Changes in China's dryland areas and NPP from 1980 to 2020

The drylands of China account for approximately 10.8% of the global drylands that are intensely affected by human activities and climate change. Dynamic changes in drylands and their subtypes (hyper-arid, arid, semi-arid, and dry subhumid), in addition to the spatiotemporal characteristics in net primary productivity (NPP) of vegetation, are crucial for the evaluation of ecosystem functions and management strategies in China. This paper defined drylands and determined the area based on the aridity index (AI). It was found that the drylands of China have expanded from 5.8 million km 2 to 6.6 million km 2 from 1980 to 2020, with an average rate of 0.019 × 10 6 km 2 (10 year) −1 . These changes were mostly driven by the mean annual temperature (MAT) and solar radiation (Srad). Among the different subtypes, the arid and semi-arid areas expanded the fastest, at the rate of 0.032 × 10 6 km 2 (10 year) −1 , with MAT being the main driving factor. However, hyper-arid areas gradually shrank at an average rate of 0.050 × 10 6 km 2 (10 year) −1 , with mean annual precipitation (MAP) as the main driving factor. The NPP of the total vegetation and the subtypes demonstrated an increasing trend in the last 20 years. The NPP of the entire drylands increased at the rate of 10.78 g C·m − 2 ·yr − 1 , which was mainly dominated by the rapid growth of NPP (5.15 g C·m − 2 ·yr − 1 ) in the dry subhumid areas. The NPP of four vegetation types (desert, grassland, forest, and cropland) demonstrated an increasing trend (19.14 Tg C·yr − 1 ), where forest and cropland showed an obvious increase, in contrast to the slight increase in grassland and desert. The study showed that the dryland areas in China may further expand in the future with increased global warming considering MAT was found to significantly contribute to the changes in the dryland areas. The contribution of forest and cropland to the total NPP of the vegetation would continue to increase with the development of eco-environmental protection projects (afforestation, construction of desert highway protection forest, etc.), western development, and construction in China.