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Article

Examining the Characteristics of Drought Resistance Under Different Types of Extreme Drought in Inner Mongolia Grassland, China

by
Jiaqi Han
1,
Jian Guo
1,*,
Xiuchun Yang
2,
Weiguo Jiang
3,
Wenwen Gao
4,
Xiaoyu Xing
2,
Dong Yang
2,
Min Zhang
2 and
Bin Xu
5
1
National Institute of Natural Hazards, Ministry of Emergency Management of China, Beijing 100085, China
2
School of Grassland Science, Beijing Forestry University, Beijing 100083, China
3
State Key Laboratory of Remote Sensing Science, Faculty of Geographical Science, Beijing Normal University, Beijing 100875, China
4
School of Hydro Science and Engineering, Taiyuan University of Technology, Taiyuan 030024, China
5
Institute of Agricultural Resources and Regional Planning, Chinese Academy of Agricultural Sciences, Beijing 100081, China
*
Author to whom correspondence should be addressed.
Remote Sens. 2025, 17(18), 3229; https://doi.org/10.3390/rs17183229
Submission received: 8 July 2025 / Revised: 22 August 2025 / Accepted: 29 August 2025 / Published: 18 September 2025
(This article belongs to the Section Remote Sensing in Agriculture and Vegetation)
Browse Figures
Versions Notes

Abstract

Highlights

What are the main findings?
  • Meadow and desert regions exhibited relatively higher resistance, while steppes showed lower resistance, possibly influenced by their climatic zones.
  • Grassland has been significantly inhibited by two-year continuous extreme drought, while exhibited varying degrees of increased resistance to discontinuous extreme drought.
What is the implication of the main finding?
  • The management departments should pay more attention to central regions where low-resistance steppe grasslands are distributed, while striving to maintain ecosys-tem stability in western and eastern regions with high resistance.
  • By increasing the proportion of drought-resistant plants may be an effective way in reaction to future extreme drought scenarios.

Abstract

Extreme drought events may become more frequent with climate change. Understanding the impact of extreme drought on grassland ecosystems is therefore crucial for the long-term sustainability of ecosystems. Here, we identified extreme drought events in the Inner Mongolia grasslands of China using long-term standardized precipitation evapotranspiration index (SPEI) data and evaluated drought resistance of the vegetation under extreme drought based on net primary production (NPP). The impact of consecutive extreme drought events and multiple discontinuous one-year extreme drought events on grasslands were further analyzed to investigate the response strategies of different grassland types to different drought conditions. We found that the frequency and area of extreme drought in 2000–2011 were significantly higher than those in 2012–2020, and the Xilingol League region showed the highest frequency of extreme drought events. Under extreme drought, vegetation resistance was positively correlated, where annual precipitation > 300 mm. The mean resistance of different grassland types followed the order: upland meadow (UM) > lowland meadow (LM) > temperate meadow steppe (TMS) > temperate desert (TD) > temperate steppe (TS) > temperate steppe desert (TSD) > temperate desert steppe (TDS). In the analysis of two cases of consecutive two-year extreme drought, all grassland types except TSD and TD showed obvious decreased resistance in the final drought year, with the highest reduction (0.16) in LM during 2010–2011, implying the widespread and significant inhibition of grassland growth by continuous drought. However, under the multiple discontinuous extreme drought events, the resistance of all grassland types showed a fluctuating but an overall increasing trend, suggesting the adaptability of grassland to drought. The results emphasize that management departments should pay more attention to regions with low resistance and enhance the stability of grassland production by increasing the proportion of drought-resistant plants in reaction to future extreme drought scenarios.

1. Introduction

Grasslands occupy 40% of the land area in the world and provide vital ecological functions such as primary production, water retention and regulation, erosion and dust control, and biodiversity conservation [1,2,3]. Over the past two decades, global climate change has increased the frequency, intensity, and duration of drought events [4,5]. Drought has become one of the most severe natural disasters in the world [6,7] and has an impact on the functioning and stability of terrestrial ecosystems [8], especially grassland ecosystems [9]. Therefore, in a scenario where extreme drought may continue to intensify in the future, investigating the response of grassland vegetation to extreme drought is crucial [10].
The stability of plant communities is a comprehensive characteristic of plant structure and function, mainly focusing on the response of vegetation to disturbances, directly related to the provision of ecosystem services [11]. Resistance is one of the suitable indicators that characterize community stability, describing the ability of plant communities to maintain their original structure and function after external disturbances [12]. Extreme drought events significantly impact the structure and function of plant communities [13]. The impact of extreme drought on vegetation growth varies in different grassland ecosystems [14]. Different grassland types have different climates due to their different locations. And there are also differences in grassland community and structure. Identifying ecologically vulnerable areas and grassland types affected by extreme drought helps provide crucial scientific evidence for government efforts to strengthen the protection of these vulnerable ecosystems under increasingly severe drought conditions in the future.
Drought resistance has usually been studied based on site experiments or satellite monitoring. On a site scale, studies typically involved manipulations such as reducing growing season precipitation [15] and reducing soil moisture [16] to simulate extreme drought and investigated the resistance of multiple species at sites, such as the shortgrass prairie in central-northern Colorado, USA [17], and the Erguna grassland in Inner Mongolia, China [18]. Remote sensing data provides an advanced way to monitor vegetation growth on a large scale [19]. Drought resistance has also been explored using long-term drought index data, which is more in line with macroscopic reality. Research on drought resistance has been conducted in the grasslands of China [20], Kansas, the USA [15], and the Tibetan Plateau [21]. Most of the current research on resistance has been based on one-year extreme drought or multi-year extreme drought on a site scale, but little is known about the impact of two-year continuous extreme drought or multi-year discontinuous drought on a large scale and over a long time. Therefore, it is essential to utilize long-term satellite data to investigate resistance under different large-scale extreme drought patterns.
In this study, we selected the grassland ecosystem of Inner Mongolia as the study area, which has various climate zones and grassland types. Firstly, we used the standardized precipitation evapotranspiration index (SPEI) to identify extreme drought events and analyze their spatial and temporal characteristics from 2000 to 2020. Secondly, we calculated the drought resistance under extreme drought conditions using net primary productivity (NPP) and compared the differences in drought resistance among the different grassland types under one-year extreme drought conditions. Finally, we investigated the characteristics of resistance under two-year continuous and discontinuous extreme drought in different grassland types.

