what causes humid subtropical climate

What causes humid subtropical climate? The humid subtropical climate is known for its combination of greater humidity in summers, but milder temperatures in winters, with consistent rainfall throughout the year.

Have you ever wondered about the origins of this entrancing climate, with its hot summers and relatively moderate winters?

Is it mainly due to a country’s geology, or does it have something to do with other factors? And what causes the south to have a humid subtropical climate?

The humid subtropical climate is formed through the complex interaction of geology, air masses, and oceanic currents. These factors come together to create the unique weather conditions characteristic of this climatic zone.

What are Humid Subtropical Climates?

what are humid subtropical climates

In humid subtropical regions, summers are hot and muggy, while the winters are rather cool.

You will typically find this environment between 20 and 35 degrees north or south of the equator.

Due to the impact of moist marine air, humid subtropical climates are most common around the coast, but they can extend inland for considerable distances.

So many countries feature humid subtropical climates.

Some of them include:

  • The southeastern United States
  • Southern Brazil
  • The southeast coast of South Africa
  • Eastern Australia
  • The region of eastern Asia spanning northern India, southern China, and Japan

An Important Consideration

According to the 1966 Trewartha update to the Koppen classification system, these subtropical climates are characterized by having eight or more months per year.

The mean air temperatures stay greater than 10 °C (50 °F) with at least one month with mean temperatures lower than 18 °C (64.4 °F). 

Fact: In humid subtropical regions, the average annual rainfall is 254 cm (100 in) close to the ocean and 63.5 cm (25 in) further inland. 

What Causes Humid Subtropical Climate?

humid subtropical climate causes

This particular climate classification is commonly observed in the subtropical areas of the globe, spanning from 25° to 40° latitude in both the northern and southern hemispheres.

The formation and maintenance of humid subtropical climates are influenced by various factors, such as:

  • Atmospheric circulation patterns
  • Geographical positioning
  • Subtropical High-Pressure Systems
  • The impact of the ocean
  • Wind Patterns
  • Orographic Effects

Let’s talk more about these factors and see how they contribute to the development of a humid subtropical climate:

Geographical Location

geographical location

In the case of humid subtropical climates, a region’s geographic position has a clear impact on the climate’s distinctive features.

In most cases, these areas are typically close to large bodies of water like oceans or seas.

These massive bodies of water provide a steady supply of moisture, increasing the regional humidity.

More importantly, this oceanic impact moderates temperature swings, keeping extremes of either heat or cold at bay.

Because of the position and the effect of neighboring bodies of water, regions like southeastern Australia, parts of South America, and eastern Japan have mild winters and hot, humid summers

Atmospheric Circulation Patterns

atmospheric circulation patterns

The determination of climate heavily relies on atmospheric circulation patterns.

The distinct circulation cells formed by the interaction between global wind patterns and the Earth’s rotation play a crucial role in shaping weather conditions.

One of the standout cells among these is the Hadley cell, which plays a significant role in shaping humid subtropical climates. 

More about the Hadley Cell

more about the hadley cell

The process begins with heated air in close proximity to the equator ascending, generating a region of reduced atmospheric pressure.

As the atmosphere rises, it transports humidity alongside it.

As the atmosphere ascends to greater heights, it undergoes a decrease in temperature, causing a cooling effect.

This cooling phenomenon triggers condensation, which subsequently leads to the release of moisture in the shape of precipitation.

This phenomenon plays a role in the elevated levels of rainfall experienced in regions with a humid subtropical climate.

Fact: The Hadley cell, known for its upward movement of humid air and subsequent precipitation, plays a crucial role in shaping the distinct climate features in many regions. 

Subtropical High-Pressure Systems

subtropical high-pressure systems

Another vital element that impacts humid subtropical climates is the existence of subtropical high-pressure systems, alongside atmospheric circulation patterns.

These expansive areas of high atmospheric pressure, known as semi-permanent anticyclones, can be found near the 30° latitude in both the northern and southern hemispheres.

