Divergent impacts of seasonal precipitation deficiency on grassland growth in drylands of Central Asia

Water availability and its timing are essential for determining dryland dynamics, and grasslands in Central Asia are particularly vulnerable to water provided by precipitation. Climate change is projected to alter the seasonal distribution of precipitation patterns and increase the frequency of extreme events. Little is known about the response of grasslands to seasonal precipitation deficiency (PD), especially considering the time lag effect. Here, we evaluated the impacts of PD on grassland growth at the seasonal scale based on the normalized difference vegetation index (NDVI). Our findings showed that grassland growth during spring was mostly affected by PD in arid regions, with PD occurring during the nongrowing season and spring causing mean standardized anomalies (SAs) of −0.83 and −0.54, respectively, for the NDVI. In semiarid and subhumid regions, summer PD caused not only the largest negative response in summer (with SAs of −0.94 and −0.80 for semiarid and subhumid regions, respectively) but also in autumn (−0.80 and −0.74). PD in autumn had a less adverse effect on grassland growth. The divergent seasonal responses primarily stemmed from shifts in the dominant factors influencing grassland growth across seasons. PD reduced soil moisture in spring and summer, which in turn affected grassland growth. However, summer PD affected autumn grassland growth primarily through the carryover effect. Our results highlighted the importance of the timing of PD and suggested that precipitation in the previous season should receive more attention when considering the relationship between vegetation and precipitation at the seasonal scale.