2. Materials and Methods

2.1. Study Area

This study was conducted in Inner Mongolia, China, where the climate ranges from arid in the west to semi-arid and semi-humid in the east. The distribution of different grassland types, including temperate desert (TD), temperate steppe desert (TSD), temperate desert steppe (TDS), temperate steppe (TS), and temperate meadow steppe (TMS), varies significantly from west to east. Additional grassland types include lowland meadow (LM) and upland meadow (UM) (Figure 1). In this study, grasslands were categorized into three main types: meadow (LM and UM), steppe (TMS, TS, and TDS), and desert (TSD and TD). Table 1 shows the vegetation characteristics of different grassland types [22]. The climatic and vegetation diversity in this region makes it an ideal area for investigating the impact of extreme drought on grassland vegetation. During the period from 2000 to 2010, grasslands in this region experienced severe overgrazing, leading to varying degrees of degradation. Since 2010, China has implemented grassland subsidy policies, resulting in the partial restoration of these ecosystems. To eliminate the impact of any variation in grassland extent, only grassland areas untouched from 2000 to 2020 were included in this study. The land use/land cover data were obtained from the Resource and Environment Science and Data Center, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Science, which provides nationwide remote sensing data of land use types (https://www.resdc.cn/DOI/DOI.aspx?DOIID=54 (accessed on 29 August 2025)) with a spatial resolution of 1 km. The grassland classification dataset is based on the 1:1,000,000 Vegetation Atlas of China [23].

2.2. Data Source and Data Processing

2.2.1. SPEI Data

Drought events are typically identified based on a range of drought indices, including the Palmer drought severity index [24], standardized precipitation index (SPI) [25], and SPEI [26,27]. Previous studies have shown that drought exerts cumulative effects on plants [28,29]. The SPEI, calculated at different time scales, integrates information on water balance (i.e., the difference between precipitation and potential evapotranspiration) for both the current month and the preceding months [30]. Consequently, SPEI values across different time periods are effective for quantifying large-scale and long-term drought conditions, especially in semi-arid and arid regions [31,32]. The SPEI data [26,27,30] were obtained from the global SPEI dataset, which was provided by the Climatic Research Unit of the University of East Anglia (http://sac.csic.es/spei/database.html (accessed on 29 August 2025)). This SPEI data provides a spatial resolution of half degree and a temporal resolution of one month. Vicente-Serrano [33] indicated that grassland vegetation activity in semi-arid regions was closely related to SPEI with short-term scales (3–6 months). The growing season of grassland vegetation in Inner Mongolia spans from June to August, coinciding with the peak annual precipitation. Therefore, SPEI data for June–August over 20 years (2000–2020) were chosen for the analysis. Based on the SPEI values, the climate conditions were classified into seven categories: extreme drought (SPEI ≤ −2), severe drought (−2 < SPEI ≤ −1.5), moderate drought (−1.5 < SPEI ≤ −1), near normal (−1 < SPEI ≤ 1), moderate wet (1 < SPEI ≤ 1.5), severe wet (1.5 < SPEI ≤ 2), and extreme wet (SPEI > 2) [34,35].

2.2.2. NPP Data

Most grasslands in northern China are located in arid and semi-arid regions, where precipitation serves as the primary limiting factor for the ecological processes of semi-arid grassland ecosystems, particularly NPP [36]. Grassland ecosystem functions, such as NPP and other aspects of carbon cycling, are particularly sensitive to precipitation changes in these regions [37]. In this study, NPP was selected as an indicator of vegetation growth. The NPP remote sensing data were derived from the Global Land Surface Satellite (GLASS) product suite (http://www.glass.umd.edu/ (accessed on 29 August 2025)), which provides data at a spatial resolution of 500 m and a temporal resolution of 8 days. The annual NPP data of 2000–2020 were downloaded and resampled to a 1 km spatial resolution using ArcGIS 10.4.

