Change Of Chahannur Lake Area And Its Causal Factors

Lake is an important part as one of the group in terrestrial hydrosphere,it not only a link button of interact in layers of the earth,but also a critical indicator of climate change and human activity.The lake named Chahannur which located interlocking zone of Hebei-Mongolia is one of the most important wetland in south of Inner Mongolia Plateau,its expanded,shrunk,and disappeared were associated closely with climate changes and human activities.Since the 1950s,wetland groups in Inner Mongolia has shrunk continuously and Chahannur Lake has became a seasonal lake.By the survey,the basin has increased 600 center pivot irrigation systems since2006 and the area of the Chahannur Lake has dried up at several times because highly extracted the groundwater.Firstly,the study data extracted the temporal and spatial distribute characters in crop growth period between April to October from 1991 to 2019 by AVHRR and MODIS NDVI data.Secondly,analysis the changes reasons of Chahannur lake area by meteorological factors such as precipitation,temperature,climate wetness index and different rain types from meteorological station belong basin.At last,extracted the temporal and spatial distribute characters of irrigated land in the basin by highly resolution NDVI data which obtained by ESTARFM(Enhanced Spatial and Temporal Adaptive Reflectance Fusion Model),combined the anthropogenic activities which including crop water demand,shortage deficit index,irrigation water demand and collected the yield and first GDP.Based on above results,we discussed the water resources using situation in Chahannur basin,and the main conclusion as follows:(1)The area changes of Chahannur lake has decreased from 76.23 km~2in 1991to 4.06 km~2in 2019,among the fruit rain years such as 2003 to 2004,the largest water area range can reached 30 km~2,but it maintained a dried phenomenon until seven years later;about in 2010 to 2014,the lake area recovered again and maximum appeared 40 km~2,but dried up again since 2015.Between the twice drought,we can see clearly the degree of the first is rather than second.(2)Analysis of climate factors showed precipitation,climate wetness index and heavy rain were decreased while little rain was increased in 1991 to 2008;with the increasingly heavy rain and climate wetness index development in 2008 to 2019,which advantage to area enlarge but not.Meanwhile,the temperature increased1.68?will no doubt raised the water evapotranspiration.(3)As anthropogenic activities,irrigated land areas has increased from152.90×103 hm~2in 2000 to 192.09×103 hm~2in 2017.Irrigation water demand far exceed available water of regional,which lead to the groundwater level falling uninterrupted.(4)After analyzed the vegetable index we found the increase of regional vegetation is dominated by irrigated agricultural areas.However,the north mountains showed an obviously degradation phenomenon.This means the biomass of the irrigated land has increased because the increase of irrigation activities,at the same time it also reduced the groundwater level,the natural grassland in mountainous areas showed a degradation phenomenon.(5)In conclusion,the lake shrinkage caused by comprehensive factors of climate change and irrigated agriculture from 1991 to 2000.It is more likely to the groundwater level decline caused by agricultural irrigation after 2000.With the irrigated scale far beyond the available water resources,the surface runoff continues to decrease and groundwater replenishing difficulty,the area of Chahannur lake shrinking rapidly even dried up.