Arid (Dry) Climates (B)
Sunday, July 5, 2026 7:39 AM
Dry climates occupy 35% of earth & are the most extensive climate over land. The dryness of a climate
depends on the moisture content of the air, its "humidity." There are 2 main types of arid climates:
- arid desert & semi-arid steppes
○ a steppe is a type of vegetation that borders the dry desert
- These types are further divided into types based on latitudinal position, there are subtropical (low
latitude) deserts & semi-arid steppes. There are midlatitude deserts and steppes as well.
These 2 types of deserts differ in dominant climatic controls (what makes them hot or dry) also the
subtropical desert is warmer than the midlatitude desert. The difference between desert & steppe
climate types is deserts receive less than 10 inches of rain annually, while steppe climates receive
10-25 inches/yr (based on Köppen's climate criteria)
a. Arid Subtropical Desert (BWh) and Subtropical Steppe (BSh)
○ Location: Usually located on western sides of the continents, between 25-30 degrees of
latitude. Some major areas classified as arid deserts are:
§ N Africa (Sahara Desert), the Arabian Peninsula, parts of Mexico, the Atacama Desert of
Peru & Northern Chile, the Kalahari & Namib Deserts of South Africa, the Great Sandy &
Great Victoria Deserts of interior Australia
- Temperature: This desert type receives insolation from the sun (clear skies & a high sun angle),
it's the high pressure sinking in this region that creates the real warming & drying, clear
conditions. This climate type has the hottest summer temperatures in the world! Sometimes,
surface heating in summer creates pockets of low pressure that rises so rapidly that it whirls
upward like a mini-tornado aka a dust devil b/c it picks up the dust from the surface as air rises in
an inward & upward spiral
- This climate is also known for having the greatest diurnal (day to night) temp range in the world.
During the day shortwave radiation heats the surface to high temps (100+ degrees F, summer)
due to the cloudless skies, but at night, the longwave radiation escapes freely & the surface loses
the day's heating. Winters are mild & don’t experience such ranges
- Precipitation:
○ As the driest climate on earth, it makes sense this is where the world's deserts are located.
1. Since temps are warm to hot in this climate region (w/ the exception of areas along west coasts),
warm air has a greater capacity for holding moisture. Since there's less moisture in the air than
the temperature can hold (low relative humidity), it's dry. The drier the air, the farther the air is
from reaching saturation, making it less likely to rain
2. Another reason for lack of rain is, there is no way for uplift of the air in the desert, necessary for
cloud formation & precipitation. B/c this region is influenced by subtropical high pressure cells
(part of Hadley’s convection cell), the air often sinks instead of rising. The sinking creates clear,
sunny & dry conditions. Upper air inversions form from the high pressure above, keeping the air
from cooling, adiabatically. This desert type is called “the subtropical arid desert” b/c of the region
in where it's located.
3. The aridity in the subtropical desert is related to parts of the desert that sit along the west coasts
in this belt. Advectional fog forms as air blows west, while there's plenty of moisture supplied to
the air near the coast, this moisture is released over the cold current before the air reaches the
land. This is why even coastal areas in this desert region are dry!
○ Precipitation in the subtropical arid desert is less than 15 inches, according to Köppen. In
places like the Atacama Desert (in Southern Peru/Northern Chile), there is no rainfall record
(one of the driest places on earth) where cold current creates stable fog deserts. Rain
happens in many deserts, normally in summertime w/ violent thunderstorms, due to intense
surface heating (convection). The showers often last a short period of time & bring flooding
to the surface that is dry aka "flash floods."
- The Subtropical Steppe/ Semi-Arid Desert (BSh) is a transitional zone that receives slightly more
precipitation & is considered "semi-arid." Steppe refers to the grassland vegetation growing in this
region.
b. Midlatitude Desert (BWk) and Midlatitude Steppe (BSk)
- Location: The midlatitude desert is a higher latitude desert located in the interiors of large
continents. There are 3 main regions classified as this type of desert:
○ the deserts of central Asia, the deserts of the western interior of the U.S. (the Great Basin
Desert) & in Southern Argentina (Patagonia Desert)
- Temperature: This desert is known for its hot summers & cold winters due to its midlatitude
location. The main difference between these two are the temp & location. It doesn't get as hot as
the subtropical desert, but winter in the midlatitude desert gets a lot colder. It has larger annual
temp ranges than the subtropical desert, but smaller diurnal ranges.
- Preciptiation: Again, precipitation is less than 15” all year. Just like the subtropical desert, the
bulk of the precipitation comes in the summer with warming and convection. In the winter, cold
fronts sweep through the middle latitudes and bring rain and snow to these deserts.