2.2.3. Meteorological Data

Temperature and precipitation data were obtained from two high-resolution datasets, the 1 km monthly mean temperature dataset (1901–2021) [38] and precipitation dataset (1990–2021) [39], respectively. The multi-year average values were calculated from the annual temperature and precipitation from 2000 to 2020.

2.3. Grassland Drought Resistance Calculation

Grassland drought resistance is usually defined as the ratio of NPP during extreme drought to NPP in the previous year [40]. However, previous studies indicate that the moisture conditions of the previous year may have a legacy effect on current year vegetation growth [41]. To account for potential deviations caused by extreme drought conditions in the preceding year, the ratio of NPP during extreme drought periods to the average NPP across multiple normal years (defined as −1 < SPEI ≤ 1) was calculated using the following equation:
R E S = N P P d r o u g h t N P P m e a n ,
where R E S represents grassland resistance under extreme drought, N P P d r o u g h t represents the NPP in the extreme drought year, and N P P m e a n represents average NPP during multiple years of normal growth (2000–2020) (−1 < SPEI ≤ 1).

2.4. Statistical Analysis Method

Statistical analysis was performed using SPSS 25.0 (SPSS, Chicago, IL, USA). We employed analysis of variance (ANOVA) to assess differences in drought resistance between multiple extreme drought years (n > 2) or between different grassland types. For comparisons involving exactly two extreme drought years (n = 2), Student’s t-tests were used. For all analyses, results were considered statistically significant at p  <  0.05,with standard errors calculated by SPSS 25.0. All graphical representations in this paper were plotted using Origin 2023 (OriginLab Corporation, Northampton, MA, USA).

2.5. Research Framework

The research framework for the key indicators’ computation and statistical analysis is displayed in Figure 2. We identified extreme drought events in the Inner Mongolia grasslands of China using long-term SPEI data and evaluated the drought resistance of the vegetation under extreme drought conditions based on NPP data. Then, we compared the resistance differences among the different grassland types under one-year extreme drought conditions. Finally, we investigated the characteristics of resistance under two-year continuous and discontinuous extreme drought in different grassland types.

3. Results

3.1. Characteristics of Resistance Under One-Year Extreme Drought

3.1.1. Spatial and Temporal Distribution of Area Under Different Climate Categories

In the period 2000 to 2020, the region exhibited a distinct temporal pattern in extreme drought conditions, characterized by an initial expansion phase that peaked around 2010, followed by a subsequent decline (Figure 3). The most severe drought years occurred during 2007 and 2010, when extreme drought affected 64.8% and 68.4% of the total area, respectively, while 2005 ranked third with 39.7% coverage. Notably, several years, including 2003, 2006, and 2008, remained completely free from extreme drought conditions. After 2012, the drought-affected area gradually decreased, with 2016 and 2017 recording 22.2% and 19.5% coverage, respectively, while wet conditions became increasingly prevalent, particularly during 2012, 2013, and 2018–2020. The year 2013 marked an exceptional climatic event when the Hulun Buir region experienced the only extreme precipitation episode of the entire 21-year period. The period from 2004 to 2010 was especially drought-prone, with five of seven years experiencing drought coverage exceeding 20%, especially in 2007 and 2010, with over 60% of the area affected by extreme drought (the highest recorded during the entire study period).

3.1.2. Characteristics of Resistance to One-Year Extreme Drought

The drought resistance of vegetation is highly correlated with the water and heat conditions of its habitat. Bivariate analysis of resistance against annual mean temperature (at 0.1 °C intervals) and precipitation (at 10 mm intervals) revealed threshold responses under extreme drought (Figure 4). As the temperature gradient increased, resistance initially decreased from 0.92 at −5.7 °C to a minimum of 0.72 at 2 °C and then increased to 0.83 at 9.7 °C. The precipitation response showed more pronounced nonlinearity, with resistance initially decreasing from 0.82 at 40 mm to 0.73 at 305 mm, then rebounding sharply to 0.90 at 570 mm, suggesting the existence of critical thresholds in both the temperature and precipitation regimes that govern drought adaptation strategies.
Under extreme drought conditions, vegetation drought resistance showed differential responses to the annual mean temperature and precipitation among grassland types (Figure 5). Grasslands with higher precipitation (UM: RES = 0.84; LM: RES = 0.80; TMS: RES = 0.78), as well as grasslands with lower precipitation (TD: RES = 0.77), were less affected by extreme drought, while grasslands with moderate precipitation (TS: RES = 0.74; TDS: RES = 0.71) showed greater vulnerability. The resistance of LM, TDS, and TSD initially decreased and then increased with an increase in precipitation, with the lowest resistance corresponding to 238 mm, 265 mm, and 225 mm of precipitation, respectively. UM, TMS, and TS showed an increase in resistance as precipitation increased, while TD was the only grassland where resistance decreased with an increase in annual precipitation. In LM, UM, TS, and TDS, resistance initially decreased and then increased as the annual mean temperature increased, with the lowest resistance corresponding to 1.85 °C, 1.29 °C, 5.64 °C, and 5.64 °C, respectively. The resistance of TMS showed a decreasing trend when the annual mean temperature increased up to 1 °C but showed no clear pattern when the temperature exceeded 1 °C. As the annual mean temperature increased, the resistance of TSD showed a slow decreasing trend, while that of TD showed the opposite trend.

