Natural Environment of Poland: Climate

Main Factors Influencing the Polish Climate

The climate of Poland is shaped by a complex interplay of geographical and meteorological factors. These include:

• Middle Latitudes: Poland's position in the mid-latitudes dictates its general temperate characteristics.
• Temperate Climate Zone: The country resides within the temperate zone, experiencing moderate temperatures and seasonal shifts.
• North Atlantic Current: This warm ocean current influences the air masses reaching Europe, providing a moderating effect.
• Zonal Atmospheric Circulation: The climate is heavily influenced by the large-scale movement of air across the globe.
• Prevailing Western Winds: Airflow predominantly comes from the West, bringing maritime influences from the Atlantic.
• High-Pressure and Low-Pressure Areas: The interaction between various pressure systems dictates weather variability.
• Movement of Weather Fronts: The constant transition of cold and warm fronts leads to frequent weather changes.
• Eurasian Continent Mass: Poland is influenced by its proximity to the massive landmass of Eurasia to the East.
• Carpathian Mountains: These mountains act as a significant physical barrier for longitudinal air flow and advection (the horizontal movement of air).

Climate Classification and General Characteristics

Poland's climate is described differently depending on the classification system used:

• Okołowicz Classification: Poland is defined as having a temperate warm transitional climate.
• Koeppen Classification: It is categorized as a warm summer humid continental climate, also known as a hemiboreal climate (Type $Dfb$).
• Weather Variability: A hallmark of the Polish climate is its highly variable weather conditions, both on a day-to-day basis and seasonally/annually.
• Regional Spatial Variety: There is a moderate to high degree of climate variety across different regions of the country.

Main Pressure Systems and Air Masses

The weather in Poland is influenced by three primary pressure systems:

1. Azores High
2. Icelandic Low
3. Siberian High

Frequency of Air Masses Over Poland

The following table represents the frequency (percentage) of different air masses over Poland based on data from Kaczorowska (1986):

• Arctic (A): Winter: $11\%$, Spring: $16\%$, Summer: $2\%$, Autumn: $10\%$, Year Average: $10\%$.
• Maritime Polar (mP): Winter: $46\%$, Spring: $33\%$, Summer: $60\%$, Autumn: $45\%$, Year Average: $46\%$.
• Continental Polar (cP): Winter: $37\%$, Spring: $45\%$, Summer: $34\%$, Autumn: $38\%$, Year Average: $38\%$.
• Tropical (T) (from Mediterranean region): Winter: $1\%$, Spring: $1\%$, Summer: $0\%$, Autumn: $0\%$, Year Average: $0.5\%$.
• Transformed Air Masses: Winter: $5\%$, Spring: $5\%$, Summer: $5\%$, Autumn: $7\%$, Year Average: $5.5\%$.

Seasonal Changes and Thermal Structure

Poland recognizes both astronomical and thermal divisions of the year.

The Four Astronomical Seasons

• Spring
• Summer
• Autumn
• Winter

The Six Thermal Seasons (according to Romer)

These seasons are defined by specific average daily temperature ($t$) thresholds:

• Pre-Spring: $(0,0^{\circ}C < t \le 5,0^{\circ}C)$
• Spring: $(5,0^{\circ}C < t \le 15,0^{\circ}C)$
• Summer: $(t \ge 15,0^{\circ}C)$
• Autumn: $(5,0^{\circ}C < t \le 15,0^{\circ}C)$
• Pre-Winter: $(0,0^{\circ}C < t \le 5,0^{\circ}C)$
• Winter: $(t \le 0,0^{\circ}C)$

Key Seasonal Trends

• Warm Period: Lasts from April to September.
• Cold Period: Lasts from October to March.
• Precipitation: Highest in the Summer; lowest in the Winter.
• Atmospheric Dynamics: The highest number of pressure systems and weather fronts occurs in Autumn and Winter.
• Temperature Extremes: The highest temperatures are typically recorded in July, while the lowest occur in January.

Precipitation and Cyclone Trajectories

Precipitation in Poland is closely linked to specific low-pressure system trajectories, as identified by Van Bebber (1888):

• Trajectory IVb: This is the most common trajectory affecting Poland, primarily through weather fronts.
• Trajectory Vb: This path is responsible for many deep low-pressure systems. It brings moist air masses from the Great Hungarian Plain, which frequently leads to heavy rainfall and flooding in Poland.

Solar Radiation and Sunshine Duration

Global solar radiation and sunshine duration vary significantly by season:

• Duration: The longest days occur in June/July (Summer), and the shortest days occur in December/January (Winter).
• Global Solar Radiation (GSR): In January, radiation levels are low across the country. In July, radiation levels are significantly higher, with spatial variation across regions.

Regional Differentiation of Climate

• Continentalism: The influence of continental air masses increases towards the East.
• West vs. East: The western part of Poland is more frequently affected by maritime Polar air masses, whereas the eastern part is more often influenced by continental Polar air masses.
• Baltic Sea Influence: The sea exerts a cooling effect in summer and a warming effect in winter in its immediate proximity.
• Favorable Conditions: The most favorable climate conditions are generally found in the western and south-western parts of the country.
• Highlands and Mountains: These regions exhibit less favorable climate conditions compared to the rest of Poland.
• Bioclimate: The Baltic seaside and the Polish mountains are characterized by the strongest stimulative bioclimate.

