## 2 Materials and Methods  
### Climatic and Geodemographic Characteristics of the Study Area  
Mongolia has a territory of 1.56 million km\({}^{2}\) and encompasses diverse types of steppe land, with varied regional climates and topographic gradients [23] (Figure 1a). The country is composed of 21 _aimags_, which are divided further into about 330 _soums_; a _soum_ is the lowest administrative unit from which livestock census data are available. Major mountain ranges (e.g., the Altai and Sayan Range in the northwest, the Khangai Range in the central region, and the Great Hingan Range in the east) intercept moisture, resulting in rain shadow regions in the west, south, and southeast [21]. Precipitation decreases gradually from the northern to the southern territory, where forest steppe, typical steppe, desert steppe, and desert occur in turn; vegetation production and biodiversity are positively correlated with precipitation [3; 27; 28].  
Moisture in the Mongolian Plateau mainly comes from the North Atlantic Ocean and Western Pacific Ocean [29; 30]. The relative contributions of the two oceans are different in the west and east, being greatly influenced by the North Atlantic and Western Pacific Oceans, respectively. Moisture originates from the Pacific Ocean flows westward to the plateau against westerly winds, entangled in the whirlpools of high and low pressures that occur; then, it migrates and disappears in mid-latitude Northeast Asia. The Great Hingan Mt. Range blocks moisture blowing in from the Pacific Ocean, forming a rain shadow on the southeast Mongolian Plateau on the west side of the mountain range. Despite its remote location, moisture from the North Atlantic Ocean moves as far east as Siberia and the drylands of East Asia with the aid of westerly winds through repeated precipitation and evaporation [31]. Moisture that flows mainly from the northwest of the plateau via Siberia is intercepted by the Altai, Sayan, and Khangai mountain ranges, forming huge rain shadows in Western and Southern Mongolia.  
Livestock numbers increased from 25.7 to 76.9 million between 1992 and 2018 across Mongolia [22]. The livestock number and density were particularly high in the north-central region of Mongolia (Figure 1b,c). Since the early 1990s, two episodic countrywide _Dzud_ events have occurred: one from 1999 to 2002 and one from 2009 to 2010, each resulting in more than 20% livestock mortality [8; 33]. The catastrophic 1999-2002 _Dzud_ called great attention to international, government, and individual harder efforts to improve pasture and livestock management and risk preparedness [11]. After the 1999-2002 _Dzud_, the national herd of Mongolia steadily grew until 2009 before dropping sharply with the 2010 _Dzud_. The period from 2003 to 2010 may therefore be considered a _Dzud_-recovery-_Dzud_ cycle. This study focused on that period and tried to characterize the climatic and biotic factors regulating the recovery process and causing the 2010 _Dzud_. This temporal limit reduces complexity in dealing with multiple _Dzud_ phenomena because each _Dzud_ can be triggered by temporally different factors [1].  
Figure 1: Maps of (**a**) Sentinel land cover of Mongolia (credit: Impact Observatory, Microsoft, and Esri) with major mountainous ranges and (**b**) livestock numbers (sheep unit, \(\times\) 10,000) and (**c**) density (sheep unit per ha) in 2009. In (**a**), altitude (DEM) is expressed in shading, and the red lines are approximate boundaries between the desert scope (DS), typical steppe (TS), and forest steppe (FS), modified from Tuvshintogtokh [32]. The black (**a**) and grey (**b,c**) lines are boundaries of _aimag_ and _soum_ districts, respectively.