Expansion of irrigation led to inland lake shrinking in semi-arid agro-pastoral region, China: A case study of Chahannur Lake

Study region: Chahannur Lake, an inland lake of the Inner Mongolia Plateau, is located in the typical agro-pastoral ecotone, China. Study focus: Change of lake area is highly sensitive to climate change and human activities, but the internal driving mechanism so far remains unclear. In this study, the spatiotemporal distribution of Chahannur Lake over the past 30 years was accurately extracted using the NDVI data, and the corresponding driver analysis was conducted. New hydrological insights for the region: Before 2000, Chahannur Lake was always remaining watery state throughout the year and the maximum area reached 90 km2; however, after 2000 it became a seasonal lake with a long-term dry state. During the observed period, the recovery of water body had only occurred in two stages both of which belonged to historically heavy rain years, and the maximum lake area was only 40 km2. Although the climate has tended to be warm and humid after 2000, it cannot completely reverse the lake’s drying. Additionally, the irrigated arable increased by 392 km2 in 2000–2017, and the increased arable consumed substantial groundwater for meeting agricultural demands, which consequently caused rapid shrinkage of the Lake. Notably, the increase of NDVI is widely distributed in irrigated arable with high water-consuming crops. Overall, groundwater over-exploitation and strong water consumption from crops have jointly led to the drying of Chahannur lake.