## 1 Introduction  
Wetland is one of the most important ecosystems in the world. It has prominent significance not only in maintaining the regional and global ecological balances, but also providing a living environment for wild animals and plants [1]. Climate change is considered as one of the most important natural factors which affect wetland landscape patterns [2]. A better understanding of wetland changes and their response to climate changes will help in interpreting current environmental problems and developing sustainable wetland planning and decision-making.  
The \"Three-River Headwaters\" (TRH) region, as the headwaters of the Yellow River, the Yangtze River and the Lancang River, is located in southern Qinghai, the hinterland of the Qinghai-Tibet Plateau, which is highly sensitive to climate change because of its fragile natural ecosystems [3]. Since the 1970s, the inter-annual variation of temperature has taken on an obvious ascending trend in the TRH region [4; 5; 6]. The rapid climate change in this region has brought serious disturbances to the ecosystem structure and function, and poses a threat to ecosystem security. During the last decade, the wetland ecosystem has continuously degraded in the TRH region due to global warming. The swamp area in the Yellow River source region was 3895.2 km\({}^{2}\) in the 1980s and this was reduced to 3247.45 km\({}^{2}\) in the 1990s, at an annual average decrease rate of 58.89 km\({}^{2}\)[7]. In the Yangtze River source region, many wetlands at the foot of mountains and on the piedmont are shrinking and drying up [8]. [PERSON] _et al._[9] analyzed the interpretation results of multi-temporal land use/cover based on remote sensing (RS) images, and found that the area of wetlands in the Yellow River source region declined sharply during the recent 10 years, and converse succession occurred on some parts of the wetlands, _i.e._, swamp-swamp meadow-meadow-desertification land-desert. [PERSON] _et al._[3] and [PERSON] _et al._[10] analyzed the grassland degradation and dynamic variation of ecosystem patterns in the TRH region from the late 1970s to 2004, and found that wetland degradation became increasingly serious, and the changes of wetland mainly occurred in the west and north TRH region, with transformation from water bodies to bottom land of rivers and from wetlands to grasslands. Through satellite observation, [PERSON] and [PERSON] [11] found that the total wetland area in the TRH region decreased by 15% from 1990 to 2000. [PERSON] _et al._[12] used multi-temporal Landsat images to monitor the Maqu wetland in the Yellow River source region, and they found that the wetland area decreased by 102.38 km\({}^{2}\) at an annual average rate of 0.74% from 1990 to 2001. Climate warming and drying was the major reason for the shrinkage of the Maqu wetland, which was exacerbated by human activities. [PERSON] _et al._[13] analyzed the spatial-temporal characteristics of alpine wetland changes from 1986 to 2000 using GIS techniques, and found that the wetland area declined by 2744.77 km\({}^{2}\) during 15 years, mainly as a result of climate warming, drying and human activities.  
Wetlands in the TRH region have seriously degraded due to integrated influence of natural events and human activities since the 1990s, which have greatly changed the spatial distribution pattern of wetlands, accelerated peat decomposition and carbon loss, and led to such ecological problems as dry regional climate, desertification and drought of wetlands, decrease in river runoff, and sharp decline of wetland biodiversity [14]. Therefore, the present study is an attempt to understand the wetland changes and its response to climate changes in the TRH region since the 1990s by RS image interpretation, climate change trend analysis, which could provide valuable and scientific basis for the management and protection of wetlands and for the contribution to the studies on global climate changes.