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[Display omitted] • The gravity center of EXD is shifting to urban population centers. • The drought risk bundle in the middle basin is relatively stable. • Western watershed soils face water scarcity risks. • The contribution of vegetation landscape increase to runoff change was 35.13% The mechanisms underlying the impacts of climate change and vegetation dynamics on hydrological drought in humid regions are still lacking. In this study, we connected the four components of meteorology-soil-vegetation-runoff to investigate the spatio-temporal response relationship between vegetation growth and different drought types. Based on the Variable Infiltration Capacity model and the Self-organizing Map Algorithm, we proposed ecological risk bundles at the grid scale to characterize the potential impacts of different types and levels of drought on vegetation. Furthermore, we quantified the driving impact of temporal and spatial changes in vegetation coverage on the propagation of meteorological-hydrological drought. The study found that the centers of gravity for the occurrence frequencies of extreme and mild drought shifted towards regions where vegetation growth was influenced by climate change. In certain regions of the watershed, vegetation exhibits significant spatial and temporal heterogeneity in its response to stress caused by different drought types. From 2004 to 2014, the stress on vegetation caused by moderate and mild meteorological droughts weakened, while soil moisture stress intensified after 2014. Simultaneously, the impacts of climate change and vegetation growth on runoff reached 48.25 % and 35.13 % respectively, and their synergistic effects triggered changes in the risk of co-concurrent return periods for hydrological drought events. Under the 100-year design return period, the co-occurrence return period of runoff shifted from its natural state of 162.9 years to 52.8 years, and the joint return period reversed its scenario, becoming shorter than the co-occurrence return period. [ABSTRACT FROM AUTHOR]

• California has shown a wide range of ombroxeric levels (OXI). • Upper strong dry level was found in the north of the State. • Lower weak arid level was found in both the Sonora and Mojave deserts. • Annual trend results have shown an increase in bioclimatic drought throughout California. • June, July and August are the months that show the highest levels of bioclimatic drought. Drought occurs naturally all over the world. Global warming has led an increase in the areas affected by this phenomenon. The study of drought involves the analysis of indicators and indices used to assess changes in the hydrological cycle of a region. A large number of indices developed for drought monitoring are based on meteorological and hydrological variables. This research has applied the Ombroxeric Index for the first time in California. It is based on the concept of ombroxericity: a condition of the territory characterised from an ombrothermic point of view, which can develop in relatively humid areas/zones, depending on the time scale of the study (i.e. monthly, seasonal or annual basis). Temperatures and precipitation from 180 meteorological stations have been considered for a period of observation from 1980 to 2016. In order to know the evolution of this index, a modified trend analysis based on the Mann-Kendall test and a modified Sen slope analysis were used. Empirical Bayesian Kriging was applied as an interpolation technique. Results are presented in both surface and contour maps. California showed a wide range of ombroxeric levels that went from upper strong dry in northern zones, to lower weak arid. Trend results showed an increase in bioclimatic drought throughout the whole State. In addition, summer showed the highest levels on the Ombroxeric Index. An increase in drought trends was observed at the seasonal level, being more pronounced in summer and spring. In both cases are increases in the central (+5 and +3.6 units year−1 respectively) and the southern (+4 and +4.5 units year−1 respectively) areas of the State. Increasing frequency and severity of droughts could have implications for the management of water resources and the survival of Californian vegetation types, such as conifers. [ABSTRACT FROM AUTHOR]

• WUE in the TP exhibited spatial heterogeneity, reduced under dry and cool conditions. • Grassland in most areas of the TP is resistant to hydroclimatic fluctuations. • Grassland in areas with lower temperature or higher precipitation has greater drought resistance. An increasing trend of hydroclimatic disturbances, such as droughts, which are projected to become more frequent and intense with global warming and climate change. Droughts adversely affect the structure and function of terrestrial ecosystems, damage vegetation growth, and even increase mortality. In this study, we assess the drought resistance (R d) of ecosystems in the Tibetan Plateau. Ecosystem water use efficiency (WUE) was used as an indicator of change in carbon and water cycles, and then ecosystem resistance in terms of change in WUE in drought years was analyzed. Our results suggested that the WUE in the Tibetan Plateau exhibited significant spatial heterogeneity and drastically reduced under dry and cool conditions. The evaluation of ecosystem drought resistance indicated that the grassland in most areas of the Tibetan Plateau is resistant to hydroclimatic fluctuations. In particular, the grassland ecosystem in areas with lower temperatures or higher precipitation exhibited greater drought resistance. Our results facilitate the identification of drought-vulnerable areas in the Tibetan Plateau to inform grassland ecosystem management and climate policy-making and sustain ecosystem stability under future climate conditions. [ABSTRACT FROM AUTHOR]

