# Monitoring Water Area Dynamics in Kashgar (2003-2023) Using Multi-Source Remote Sensing Data
## 2 Materials and Methods  
### Study Area  
Kashgar, formerly known as Shule, meaning \"a place where jade gathers\", is situated in the westernmost region of Xinjiang Uygur Autonomous Region, China. Geographically, it is located between 71\({}^{\circ}\)39\({}^{\prime}\) and 79\({}^{\circ}\)52\({}^{\prime}\) east longitude, and 35\({}^{\circ}\)28\({}^{\prime}\) and 40\({}^{\circ}\)16\({}^{\prime}\) north latitude, encompassing a total land area of 1.62 \(\times\) 10\({}^{5}\) square kilometers [18]. With 12 cities and counties under its jurisdiction, Kashgar has a population of 4.51 million. Bordering or adjacent to eight countries, including Kyrgyzstan, Tajikistan, Afghanistan, Pakistan, and India, Kashgar serves as a confluence of Eastern and Western economies and cultures, and is the heart city of southern Xinjiang. It is a crucial gateway for China's engagement with Central Asia and South Asia [19]. As a significant node on the ancient Silk Road, Kashgar was once the capital of Shule, one of the 36 countries in the Western Regions, boasting a profound historical and cultural heritage. In 1986, Kashgar was designated by the State Council as a famous historical and cultural city in China. The distribution of the study area is illustrated in Figure 1.  
Figure 1: Overview of the study area.  
Kashgar is situated within a temperate continental climate zone, characterized by four distinct seasons, high evaporation rates, and spatially and temporally uneven precipitation [18]. The terrain exhibits a southwest-high, northeast-low topography, with dominant landforms comprising the Tarim Basin, Tianshan Mountains, and Kunlun Mountains trough fold belt [15]. Gases are concentrated in the region, with the Lyushgar and Yarkand River oases being particularly prominent. Water resources display a typical pattern of \"spring drought, summer flood, autumn shortage, and winter dryness\", closely linked to the sensitivity of glacial meltwater and precipitation to temperature fluctuations [20]. The Pamir Plateau, Kunlun Mountains, and Kunlun Glaciers are extensively distributed, providing relatively stable water resources and serving as \"solid water reservoirs\". However, the regional hydrological cycle system is fragile, with uneven temporal and spatial distribution of water resources [21]. By the mid-20 th century, numerous large and small reservoirs had been constructed, boasting a total storage capacity of 1.339 billion cubic meters. With the exception of the Sujikake Reservoir, most reservoirs lack effective dead storage capacity.  
Kashgar's water system is significantly influenced by topography and regional precipitation. Rivers originate from glaciers and alpine snow belts, disappearing after traversing the plains. Influenced by mountain snowmelt, rivers exhibit pronounced annual low-water and flood variations. They are all fed by ice and snow meltwater, with the main streams themselves not generating flow. The region encompasses five major rivers and three short-distance rivers. The unique geographical environment has fostered two concentrated oases: the Yarkand River and Kashgar River basins [22]. The Yarkand River Basin features numerous tributaries, with the Keleqing and Taskorgan rivers being the two primary tributaries. Originating from the northern Karakoram Mountains, they flow westward to southward, ultimately reaching the northeast. These are typical arid inland rivers, exhibiting \"corridor oasis\" characteristics. The Kashgar River Basin comprises six rivers: Kezi, Gaizi, Kushan, Aigziya, Chakmak, and Buguz rivers. Among these, the Kezi, Gaizi and Kushan rivers are the main tributaries, accounting for 91% of the average annual runoff of the Kashgar River Basin [23].