(ORDO NEWS) — American scientists have shown that the reduction in the number of rainy days per year, associated with global warming, contributes to the earlier appearance of the first leaves on the trees of northern countries. According to the new model, every ten years spring will come 1 to 2 days earlier.
The increase in average annual temperatures associated with climate change leads to the fact that spring comes faster in the northern countries – the first leaves appear on the trees earlier.
Now, however, scientists from Ohio State University have shown that not only temperature contributes to the earlier onset of spring, but also a decrease in the number of rainy days per year.
In previous studies and forecasts, scientists either did not consider this factor at all, or took into account the total amount of precipitation, but not the frequency of rain.
Scientists have now calculated that a decrease in rainfall frequency will cause spring in the Nordic countries to arrive on average 1-2 days earlier each decade, compared to previous models.
During the research, scientists analyzed information collected in the regions of the United States, Europe and China, which are located above the 30th degree north latitude.
The data included the dates of observation of the first signs of leaves on the trees. The authors also used satellite images taken from 1982 to 2018, which recorded the moment when the vegetation began to turn green.
The scientists compared the information obtained with data on the number of rainy days in each month in the study areas.
It turned out that as the number of rainy days decreased from year to year due to global warming, spring came earlier. The only exception was the grasslands of arid regions, where the lack of rain, on the contrary, slightly delayed the onset of spring.
Scientists have proposed several possible explanations for this relationship. First of all, rainy days are cloudy, meaning the plants receive less sunlight, which stimulates the growth of their leaves.
In addition, the absence of clouds is associated with an increase in daytime temperatures, since the sun warms the earth and air better. At the same time, nighttime temperatures without clouds to trap heat will also fall faster. This temperature contrast signals to plants that it is time to open their leaves.
The scientists used these findings to create a new model that estimates the arrival of spring until the year 2100. Existing models suggest that the period of leaf emergence will shift by 5 to 10 days by the end of the 21st century.
However, if we take into account the reduction in the number of rainy days, forecasts show that every decade spring will come 1 to 2 days earlier than expected.
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