How extreme precipitation in 2010 altered urban heat island behaviour in Debrecen

Earlier examinations of the urban heat island (UHI) characteristics in Debrecen revealed unusual behaviour in the years 2010 and 2011, while the following years exhibited characteristics expected according to the literature. The year 2010 in Hungary was characterised by anomalously high precipitation with several extreme events, including two Mediterranean cyclones in the spring, numerous convective systems in the summer, and several slow-moving frontal passages in the autumn. These led – both country-wide and in Debrecen – to record-high annual precipitation, and significant deviations in other meteorological elements like soil moisture and near-surface humidity characteristics. It is possible that the development of the urban heat island (UHI) in Debrecen was also affected. This study investigates the unusual behaviour of the UHI in 2010 and early 2011, focusing on how the excessive precipitation influenced the urban climate. Data from 2010 to 2015 were analysed, originally including temperature, humidity, wind, precipitation, cloud cover and soil moisture measurements from a city and a rural station. The current analysis shows that the high precipitation caused significant changes in soil moisture and relative humidity in the rural area, possibly leading to an increased latent heat flux at the expense of sensible heat. This might have reduced the UHI intensity during both day-time and night-time. With this, the study proposes a potential explanation for how long-term high precipitation can have lasting effects on UHI development, which may contribute to a deeper understanding of the interactions between extreme weather events and urban climate dynamics, which is crucial for urban planning and climate adaptation strategies in the context of climate change.