Seasonal Drought Dynamics and the Time-Lag Effect in the MU Us Sandy Land (China) Under the Lens of Climate Change  
[PERSON]  
1 College of Water Conservancy and Civil Engineering, Inner Mongolia Agricultural University,  
Hohhot 010018, China; [EMAIL_ADDRESS] (F.W. ); [EMAIL_ADDRESS] (Y.Z.) [PERSON]  
1 College of Water Conservancy and Civil Engineering, Inner Mongolia Agricultural University,  
Hohhot 010018, China; [EMAIL_ADDRESS] (F.W. ); [EMAIL_ADDRESS] (Y.Z.) [PERSON]  
2  
[PERSON]  
1 College of Water Conservancy and Civil Engineering, Inner Mongolia Agricultural University,  
Hohhot 010018, China; [EMAIL_ADDRESS] (F.W. ); [EMAIL_ADDRESS] (Y.Z.) [PERSON]  
3  
[PERSON]  
1 College of Water Conservancy and Civil Engineering, Inner Mongolia Agricultural University,  
Hohhot 010018, China; [EMAIL_ADDRESS] (F.W. ); [EMAIL_ADDRESS] (Y.Z.) [PERSON]  
1 College of Water Conservancy and Civil Engineering, Inner Mongolia Agricultural University,  
Hohhot 010018, China; [EMAIL_ADDRESS] (F.W. ); [EMAIL_ADDRESS] (Y.Z.) [PERSON]  
5 State Key Laboratory of Desert and Oasis Ecology, Key Laboratory of Ecological Safety and Sustainable Development in Arid Lands, Xinjang Institute of Ecology and Geography, Chinese Academy of Sciences,  
Urumqi 830011, China; [EMAIL_ADDRESS] (Correspondence: [EMAIL_ADDRESS]  
ecotone, large-scale climate change is characterized by reduced rainfall and increased temperatures, leading to land degradation and agricultural disasters [3]; in addition, human activities change the surface circumstances (such as shifting land utilization, water conservancy project regulation and storage) through direct and indirect ways, and then affect the natural processes, such as hydrological cycle processes, and ultimately act on regional drought [4]. Owing to the combined consequences of intense human behavior and changing climate, drought events occur frequently and persist globally, resulting in serious damage to ecosystem services, depletion of surface and groundwater resources, land desertification, and crop yield reduction, which hinders social and economic sustainable development [5]. Research indicates that the worldwide economic damages resulting from drought were assessed to have reached USD 124 billion between 1998 and 2017. The frequency and length of droughts have grown by 29% since 2000, impacting around 1.4 billion individuals [6]. The temperate dry and semi-arid zones are home to the MUSL, one of the most important ecologically sensitive areas and important agricultural production bases in China. Due to the dual constraints of climate change and overgrazing, rainfall in the region is reduced, aggravating desertification and worsening the drought situation [7; 8]. Drought directly causes crop yield reduction in the region and indirectly causes land desertification, further increasing the frequency of extreme climate events such as sandstorms, affecting air quality both inside and outside the region, and adversely affecting the growth of local agriculture and animal husbandry [9; 10]. In addition, MUSL is an important part of the ecosystem of the Loess Plateau, which is crucial for windbreak along with sand fixation and maintaining regional ecological balance [11]. Therefore, it is essential to investigate the mechanism as well as pattern underlying drought development in MUSL. At present, remote sensing has become the main means of drought monitoring, and the drought index is the quantitative expression of drought degree. Numerous researchers have conducted extensive study work with different drought indexes. For example, [PERSON] et al. [12] used the ESTARFM model to extract vegetation temperature condition index (VTCI) from Sentinel-2 as well as low spatial resolution MODIS images. They then analyzed its relationship with the fused VTCI, applying Terra MODIS VTCI metadata. Their findings demonstrate that the fused VTCI drought monitoring ability is better than Terra MODIS VTCI. However, VTCI is susceptible to cloud cover, vegetation type, sensors, and other factors, resulting in reduced reliability.