黄淮海平原植被日光诱导叶绿素荧光对骤旱的响应

Response of Solar-induced Chlorophyll Fluorescence to Flash Drought in Huang-Huai-Hai Plain

为探明黄淮海平原骤旱的时空分布及其对植被光合作用的影响,基于ERA5气候再分析资料和SMCI1.0土壤湿度数据集,分析了黄淮海地区2001—2020年气候要素时空变化特征,识别了骤旱事件并研究其演变规律和主要气象影响因子,对比星载日光诱导叶绿素荧光(Solar-induced chlorophyll fluorescence,SIF)、标准化差异植被指数(Normalized difference vegetation index,NDVI)以及增强植被指数(Enhanced vegetation index,EVI)对骤旱的响应,探究了不同类型植被光合作用对骤旱的敏感性。结果表明:黄淮海地区2001—2020年整体呈暖湿化趋势,北部地区增温明显。黄淮海北部和东南部地区骤旱频发,大部分地区发生超过20次骤旱,累计受旱时长超过90候,且骤旱多发生于秋季。黄淮海地区年骤旱次数和累计骤旱时长整体呈上升趋势,增加速率分别为0.6次/(10a)和2.2候/(10a),且呈上升趋势的格点主要位于骤旱频发区。研究区骤旱次数与气温(显著正相关)、风速(负相关)以及降水量(负相关)的相关性较高。相较于NDVI和EVI,SIF随土壤水分的变化更加同步,适用于骤旱监测。黄淮海地区灌木植被SIF对骤旱最敏感,但存在较大的不确定性,农田、森林和草地等植被类型光合作用对骤旱的响应逐渐降低,但不同植被SIF与骤旱次数的最大相关系数均较为接近。

Aiming to study the temporal and spatial distribution of flash drought in the Huang-Huai-Hai Plain and its impacts on vegetation photosynthesis,the spatiotemporal variations of climate variables and flash drought events of the Huang-Huai-Hai Plain in 2001—2020 were firstly identified based on the reanalysis datasets of ERA5 and SMCI1.0.Daily soil moisture data for each layer were used to calculate the pentad-averaged(5 d)values and further converted into soil moisture percentile.A flash drought event was recognized when the soil moisture percentile declined from 40%to 20%within four pentads.In this way,temporal-spatial distributions were analyzed for the times and duration of flash drought in the Huang-Huai-Hai Plain.Meanwhile,solar-induced chlorophyll fluorescence(SIF),normalized difference vegetation index(NDVI)and enhanced vegetation index(EVI)were used to represent growth statues of vegetation.Variations in SIF,NDVI,and EVI were compared along with the dynamics of soil moisture changes.The correlation coefficient between SIF and the times of flash droughts was also used to study the photosynthesis of different vegetation types responding to flash drought.The results indicated a warming and humidifying environment of the Huang-Huai-Hai Plain in 2001—2020.Flash drought was more severe in the northwest and southeast of this region.Most areas experienced more than 20 times of flash drought events with a cumulative duration exceeding 90 pentads in 2001—2020.Meanwhile,increasing trends were found for both times and duration of flash drought for most areas in the Huang-Huai-Hai Plain,with rising rates of 0.6 times per 10 a and 2.2 pentads per 10 a,respectively.Notably,the areas with increasing trends were mainly located in the areas with frequent flash drought events.Temperature(significant positive correlation),wind speed(negative correlation),and precipitation(negative correlation)were the three most related meteorological variables with flash drought.Compared with the NDVI and the EVI,SIF varied more synchronously with soil moisture during flash drought events.Furthermore,responses of photosynthesis to flash drought were different among the four vegetation types.Shrubland photosynthesis had the highest sensitivity to flash drought,followed by farmland,forest,and grassland.However,the largest correlation coefficients were similar among the four vegetation types in the Huang-Huai-Hai Plain.