3.2. Characteristics of Resistance in Areas Under Two-Year Continuous Extreme Drought

3.2.1. Distribution Characteristics of Two-Year Continuous Extreme Drought

During the period from 2000 to 2020, a total of five two-year continuous extreme drought events were recorded (Figure 6), with the largest affected areas occurring in 2009–2010 (13.1% of the study area) and 2010–2011 (10.5%), while the remaining three events (2001–2002, 2004–2005, and 2016–2017) each affected less than 3% of the region. This study primarily focused on the two most severe extreme drought events, which had the largest areas. The 2009–2010 extreme drought event mainly affected the western part of Alxa League, Bayannur League, Baotou City, and Chifeng City and parts of Xilingol League, while the 2010–2011 events mainly occurred in the western part of Xilingol League, with limited impacts near the border regions of Alxa League and Ordos City.
Analysis of the extreme drought distribution across grassland types showed that the largest area of extreme drought in 2009–2010 was mainly in TS, TDS, and TMS, while the subsequent 2010–2011 occurrence was primarily in TS, TDS, and TSD. Continuous drought events during these three years were negligible.

3.2.2. Characteristics of Resistance to Two-Year Continuous Extreme Drought

During the 2009–2010 drought event, all grassland types exhibited varying degrees of resistance decline, with notable differences between the first and second drought years, except UM (which also showed remarkable differences between years but increased resistance) (Figure 7a). In the initial drought year (2009), desert-type grasslands demonstrated superior resilience, with TD, TSD, and TDS showing the highest resistance values of 0.90, 0.87, and 0.81, respectively. The remaining four grassland types clustered within a narrow resistance range of 0.75–0.77. In the second year, most grassland types showed a significant reduction in resistance. The most substantial declines occurred in desert grasslands, with TD, TSD, and TDS decreasing by 0.08, 0.11, and 0.10, respectively. TS showed a more moderate reduction (0.06), while LM and TMS were able to maintain their resistance levels from the previous year, with only a slight decrease of 0.04 and 0.02, respectively. Notably, UM was the sole grassland type that actually increased its resistance (+0.03) during the study period, suggesting unique adaptive mechanisms in this ecosystem. Similarly, during the 2010–2011 drought event, LM and TDS showed higher resistance in the first year of extreme drought (0.91 and 0.85, respectively), while TDS, TSD, and TD had lower resistance (0.76, 0.76, and 0.79, respectively) (Figure 7b). Both meadow and steppe types (LM, TS, and TDS) showed varying degrees of reduction in resistance in the second year, particularly in LM, which had the highest reduction of 0.16, followed by TS (0.11) and TDS (0.06). In western desert areas with low moisture, a slight increase in resistance to extreme drought was observed in the second year, with TSD and TD both increasing slightly.

3.3. Characteristics of Resistance in Areas Under Discontinuous Extreme Drought

3.3.1. Eastern Part of Inner Mongolia

Hulun Buir was selected as a representative area of the eastern part of Inner Mongolia, with mainly TMS, TS, LM, and UM, among which UM is distributed only in the Hulun Buir region. In this region, three extreme drought events occurred over 21 years (in 2004, 2007, and 2016), with large areas affected each time. In the first extreme drought event of 2004, LM, UM, and TMS showed higher resistance (RES = 0.81, 0.90, and 0.83, respectively), while TS showed the lowest resistance (RES = 0.69) (Figure 8). The year 2005 experienced moderate drought, and 2006 was a normal year. During the second extreme drought event of 2007, the resistance of all species decreased slightly (by 3.75% for LM, 2.24% for TS, 11.20% for TM, and 12.78% for TMS). During the period from 2008 to 2015, the region experienced a normal climate or moderate drought; however, the only extremely high precipitation event was recorded in 2013. When extreme drought occurred again in 2016, the resistance of vegetation increased significantly to values slightly higher than 1, and the vegetation was almost unaffected by extreme drought, marking a significant improvement compared with the previous two drought events.

