Impact analysis of COVID-19 pandemic control measures on nighttime light and air quality in cities.

The COVID-19 pandemic has profoundly affected human society on a global scale. COVID-19 pandemic control measures have led to significant changes in nighttime light (NTL) and air quality. Four cities that were severely impacted by the pandemic and that implemented different pandemic control measures, namely, Wuhan (China), Delhi (India), New York (United States), and Rome (Italy), were selected as study areas. The Visible Infrared Imaging Radiometer Suite (VIIRS) and air quality data were used to study the variation characteristics of NTL and air quality in the four cities in 2020. NTL brightness in Wuhan, Delhi, New York, and Rome decreased by 8.88%, 17.18%, 8.21%, and 6.33%, respectively, compared with pre-pandemic levels; in the resumption phase Wuhan and Rome NTL brightness recovered by 13.74% and 3.38%, but Delhi and New York decreased by 16.23% and 4.99%. Nitrogen dioxide (NO2) concentrations in the lockdown periods of Wuhan, Delhi, New York, and Rome decreased by 65.07%, 68.75%, 55.59%, and 56.81%, respectively; PM2.5 decreased by 49.25%, 69.40%, 52.54%, and 66.67%. Air quality improved, but ozone (O3) concentrations increased significantly during the lockdown periods. The methods presented herein can be used to investigate the impact of pandemic control measures on urban lights and air quality.

Habitat configuration of the Yangtze finless porpoise in Poyang Lake under a shifting hydrological regime.

Habitats of freshwater cetaceans are under increasing threats of deterioration globally. A complete understanding of long-term variations of habitat configurations is therefore critical. Poyang Lake in China contains a large and stable population of the Yangtze finless porpoise, a critically endangered freshwater cetacean species. However, constant water decline and intensified human activities in the lake since 2000 have led to uncertainty for porpoise conservation. We address this issue via remote sensing and hydrodynamic modeling of nine environmental variables during different seasons over the past two decades. The MaxEnt model was used to extrapolate changes in likely habitat configurations of the porpoise, and MARXAN algorithms delineated habitat protection priorities in different seasons. Results illustrate that flow velocity, water depth, Chl-a concentration, distance to grassland and boats greatly affect the porpoise distribution. Shifts in these environmental variables can lead to significant habitat decreases in all seasons. In particular, unstable hydrological regimes may force the porpoises to live in habitats with lower water depths for suitable flow velocity conditions in the dry season, and habitats are increasingly infringed by grassland and mudflats. High protection priority areas such as the northern channel and the estuaries of the tributaries urgently need long-term systematic and targeted surveys of ecosystem functionality and flexible management of anthropogenic activities. Combining remote sensing with hydrodynamic and species distribution models can also assist in understanding the situation of other aquatic species.