PL
In recent years, high daytime temperatures during summer have become the norm in our country. Progressive climate change is also causing an increase in minimum air temperatures. This phenomenon is known as tropical nights. They occur when the minimum nighttime temperature does not fall below 20°C (68°F). Until recently, warm, even scorching, evenings were associated primarily with trips to Mediterranean countries. Today, however, this phenomenon is becoming increasingly common in our climate, especially during longer and more intense heatwaves.
Persistently high temperatures after sunset, especially in highly urbanized areas, pose a significant threat to the environment and people. Water levels, which can already be alarming in spring months, drop even further during summer heatwaves. High temperatures accelerate water evaporation from the earth’s surface, thus exacerbating drought. A lack of adequate water supply impairs plant growth, which consequently leads to reduced yields. The increased frequency of tropical nights also negatively impacts our health. Physiological discomfort caused by persistent high temperature at night manifests itself in, among other things, difficulty falling asleep, decreased sleep quality, and irritability.
A night that brings no relief from the heat
We are accustomed to temperatures rising during the day, especially in the afternoon, and dropping at night. The lower temperatures after sunset provided respite for the heated surface, which could slowly release its stored heat. This cooling helped reduce water loss through evaporation and prepared the soil for better absorption of rainwater in the following days. Today, however, as we struggle with nights when the temperature does not drop sufficiently, this mechanism becomes much less effective.
This is especially important during periods of prolonged and frequent heatwaves. This creates problems with retaining adequate amount of water in the soil, as well as with plant water loss through transpiration.
Of course, this process is not the same during every hot night. Many factors contribute to this, including humidity, wind, cloud cover, and water availability. However, this process is very dangerous, especially during periods of prolonged heatwaves. Persistent high temperatures throughout the day mean that the environment has less time to cool the surface, which would facilitate water infiltration into the soil and reduce water resource losses.
No change in total precipitation
A frequently discussed topic in the context of drought is the monthly or annual rainfall total, which serves to confirm or deny the severity of the problem. However, this parameter is not the only determinant of water balance in a given area. In addition to the amount of precipitation, we should also take under consideration how much water we lost, partly due to evaporation. The water balance also includes water retention – both on the surface and in the ground. During periods of intense heat, during which evaporation increases and, consequently, retention is impaired – the water balance is disturbed.
The nature of the precipitation also plays a significant role. Short, intense rainfall and storms do not replenish water resources effectively enough. This is because the dry soil is unable to provide adequate conditions for precipitation water to infiltrate it. Instead, the water runs off the surface and then flows into rivers and lakes, from where it evaporates again at a rapid rate during the next heat wave.
Therefore, the hydrological situation of a region is determined not only by how much rain falls, but above all by how much water remains in the landscape, in the soil, for a longer time and use, among others, by plants.
The vicious cycle of drought and heat
During a prolonged heatwave, not only evaporation increases but also plant water demand. This often leads to a water deficit in the soil, known as a soil (agricultural) drought. During this time, plants can experience water stress. This condition leads to impaired plant function due to water deprivation.
As rainfall deficits deepen, the problem of soil water deficiency also deepens. Consecutive hot days and nights are often the cause – when nighttime temperatures remain high, the environment receives no respite from the thermal stress.
A single night with temperatures above 20°C does not necessarily mean drought. However, a series of hot days and nights, especially when combined with a rainfall deficit, can contribute to a worsening water deficit.
More than just temperature changes
Tropical nights evoke the broader picture of climate change. Rising temperatures increase the likelihood of certain extreme weather events, such as severe storms and lightning, as well as flash floods and flooding. Changing and increasingly unpredictable atmospheric conditions also negatively impact water management and reduce the environment’s resilience to high temperatures.
Climate change primarily leads to an increase in the frequency and intensity of extreme weather events.
Poland increasingly susceptible to summer water shortages
The combination of high temperatures, long periods without precipitation, low soil moisture, and limited surface water resources is particularly dangerous for the environment and for us. Therefore, when observing summer weather, it’s important to consider more than just the forecast maximum temperature. Equally important are the minimum air temperature, how long high temperatures will persist, whether nights will bring cooling, and when and in what form precipitation will occur.
The occurrence of tropical nights demonstrates how significantly climate conditions have changed in our country. When a hot day is not followed by a cool night, and subsequent days bring only further high temperatures, the water balance can become increasingly unfavorable. Therefore, in the face of climate change, the question of not only how much rain will fall but also how much water can be retained in the environment – in the soil, meadows, and forests – is becoming increasingly important.
However, we are not completely powerless in this situation – thanks to retention, to which each of us can contribute, we are able to counteract the effects of drought, improving our country’s water balance. More information on examples of natural retention measures and how to improve the hydrological situation locally is available on our website.
