Impacts of snow cover duration on vegetation spring phenology over the Tibetan Plateau

Aims Snow cover occupies large percentage of land surface in Tibetan Plateau.Snow cover duration(SCD)during non-growing seasons plays a critical role in regulating alpine vegetation’s phenology by affecting the energy budgets of land surface and soil moisture con-ditions.Different period’s snow cover during non-growing season may have distinct effect on the vegetation’s phenology.Start of season(SOS)has been observed advanced under the ongoing cli-mate change in the plateau,but it still remains unclear how the SCD alters the SOS.This study attempts to answer the following questions:(i)What is the pattern of spatial and temporal variations for SCD and grassland SOS?(ii)Which period’s SCD plays a critical role in grassland’s SOS?Methods The remote sensing datasets from the Moderate Resolution Imaging Spectroradiometer(MODIS)were utilized to compute the SOS and SCD on the Tibetan Plateau over 2003-2015.The Asymmetric Gaussian function was applied to extract SOS.We also explored the spatial pattern and temporal variation of SOS and SCD.Then,by using linear correlation coefficients,we investigated the driving effects of different period’s non-growing season SCD on SOS.Important Findings The non-growing season SCD slightly decreased during 2003-2015,while SOS exhibited an overall advancing trend.Advanced trends in SOS were observed in the eastern plateau,and the delayed trends were mainly founded in western plateau.Snow cover area exhibited two separate peaks during autumn and late winter over the plateau.Extended SCD regions mainly distributed in middle-east of the plateau,while shrunken SCD distributed in other regions of the plateau.SCD of different seasons caused distinct effects on vegetation SOS.Lengthened autumn SCD advanced SOS over the eastern plateau.The slightly lengthened SCD postponed SOS over the western plateau.In the wet meadow regions,advanced SOS was positively associated with SCD during the entire non-growing season,whereas for the dry steppe,SCD over the preseason played a more dominant role.The SCD of previous autumn and winter also showed lag effect on SOS over meadow regions to a certain extent.This study confirmed the importance of SCD to phenological pro-cesses at the beginning of growing season and further suggested that role of SCD should be discriminated for different periods and for dif-ferent heat-water conditions.With the lag effects and SCD’s distinct effect of different seasons considered,predictions on the Tibetan Plateau’s spring phenology could be improved.

Snow effects on alpine vegetation in the Qinghai-Tibetan Plateau

Understanding the relationships between snow and vegetation is important for interpretation of the responses of alpine ecosystems to climate changes.The Qinghai-Tibetan Plateau is regarded as an ideal area due to its undisturbed features with low population and relatively high snow cover.We used 500 m Moderate Resolution Imaging Spectroradiometer(MODIS)datasets during 2001–2010 to examine the snow–vegetation relationships,specifically,(1)the influence of snow melting date on vegetation green-up date and(2)the effects of snow cover duration on vegetation greenness.The results showed that the alpine vegetation responded strongly to snow phenology(i.e.,snow melting date and snow cover duration)over large areas of the Qinghai-Tibetan Plateau.Snow melting date and vegetation green-up date were significantly correlated(p<0.1)in 39.9% of meadow areas(accounting for 26.2% of vegetated areas)and 36.7% of steppe areas(28.1% of vegetated areas).Vegetation growth was influenced by different seasonal snow cover durations(SCDs)in different regions.Generally,the December–February and March–May SCDs played a significantly role in vegetation growth,both positively and negatively,depending on different water source regions.Snow’s positive impact on vegetation was larger than the negative impact.