Digging Deep: The deserts of the world are spreading further North

Digging Deeper: The world’s deserts are expanding further north
A recent study shows that the world’s deserts have been moving north since the 1980s, and have actually moved more than the proverbial inch. Hu and Han (2022) reported in Geophysical Research Letters that in geographic regions such as Central Asia, desert biomes have moved hundreds of kilometers. The area is very vulnerable to even the smallest variations in temperature and precipitation. A 2016 risk assessment by the World Bank highlights how the impacts of the weather could send the region’s economy – especially agriculture – into a vicious cycle of “shock-recovery-shock” that increases the burden of poverty and “compromises long-term growth”. .’

The study models these climate changes based on air temperature and precipitation data for Central Asia since 1960 over a span of more than sixty years. They then divided the area into eleven different climate types. These eleven climate types are mostly derived from the climate classification introduced in the 1930s by the German-Russian climatologist Wladimir Koeppen and further developed by the American geographer Glenn Thomas Trewartha in the 1970s/1980s.

Data for the study were taken from the European Center for Medium-Range Weather Forecasts (ECMWF) and the Copernicus Climate Change Service (C3S) and complemented by the Climatic Research Unit’s gridded time series, which provides very high resolution climate data.
It was found that in the last two to three decades, the precipitation and temperature profiles characteristic of the desert biome have spread eastward and northward. The actual measurements are pretty self-explanatory. Some areas recorded an average annual temperature of 5 °C higher in the period 1990-2020 than in the period 1960-79. The range covers areas in northern Uzbekistan and Kyrgyzstan, southern Kazakhstan and around the Junggar basin in northwestern China. The study predicted a cascading effect. Many of the surrounding areas have dried out as the region is witnessing a general increase in temperature, which is speeding up the de-icing process.
The analysis shows that not only did the temperate boreal steppes turn into mildly cold deserts with precipitation limited to the winter months and drought in the summer; it also seems that the mild boreal steppe also extended into the broad forests of the north and east. At the same time, in the higher latitudes of the north, especially in Kazakhstan, evergreen forest/aerial forest spread north and south, making the area wetter. These contemporaneous changes have made the temperature gradient between mid- and high-latitudes quite steep – like an envelope of cool/humid climates around a dry desert/steppe biome. This also has many consequences in relation to the atmosphere, preventing cloud formation and thus ensuring a drier climate.

A key issue here is how local ecosystems respond to disturbance. As the temperature rises, it accelerates the loss of moisture from the soil through evaporation, creating a drought-like situation. As the structure of the plant community changes – the landscape is gradually dominated by plants adapted to warmer conditions – the structure of the faunal community will also change.
Also, the response of all biomes to changes in temperature and precipitation is uniform. For example, in the mountains of northwestern China, rising temperatures have led to an increase in the proportion of precipitation that falls as rain, as opposed to rainfall. The phenomenon of glacier retreat is increasing at an unprecedented rate, a study says. This has many consequences for downstream habitats, reducing the amount of meltwater that reaches lowlands with agricultural settlements.

“[I]n the future, when the glaciers recede and there are fewer snowdrifts; [] warmer climates at higher elevations allow more precipitation to fall in liquid form. This will reduce snow accumulation in the winter months and leave less snowpack to create meltwater and support streams and groundwater in warm weather,” explained Professor Steve Hu of the University of Nebraska-Lincoln in an email to indianexpress.com, the first author of the article. These rapid disturbances and oscillations between floods and droughts and the ultimate lack of available irrigation water can actually make agriculture extremely vulnerable. However, at present, the rapid pace of glacier retreat is increasing the volume of groundwater and surface water, including lakes, in western China’s Xinjiang province and similar mountainous areas. “But this is probably at the expense of more sustainable meltwater,” Professor Hu pointed out in a press release.