Sunday, July 5, 2026 7:39 AM
Dry climates occupy 35% of earth & are the most extensive climate over land. The dryness of a climate
depends on the moisture content of the air, its "humidity." There are 2 main types of arid climates:
- arid desert & semi-arid steppes
○ a steppe is a type of vegetation that borders the dry desert
- These types are further divided into types based on latitudinal position, there are subtropical (low
latitude) deserts & semi-arid steppes. There are midlatitude deserts and steppes as well.
These 2 types of deserts differ in dominant climatic controls (what makes them hot or dry) also the
subtropical desert is warmer than the midlatitude desert. The difference between desert & steppe
climate types is deserts receive less than 10 inches of rain annually, while steppe climates receive
10-25 inches/yr (based on Köppen's climate criteria)
a. Arid Subtropical Desert (BWh) and Subtropical Steppe (BSh)
○ Location: Usually located on western sides of the continents, between 25-30 degrees of
latitude. Some major areas classified as arid deserts are:
§ N Africa (Sahara Desert), the Arabian Peninsula, parts of Mexico, the Atacama Desert of
Peru & Northern Chile, the Kalahari & Namib Deserts of South Africa, the Great Sandy &
Great Victoria Deserts of interior Australia
- Temperature: This desert type receives insolation from the sun (clear skies & a high sun angle),
it's the high pressure sinking in this region that creates the real warming & drying, clear
conditions. This climate type has the hottest summer temperatures in the world! Sometimes,
surface heating in summer creates pockets of low pressure that rises so rapidly that it whirls
upward like a mini-tornado aka a dust devil b/c it picks up the dust from the surface as air rises in
an inward & upward spiral
- This climate is also known for having the greatest diurnal (day to night) temp range in the world.
During the day shortwave radiation heats the surface to high temps (100+ degrees F, summer)
due to the cloudless skies, but at night, the longwave radiation escapes freely & the surface loses
the day's heating. Winters are mild & don’t experience such ranges
- Precipitation:
○ As the driest climate on earth, it makes sense this is where the world's deserts are located.
1. Since temps are warm to hot in this climate region (w/ the exception of areas along west coasts),
warm air has a greater capacity for holding moisture. Since there's less moisture in the air than
the temperature can hold (low relative humidity), it's dry. The drier the air, the farther the air is
from reaching saturation, making it less likely to rain
2. Another reason for lack of rain is, there is no way for uplift of the air in the desert, necessary for
cloud formation & precipitation. B/c this region is influenced by subtropical high pressure cells
(part of Hadley’s convection cell), the air often sinks instead of rising. The sinking creates clear,
sunny & dry conditions. Upper air inversions form from the high pressure above, keeping the air
from cooling, adiabatically. This desert type is called “the subtropical arid desert” b/c of the region
in where it's located.
3. The aridity in the subtropical desert is related to parts of the desert that sit along the west coasts
in this belt. Advectional fog forms as air blows west, while there's plenty of moisture supplied to
the air near the coast, this moisture is released over the cold current before the air reaches the
land. This is why even coastal areas in this desert region are dry!
○ Precipitation in the subtropical arid desert is less than 15 inches, according to Köppen. In
places like the Atacama Desert (in Southern Peru/Northern Chile), there is no rainfall record
(one of the driest places on earth) where cold current creates stable fog deserts. Rain
happens in many deserts, normally in summertime w/ violent thunderstorms, due to intense
surface heating (convection). The showers often last a short period of time & bring flooding
to the surface that is dry aka "flash floods."
- The Subtropical Steppe/ Semi-Arid Desert (BSh) is a transitional zone that receives slightly more
precipitation & is considered "semi-arid." Steppe refers to the grassland vegetation growing in this
region.
b. Midlatitude Desert (BWk) and Midlatitude Steppe (BSk)
- Location: The midlatitude desert is a higher latitude desert located in the interiors of large
continents. There are 3 main regions classified as this type of desert:
○ the deserts of central Asia, the deserts of the western interior of the U.S. (the Great Basin
Desert) & in Southern Argentina (Patagonia Desert)
- Temperature: This desert is known for its hot summers & cold winters due to its midlatitude
location. The main difference between these two are the temp & location. It doesn't get as hot as
the subtropical desert, but winter in the midlatitude desert gets a lot colder. It has larger annual
temp ranges than the subtropical desert, but smaller diurnal ranges.
- Preciptiation: Again, precipitation is less than 15” all year. Just like the subtropical desert, the
bulk of the precipitation comes in the summer with warming and convection. In the winter, cold
fronts sweep through the middle latitudes and bring rain and snow to these deserts.
