Climate change is rapidly shortening the growing season in Central Asia, according to a new study that compiled data on vegetation cover over the past two decades. While the study focuses on wild trees and grasses rather than crops, the trend could dash hopes of increasing agricultural production and heighten fears about food security.
The growing season (the time interval between the first shoots in spring and wilting of plants in autumn) has become longer in most areas in the middle latitudes of the northern hemisphere, which is to be expected in the context of global warming.
But in much of Central Asia, the picture is reversed. The growing season for plants starts later and ends earlier, despite the region's climate warming faster than the global average, according to an independent peer-reviewed study published this month in the journal Science of the Total Environment.
This seemingly paradoxical situation can be explained by a change in the nature of precipitation. Vegetation cover is "more sensitive to fluctuations in precipitation" than to fluctuations in temperature, the study said. Whereas most of Central Asia has become increasingly arid, which could lead to a shorter growing season, where precipitation has increased, there seems to be an early end of the period as well. Because rainfall is a more complex variable than temperature, in both cases (rainier and drier areas), yields on these lands are likely to decline.
Lizhou Wu of Nanjing University of Information Science and Technology in China and his co-authors begin the study with temperature and precipitation data collected between 2000 and 2019. They compare it to native plant growth measured over the same time interval using satellite sensors and land sampling points. They then divide this giant region, which encompasses the five states of Central Asia and most of western China, into six ecological zones, which they divide in height in 1000-meter increments.
As a result, a huge array of data was obtained, among which there is statistically significant information confirming the reduction in the duration of the growing season. Here is some of them:
- In 2019, 73.4 percent of the study area experienced a shorter growing season compared to 2000. On average, this period is reduced by 0.89 days per year.
- The most affected were central and western Kazakhstan, as well as the Syr Darya basin, which covers southern Kazakhstan and eastern Uzbekistan.
- Due to the rise in temperature in the Tien Shan mountains (located in Kyrgyzstan, Tajikistan and extending to Xinjiang), the growing season now begins earlier - it has moved one day in a decade. At the same time, due to a decrease in the amount of precipitation, the growing season, as a rule, also ends earlier - by 3, 7 days per decade - which reduced the total growing season.
- In the westernmost part of Kazakhstan and on a large territory of Turkmenistan and Uzbekistan, the precipitation regime remains stable. But Wu and his colleagues found that the growing season ended earlier in those years when there was more rainfall than normal.
- The same pattern was observed in the Tarim River Basin in China's Xinjiang Province, where precipitation increased more than any other area mentioned in the study, and the growing season, in contrast, was significantly reduced.
- And here is an interesting observation, seemingly not related to climate change: with an increase in altitude for every 1000 meters, the growing season decreases by an average of 11, 7 days. But in Northern Kazakhstan, the reduction is 50.7 days for every 1000 meters.
Fortunately, the growing season is not the same as productivity, which is measured in agriculture in terms of net primary production (NPP) used for animal feed. Many crops can be harvested well before the end of the growing season. In addition, as noted above, the authors base their conclusions on the analysis of wild flora: steppe grasses, shrubs (saxaul) and trees (larch and poplar), rather than agricultural crops.
Incidentally, Wu and his colleagues found a small increase in NPP in most of the study area, with the exception of western Kazakhstan, where there was a significant decrease. Local shepherds use meadow steppes for grazing. This situation is highlighted by the extreme drought, which is currently starving thousands of cows and horses in the region. Even before this year's crisis, there were numerous signs of food insecurity across Central Asia, prompting authorities to impose export restrictions. On July 26, Kazakhstan introduced further restrictions, this time on livestock feed.
Publicly funded science often meets the needs of the government, which allocates funds for it. The research by Wu and his colleagues was made possible by the support of the Chinese Academy of Sciences, which sponsors much of the current research on climate and agriculture in Central Asia. Indeed, this study echoes some of Beijing's strategic priorities: numerous agreements recently concluded with the authorities of Central Asian countries have highlighted the region's potential to provide China with food.
However, the study is not encouraging as the data it contains once again points to the devastating impact of climate change on Central Asia. Unless, of course, it will push the local authorities to solve the problems existing in the agricultural sector, including the irrational use of water and other resources, which are described in detail in scientific work.
