Search

This study examines the expansion of drylands and regional climate change in northern China by analyzing the variations in aridity index (AI), surface air temperature (SAT), precipitation and potential evapotranspiration (PET) from 1948 to 2008. It is found that the drylands of northern China have expanded remarkably in the last 61 years. The area of drylands of the last 15 years (1994–2008) is 0.65×106 km2 (12%) larger than that in the period 1948–62. The boundary of drylands has extended eastward over Northeast China by about 2° of longitude and by about 1° of latitude to the south along the middle-to-lower reaches of the Yellow River. A zonal band of expansion of semi-arid regions has occurred, stretching from western Heilongjiang Province to southern Gansu Province, while shifts to the east of semi-arid regions in dry subhumid regions have also occurred. Results show that the aridity trend of drylands in northern China is highly correlated with the long-term trend of precipitation and PET, and the expansion of semi-arid regions plays a dominant role in the areal extent of drylands, which is nearly 10 times larger than that in arid and subhumid regions.

This study analyzes areal changes and regional climate variations in global semi-arid regions over 61 years (1948–2008) and investigates the dynamics of global semi-arid climate change. The results reveal that the largest expansion of drylands has occurred in semi-arid regions since the early 1960s. This expansion of semi-arid regions accounts for more than half of the total dryland expansion. The area of semi-arid regions in the most recent 15 years studied (1990–2004) is 7 % larger than that during the first 15 years (1948–1962) of the study period; this expansion totaled 0.4 × 106 and 1.2 × 106 km2 within the American continents and in the Eastern Hemisphere, respectively. Although semi-arid expansion occurred in both regions, the shifting patterns of the expansion are different. Across the American continents, the newly formed semi-arid regions developed from arid regions, in which the climate became wetter. Conversely, in the continental Eastern Hemisphere, semi-arid regions replaced sub-humid/humid regions, in which the climate became drier. The climate change in drying semi-arid regions over East Asia is primarily dominated by a weakened East Asian summer monsoon, while the wetting of semi-arid regions over North America is primarily controlled by enhanced westerlies.