Causes of High Rainfall – Every year, most areas in Indonesia experience floods, especially in the lowlands. The problem of flooding is currently not completely resolved, in fact it is increasing, both in intensity and frequency.
In general, this flood natural disaster is caused by high rainfall intensity. In addition, the duration of high-intensity rainfall also determines the arrival of floods in an area.
Then, what causes high rainfall in Indonesia? What are the characteristics of rainfall in our country?
So that Sinaumed’s can understand it, let’s look at the following review!
7 Causes of High Rainfall in Indonesia
There are seven causes for the high rainfall that occurs in Indonesia, one of which is the La Nina phenomenon. Well , here is an explanation of the seven causes.
1. Madden Julian Oscillation (MJO)
This phenomenon was discovered by two researchers namely Rolland Madden and Paul Julian in 1971 who at that time were studying periodic oscillations (shaking or vibration) in the tropical Pacific region.
The Madden Julian Oscillation (MJO) is a system of oscillations (wobbles or vibrations) of interaction between the atmosphere and the sea, which propagates from west to east around the Maritime Continent Equator or Benua Maritim Indonesia (BMI) region for about 30-60 days. This MJO phenomenon usually develops and will be dominantly seen around the southern Indian Ocean to the east, passing through Australia and the western Pacific Ocean.
This MJO phenomenon certainly has an impact on the high rainfall in Indonesia during the rainy season. In the period from June to August, this MJO phenomenon has had an impact in the form of:
- Wet and dry periods change
- Monsoon change
- Changes in tropical cyclone activity
Meanwhile, in the period from December to February, the impacts are in the form of:
- Wet and dry periods change
- Expansion of tropical moisture plumes to higher latitudes, eventually causing heavy rains in mid-latitude regions
- Monsoon change
- Changes in tropical cyclone activity
- ENSO Changes through Kelvin Waves in the ocean
2. La Nina
La Nina is a form of natural phenomenon that occurs as a result of the interaction between the sea surface and the atmosphere in the tropical Pacific. What happens in this phenomenon is when the sea surface temperature in the tropical Pacific Ocean, the central and eastern parts are colder than normal conditions, then followed by a change in the atmospheric circulation above it, usually in the form of an increase in the easterly trade wind which is stronger than normal conditions and can last for several months.
This of course has an impact on global climate patterns, especially in tropical regions such as Indonesia where the weather becomes “wetter”. The La Nina phenomenon can significantly increase rainfall from October to November at the start of the rainy season.
3. Tropical Cyclone Seeds
Tropical cyclone is a natural phenomenon in the form of a large force storm. Even the average radius can reach 150 to 200 km!
This tropical cyclone phenomenon is formed over the ocean which has a warm sea surface temperature, approximately more than 26.5 ºC. In addition, strong winds rotating near the center of this storm have wind speeds of more than 63 km/hour.
This tropical cyclone seed can also potentially increase the growth of rain clouds so that it affects high rainfall. When this phenomenon occurs, the public is advised to remain vigilant because several areas in Indonesia will usually be affected in the form of heavy rains and strong winds.
This phenomenon also has local names, for example typhoon (typhoon) in the Pacific region, willy-willy in the Australian region, baguio in the Philippines, and hurricane in the Americas.
4. Intertropical Convergence Zone (ITCZ)
The phenomenon of the ITCZ or Intertropical Convergence Zone is a meeting between trade winds from the northern hemisphere and the southern hemisphere, then surrounds the earth around the equator.
The wind meeting area will form a rain-producing cloud around the area. The rain that is produced from these clouds will later have high rainfall and occur continuously.
The ITCZ phenomenon does not always stay in one area, therefore it will always move depending on the annual sun movement.
In January, usually the ITCZ line will be in Indonesia, so that month will experience hot weather. The hot weather causes the lifting of air masses so that it affects the high rainfall.
5. Kelvin and Rossby
The phenomenon of Kelvin Waves and Rossby Waves is an atmospheric wave phenomenon that actively occurs around the area of South Sumatra and Java Island. Equatorial Rossby Waves and Kelvin Waves are atmospheric dynamics which indicate the potential for the growth of rain clouds on a wide scale around the active phase region they pass through.
Kelvin waves will move from the direction of the Indian Ocean towards the Pacific Ocean, passing through Indonesian territory for 30-40 days along with the MJO ( Madden Julian Oscillation ). Meanwhile, the Rossby wave will move the opposite of the Kelvin wave, namely from the Pacific Ocean towards the Indian Ocean.