3.3.2. Central Part of Inner Mongolia

Xilingol League was selected as a representative area of the central part of Inner Mongolia, with mainly TMS, TS, and TDS. This region experienced a total of four major extreme droughts in 21 years (in 2005, 2007, 2010, and 2017), along with moderate to severe wet conditions in 2012. In areas with less precipitation, grassland showed lower resistance (TDS, 0.59; TS, 0.62) under the first extreme drought event. The climate in 2006 was normal. In 2007, an extreme drought event was recorded, which was significantly worse than the drought in 2005. The resistance in TDS increased by 34.42%, and that in TSD increased by 50.72%. The climate in 2008 was normal, while 2009 was in a state of moderate and severe drought. In the extreme drought event of 2010, the resistance decreased significantly compared with that in 2007, but was still higher than that in 2005. The resistance in TDS and TSD decreased by 17.70% and 21.05%, respectively. During the period from 2011 to 2016, moderate and severe wetness was recorded in 2012 and drought was recorded in 2011, 2014, and 2015, while 2013 and 2016 were normal years. In 2017, resistance to extreme drought increased significantly, exceeding 0.8 (Figure 9). The resistance of TS and LM was relatively stable, ranging from 0.73 to 0.83, with small fluctuations. Despite 2010 being the year with the most severe extreme drought in 21 years, the resistance of LM and TS did not change significantly. Resistance can reach 0.73 and 0.78 when drought occurs for the first time, which is much higher than the resistance of TSD and TDS. In the following three extreme drought events, resistance fluctuated upwards. The results obtained in this region suggest that after experiencing multiple extreme drought events, the drought resistance of all grassland types in Xilingol League can reach a high level (>0.8).

3.3.3. Western Part of Inner Mongolia

In the representative areas of western Inner Mongolia, including Alxa League, Bayannur City, and Ordos City, where precipitation is relatively low, the main grassland types are TDS, TSD, and TD. The area experienced extreme drought in 2005 and 2010, with a notable gradual reduction in drought extent observed annually since 2011. During the first extreme drought event of 2005, TS showed the highest resistance (0.74), followed by temperate desert (0.70), TDS (0.56), and TSD (0.59) (Figure 10). In the second extreme drought event, the resistance of TS showed a slight but significant change, while that of TSD, TDS, and TD increased significantly by 22.25%, 28.56%, and 17.38%, respectively. In the area with the least precipitation in 2010, TD had the strongest resistance (0.82), while the resistance of the other three types of grasslands ranged from 0.72 to 0.76, all of which were high.

4. Discussion

4.1. Characteristics of Extreme Drought Resistance from 2000 to 2020

In recent years, the frequency and intensity of extreme drought have increased significantly on a global scale because of climate change [42]. The results showed that the frequency and scope of extreme drought in Inner Mongolia were high in the first 12 years, but the probability of extreme drought decreased significantly in the following 9 years, while humid conditions increased significantly. This result was different from the latest report in terms of a short-term time scale [42]. In recent decades, because of overgrazing and rapid urbanization, the desert area has continued to expand [43]. During the period from 2000 to 2011, Inner Mongolia experienced severe overgrazing, together with severe grassland degradation. These land-use changes have led to significantly increased evaporation, which may lead to greater influence of extreme drought. Since 2011, China has implemented a grassland subsidy policy in Inner Mongolia, with a cumulative investment of CNY 45.5 billion over the past 10 years. Consequently, grassland vegetation cover has shown an increasing trend, and some reduction in grassland degradation has been observed. The implementation of the subsidy policy has improved vegetation to a certain extent while reducing the influence of extreme drought.
The probability of extreme drought events in the arid and semi-arid regions of western and central Inner Mongolia was higher than that in the humid eastern region, which was consistent with the results of a previous study [44]. Recent research showed that the SPEI in northeastern Inner Mongolia had been on a long-term upward trend, with no drought, which was consistent with the results of this study. The central area of Inner Mongolia experienced the most frequent extreme drought events, with large-scale extreme drought in 4 of the last 21 years. According to Wang, Liu, and Guo [44], the central region of Inner Mongolia displayed the largest variation in drought indices and was the most susceptible to extreme drought. In the current study, the drier the area, the more likely it was to experience extreme drought for two continuous years, which was consistent with previous research [44].

4.2. Characteristics of Resistance in Different Grassland Types

4.2.1. One-Year Extreme Drought

In this study, resistance in steppe- and meadow-type grasslands was positively correlated with precipitation under extreme drought. Experimental results from 64 different locations distributed worldwide demonstrated that the resistance of grassland ecosystems to extreme drought was positively correlated with annual precipitation [14]. This was consistent with previous research on grassland ecosystems [45]. Compared with wet grassland ecosystems, relatively dry grassland ecosystems are more limited by water availability [46] and therefore are more sensitive to extreme drought [45]. However, the resistance of TD was around 0.8, which was as high as that of the most humid LM and UM. This may be because plants evolve drought-tolerant strategies when living in long-term water-deficient environments [47].
In this study, the resistance of Erguna grassland was slightly higher than the experimental results [18]. Erguna is located in the transitional zone between grassland and forest ecosystems in northeastern Inner Mongolia, with high species richness and strong resistance to extreme drought. In the warm grasslands of Xilingol League, the resistance under extreme drought was 0.65, according to the experimental results of the Stipa grandis plot, while the average resistance of TS in this study was 0.74, which was higher than the experimental results. The experimental results showed that the biomass of Poaceae plants did not change under extreme drought, while the biomass of non-Poaceae plants decreased by more than 33% [18]. The resistance calculation in this study had certain limitations. This study was based on 1 km resolution NPP data, which differs significantly from the 1 m resolution in experiments. The study primarily revealed resistance at the regional scale, which may introduce some errors when investigating extreme droughts occurring in small and discontinuous areas. Additionally, different grassland types had significant variations in vegetation cover and NPP. Using a multi-year normal NPP as background values for resistance calculation may introduce some errors, especially in the case of TD and TSD, where NPP values are relatively small.

