys with dense winter wheat planting, indicating the joint amplification of meteorological conditions and underlying surface features. The results can support regional decision-making for harvest-season early warning, risk zoning, and disaster risk reduction in the HHHP.

In order to determine the generating capacity of negative air ions (NAIs) and its relationship with human activities, the NAIs in different functional areas of Hefei, China, were analyzed. And the half residence time was studied by simulated experiments. The results showed that the natural attenuation law of NAIs was complied with this equation: C(t) = 2986.6 × e–0.0141t. Based on the attenuation equation, the coagulation rate α = 0.0141, and the lifespan was about 49.16 min. Combined with the NAIs concentration monitored in different functional areas, it was found that there was a huge difference in background concentration and environmental production or consumption. The background concentration in urban forest area was much higher, indicating that plants were the main source of NAIs. Among them, the urban forest area (UF), water area (WA), culture and education area (CEA) and residential area (RA) produced NAIs, while others consumed. There was a threshold value for the consumption by human activities, which was generally no more than 30% and can reach 50% when the activity was intense. However, no threshold value was found for vehicle activities. These results can provide reference for other mid-latitude inland cities to optimize urban design, and build ‘resilient cities’.