Assessment of drought and its impact on winter wheat yield in the Chinese Loess Plateau

Drought has pronounced and immediate impacts on agricultural production,especially in semi-arid and arid rainfed agricultural regions.Quantification of drought and its impact on crop yield is essential to agricultural water resource management and food security.We investigated drought and its impact on winter wheat(Triticum aestivum L.)yield in the Chinese Loess Plateau from 2001 to 2015.Specifically,we performed a varimax rotated principal component analysis on drought severity index(DSI)separately for four winter wheat growth periods:pre-sowing growth period(PG),early growth period(EG),middle growth period(MG),and late growth period(LG),resulting in three major subregional DSI dynamics for each growth period.The county-level projections of these major dynamics were then used to evaluate the growth period-specific impacts of DSI on winter wheat yields by using multiple linear regression analysis.Our results showed that the growth period-specific subregions had different major DSI dynamics.During PG,the northwestern area exhibited a rapid wetting trend,while small areas in the south showed a slight drying trend.The remaining subregions fluctuated between dryness and wetness.During EG,the northeastern and western areas exhibited a mild wetting trend.The remaining subregions did not display clear wetting or drying trends.During MG,the eastern and southwestern areas showed slight drying and wetting trends,respectively.The subregions scattered in the north and south had a significant wetting trend.During LG,large areas in the east and west exhibited wetting trends,whereas small parts in south-central area had a slight drying trend.Most counties in the north showed significant and slight wetting trends during PG,EG,and LG,whereas a few southwestern counties exhibited significant drying trends during PG and MG.Our analysis identified close and positive relationships between yields and DSI during LG,and revealed that almost all of the counties were vulnerable to drought.Similar but less strong relationships existed for MG,in which northeastern and eastern counties were more drought-vulnerable than other counties.In contrast,a few drought-sensitive counties were mainly located in the southwestern and eastern areas during PG,and in the northeastern corner of the study region during EG.Overall,our study dissociated growth period-specific and spatial location-specific impacts of drought on winter wheat yield,and might contribute to a better understanding of monitoring and early warning of yield loss.

Impact of Droughts on Winter Wheat Yield in Different Growth Stages during 2001–2016 in Eastern China

Remote sensing can provide near real-time and dynamic monitoring of drought. The drought severity index(DSI), based on the normalized difference vegetation index(NDVI) and evapotranspiration/potential evapotranspiration(ET/PET), has been used for drought monitoring. This study examined the relationship between the DSI and winter wheat yield for prefecture-level cities in five provinces of eastern China during 2001–2016. We first analyzed the spatial and temporal distribution of droughts in the study area. Then the correlation coefficient between drought-affected area and detrended yield of winter wheat was quantified and the impact of droughts of different intensities on winter wheat yield during different growth stages was investigated. The results show that incipient drought during the wintering period has no significant impact on the yield of winter wheat, while moderate drought in the same period can reduce yield. Drought affects winter wheat yield significantly during the flowering and filling stages. Droughts of higher intensity have more significant negative effects on the yield of winter wheat. Monitoring of droughts and irrigation is critical during these periods to ensure normal yield of winter wheat. This study has important practical implications for the planning of irrigation and food security.

基于遥感DSI指数的干旱与冬小麦产量相关性分析

利用2000—2012年MODIS ET/PET和NDVI数据集构建干旱指数(DSI),监测山东省和河南省冬小麦主产区的农业干旱,并在地级市尺度上进一步评估冬小麦关键生育期干旱对冬小麦产量的影响。结果表明:2010年9月—2011年2月山东省特大干旱过程显示的DSI不仅能监测气象干旱,还能较好地反映农业干旱在空间上的差异性以及时间上的演变。不同冬小麦生育期干旱对冬小麦产量影响不同,灌浆期干旱对冬小麦产量的影响最大,干旱致使土壤水分亏缺,影响了作物正常的灌浆强度,进而导致作物减产;其次是拔节期;返青期干旱对产量基本没有影响。

淮河流域冬小麦主要生育期旱涝时空特征及对产量的影响

旱涝灾害在淮河流域发生频繁,对农作物产量影响较大。该文基于淮河流域1961-2014年140个气象站逐日降水、气温数据,利用标准化降水指数(standardized precipitation index,SPI)和标准化降水蒸散指数(standardized precipitation evapotranspiration index,SPEI)定量分析冬小麦各生育期气候特征,结合1961-2012年20个站点冬小麦单产数据计算标准化产量残差(standardized yield residuals,SYR),探讨冬小麦主要生育期旱涝灾害对其产量的影响。结果表明:1)冬小麦各生育期气温均呈显著上升趋势(P<0.05),气温呈南高北低、西高东低的格局,东部趋势高于西部且返青抽穗期大部分站点趋势值最高,而降水量沿纬度变化与气温一致,其变化趋势在冬小麦各生育期差异明显。2)冬小麦返青抽穗期干旱增加趋势最大(P<0.05),旱涝灾害在全生育期、返青抽穗期和灌浆成熟期主要受气温影响,在冬前生长期和越冬期主要受降水量影响,同时冬小麦各生育期SPEI干旱化趋势大于SPI。3)除冬前生长期外,SYR与SPI和SPEI均呈负相关关系,以返青抽穗期相关性最高,在返青抽穗期达到中度干旱或中度湿润时产量减少。该研究尝试明晰淮河流域发生在冬小麦生育期的旱涝灾害对其产量的影响,为冬小麦生育期防灾减灾提供基础支撑。