„Landscape heat islands” and their impact on climatic energy and water balance

Abstract

Comparing the patterns of surface temperature on infrared satellite images to land cover and global radiation, different surface temperatures can be assigned to different surface coverage. During summer, water and forest surfaces have the lowest temperatures. Evaporation of a lake or transpiration of a forest can provide a better cooling effect compared to that of agricultural land or meadow. Water vapour transfers the heat away from the surface through latent heat fluxes. The efficiency of cooling is smaller in dry areas. Hot spots, similar to urban heat islands, are formed. We can call these places „landscape heat islands”. The lower level of evaporation leaves more energy in the landscape and undermines the effectiveness of the heat distribution process as well. Instead of providing negative feedback (heat regulation), it generates positive feedback (collapse of the heat regulation system). Having access to less water to evaporate, results in a smaller cooling effect, however increasing temperature generates more demand for water to moderate that heat. We can interpret these „landscape heat islands” as a symptom, indicating a serious disorder of natural heat distribution processes. The annual mean temperature in Hungary has increased by 1.5 °C between 1901 and 2011, and further 1–3.5 °Cwarming is estimated until the end of this century. Average annual precipitation in Hungary was 580 mm in 30 years of 1981–2010, evapotranspiration was 537 mm, with potential evapotranspiration around 750 mm/year. The amount of energy required to evaporate 537 mm of water in Hungary (48 km3 of water) is 124 892.8 PJ. The total energy consumption of the country in 2018 was 1 126.5 PJ, and this is only 0.9%- of the total amount of energy lifted off the surface as latent heat through natural cooling processes. The surface temperature on the Hungarian ’Great Plane’ reaches 40 °C in most places. These numerous small landscape heat islands are combined into one large landscape heat island. The water demand is overwhelming, while there is less and less water to evaporate, so dry lands convert more energy from the incoming solar radiation to sensible heat, and the temperature is increasing further with even more demand for water. Water has an inevitable role on Earth as a mediator of energy in the heat distribution process. Water is key in transporting climatic energy in the form of latent heat-fluxes from places with positive energy balance to cooler places. The amount of water circulating in hydrological cycles well exceeds the amount of water demanded by our civilisation. The primary function of water is to distribute energy, thus creating and maintaining stabilized conditions for life on the continents. The key to water safety for human use is to provide a sufficient amount of water for the hydrological cooling processes. If we miss supporting this water demand, we will soon run out of supplies for ourselves – if we do meet the demand for water for the hydrological cooling processes, there will be a sufficient amount of water we can redirect to human use, and then return to the natural cycle. Maintaining this permanent loop is the key to water safety. If a car’s cooling system breaks down and the cooling water drains, no matter how luxurious the vehicle is, we may not be able to get far with it. We need to think similarly about the landscape, for it to work, its cooling water must be constantly provided. There is no technical solution to today's environmental problems, the only way is to get to know and support the natural processes better.