1. Land-Atmosphere Feedback:
Land surface conditions can influence the state of the atmosphere, and vice versa. During the summer, the vast expanses of dry and bare land in China, particularly in the northern and western regions, absorb more solar radiation, leading to increased surface temperatures. This intense heating of the land surface results in the formation of thermal lows—areas of low atmospheric pressure—over these regions.
2. Atmospheric Circulation Patterns:
The thermal lows created overheated landmasses alter atmospheric circulation patterns. As warm air rises from these areas, it leads to the formation of convective clouds and localized precipitation. However, the sinking air in the surrounding regions suppresses rainfall and contributes to clear skies and less cloud cover. This further intensifies surface heating and exacerbates drought conditions.
3. Subsidence and Dry Air Masses:
The descending motion of air from the thermal lows leads to subsidence, a phenomenon where the air compresses and warms as it sinks. This subsidence prevents the upward movement of moisture and inhibits cloud formation. Consequently, the sinking air masses become stable and dry, suppressing precipitation and contributing to persistent晴天.
4. Enhanced Solar Radiation:
The lack of cloud cover and the absence of aerosols in the atmosphere due to reduced industrial activities during the COVID-19 pandemic allowed more solar radiation to reach the Earth's surface. This increased solar insolation further intensified land surface heating and contributed to soaring temperatures.
5. Soil Moisture Feedback:
The sustained dry conditions and limited rainfall resulted in depleted soil moisture. Dry soil has a low capacity to retain heat, causing rapid surface heating during the day. At night, the heat stored in the dry soil is released back into the atmosphere, contributing to higher night-time temperatures and amplifying the heatwave intensity.
6. Amplification by Urbanization:
Urbanization in China has also played a role in amplifying the extreme weather conditions. Urban areas with dense infrastructure, buildings, and paved surfaces absorb and trap heat, creating urban heat islands. These islands of higher temperatures further influence local atmospheric circulation and exacerbate heatwave conditions.
In summary, the complex interactions between land surface conditions, atmospheric circulation patterns, and human-induced factors converged to create the perfect recipe for China's extreme weather in the summer of 2022. The interplay of these land-atmosphere processes intensified heatwaves, prolonged droughts, and triggered widespread wildfires, posing significant challenges to ecosystems, agriculture, water resources, and public health across the country.
