Will there be more extreme rainstorms in the future? Here is the explanation

Produced by: Science Popularization China

Author: Half Lazy (Institute of Atmospheric Physics, Chinese Academy of Sciences)

Producer: China Science Expo

Huabei: It’s so unfair, why am I always the one who gets hurt?

North China has experienced "ups and downs" in the past two months. Not long after June, which set the longest period of extreme high temperatures in the region's history, July is here again singing "Let all the rain fall."

Since July 29, many areas in North China and the Huanghuai region have experienced heavy rain, with local areas experiencing extremely heavy rain. From 20:00 on July 29 to 11:00 on August 1, the average precipitation in Beijing reached 263.8 mm, and the city's largest precipitation occurred in the Wangjiayuan Reservoir in Changping, reaching 744.8 mm. From 8:00 on July 29 to 7:00 on August 1, the cumulative precipitation at the Liangjiazhuang Station in Zhaozhuang, Lincheng reached 1,003 mm, which is "a year and a half" of rain.

(Image source: National Climate Center and Central Meteorological Observatory)

Actual precipitation situation in Beijing, Tianjin and Hebei (8:00 a.m. on July 29 to 7:00 a.m. on August 1)

(Photo source: Hebei Weather)

In fact, July to August every year is the rainy season in North China. Why is the rain so heavy this year? I believe everyone knows that this year it was affected by the typhoon.

I wonder if you still remember the heavy rain in Zhengzhou on July 20, 2021. The maximum hourly rainfall in Zhengzhou on that day reached 201.9 mm, breaking the historical extreme hourly rainfall in mainland my country. The extreme rainstorm at that time also had typhoon "accomplices". The Pacific Typhoon "Fireworks" and the South China Sea Typhoon "Chapaka" continuously transported water vapor to Henan Province, and the superposition of other factors such as the abnormally northerly subtropical high pressure caused the "once-in-a-millennium" rainstorm to occur.

Two typhoons were the accomplices of the heavy rain in Zhengzhou on July 20

(Photo source: China Weather)

The situation of heavy rains in North China this year is somewhat similar.

Typhoon No. 5 "Dusurui" landed in Fujian on July 28, carrying abundant moisture and continuing northward, bringing precipitation to more than ten provinces along the way. The moisture also stagnated in the North China and Huanghuai areas under the control of the subtropical high pressure. Then, Typhoon No. 6 "Kanoo" strengthened into a strong typhoon on July 30 and a super typhoon on August 1.

The aggressive "Kanu" continued to provide long-range water vapor assistance to "Dusurui" which traveled thousands of miles during this round of heavy rain. Combined with the outer water vapor of the subtropical high pressure, it was stabilized in North China under the obstruction of the Taihang Mountains to the west of Beijing-Tianjin-Hebei, bringing continuous heavy rains. Due to the uplift of the terrain, it caused extreme heavy rains in the mountainous areas.

In short, the combination of the double typhoons, the abundant water vapor supply chain outside the subtropical high pressure, the stagnation of the subtropical high pressure, and the terrain, the three parties "cooperated" and "helped" the rainstorm to "lay down" the mountains and rivers in North China, and took down the red warning sign in one fell swoop . It eventually caused mountain torrent disasters such as mudslides and landslides in mountainous areas, as well as urban waterlogging.

This round of heavy rain weather situation map

(Photo source: China National Meteorological Administration)

El Nino: I will not necessarily make typhoons more numerous and stronger

At present, the equatorial central and eastern Pacific has entered the El Niño state, with an intensity reaching above medium. The sea temperature is still continuing to rise and will most likely continue until winter.

Will El Niño, far away at the equator, affect this rainstorm?

Sea surface temperature changes (El Niño key areas are marked with black boxes)

(Image source: National Oceanic and Atmospheric Administration, NOAA)

The key area of ​​El Niño seems to be far away from us, but it can indirectly affect my country's weather by affecting the monsoon and the subtropical high pressure in the western Pacific, which can easily bring about floods in the south and droughts in the north, and will affect the frequency, intensity and trajectory of typhoons in my country to a certain extent.

The northwest Pacific Ocean, which corresponds to the coastal area of ​​my country, is the most active typhoon-generating area in the world, accounting for almost one-third of the world's annual typhoon generation. In El Niño years, the sea temperature in the eastern Pacific is abnormally high, and the sea temperature in the western Pacific is low. The subtropical high pressure and summer monsoon are southerly and strong, and downdrafts prevail, which suppresses convective activities. The strength of convective activities affects the heat and water vapor provided to the atmosphere during the interaction between the sea and the air, which is very important for the formation and development of typhoons.

Therefore, in El Nino years, the number of typhoons generated and landing on China's coast is lower than in normal years . At the same time, the typhoon source area moves southeastward, which will extend the path of the typhoon to the northwest before landing and prolong its growth time. Therefore, the overall landing intensity is stronger and more northerly.

However, El Nino is only one of the main factors affecting climate change in China, not the dominant factor. Its occurrence does not mean the occurrence of a specific meteorological anomaly. The impact of each El Nino will vary greatly depending on the time and region of occurrence. Therefore, the occurrence and impact of a specific typhoon need to be analyzed in combination with the specific weather situation.

In this round of heavy rain, the formation and development of the two typhoons will be potentially affected by El Niño, but the impact mechanism will have to wait for scientists' detailed analysis after this round of heavy rain.

The impact of El Niño events on the northern hemisphere winter and summer

(Image source: National Oceanic and Atmospheric Administration, NOAA)

The future of typhoons: more frequent or more extreme?