• Lagged and cumulative effects of drought on global grassland GPP are assessed. • 74.85% of the grassland shows lagged response to drought, mainly with a time scale of 1 month. • 59.06% of the grassland is affected by drought cumulatively, mainly within 2–4 months. • The cumulative effect is stronger in relatively arid area than in relatively humid area. • Globally, the cumulative effect exceeds the lagged effect for grassland productivity. Drought has large impacts on the vegetation growth of global terrestrial ecosystems, particularly grasslands. Extensive in-situ studies have shown that the impact of drought on vegetation growth has lagged and cumulative effects, but it is not well known how grassland productivity (gross primary production or GPP) responds to drought over time at large scales. Here, we investigated the spatiotemporal patterns of lagged and cumulative effects of drought on global grassland GPP using an OCO-2 solar-induced chlorophyll fluorescence (SIF) based GPP product (GOSIF GPP) and the Standardized Precipitation Evapotranspiration Index (SPEI). The results showed that globally, 88.37% of the grassland had a lagged response to drought, with a lagged time scale of mainly 1 month. With the increase in soil water availability, the magnitude of the lagged effect gradually weakened. Grasslands in semiarid and semi humid conditions that were adaptable to periodic drought responded fastest to drought. Globally, more than three quarters (78.55%) of the grassland was affected by the cumulative effect of drought. The accumulated months occurred at longer time scales (8 ∼ 10 months) for the region at 40°N–55°N, which is relatively arid. The cumulative effect in relatively arid areas was stronger than that in relatively humid areas, indicating that grasslands in more arid areas had stronger tolerance to drought. More importantly, we found that the cumulative effect of drought on grassland GPP was stronger than the lagged effect. This study highlights the great importance of considering the legacy effect, especially the cumulative effect, of drought on grassland productivity, which would advance our understanding of the impact of climate change on the carbon and water cycles of terrestrial ecosystems. [ABSTRACT FROM AUTHOR]

[Display omitted] • The response of ecosystem WUE to soil moisture drought was quantitatively examined. • WUE increased significantly in most vegetated areas of the world during 1982–2018. • Drought had approximately 4-month lagged effect on WUE. • Drought-resilient ecosystems were concentrated in the Northern Hemisphere. Water use efficiency (WUE) is an ecological indicator reflecting the link between carbon and water cycles in terrestrial ecosystems, which is often affected by drought disturbance. However, knowledge about the influences of soil moisture drought on WUE is still lacking. Therefore, this paper aims to quantify the lagged effect and impact of soil moisture drought on terrestrial ecosystem WUE from 1982 to 2018 using ERA5 and Global Land Surface Satellite (GLASS) datasets. Drought conditions are described by the soil moisture anomaly percentage index (SMAPI). The lagged effect of drought on WUE is measured by the month with the maximum significant correlation between SMAPI and WUE. The impact of drought on WUE is estimated through the relative change of WUE during drought and non-drought periods. The results showed that: (1) Drought had an approximately 4-month lagged effect on WUE, which was observed in 70.87% of the global vegetated areas. The lagged effect of drought on WUE was a short period (1–4 months) for shrubland and sparse vegetation, middle and long periods (5–12 months) for forest. (2) When drought occurred, WUE decreased by 36.95% in the Tibetan Plateau and 24.93% in West Africa, while WUE in North Europe, Alaska/N.W. Canada, and West Asia increased by 14.64%, 8.83%, and 8.53%, respectively. The negative and positive impacts of drought on WUE in each vegetation type were commensurate. Our results provide useful information for understanding the response of ecosystem carbon and water cycles to drought.. [ABSTRACT FROM AUTHOR]