So, what do these two phenomena have in common? The similarity is that both of them contribute to the increase in rainfall and the growth of rain clouds in the Indonesian region.
6. Asian Monsoon
Monsoon winds are winds that blow periodically, for at least three months. This phenomenon can cause an increase in the mass of wet air and of course affect the high rainfall around Indonesia.
There are two global monsoons that affect monsoon conditions around the Indonesian Maritime Continent, namely the summer Asian monsoon and the winter Australian monsoon.
The Asian summer monsoon occurs on the Asian continent with the formation of a low pressure center on the continent. Meanwhile, at the same time there is the Australian winter monsoon which is also occurring, so the atmosphere above the continent will be under high pressure.
In the rainy season, this monsoon wind is always there and occurs in Indonesian territory, namely from January to February.
The flow of the Asian monsoon winds can cause the formation of convective clouds which later have the potential for bad weather, heavy rain, thunderstorms and strong winds. There are two types of monsoon winds, namely the west monsoon wind and the east monsoon wind.
7. Warming of Sea Surface Temperatures
The temperature of the sea surface to be warm can be caused by two factors, namely due to the presence of sunlight and the meeting of two hot ocean currents. An increase in sea surface temperature can of course cause evaporation so that later it creates rain clouds.
This evaporation can also increase the intensity of rain, storm waves, and tropical cyclones around Indonesia and globally. So, this increase in sea surface temperature will also be related to the El Nino and La Nina phenomena.
When there is an increase in sea surface temperature, the chances of La Nina will also increase. Conversely, if the sea surface temperature decreases, then the El Nino phenomenon will occur.
Characteristics of Rainfall in Indonesia
Based on the general pattern that often occurs, rainfall in Indonesia can be divided into 3 types, namely monsoon type, local type, and equatorial type.
1. Monsoon Type
This type of monsoon rainfall is influenced by monsoons, especially the west monsoon. The west monsoon is a wind that is driven by high pressure and low pressure around the continents of Asia and Australia alternately, especially from December to February.
In these months, in the Northern Hemisphere there will be winter, the result will be high pressure cells on the Asian continent. Meanwhile, in the Southern Hemisphere there will be summer, so a low pressure cell occurs on the Australian continent.
This difference makes the air pressure blowing on the two continents, so from December to February high pressure winds will blow in Asia towards low pressure in Australia. Well, this wind is called the West Monsoon Wind. The west monsoon will usually be more humid and rainy than the east monsoon.
2. Local Type
The next rainfall characteristic is the local type, which is influenced by local physical environmental conditions, in the form of waterscapes as a source of evaporation to mountains as rain catchment areas.
This local type of rainfall pattern is dependent on the magnitude of the influence of local conditions, which are related to the presence of mountains, oceans, other waterscapes, to the occurrence of intensive local warming.
The forming factor of this type of rainfall is the rise of air towards the highlands or mountains due to intense local heating. Usually, local type rainfall occurs in the areas of Sulawesi, Maluku and Papua.
For its duration, the local type occurs only once the maximum monthly rainfall in one year.
3. Equatorial Type
Furthermore, there is the equatorial type of rainfall, the process of which occurs is related to the movement of the convergence zone to the north and south following the apparent movement of the sun.
The convergence zone is the area where two air masses (wind) meet from the two hemispheres, then the air moves upward. The process of moving the wind towards a point and then moving upwards is called convergence, while the place where convergence occurs is called the convergence area.
The convergence area is relatively narrow and is in low latitudes which is commonly called the Intertropical Convergence Zone (ITCZ).
So, those are the seven causes of high rainfall in Indonesia. Of these causes, indeed everything is the will of nature and we as humans cannot prevent the high rainfall that often occurs.
Book Recommendations & Related Articles
Source:
http://meteo.bmkg.go.id/
HOME PAGE
https://dpu.kulonprogokab.go.id/
Tukidi. (2010). Rainfall Character in Indonesia. Journal of Geography UNNES, Vol.7, No.2.
Suhardi, Budi. et al. (2018). Effect of Madden Julian Oscillation on Extreme Rainfall Events in West Java Province (Case Study in Sukabumi District). Journal of Geography, Education and Environment (JGEL), Vol.2, No.2
Yulihastin, Erma. (2010). Asian Monsoon Interaction Mechanism and Enso. Aerospace News, Vol.11, No.3.