Proportion of vegetated area in the dominant desert and grassland biomes of the Mongolian Plateau covered by < − 1 standardized anomalies of EVI and EVI2 during June–July–August (JJA) in summer and January–February (JF) land surface temperature anomalies in winter

Table 2. 
Proportion of vegetated area in the dominant desert and grassland biomes of the Mongolian Plateau covered by < − 1 standardized anomalies of EVI and EVI2 during June–July–August (JJA) in summer and January–February (JF) land surface temperature anomalies in winter. Summer droughts of 2001 and 2009 and dzud of 2010 are highlighted in bold.

Abstract
Climate change has led to more frequent extreme winters (aka, dzud) and summer droughts on the Mongolian Plateau during the last decade. Among these events, the 2000–2002 combined summer drought–dzud and 2010 dzud were the most severe on vegetation. We examined the vegetation response to these extremes through the past decade across the Mongolian Plateau as compared to decadal means. We first assessed the severity and extent of drought using the Tropical Rainfall Measuring Mission (TRMM) precipitation data and the Palmer drought severity index (PDSI). We then examined the effects of drought by mapping anomalies in vegetation indices (EVI, EVI2) and land surface temperature derived from MODIS and AVHRR for the period of 2000–2010. We found that the standardized anomalies of vegetation indices exhibited positively skewed frequency distributions in dry years, which were more common for the desert biome than for grasslands. For the desert biome, the dry years (2000–2001, 2005 and 2009) were characterized by negative anomalies with peak values between −1.5 and −0.5 and were statistically different (P < 0.001) from relatively wet years (2003, 2004 and 2007). Conversely, the frequency distributions of the dry years were not statistically different (p < 0.001) from those of the relatively wet years for the grassland biome, showing that they were less responsive to drought and more resilient than the desert biome. We found that the desert biome is more vulnerable to drought than the grassland biome. Spatially averaged EVI was strongly correlated with the proportion of land area affected by drought (PDSI <− 1) in Inner Mongolia (IM) and Outer Mongolia (OM), showing that droughts substantially reduced vegetation activity. The correlation was stronger for the desert biome (R2 = 65 and 60, p < 0.05) than for the IM grassland biome (R2 = 53, p < 0.05). Our results showed significant differences in the responses to extreme climatic events (summer drought and dzud) between the desert and grassland biomes on the Plateau.

表2. 蒙古高原优势荒漠与草原生物群系内，夏季6-8月（JJA）增强型植被指数（Enhanced Vegetation Index, EVI）与第二代增强型植被指数（EVI2）标准化距平小于-1的植被区域占比，以及冬季1-2月（JF）的地表温度距平。其中2001年、2009年夏季干旱事件与2010年冬灾（dzud）已以粗体标注。

摘要
近十年来，气候变化导致蒙古高原极端冬季气候事件（又名dzud）与夏季干旱事件发生频率显著升高。其中，2000-2002年复合型夏季干旱-冬灾事件与2010年冬灾事件对植被造成的破坏最为严重。本研究以十年平均值为参照，分析了近十年来蒙古高原植被对上述极端气候事件的响应特征。首先，我们借助热带降雨测量任务（Tropical Rainfall Measuring Mission, TRMM）降水数据与帕默尔干旱指数（Palmer Drought Severity Index, PDSI）评估了干旱的严重程度与影响范围；随后，通过绘制2000-2010年期间中分辨率成像光谱仪（Moderate Resolution Imaging Spectroradiometer, MODIS）与甚高分辨率辐射计（Advanced Very-High-Resolution Radiometer, AVHRR）反演的植被指数（EVI、EVI2）及地表温度距平图，分析了干旱对植被的影响。研究发现，干旱年份的植被指数标准化距平呈正偏态分布，且该特征在荒漠生物群系中较草原生物群系更为显著。对于荒漠生物群系，干旱年份（2000-2001年、2005年与2009年）的植被指数距平为负值，峰值区间介于-1.5至-0.5之间，且与相对湿润年份（2003年、2004年与2007年）的距平分布存在统计学意义上的显著差异（P<0.001）。与之相反，草原生物群系的干旱年份距平分布与相对湿润年份无统计学差异（P<0.001），表明草原植被对干旱的响应更为迟钝，且相较于荒漠植被具有更强的恢复力。本研究证实，荒漠生物群系较草原生物群系对干旱更为脆弱。空间平均增强型植被指数与内蒙古（Inner Mongolia, IM）及外蒙古（Outer Mongolia, OM）受干旱影响（PDSI<-1）的土地面积占比呈显著相关关系，表明干旱事件会显著降低植被活动强度。其中，荒漠生物群系的相关强度（决定系数R²分别为65与60，P<0.05）高于内蒙古草原生物群系（决定系数R²=53，P<0.05）。本研究结果表明，蒙古高原的荒漠与草原生物群系对极端气候事件（夏季干旱与冬灾）的响应特征存在显著差异。