Chapter 5 : Climate

“In spring, the rain comes after thunder; in summer, the rain stops after thunder.”

“Do not store away your winter coats before Dragon Boat Festival.”

 

These are weather-related proverbs created by our ancestors from experience. Meteorologists reach roughly the same conclusions from scientific observation.

 

Climate

        We already know from Chapter 4 that the short term variations in temperature, rainfall, etc. are called "weather.” What, then, is “climate”?

        Table 5-1 shows the average monthly temperature and rainfall for Taitung City. We can see the average temperature in October in Taitung is 24.8℃, and that the average annual rainfall is 1831.6 mm. Find the sum of the average monthly temperatures of January to December and then divide it by 12. The quotient is the average annual temperature of Taitung. The long term average of weather is called “climate.” Climate includes the following information: whether the weather here is relatively cold or hot, whether there is a significant difference in temperature between winter and summer, and whether there is abundant rainfall.

 

        Table 5-1 Climate Data for Taitung (1901~1995)

Month	Jan.	Feb.	Mar.	Apr.	May	Jun.	Jul.	Aug.	Sep.	Oct.	Nov.	Dec.	Annual
Temperature(℃)	18.9	19.3	21.1	23.5	25.7	27.2	28.1	27.8	26.9	24.8	22.5	20.1	Annual Average Temperature:23.8
Rainfall(mm)	40.2	42.9	54.8	78.9	159.9	236.7	305.5	295.4	315.9	176.0	82.9	42.5	Annual Rainfall:1831.6

 

Data Source: Central Weather Bureau

 

 

Climate Factors

        Since climate is the long term average state of weather, climate factors are the same as weather factors. Climate factors include temperature, rainfall, barometric pressure and wind.

        On a map, if points that have the same temperature at the same time are connected together, they will form a smooth curve. Such curves are called “isotherms.” Figures 5-1 and 5-2 show isotherm maps of Taiwan in January and July.

        If points of the same rainfall at the same time are connected together, the resulting curves are called “isohyets” or isohyetal lines.

 

▲ Figure 5-1 January Isotherm Map of Taiwan

▲ Figure 5-2 July Isotherm Map of Taiwan

 

 

Climate Types

        Climate maps can tell us a great deal.

        Figure 5-1 is a temperature map. By reading this map, we can reach two conclusions about temperature in winter. Take January for example. First, the temperature in the mountains is lower than that on the plains. Second, northern Taiwan is cooler than southern Taiwan.

        Figure 5-2 shows us that, except for high mountain areas, the summer temperatures of Taiwan--taking July for example--are above 20℃.

        Figure 5-3 is a precipitation map. It shows us that Taiwan has abundant rainfall. It also shows three contrasts: there is more rainfall in the mountains than on the plains, more on the east coast than on the west coast, and more in the north than in the south.

        In sum, these three figures show us that Taiwan’s climate has the following features: a warm winter, a hot summer, and abundant rainfall. What are the factors that cause these climate features?

1.      Terrain: In terms of temperature, the higher the altitude, the lower the temperature; conversely, the lower the altitude, the higher the temperature. In terms of rainfall, the slope facing the wind—the windward slope—gets more rainfall than the slope facing away from the wind—the leeward slope.

2.      Monsoon: During the summer, a southwest wind blows into Taiwan from the South China Sea, bringing abundant precipitation. While in winter, a northeast wind blows in from the East China Sea, often leaving northern Taiwan overcast and rainy.

3.      Latitude: in the northern hemisphere, the more southerly the latitude, the higher the temperature; by contrast, the more northerly the latitude, the lower the temperature. The Tropic of Cancer divides Taiwan’s climate into two types: To the south we find “Tropical Monsoon Climate,” while to the north there is “Subtropical Monsoon Climate.”

 

▲ Figure 5-3 Annual Rainfall Map of Taiwan

 

Weather Disasters

        The most common weather disasters of Taiwan are drought, torrential rain, typhoons, and cold.

1.      Drought: The southwest plains often suffer drought in winter. Although the dry weather during winter is quite comfortable for human beings, winter water shortages cause problems for agricultural irrigation and industrial production. They may also interfere with daily life.

2.      Torrential Rain: The rainfall distribution of Taiwan differs greatly depending on time and place. During the Plum Rains Season from May to June or the typhoon season from June to September, heavy rainfall is common, causing debris flows, landslides, and flooding, which cause severe damage to roads, crops, fish farms, and property. Torrential rain can be very dangerous.

 

3.      Typhoon: Typhoons are common during summer and fall. Three to four typhoons hit Taiwan on average every year. They bring abundant rainfall, but the howling wind and torrential rain often cause great property losses. They can even cost human lives.

 

4.      Cold: Taiwan has a warm winter. But sometimes when cold fronts arrive, the temperature will plunge to less than 10℃. The cold often causes serious damage to crops and fish farms.