By Tamanna Akter
Since 1980, the world’s temperature has increased by about 0.8 ℃ (around 1.44°F). If trends continue, global temperatures can increase up to 4 ℃ (around 6°F) by 2081-2100. One of the major consequences of such temperature rise is increased global aridity.
Aridity can be defined as the degree of the climate’s dryness at any given location. It is the “demand” or “drying power” of the atmosphere to remove water from the land surface. To express the changes in aridity, the Aridity Index (AI) = Precipitation (P) / Potential evapotranspiration (PET). Decreases in the AI mean conditions are becoming drier, and in contrast, increases mean conditions are getting wetter.
Drylands are well known as areas with high temporal and spatial rainfall variability, namely grasslands, rangelands, and woodlands. There are four subtypes of drylands i.e., dry sub humid, semi‐arid, arid, and hyper‐arid. Drylands alone occupy more than 41% of the global land area while providing food security, habitat sustainability and preserving biodiversity. For instance, about 27% and 23% of the world’s milk and meat supplies come from grasslands. In addition, drylands preserve more than one-third of global soil organic carbon. Soil organic carbon or SOC is a component of soil organic matter which makes up just 2–10% of most soil’s mass and contributes to the physical, chemical and biological function of agricultural soils. SOC plays a significant role in mitigating climate change by reducing carbon dioxide in the atmosphere. In addition, Grasslands alone preserve up to 10% of terrestrial carbon and can store about 70 tones/hectare of soil carbon. Terrestrial carbon is known as the carbon cycle on land stored within biomass, such as tropical and temperate forests. Furthermore, these lands provide shelter to more than 2 billion people around the world, mostly in developing nations across Africa and Asia. Changes in prevailing climate will interrupt dryland ecosystems accompanied by shifts in key climate variables, including precipitation, relative humidity, solar radiation and wind speed. Such changes will eventually affect more than 44% of the world’s food system, and millions of people depending on it.
Based on the current observed climatic conditions (1981-2010), recent studies expect some drylands will become drier and/or wetter in the future (2017-2100). While comparing aridity maps, the predominance of increased aridity is noticeable. Regions such as North America, the northern fringe of Africa, the Mediterranean, southern Africa, coastal regions of Australia, the Middle East and central Asia (e.g. Iraq, Iran, Afghanistan) and South America (especially eastern Brazil, southern Argentina and coastal Chile) will witness the expansion of drylands. Moreover, arid and hyper-arid climates are projected to expand into semi-arid ones in northern Africa i.e., Morocco, Algeria and Tunisia. In the case of southern Africa, semi-arid regions are expected to stretch northward and eastward, with the increased aridity strongly impacting Namibia and Botswana. On the contrary, wetter drylands will be observed in regions of tropical Africa, India and parts of north-western China. A poleward shift of northern African drylands has been projected in the southern Sahara countries along with the expansions of hyper-arid and arid regions in the northern fringe of Africa.
Preserving and restoring the unique environment drylands provide to withstand climatic variabilities is crucial now more than ever. Introducing more climate change mitigation and adaptation strategies such as planting drought-tolerant and water-efficient crops, diversifying herds, and maintaining livestock mobility across communal lands and borders, is pertinent to protecting and maintaining drylands. Integration of local governance can play a significant role in conserving this valuable resource to ensure a safer, more sustainable future.