毛乌素沙地植被物候变化及其对气候的响应

Changes in vegetation phenology and its responses to climatic factors in the Mu Us Desert

【目的】探讨毛乌素沙地植被物候长期趋势特征和年际波动及其与气象因素的关系。【方法】本研究利用2001-2020年的MODIS MOD13Q1归一化植被指数(NDVI),在TIMESAT3.3软件中利用动态阈值法提取毛乌素沙地植被物候指标,包括生长季开始日期(SOS)、生长季结束日期(EOS)和生长季长度(LOS),分析SOS与EOS的长期趋势与年际波动的时间特征和空间分布特征,并利用偏相关性分析法探究其与气温和降水量的关系。【结果】(1)物候指标的多年均值表现出显著的空间变异:SOS平均在第(140±15)天(儒略日),从西到东以及从北向南逐渐提前;EOS平均在第(291±6)天,从北向南逐渐推迟;LOS平均在(151±18)d,从西到东以及从北向南长度逐渐延长。(2)物候指标在研究期内整体趋势:SOS呈现提前趋势(0.58 d/a);EOS呈现推迟趋势(-0.25 d/a);LOS呈现显著延长趋势(0.83 d/a)。物候长期趋势也表现出显著的空间变异,总体上由西向东逐渐变慢。(3)毛乌素沙地植被物候(SOS、EOS)的长期趋势与年际波动都受同样的气象因子影响。毛乌素沙地SOS的长期趋势与年际波动都与季前第一个月的温度与降水呈负相关,EOS的长期趋势与年际波动都与季前第一个月的温度与季前累计降水呈正相关。【结论】随经度和纬度的增加,毛乌素沙地SOS与LOS分别呈现提前和延长的趋势。SOS的提前和EOS的推迟导致LOS呈现延长的趋势,且西部区域LOS延长的速率高于东部区域;SOS与EOS的长期趋势与年际波动在降水较多的中东部地区主要受温度影响而分别提前和推迟,而在降水偏少的西部地区,SOS和EOS的长期趋势与年际波动主要受降水影响而分别提前和推迟。

[Objective]This study aimed to quantify the long-term trends and interannual variability(IAV)of vegetation phenology in the Mu Us Desert during 2001-2020,and to examine the phenological responses to climatic factors.[Method]We extracted vegetation phenology from the normalized difference vegetation index(NDVI)timeseries,which was calculated from the MODIS MOD13Q1 product,using the dynamic threshold method in TIMESAT3.3.Extracted phenological indices included the start of growing season(SOS),the end of growing season(EOS),and the length of growing season(LOS).Partial correlation analysis was used to examine the relationships between phenological indices and climatic factors.[Result]Multi-year mean phenological indices showed distinct spatial variations:average SOS was the(140±15)th day of year(Julian day),displaying an advancing pattern from west to east and from north to south;average EOS was the(291±6)th day of year,displaying a delaying pattern from north to south;and LOS averaged(151±18)d,displaying an extending pattern from west to east and north to south.All phenological indices showed long-term trends during the study period:mean regional SOS across the Mu Us Desert showed an advancing trend(0.58 d/year);mean regional EOS showed a delaying trend(0.25 d/year);and LOS showed an extending trend(0.83 d/year).Temporal trends in phenological indices also showed significant spatial variations,weakening from west to east.The decadal trends and interannual variability of vegetation phenology(SOS and EOS)were influenced by the same set of climate factors:SOS was negatively correlated with the previous-month temperature and precipitation;while EOS was positively correlated with the temperature in the previous month and cumulative precipitation over the previous months.[Conclusion]Significant longitudinal and latitudinal patterns are observed for SOS and LOS in the Mu Us Desert,and the temporal phenological trends are strengthened from east to west.The temporal trends of phenological indices are mainly reflected by advancing SOS and extending LOS.Advances in SOS and delays in EOS are mainly attributable to rising temperature in central and eastern Mu Us Desert,but are mainly explained by precipitation in the western regions with less precipitation.