4.2.2. Two-Year Continuous Extreme Drought

The resistance of most grassland types in the second year was lower than that in the first year. Areas with more precipitation showed higher resistance, and the resistance decreased in the second year. This is consistent with the results of plot experiments. In 2010–2011, two desert types showed higher resistance in the second year during extreme drought, possibly because of the adaptation of vegetation to extreme drought conditions.
Dominant species are better able to utilize resources than non-dominant species, which ensures their higher stability when facing environmental disturbances or climate change [48,49]. The results of site experiments in a previous study showed that the cumulative effect of multiyear extreme drought on vegetation NPP is mainly caused by changes in non-dominant species [18]. In humid grassland areas, species richness is higher, and the proportion of dominant species is lower. After continuous extreme drought events, the productivity of dominant species decreases less than that of non-dominant species. Dominant species, which have higher resistance, usually belong to the Poaceae family.

4.2.3. Discontinuous Extreme Drought

Previous studies on moist grasslands show that NPP can recover to control levels just one year after the end of an extreme drought [50], suggesting that vegetation productivity usually recovers to normal levels in the year after an extreme drought. In the Hulun Buir region, during the extreme drought in 2004, LM, UM, and TMS showed relatively high resistance, while TS showed lower resistance. After the extreme drought stopped for two years, the resistance of LM and TS showed no significant change in 2007, indicating that these grasslands could recover to normal levels after the extreme drought, and their resistance could maintain the previous level in 2005, when a later extreme drought occurred. However, the resistance of UM and TMS decreased slightly during the second extreme drought event. UM comprises perennial grass species that may not recover to normal levels in the short term after an extreme drought, which reduces their ability to withstand another extreme drought event. In the Xilingol region, LM and TS were less affected by extreme drought, similar to the results obtained in the Hulun Buir region. In the western region, when extreme drought occurs again, TDS, TSD, and TD could adapt better and show higher resistance. This may be the result of arid areas adapting to extreme drought.

4.3. Factors Influencing Resistance Under Extreme Drought

Moisture is the most important factor determining the occurrence of extreme drought and a significant factor affecting the aboveground biomass (AGB) of grassland ecosystems [51]. The impact of extreme drought on AGB varies in different grassland ecosystems [14], which is consistent with the findings of this study. As annual precipitation increased, the resistance of desert-steppe-meadow (west to east) showed a high–low–high pattern. Under extreme drought, wet grassland ecosystems exhibit higher resistance than dry grassland ecosystems, owing to their higher soil moisture content, which may result in higher resistance to extreme drought [14,45]. However, plants in dry desert ecosystems have probably adapted to dry environments and thus may have higher resistance to extreme drought than those in wet grassland ecosystems [52], which is consistent with the findings of this study.
In addition to precipitation, soil moisture plays an important role in vegetation growth. With an increase in the duration of extreme drought, the resistance of different ecosystems changes, possibly because of the reduction in soil moisture content [53]. In meadow ecosystems, where soil moisture is relatively high, resistance did not change significantly after two years of continuous extreme drought, possibly because soil moisture remains at the same level or decreases only slightly. In steppe and desert ecosystems, soil moisture was relatively low, and continuous extreme drought events could cause a significant reduction in soil moisture, leading to a decline in drought resistance in the second year. The negative impact of extreme drought in this region may have a cumulative effect, with resistance decreasing as the duration of extreme drought increases [16]. This study has some limitations, as it did not consider the propagation pattern of extreme drought. Drought propagation refers to the transmission process of drought signals through atmospheric, soil, and hydrological systems, characterized by a time-lag effect; that is, soil or hydrological droughts typically occur later than meteorological droughts. The SPEI is a meteorological drought indicator that directly reflects the severity of meteorological drought. However, when the SPEI indicates extreme drought, the soil may not yet have reached an extreme drought state, while the condition of soil moisture is directly related to grassland growth. Therefore, further in-depth analysis from the perspective of soil drought is necessary.

5. Conclusions

In this study, we explored the characteristics of grassland resistance under one-year extreme drought, two-year continuous extreme drought, and discontinuous extreme drought. The primary conclusions are as follows:
The spatial extent of extreme drought exhibited distinct temporal dynamics during the 2000–2020 period, characterized by an initial expansion phase that reached its maximum coverage around 2010–2011, followed by a consistent decline after 2012.
  • Meadow and desert regions exhibited relatively high resistance (0.77~0.84), while steppes showed lower resistance (0.71~0.74), possibly influenced by their climatic zones.
  • Continuous drought generally hinders grassland growth, as evidenced by all grassland types experiencing a decline in resistance in the final year compared to the initial, except TSD and TD.
  • Grassland that experienced discontinuous extreme drought exhibited varying degrees of increased resistance. During the final extreme drought events across the respective regions, all grassland types in the eastern regions demonstrated resistance exceeding 1.0, while central areas surpassed 0.8 and western zones maintained values above 0.7, which bodes well for enhancing vegetation stability under future extreme droughts.
These findings have crucial implications for the evaluation of extreme drought impacts on grasslands. Overall, we suggest that management should pay more attention to central regions where low-resistance steppe grasslands are distributed, while striving to maintain ecosystem stability in western and eastern regions with high resistance. This may enhance the stability of biomass production in a future climate with longer and more intense extreme droughts.

