Light pollution trends for International Dark Sky Places using VIIRS nighttime light composite data

Abstract International Dark-Sky Places (IDSPs) is a global project led by the International Dark-Sky Association (IDA) to protect dark-sky areas for astronomical observation and astro-tourism. Currently, there are 216 IDSPs in the world. This study analyses light pollution trends in International Dark-Sky Places (IDSPs) using VIIRS night light composite data. IDSPs are mostly located near urbanised areas in Europe and away from urbanisation in North America. Dark and large areas away from urbanisation in South America, Africa, Central Asia and Australia offer great potential. Linear regression analysis shows that in 94% out of 216 places there is no change in artificial light at nigh (ALAN). There is a decrease in the level of artificial light in 3% and an increase in the level of artificial light in 3%. Unlike the linear regression analysis, Mann–Kendall and Sen slope analyses revealed significant statistical changes at the 105 sites (78 increasing and 27 decreasing). Machine learning models including decision tree regression (DTR), random forest regression (RFR) and gradient boosting regression (GBR) provided good predictive accuracy (R ^2 2 > 0. 6). Seasonal patterns were assessed using the Lomb–Scargle periodogram, but detected periodicities were considered false positives. These results emphasise the need for strategic planning to reduce light pollution in IDSPs, especially in underused areas.