Weather stations are key facilities to record long-term change in surface air temperature (SAT) in land. However, some weather stations are located in or near cities, and they may suffer from relocations due to the expansion of the cities and the resulting deterioration of observing settings. This is especially true in developing regions like China mainland. Most of the national stations in this region have been relocated for at least one time.
The practice has led to breakpoints in the SAT data series, and researchers have to make an adjustment called homogenization before they go further to analyze long-term change in SAT. Different homogenization procedures produced different results of the SAT trends, with some effectively restoring the urbanization effect in the historical SAT records. Thus the homogenization will bring in a new bias in the site and regional SAT data series.
Each country or region may have different practices when the weather stations are engulfed by buildings. What are you seeing in your countries or regions? Have the observational stations been also moved away from urban areas? How do you think about the possible influence of urbanization on the historical SAT records no matter what strategies have been practiced?
Interesting and practical question Prof Guoyu Ren , in developing and rapidly
evolving economies such as India, this concern resonates deeply, particularly in regions undergoing dynamic land-use transformations, often under the aegis of initiatives like "Smart City" developments. In these scenarios, meteorological stations that have been consistently recording data (SAT) over extended periods encounter disruptions, potentially compromising the integrity and continuity of the data. This phenomenon necessitates rigorous methodologies to ensure data homogeneity and compensate for any anomalies introduced by such transitions.
In India, the central agency, the India Meteorological Department (IMD) is responsible for maintaining and managing weather stations and the relocation of stations is done with meticulous care to ensure the continuity and integrity of meteorological data. The India Meteorological Department (IMD) often applies data homogenization techniques to maintain data consistency post-relocation. The standard practice adopted is moving the stations with similar climatic conditions to the original, and occasionally, both old and new stations operate simultaneously to gauge data variations. Additionally, any relocation or significant station event is thoroughly documented, and regular equipment maintenance and calibration are prioritized, ensuring optimal accuracy in readings. But even after all these measures, it is highly unlikely to have the data completely error-free.
Thank you Ashish for your comments.
India is a country that is experiencing rapid development and urbanization, and weather station relocation would be also a problem at present, and will be probably so in near future. However, the relocations of stations may be causing a little bit different change in surface air temperature (SAT) from that in northern China, because the diurnal and seasonal variation in urban heat island intensity in Indian cities may have been characterized by a larger value at daytime and summertime.
Is there any analysis on influence of relocation and data homogenization on estimate of SAT trend and urbanization effect (bias) in the SAT data series in India?
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