Author Contributions

Conceptualization, J.H. and J.G.; methodology, J.H. and J.G.; software, J.H., W.G. and X.X.; validation, J.G., X.Y. and W.J.; formal analysis J.H. and J.G.; investigation, J.H. and J.G.; resources, J.H. and J.G.; data curation, J.H., X.X., D.Y. and M.Z.; writing—original draft preparation, J.H.; writing—review and editing, J.H., J.G., X.Y., W.J. and B.X.; visualization, J.H. and J.G.; supervision, J.G.; project administration, J.G.; funding acquisition, X.Y. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the Research grants from National Institute of Natural Hazards, Ministry of Emergency Management of China (ZDJ2024-27).

Data Availability Statement

Dataset available on request from the authors.

Acknowledgments

We are also grateful to the Data Center for Resources and Environmental Sciences, Chinese Academy of Sciences (RESDC) (https://www.resdc.cn/DOI/DOI.aspx?DOIID=54 (accessed on 29 August 2025)). We thank the editor and anonymous reviewers of the journal for their valuable comments and suggestions, which helped improve this paper.

Conflicts of Interest

The authors declare no conflicts of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

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Figure 1. Geographical maps of Inner Mongolia showing various administrative divisions and the distribution of different grassland types.
Figure 1. Geographical maps of Inner Mongolia showing various administrative divisions and the distribution of different grassland types.
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Figure 2. Research framework used in this study.
Figure 2. Research framework used in this study.
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Figure 3. Proportion of area under different climate categories.
Figure 3. Proportion of area under different climate categories.
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Figure 4. Effect of changes in precipitation and temperature on resistance to extreme drought. (a,b) Effect of precipitation (a) and temperature (b) gradients.
Figure 4. Effect of changes in precipitation and temperature on resistance to extreme drought. (a,b) Effect of precipitation (a) and temperature (b) gradients.
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Figure 5. Average multi-year resistance of vegetation to extreme drought for one year. Different capital letters indicate significant (p < 0.05) differences in resistance between grassland types. Error bar represents ±1 standard error. Grassland types include upland meadow (UM), lowland meadow (LM), temperate meadow steppe (TMS), temperate steppe (TS), temperate desert steppe (TDS), temperate steppe desert (TSD), and temperate desert (TD).
Figure 5. Average multi-year resistance of vegetation to extreme drought for one year. Different capital letters indicate significant (p < 0.05) differences in resistance between grassland types. Error bar represents ±1 standard error. Grassland types include upland meadow (UM), lowland meadow (LM), temperate meadow steppe (TMS), temperate steppe (TS), temperate desert steppe (TDS), temperate steppe desert (TSD), and temperate desert (TD).
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Figure 6. Spatiotemporal distribution of two-year continuous extreme drought events.
Figure 6. Spatiotemporal distribution of two-year continuous extreme drought events.
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Figure 7. Resistance of different types of grasslands to two-year continuous extreme drought. Different capital letters indicate significant (p < 0.05) differences in resistance between grassland types. Different lowercase letters indicate significant (p < 0.05) differences in resistance between extreme drought years. Error bar represents ±1 standard error. Grassland types include upland meadow (UM), lowland meadow (LM), temperate meadow steppe (TMS), temperate steppe (TS), temperate desert steppe (TDS), temperate steppe desert (TSD), and temperate desert (TD). (a) 2009–2010 drought event. (b) 2010–2011 drought event.
Figure 7. Resistance of different types of grasslands to two-year continuous extreme drought. Different capital letters indicate significant (p < 0.05) differences in resistance between grassland types. Different lowercase letters indicate significant (p < 0.05) differences in resistance between extreme drought years. Error bar represents ±1 standard error. Grassland types include upland meadow (UM), lowland meadow (LM), temperate meadow steppe (TMS), temperate steppe (TS), temperate desert steppe (TDS), temperate steppe desert (TSD), and temperate desert (TD). (a) 2009–2010 drought event. (b) 2010–2011 drought event.
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Figure 8. Resistance in the eastern part of Inner Mongolia under discontinuous extreme drought. Different capital letters indicate significant (p < 0.05) differences in resistance between grassland types. Different lowercase letters indicate significant (p < 0.05) differences in resistance between extreme drought years. Error bar represents ± 1 standard error. Grassland types include upland meadow (UM), lowland meadow (LM), temperate meadow steppe (TMS), and temperate steppe (TS).
