Study on dynamic changes of land desertification in the circum-lake zone of the Qinghai Lake in the past 30 years supported by Remote Sensing and Geographical Information System

The circum-lake zone of the Qinghai Lake is one of the most serious regions of desertification on the Qinghai-Tibetan Plateau. Based on Remote Sensing （RS） and Geographical Information System （GIS） techniques, the four sets of remote sensing images acquired in 1976, 1987, 1995, and 2006 were selected to conduct thematic information extraction in 14,300 km2 of land in the circum-lake zone using the Earth Resource Data Analysis System （ERDAS） image and information processing function. In the meantime the off-site interpretation and filed check-correction methods were used to recon- struct the temporal-spatial dynamic changes and differentiation patterns of land desertification in the circum-lake zone in the past 30 years, and based on this, the developmental trend of land desertification in the next 20 years was predicted. The results of the study show that in the past 30 years land desertification in the region experienced a continuous fluctuation between rapid- and slow-development processes in time, while in space it exhibited a few small patchy distributions or sporadic distributions in many places while at the same time, four large sand-dominated distributions stood out and evolved into a circum-lake belt differentiation pattern with a lakeside dike as the connecting line. Due to the integrated effects of climate changes, human activities and artificial rehabilitation, land desertification area in the region in the next 20 years will exhibit an increasing trend in the first 15 years and then increase at a slower rate, and afterward occur in a reverse, decreasing trend.

Climate change and sandy land development in Qinghai Lake Watershed,China

The Qinghai Lake Watershed,containing the largest saline lake in northwest of China,has suffered from severe sandy land development in recent years.This paper analyzcs its daily precipitation,temperature,and wind from 1958 to 2001,and the spatial and temporal distributions of sandy land through the interpretation of remote sensing images covering four years(1977,1987,2000,and 2004).Results showed that since the middle of the 1960s,the daily precipitation(P)of 0<P≤5 mm decreased,while the P>20 mm increased significantly(S<0.05)in their annual total amounts and days.The maximum daily precipitation also increased significantly.Both the maximum dry spell and the total dry spell of more than ten days had a significant upward trend.Since the beginning of the 1960s,all the extremely high,extremely low and mean temperatures increased signifi-cantly(S<0.01),at a rate of 0.1℃/10a,0.2℃/10a,and 0.2℃/10a,respectively.The days with extremely high temperature had a significant upward trend,while the days with extremely low temperature had a significant downward trend.The Qinghai Lake was significantly shrinking(S<0.01)and provided abundant sediments for Aeolian erosion.The NNW wind prevailed in the watershed,and the largest scale wind was from the west and concentrated on the dry months.As a result,the sandy land was mainly born on the east bank of Qinghai Lake.The total sandy land area in the watershed had grown from 587.4 km^(2),660.7 km,697.6 km^(2) to.805.8 km^(2),accordingly,its area percentage growing from 2.0%,2.2%,2.4% to 2.7%,respectively.