What is worrying is that, in the context of global warming, the frequency of El Niño has greatly increased in the past 30 years compared with the past few centuries, and its climate impact will be significantly enhanced, which may cause greater climate disasters in the future. A study published in Scientific Reports pointed out that from 2010 to 2019, strong typhoons tended to land in southeastern China, with stronger intensity and moving northward. Some studies have also shown that the number and proportion of strong typhoons in the world will increase in the future.

In addition, the average speed of typhoons slowed down by 10% in the 70 years from 1949 to 2016. Although the speed of typhoons has slowed down, the wind speed has not weakened at all, which will cause typhoons to stay in the region longer, significantly increase precipitation, and bring greater disaster risks. In addition, climate warming increases the possibility of typhoons reaching level 3 or higher. Between 1979 and 2017, the probability of typhoons developing into level 3 or higher typhoons increased by 8% per decade.

There are also studies that quantify the impact of anthropogenic warming on typhoon-induced damage in China's southeastern coast in the late 21st century. The study found that under the high-emission scenario of RCP8.5 (i.e., no climate mitigation policies and continued increase in greenhouse gas concentrations), the 10 super typhoons in the region from 2013 to 2019 at the end of the 21st century will have an average increase of 12%±4% in landfall intensity, 25%±23% in rainfall, and 128%±70% in economic losses compared with historical simulations.

Even in the lower-emission RCP4.5 scenario (i.e., with certain government intervention, total radiative forcing is stabilized at 4.5 W/m2 in 2100), typhoon losses in Zhejiang, Fujian, Guangdong, and Hainan (four typhoon-prone provinces in the southeastern coastal area) are projected to increase by 71%, 170%, 20%, and 85%, respectively, by the end of the 21st century.

Direct economic losses of 10 super typhoons under historical and future climate conditions (CPI-2013 adjusted losses). (a) Estimated direct losses from historical simulations of 10 super typhoons. (b) Estimated change in direct economic losses for CMIP5 average RCP8.5 relative to historical estimates. (c) Estimated change in direct economic losses for CMIP5 average RCP4.5 relative to historical estimates. (d) Projected change in direct economic losses for HiFLOR RCP4.5 relative to historical estimates.

(Image source: Reference 1)

As for the phenomenon of multiple typhoons occurring simultaneously in the same ocean basin (tropical cyclone cluster events, called multi-typhoon events in the Northwest Pacific), similar to this year, for the Northwest Pacific, although the frequency will be significantly reduced in the future, the possibility of the region and countries being hit by multiple typhoons in a short period of time will increase significantly, and the threat to the coast of South China, the coast of the eastern Pacific, the coast of the Gulf of Mexico, and the west coast of Africa may increase. Because its continuous and cumulative impact exceeds the impact of a single tropical cyclone, it may cause more extreme precipitation, strong winds, and storm surges.

Projected changes in the frequency (a, d, g), duration (b, e, h) and ratio (ratio of tropical cyclone cluster frequency to all typhoon frequency) of tropical cyclone cluster events in the future; c, f, i) of the CMIP6-HighResMIP model over the western North Pacific (WNP) (top), the eastern North Pacific (ENP) (middle) and the North Atlantic (NA) (bottom)

(Image source: Reference 2)

Conclusion

Mother Ocean nurtures life, as well as weather and climate phenomena with different characteristics, such as El Nino/La Nina events, typhoon activities, and various extreme weather and climate events. Better understanding and prediction of the ocean is particularly important today as the impact of climate change is becoming increasingly serious, but unfortunately, our understanding of this process is far from enough.

Average temperature in the first 23 days of July from 1940 to 2023

(Photo source: United Nations Meteorological Organization)

With the end of the "global warming era" and the arrival of the "global boiling era", extreme weather may become the new normal in our future lives. In the increasingly unpredictable weather, how to actively adapt may become our new compulsory course.

References

1. Huang, M., Wang, Q., Liu, M. et al. Increasing typhoon impact and economic losses due to anthropogenic warming in Southeast China. Sci Rep 12 , 14048 (2022).

2. Fu, Z.-H., Zhan, R., Zhao, J., Yamada, Y., & Song, K. (2023). Future projections of multiple tropical cyclone events in the Northern Hemisphere in the CMIP6-HighResMIP models. Geophysical Research Letters, 50, e2023GL103064.

3. Feng, X., Li, M., Li, Y. et al. Typhoon storm surge in the southeast Chinese mainland modulated by ENSO. Sci Rep 11 , 10137 (2021).

4. Zhou, Y. et al. Revealing the effects of the El Nino-Southern oscillation on, tropical cyclone intensity over the western North Pacific, from a model sensitivity study. Adv. Atmos. Sci. 30 (4), 1117–1128 (2013).

5. Kossin JP . A global slowdown of tropical-cyclone translation speed[J]. Nature, 2018, 558(7708):104-107.

6. Kossin JP, Knapp KR, Olander TL, et al. Global increase in major tropical cyclone exceedance probability over the past four decades[J]. Proceedings of the National Academy of Sciences, 2020,117 (22): 11975-11980.

7. Hu K, Chan J, Gang H, et al. A train-like extreme multiple tropical cyclogenesis event in the Northwest Pacific in 2004[J]. Geophysical Research Letters, 2018.

8. Li Hui, Wan Xia, Liu Zhao, et al. Talking about things related to El Niño[N]. China Meteorological News, 2020-05-22.