Figure 8. Resistance in the eastern part of Inner Mongolia under discontinuous extreme drought. Different capital letters indicate significant (p < 0.05) differences in resistance between grassland types. Different lowercase letters indicate significant (p < 0.05) differences in resistance between extreme drought years. Error bar represents ± 1 standard error. Grassland types include upland meadow (UM), lowland meadow (LM), temperate meadow steppe (TMS), and temperate steppe (TS).
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Figure 9. Resistance in the central part of Inner Mongolia under discontinuous extreme drought. Different capital letters indicate significant (p < 0.05) differences in resistance between grassland types. Different lowercase letters indicate significant (p < 0.05) differences in resistance between extreme drought years. Error bar represents ± 1 standard error. Grassland types include lowland meadow (LM), temperate steppe (TS), temperate desert steppe (TDS), and temperate steppe desert (TSD).
Figure 9. Resistance in the central part of Inner Mongolia under discontinuous extreme drought. Different capital letters indicate significant (p < 0.05) differences in resistance between grassland types. Different lowercase letters indicate significant (p < 0.05) differences in resistance between extreme drought years. Error bar represents ± 1 standard error. Grassland types include lowland meadow (LM), temperate steppe (TS), temperate desert steppe (TDS), and temperate steppe desert (TSD).
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Figure 10. Resistance in the western part of Inner Mongolia under discontinuous extreme drought. Different capital letters indicate significant (p < 0.05) differences in resistance between grassland types. Different lowercase letters indicate significant (p < 0.05) differences in resistance between extreme drought years. Error bar represents ± 1 standard error. Grassland types include temperate steppe (TS), temperate desert steppe (TDS), temperate steppe desert (TSD), and temperate desert (TD).
Figure 10. Resistance in the western part of Inner Mongolia under discontinuous extreme drought. Different capital letters indicate significant (p < 0.05) differences in resistance between grassland types. Different lowercase letters indicate significant (p < 0.05) differences in resistance between extreme drought years. Error bar represents ± 1 standard error. Grassland types include temperate steppe (TS), temperate desert steppe (TDS), temperate steppe desert (TSD), and temperate desert (TD).
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Table 1. Vegetation characteristics of different grassland types.
Table 1. Vegetation characteristics of different grassland types.
Grassland TypeVegetation Life FormDominant Grass SpeciesCoverage
(%)		Group
Upland meadowMesophytic perennial grassesCarex pediformis, Vicia amoena, Sanguisorba officinalis, Calamagrostis epigejos, Bromus inermis80–100meadow
Lowland meadowMesophytic perennial grassesAchnatherum splendens, Agrostis gigantea, Suaeda heteropera, Puccinellia tenuiflora80–95meadow
Temperate meadow steppeMesoxerophytic perennial tufted grasses and root grassesStipa baicalensis, Leymus chinensis, Filifolium sibiricum70–90steppe
Temperate steppeXerophytic perennial tufted grasses, xerophytic short shrubsStipa grandis, Stipa krylovii, Stipa bungeana, Cleistogenes squarrosa, Agropyron cristatum, A. frigida, Caragana sinica40–70steppe
Temperate desert steppeSuper xerophytic semishrubs, shrubs, and xerophytic grassesStipa tianschanica var. klemenzii, Stipa tianschanica var. gobica, Stipa breviflora, Cleistogenes songorica, Artemisia frigida, Allium mongolicum, Allium aflatunense30–40steppe
Temperate steppe desertSuper xerophytic semishrubs, shrubs, and xerophytic grassesSeriphidium gracilescens, Seriphidium terrae-albae, Seriphidium borotalense, Sympegma regelii, Reaumuria soongorica, Anabasis brevifolia, Stipa glareosa20–30desert
Temperate desertExtremely xerophytic short shrubs, short semishrubsLyonia ovalifolia, Salsola laricifolia, Reaumuria songarica, Kalidium foliatum, Artemisia desertorum, Psammochloa villosa0–20desert
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Han, J.; Guo, J.; Yang, X.; Jiang, W.; Gao, W.; Xing, X.; Yang, D.; Zhang, M.; Xu, B. Examining the Characteristics of Drought Resistance Under Different Types of Extreme Drought in Inner Mongolia Grassland, China. Remote Sens. 2025, 17, 3229. https://doi.org/10.3390/rs17183229

AMA Style

Han J, Guo J, Yang X, Jiang W, Gao W, Xing X, Yang D, Zhang M, Xu B. Examining the Characteristics of Drought Resistance Under Different Types of Extreme Drought in Inner Mongolia Grassland, China. Remote Sensing. 2025; 17(18):3229. https://doi.org/10.3390/rs17183229

Chicago/Turabian Style

Han, Jiaqi, Jian Guo, Xiuchun Yang, Weiguo Jiang, Wenwen Gao, Xiaoyu Xing, Dong Yang, Min Zhang, and Bin Xu. 2025. "Examining the Characteristics of Drought Resistance Under Different Types of Extreme Drought in Inner Mongolia Grassland, China" Remote Sensing 17, no. 18: 3229. https://doi.org/10.3390/rs17183229

APA Style

Han, J., Guo, J., Yang, X., Jiang, W., Gao, W., Xing, X., Yang, D., Zhang, M., & Xu, B. (2025). Examining the Characteristics of Drought Resistance Under Different Types of Extreme Drought in Inner Mongolia Grassland, China. Remote Sensing, 17(18), 3229. https://doi.org/10.3390/rs17183229

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