Traditionally, many of us say that summertime in the Philippines is about to end and give way to the rainy season. While this is a good metaphor that allows us to be understood by those living in temperate regions, where there are four distinct seasons, this is not technically accurate.
Since we are in the tropical zone, our seasons are defined neither by the length of daylight nor the intensity of sunlight. Instead, it is defined by the amount of rainfall. This is why we do not have the same kinds of seasons experienced in temperate regions of the world: summer, autumn, winter, and spring. Instead, we have the dry season and the wet season.
This year, the Philippine Atmospheric, Geophysical, and Astronomical Services Administration (PAGASA) declared March 22 to be the official start of the dry season. Meanwhile, in a statement made last week, PAGASA said that the rainy or wet season will probably start later this week, close to the middle of June.
What is summer, anyway? In temperate regions, summer is the time of the year when daytime is significantly longer than nighttime. Because of the significant increase in the amount of daylight, summer is a season when the temperature is higher than in other times of the year.
In temperate regions of the northern hemisphere, summer is linked with the Summer Solstice, which happens between June 20 and 22. This year’s northern Summer Solstice will happen on June 21. Summer solstice is the longest day of the year.
Opposite to the Summer Solstice is what is known as the Winter Solstice, or the shortest day of the year. In the northern hemisphere, Winter Solstice happens between December 21 and 22. This year it falls on the 22nd of December.
Things are the other way around in the southern hemisphere: June 21 is the winter solstice while December 22 is the summer solstice.
The differences in length of day between the solstices is significant in temperate regions. Take, for instance, Seoul in the Republic of Korea. On June 21, Seoul will experience 14 hours and 46 minutes of daylight, with additional several hours of twilight. Meanwhile, on December 22, Seoul will have only 9 hours and 34 minutes of daylight.
Contrast this to, say, Cebu City. On June 21, Cebu City will experience 12 hours and 44 minutes of daylight. Meanwhile, on December 22 it will have 11 hours and 31 minutes of daylight. A similar observation can be made of any other city in the Philippines.
In other words, technically there is no “summer” season in the Philippines, at least not in the way the word is used by people living in temperate regions such as Korea or the United States.
Of course the dry season that runs from March to the first week of June feels like our summer, which is why the word “summer” is a useful way of describing this time of the year. After all, this is the time of the year we go to the beach, have local summer vacations, and turn up our air conditioning machines the most.
This is why seasonal variations in the amount of rain determine our seasons. For example, Manila City receives an average of less than 21 mm of rainfall from January to March. During the wet season, however, the city receives significantly more: 280 mm in June, 360 mm in July, and 480 mm in August, its rainiest month.
The rains in the Philippines are brought by the prevailing winds. This is why PAGASA uses the winds to determine the official start of the dry and wet seasons. Roughly speaking, when the northeasterly winds dominate, they bring drier weather. Meanwhile, when the southwesterly winds prevail, they bring heavy rains. Locally, we call them Amihan
All of this is relative. It applies most accurately to the western part of the country, where there is a somewhat pronounced difference between the wet and dry seasons. In the eastern part of the country, it is relatively wet throughout the year, although during the rainy season the rains are even heavier.
Between these two regions, there are areas where the rain is more or less evenly distributed throughout the year. In such places, the difference between the wet and dry seasons is not so pronounced. Cebu City is an example of a place that experiences this type of climate. In Davao City, the distribution of rainfall throughout the year is even more even.
In summary, because the Philippines is in the tropical zone, the seasons are not determined by the amount of daylight. Rather, they are determined by the amount of rainfall, which varies throughout the year and from one part of the country to another because of seasonal variations in the prevailing wind patterns.