The weather in Taipei City in January 2021: The cold, the hot, and the dry

Similar to last time in December 2020 I want to review the weather for January 2021 in Taipei City. If you haven’t seen my last article, then you can read it here: How was the weather in December 2020? A review of weather data for Taipei City. Again I am looking at data from the weather station in Taipei City (Central Weather Bureau Station Taipei, No. 466920). So everything I write here will only apply for Taipei City. If you live in other parts of Taiwan, then the presented data and my comments will not apply to you. The data I am using here can be downloaded from the CWB Observation Data Inquire System (CODiS) and the long-term averages for Taiwan can be found on the website of the Central Weather Bureau Taiwan.

The long-term average is the average climate data for a time period of 30 years. In this case it is data collected from 1991 to 2020. The long-term average can be considered to represent normal conditions. By comparing recent data with the long-term average scientists can say if climate data, e.g. temperature, precipitation, sunshine, in a region were normal or exceptional.

For this weather review I am using temperature in °C, precipitation in mm, sunshine duration in hours and cloud amount. The temperatures presented here are the monthly average, which is calculated from the daily average, as well as the monthly average minimum and monthly average maximum temperature, which are calculated from the daily minimum and daily maximum temperature. In other terms these are the coldest and hottest temperatures measured within one day.

The amount of precipitation is the sum of the daily precipitation in mm. One mm precipitation equals 1 liter of rain water on 1 square meter, or 1 mm precipitation equals 0.001 m3 of rain water.

Sunshine duration is the sum of the daily durations and expressed in hours.

The cloud amount is an index number that ranges from 0 (no clouds) to 10 (fully covered sky). The values presented here are the monthly averages calculated from the daily averages.    


January 2021 was in terms of temperature quite interesting. It started very cold and ended very hot. The first two weeks of January were very cold with temperatures dipping down to 6.8°C. In these two weeks whole Taiwan was in the grip of a few cold surges coming from the north-west by the winter monsoon. There was even snow in the high mountain areas, as well as in the Yangmingshan mountain north of Taipei City.

Focus Taiwan “First winter snow falls on mountains across Taiwan
Taiwan News “Snow falls on Taipei’s Yangmingshan

But the winter didn’t last long in the Taipei area and from January 14th the temperatures rose and peaked in Taipei City at 29.8°C on January 21st at 2:37 p.m. This was the hottest day in January since 20 years, according to the data from the Central Weather Bureau.

The monthly average temperature for January 2021 in Taipei City was 16.0°C, which is slightly lower than the long-term average of 16.6°C. Likewise the monthly average minimum temperature of 13.4°C was 1°C lower than the long-term average of 14.4°C. Same goes for the monthly average maximum temperature of 19.2°C, which was slightly lower than the long-term average of 19.6°C.

When looking at the average values for the temperature, then January 2021 was a cold month. Cooler than the long-term average and even one of the cooler Januaries in the past 20 years. But we need to be a bit careful with the average temperatures here! Because they are hiding the large temperature variation that happened this year. I made another graph that shows only the daily minimum and maximum temperatures for each January in the last 20 years. Basically the coldest and hottest temperature that was recorded during one month. And you can see something interesting happening here.

From 2000 to 2009 the minimum and maximum temperatures have been relatively constant each month. Maximum temperatures have been around 27°C and minimum temperatures around 9°C. Also the differences between maximum and minimum was pretty constant over time. This means that maximum and minimum temperatures got simultaneously higher or lower. For example, in 2005 the maximum temperature was 26.2°C and the minimum was 7.6°C. In the next year 2006 the maximum was 27.7°C and the minimum was 8.8°C. However, since 2010 temperatures start to get more extreme and differences between maximum and minimum temperatures are getting larger. Especially for the last two years we can see that the temperatures in January are getting lower but at the same time they are getting higher than in the previous years. The next graph is to illustrate the changing temperature difference.

The line is the temperature difference between the highest and lowest temperature measured in January of that particular year. Until 2009 it is almost a horizontal line, which means, that even though the temperatures changed, the difference between them was almost constant. But since 2010 the differences start to fluctuate from each year, and for the last two years the temperature differences are increasing, which means that the temperature differences between maximum and minimum are getting more exteme.

Long story short. Even though the average temperatures for January 2021 in Taipei City indicate that the month was cooler than the average, the maximum and minimum temperatures measured in January 2021 show that this month was actually one of the coldest and hottest Januaries in the last 20 years. Additionally, we can see the temperature differences getting more extreme since 2020.

Now it would be good, if science could kick in and explain what this means and why this happens. As a scientist myself, this would be my part now. Unfortunately, this is currently beyond my expertise and I don’t want to speculate about this. However, I will look into this and read relevant literature, so that in the future I can explain these observations better.

Precipitation/ Rainfall

December 2020 was wet and grey in Taipei City. Luckily January 2021 started dry and sunny, and continued for the rest of the month. The total amount of precipitation in Taipei City was with 41 mm very low. This is half of the long-term average of 93.8 mm (dashed blue line in graph) for January. But can we be really lucky about it? Over the last eight years Januaries have been much drier than the years before, except for the years 2016 and 2018 that were exceptionally wet.

Similar to the temperatures we see here again extreme values. Since 2014, Januaries were much drier than the long-term average, with the total amount of precipitation ranging from 20 mm to 45 mm per month. Except for 2016 and 2018, which were extreme wet month with a total amount of precipitation of 256 mm and 255.8 mm, respectively. Before 2014 the variation in total monthly precipitation was not that extreme, and the values were much closer to the long-term average. It seems that it is getting dryer and dryer in Taiwan. There is still plenty of rainfall in the north, but in central and southern Taiwan droughts have become more and more frequent. I noticed by myself that during the last few years the amount of precipitation has become less in Taiwan. Last year 2020 was exceptionally bad, because no typhoon made landfall on Taiwan or came close to the island. For central and southern Taiwan this is a big problem, because the precipitation brought by typhoons replenishes the reservoirs. The annual precipitation, particularly in southern Taiwan, is often not enough the keep the reservoirs full. Currently the drought situation in southern Taiwan is manageable, but if this trend continues, it will become a serious problem for the country.

Sunshine and clouds

Since there was not much rain in January 2021, we can expect a lot of sunshine. With 124.5 hours of sunshine, January 2021 was one of the sunnier Januaries in Taipei City. Likewise, the cloud amount with a cloud index of 6.5 (10 is maximum) was one of the lowest in the last 20 years. Overall Januaries are mostly sunny in Taipei City.

Some final remarks

This was the second time that I write about weather data in Taipei City. Even though this type of blog articles doesn’t attract views, it is a good practice for me. On one side I am using this to learn how to present data and scientific observations to non-scientists. The part I am currently learning with this is story telling with data and data visualization. Even though as a scientist I should now this, in reality, it is not very necessary for scientific publications.

For this article I spend a lot of time learning how to analyze data and draw graphs with R (“…a free software environment for statistical computing and graphics”) and ggplot2 (“…a system for declaratively creating graphics, based on The Grammar of Graphics“). Before I used Excel, but this has serious limitations when it comes to data visualization. The graphs presented here are not great, I know. For the next article about the weather in February I already have ideas how to improve them.

Image by Pixaline from Pixabay

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