Tropical wet climate
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Tropical Wet Climate: Insights from Recent Research
Strengthening Contrast Between Wet and Dry Regions
Recent studies indicate a significant strengthening of the contrast between wet and dry regions in the tropics due to human influence. Climate models, reanalyses, and observational data all show that rainfall in ascending regions is increasing, while it is decreasing in descending regions. This trend is supported by data from the latest model intercomparison project (CMIP6) and blended satellite and in situ data from 1988 to 20191. The primary driver of these changes is the increase in greenhouse gases, with natural forcings such as volcanic eruptions also playing a role1.
Historical Wet Periods and Climate Anomalies
Long-term records from northeastern Brazil reveal that wet periods in this region, which is currently semi-arid, have been linked to distant climate anomalies over the past 210,000 years. These wet periods coincide with weak East Asian summer monsoons, cold periods in Greenland, and other global climate events. The southward displacement of the Intertropical Convergence Zone (ITCZ) is believed to explain these wet periods, which likely influenced the distribution of rainforests in the region2.
Observed and Simulated Precipitation Trends
Global warming is expected to enhance the fluxes of fresh water between the surface and atmosphere, causing wet regions to become wetter and dry regions drier. Observations and climate model simulations from 1850 to 2100 show that precipitation over dry tropical land has decreased and is projected to continue decreasing. Conversely, wet tropical oceans are experiencing increased precipitation with warming3. These trends are driven by spatial changes in atmospheric circulation and are expected to continue into the 21st century3.
Current Changes in Tropical Precipitation
Satellite data and climate models reveal that wet regions in the tropics are experiencing an increase in the frequency of extreme precipitation events, while dry regions are becoming drier. The Global Precipitation Climatology Project (GPCP) data from 1988 to 2008 show that wet regions have seen a 1.8% increase in precipitation per decade, while dry regions have seen a 2.6% decrease per decade4. This trend is consistent with model simulations and highlights the impact of global warming on tropical precipitation patterns4.
Wet and Dry Spell Characteristics
An analysis of satellite-based daily rainfall observations shows that wet and dry spell characteristics in the tropics exhibit distinct patterns. Humid regions, such as the Amazon and Pacific Ocean, predominantly experience 2-4 day wet spells, while arid regions, like South Australia, have wet spells that peak at 1 day. Conversely, dry spells in arid regions last 3-4 days, while in humid regions, they last only 1 day. These patterns are influenced by both chance and organized convection6.
Amazonian Precipitation Trends
Amazonian rainfall, which plays a critical role in the global climate system, has significantly increased during the wet season over recent decades. From 1979 to 2015, tropical Amazonian precipitation increased by approximately 180 to 600 mm. This change is largely attributed to the warming of tropical Atlantic sea surface temperatures, which enhance moisture transport convergence over the Amazon region9. These changes have significant implications for the local hydrological cycle and the global climate system9.
Changes in Rainy Season Length
Projections for changes in tropical rainy season lengths under global warming scenarios indicate a robust shortening of the rainy season in large parts of the tropics. For example, tropical Africa and northeastern Brazil are expected to experience a shorter rainy season with a mean reduction of about 7 days under a 1.5°C warming scenario. These changes are largely unrelated to overall precipitation trends, highlighting the importance of investigating temporal characteristics separately10.
Conclusion
The tropical wet climate is undergoing significant changes due to global warming and other external forcings. The contrast between wet and dry regions is strengthening, with wet regions becoming wetter and dry regions drier. Historical records and current observations both indicate that these changes are part of a broader pattern influenced by global climate anomalies and atmospheric circulation changes. Understanding these trends is crucial for managing water resources and mitigating the impacts of climate change in tropical regions.
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Human influence strengthens the contrast between tropical wet and dry regions
Human influence, primarily from increasing greenhouse gases, has sharpened the contrast between wet and dry regions in the tropics and subtropics, with rainfall in wet regions increasing and a slight decrease in dry regions.
Wet periods in northeastern Brazil over the past 210 kyr linked to distant climate anomalies
Wet periods in northeastern Brazil over the past 210 years are linked to distant climate anomalies, suggesting a rapid global reorganization of the ocean-atmosphere system.
Highly CitedObserved and simulated precipitation responses in wet and dry regions 1850–2100
Global warming is projected to cause wet regions to become wetter and dry regions drier, affecting water resource management in the tropics.
Highly CitedCurrent changes in tropical precipitation
Tropical precipitation trends show smaller magnitudes and closer to model simulations, with increased frequency of extreme events in wet regions.
Highly CitedStatistical analysis of the temperature-humidity complex and time of wetness of a tropical climate in the Yucatán Peninsula in Mexico
Daily changes in temperature and relative humidity provide better information on the atmospheric temperature-humidity complex in tropical humid climates, aiding in better understanding of material degradation processes and rates.
Wet and dry spell characteristics of global tropical rainfall
Tropical rainfall distributions show universality, with humid regions having 2-5 day wet spells and arid regions having exponential wet spell duration distributions, with 3-4 day dry spells contributing to dryness.
Highly CitedA multi-proxy climate record from a northwestern Botswana stalagmite suggesting wetness late in the Little Ice Age (1810–1820 CE) and drying thereafter in response to changing migration of the tropical rain belt or ITCZ
Bone Cave stalagmite records wet conditions in the Little Ice Age (1810-1820 CE) and drier conditions in the twentieth century, likely due to the shifting migration of the Inter-Tropical Convergence Zone.
Patterns of the seasonal response of tropical rainfall to global warming
Tropical rainfall patterns are influenced by global warming, with warm regions likely to become wetter and seasonally high rainfall anomalies expected in already wet regions.
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