The influence of these high-pressure systems is crucial in molding the climate patterns of humid subtropical areas. 

How Does the System work?

how the system works

The descending air linked to these systems inhibits cloud development, resulting in unobstructed skies and minimal rainfall.

The descending air results in a stable atmosphere, leading to the characteristic warm and arid weather found in these regions.

Still, the presence of expansive water masses nearby mitigates the dryness.

The existence of neighboring oceans or seas offers a moisture supply, which adds to the humidity and leads to the humid characteristic of humid subtropical climates. 

Prevailing Wind Patterns

prevailing wind patterns

The prevailing wind patterns, specifically the trade winds and westerlies, play a significant role in shaping humid subtropical climates.

The trade winds in the northern hemisphere blow in an eastward direction, while the prevailing westerlies move westward.

The meeting point of these wind systems in the subtropical areas forms a convergence zone famously called the Intertropical Convergence Zone (ITCZ)

The Role of the ITCZ

the role of the itcz

The ITCZ is characterized by the upward movement of air masses, creating regions with reduced atmospheric pressure.

When the air ascends, it undergoes a cooling process, leading to condensation and subsequent precipitation, which ultimately leads to a substantial amount of rainfall.

The coming together of air masses in subtropical regions plays a role in the development of humid subtropical climates.

The dominant wind patterns have a notable impact on the movement of moisture and the way rainfall is distributed, shaping the unique features of humid subtropical climates. 

Oceanic Influences

The impact of neighboring oceans and expansive water bodies on humid subtropical climates cannot be emphasized enough.

The existence of these water bodies greatly influences the climate attributes of these areas.

oceanic influences

Air masses that come from the sea, known as maritime air masses, carry moisture with them as they move towards the land.

This in turn adds to the overall humidity of the region.

Furthermore, the oceanic impact’s moderating influence aids in alleviating temperature extremes, leading to more moderate winters and refreshing summers in contrast to continental climates

An Important Consideration

The existence of warm ocean currents, like the Gulf Stream and Kuroshio Current, additionally amplifies the moisture and vitality in the air.

The presence of these ocean currents ensures a consistent source of moisture, which plays a significant role in enhancing the humid subtropical climate.

Fact: The connection between the sea and the air in different areas forms a distinct weather pattern distinguished by ample precipitation and elevated moisture levels. 

Orographic Effects

orographic effects

Orographic impacts have a notable influence on the formation of humid subtropical climates, contributing to their intricate nature.

When the dominant winds come across a chain of mountains, it makes the damp air to rise.

It is especially true in the areas like the Appalachian Mountains in the southeastern part of the United States or the Eastern Ghats in eastern India.

The process of orographic uplift initiates a sequence of atmospheric alterations, which gives rise to subtropical climates. 

How Does the Process work?

how the orographic effects work

When the air ascends, it experiences adiabatic cooling, resulting in the attainment of its dew point and consequent condensation.

The concentrated moisture subsequently forms as precipitation in the form of rain on the side of the mountains facing the wind.

The phenomenon referred to as orographic rainfall is responsible for the significant amounts of precipitation found in humid subtropical areas. 

The Impact of Rain Shadow Phenomenon

the impact of rain shadow phenomenon

When the air descends on the opposite side of the mountains, it experiences adiabatic warming, resulting in the creation of a rain shadow phenomenon.

The rain shadow phenomenon leads to less moisture on the side sheltered from the prevailing winds.

This causes a noticeable difference in rainfall distribution over relatively small areas.

Fact: Because of the abundance of rainfall, you are likely to witness lush, green landscapes in humid subtropical regions.


What causes humid subtropical climate?

Location, atmospheric circulation, prevailing wind systems, etc., all play a role in creating humid subtropical climates.

Having access to adequate moisture and temperature regulation is dependent on the region’s closeness to oceans and the interaction of air masses with mountain ranges. 

Learning about these causes is essential as it helps make informed decisions regarding urban planning, agriculture, and infrastructure development.