Describe and explain the main characteristics of the climate in the regions listed in the syllabus (tropical rainforest and tropical desert): temperature – mean temperature of the hottest month, mean temperature of the coolest month, therefore the annual range; rainfall – the amount and seasonal distribution; other climate features – wind, cloud, humidity, etc.
Tropical rainforests climate varies slightly depending on the location of the rainforest. Generally, the average temperature in the hottest month is between 31 and 33oC and the average temperature in the coldest month is between 29oC and 31oC. The temperature range throughout the year is very small, often not more than 2 or 3oC.
Rainfall is relatively constant throughout the year but again this can depend on the location of the rainforest. Northern Hemisphere rainforests are likely to have a slightly drier period in the Winter months as the sun is in the Southern Hemisphere and drags the low-pressure zone slightly further south. The wetter and drier months would be the reverse in the Southern Hemisphere.
Humidity is high due to significant evaporation as the sun rays are the most intense around the equator. Transpiration is also high due to the density of vegetation.
Tropical rainforests experience high cloud coverage levels, especially in the wettest months. Mornings may be sunny and then as the day progresses and evaporation levels increase and the cloud cover increases. Tropical rainforests are low-pressure zones and therefore have unsettled weather, wind, rain and cloud.
Latitude and Low Pressure
Tropical rainforests are located in equatorial regions often between 5 degrees North and South. These latitudes are in the Equatorial Low zone which means that they experience rising air due to the temperature and high levels of cloud and rainfall.
The Equatorial Low zone also has high sea temperatures which result in high evaporation. This brings significant rainfall to the land masses as moist warm air is forced to rise over the land. Tropical storms are common and also bring heavy rainfall.
Tropical Rainforest Vegetation
Vegetation in the rainforest must compete for the available light. The most successful plants and trees have adapted to capture as much sunlight as possible to increase the rate at which they can photosynthesise. Many of the plants have waxy pointed leaves to reduce water staying on the leaves which would place great strain on the branches.
These are trees that have managed to grow taller than all the other and extended beyond the main canopy of the rainforest.
The top layer of the rainforest where the tall trees spread their branches out to capture as much sunlight as possible. The success of the trees in the canopy means that below them there is quite deep shade.
Tall trees in the rainforest have needed to establish a stable base to support them in the deep soil. They have to be able to resist wind in often moist soft soil. Buttress roots are the triangular roots that stick out from the sides of the trees in various directions and provide much more stability that solely underground roots.
Lianas utilise the growth of other trees to reach the sunlight. Rather than competing with them they wrap themselves round the trunks of tall trees and climb up them to reach the light. It is an effective strategy since it vastly reduces the amount of growth that they require and they don’t have to worry about stabilising themselves.
Epiphytes are plants that have adapted to survive without soil. They are often called air plants since they can survive high up in the air on trees branches. They catch water from the rainfall, get plenty of sunlight for photosynthesis.
The lower layer of vegetation in the rainforest receives little sunlight. Plants must capture as much of the little light that penetrates to this layer and so often have large leaf areas.
The majority of wildlife in the rainforest is found in the canopy. Insects and birds inhabit this layer in great numbers and there is a vast range on them. Tropical rainforests have the greatest species diversity of any ecosystem. Primates such as sloths,monkeys and orang-utans move through the upper layers.
The moist climate and warm temperatures provide ideal conditions for decomposers and the forest floor is home to a range of insects, fungi and bacteria that break down the leaf litter and fallen trees returning the nutrients to the soil.
Describe and explain the main characteristics of the climate in tropical deserts: temperature – mean temperature of the hottest month, mean temperature of the coolest month, therefore the annual range; rainfall – the amount and seasonal distribution; other climate features – wind, cloud, humidity, etc.
Tropical desert climate is characterised by high daytime temperatures and very low rainfall (less than 250 mm per year). They are generally located between 23 degrees and 30 degrees North and South. Tropical desert latitude results in higher summer temperatures and lower winter temperatures (according to whether they are in the north or south hemisphere).
Deserts experience very little cloud cover and have low levels of humidity. Winds exist and often come from the same direction which shapes the dunes/landscape.
Latitude & High Pressure
Tropical deserts are located in the Sub-tropical high-pressure zone.
Descending dry air creates very clear skies and stable weather conditions.
The sun’s rays are intense at these locations resulting in high daytime temperatures but a night the lack of cloud cover means the temperature drops significantly giving cold nights.
Mountain ranges may play a part in the creation of deserts. In cases when the wind tends to come from the same direction, the air that has passed over the mountain and comes down the other side is often dry. This creates clear sunny skies and brings very little precipitation.
Tropical Desert vegetation
Plants usually have roots that spread out over a wide area but at shallow depth in the soil to enable them to absorb as much water as possible after any rain.
Spines or spikes are characteristic of plants in the desert as they need to protect themselves from being eaten by animals looking for sources of moisture.
Many cacti have ridges running down their length and this design allows them to swell substantially when water is available in order to store it for dry periods.
Wildlife in Tropical Deserts
- Wide feet spread the weight on the sand to stop them sinking in.
- Humps on their backs enable them to store additional water.
- Long eyelashes help keep sand blown by the wind out of their eyes.
Grab a Pen and Start Improving Exam Technique
1) Explain the high annual precipitation levels found in tropical rainforest areas. [2 marks]
2) Explain how plants in tropical rainforests have adapted to their environment and climate. [5 marks]
3) Describe the process of the rain shadow effect in desert formation. [3 marks]
4) Explain the relationship between the climate and vegetation characteristics in hot deserts [5 marks]
5) With reference to a named example, describe the ways in which human actions are threatening the natural environment in a desert or tropical rainforest area. [7 marks]