Climate of the Polish Mountains

Mountainous regions possess unique climatic properties, some of which resemble the Alpine climate:

• Temperature: Lower minimum and maximum temperatures than the lowlands.
• Contrast: Higher weather contrasts and stronger winds.
• Calm Frequency: Mountains have a lower frequency of calms, but valleys, canyons, and basins have a higher frequency of calms due to topography.
• Thermal Inversion: Common in valleys and basins, where cold air settles below warmer air.
• Altitudinal Zonation: Climate characteristics change distinctly with elevation.
• Pre-storm Indicators: A sudden drop in atmospheric pressure often precedes storms.
• Specific Weather Phenomena: Increased frequency of thunderstorms, fog/mist, heavy rain, snowfall, blizzards, and hard rime.
• Optical Phenomena: Occurrences such as the Brocken spectre and glory rings.
• Foehn Wind (Halny): A warm, dry, gusty wind occurring in the Tatra mountains, often accompanied by a distinct "wall of clouds" and lee waves (atmospheric waves influencing cloud formation).

Climate Change and its Consequences

Ongoing climate changes in Poland involve several critical aspects:

• Severe Phenomena: Increased occurrence of severe weather and hydrological hazards (e.g., floods, heat waves).
• Precipitation Trends: A decrease in the total sums of precipitation despite more intense individual events.
• Extreme Temperatures: A rise in extreme seasonal and annual temperatures.
• Societal Impact:     * Negative health impacts and increased mortality.     * Decreased life expectancy.     * Increased demand for water and electricity resources.     * Economic disturbances and damage to infrastructure and transportation.

Urban Climate Specifics

Urbanized areas like Warsaw exhibit a microclimate distinct from the surrounding natural areas.

Natural vs. Urbanised Areas

• Natural Areas: Characterized by high photosynthetic activity, carbon dioxide absorption, oxygen production, high interception of rain, and high evapotranspiration.
• Urbanised Areas: Characterized by reduced photosynthesis, low interception, high impermeability, high runoff, low evaporation, and very low transpiration.

Urban Climate Characteristics

• Anthropogenic Heat: Heat produced by human activity (buildings, transport).
• Thermal Islands: Occurrence of Urban Heat Islands (UHI) and Urban Cold Islands.
• Pollution: Increased air pollution and the formation of dust domes and thermal plumes.
• Irradiance/Insolation: Decreased irradiance and sunshine duration compared to rural areas.
• Oxygen: Reduced oxygen levels.
• Precipitation: Cities often see an average increase in precipitation; for example, Warsaw totals approximately $600-650\,mm$ depending on the specific urban zone.

Case Study: Warsaw

• GSR Differences: Research (Nelken, Leziak 2016) shows significant differences in daily sums of Global Solar Radiation between urban stations (IGF UW) and rural stations (Belsk), measured in $MJ \cdot m^{-2}$.
• Hazards: Future scenarios (e.g., scenario 8.5 for 2081-2090) predict an annual increase in the number of days with minimum temperatures ($T_{min}$) exceeding $20^{\circ}C$.

Climate Response: Assessment, Mitigation, and Adaptation

Cities must engage in three tiers of climate action:

1. Assessment:     * Exposure: Assessing present and future exposure to negative climate conditions.     * Vulnerability: Assessing how susceptible the city, its inhabitants, and infrastructure are to these conditions.     * Hotspots: Delimitating zones of high exposure and high vulnerability.

2. Mitigation: Reducing predicted changes to minimize negative effects. Actions include:     * Increasing green areas.     * Protecting building-free zones.     * Reducing traffic and using zero-emission vehicles.     * Moving away from fossil fuels.     * Implementing energy-saving technologies.

3. Adaptation: Adjusting economy and society to unavoidable changes. Actions include:     * Upgrading infrastructure to remain operational under heat or water stress.     * Implementing procedures for city administration and industry adjustment.     * Monitoring hotspots and troubleshooting climate-related problems.

Extreme Weather Events in Poland

Poland experiencing various extreme events, the majority of which occur during the warm period (Spring and Summer):

• Types: Floods (including urban flash floods), heavy rains, hail, heat waves, cold waves, severe thunderstorms, tornadoes, downbursts, and squall lines.
• Drivers: Occurrence depends on atmospheric circulation and air mass buoyancy. High risk is associated with cyclonic circulation and advection from the south-eastern quadrant.
• CAPE: Convective Available Potential Energy ($CAPE$) is a key metric for measuring the potential for severe weather. Data is collected at stations like Łeba, Legionowo, and Wrocław.
• High Wind Risk Zones: While excluding mountain peaks, specific zones across the Polish lowlands are identified as high-risk for severe winds.
• Tornadoes: Historical data (Leziak 2014) confirms the periodic occurrence of tornadoes in Poland, though the annual number of cases fluctuates.