Multiple lines of evidence suggest climate change will result in increased precipitation variability and consequently more frequent extreme events. These hydroclimatic changes will likely have significant socioecological impacts, especially across water‐limited regions. Here we present an analysis of daily meteorological observations from 1976 to 2019 at 337 long‐term weather stations distributed across the western United States (US). In addition to widespread warming (0.2 °C ± 0.01°C/decade, daily maximum temperature), we observed trends of reduced annual precipitation (−2.3 ± 1.5 mm/decade) across most of the region, with increasing interannual variability of precipitation. Critically, daily observations showed that extreme‐duration drought became more common, with increases in both the mean and longest dry interval between precipitation events (0.6 ± 0.2, 2.4 ± 0.3 days/decade) and greater interannual variability in these dry intervals. These findings indicate that, against a backdrop of warming and drying, large regions of the western US are experiencing intensification of precipitation variability, with likely detrimental consequences for essential ecosystem services.

Soil water availability determines the feedback of ecosystem carbon cycle to climate warming.

The dynamics of net primary productivity (NPP) and its partitioning to the aboveground versus belowground are of fundamental importance to understand carbon cycling and its feedback to climate change. However, the responses of NPP and its partitioning to precipitation gradient are poorly understood. We conducted a manipulative field experiment with six precipitation treatments (1/12 P, 1/4 P, 1/2 P, 3/4 P, P, and 5/4 P, P is annual precipitation) in an alpine meadow to examine aboveground and belowground NPP (ANPP and BNPP) in response to precipitation gradient in 2015 and 2016. We found that changes in precipitation had no significant impact on ANPP or belowground biomass in 2015. Compared with control, only the extremely drought treatment (1/12 P) significantly reduced ANPP by 37.68% and increased BNPP at the depth of 20–40 cm by 80.59% in 2016. Across the gradient, ANPP showed a nonlinear response to precipitation amount in 2016. Neither BNPP nor NPP had significant relationship with precipitation changes. The variance in ANPP were mostly due to forbs production, which was ultimately caused by altering soil water content and soil inorganic nitrogen concentration. The nonlinear precipitation-ANPP relationship indicates that future precipitation changes especially extreme drought will dramatically decrease ANPP and push this ecosystem beyond threshold.

The continually increasing nitrogen (N) deposition is expected to cause a saturation response of ecosystem aboveground net primary productivity (ANPP). However, its underlying mechanisms, especially for the decrease of ANPP under high N addition rate, remain poorly understood. A field manipulative experiment was conducted to investigate the response of ANPP to six levels of N addition rate (0, 2, 4, 8, 16, and 32 g N·m⁻²·year⁻¹) in an alpine meadow during 2015–2017. We specifically explored four possible mechanisms, light limitation, biodiversity loss, soil acidification, and ammonium toxicity, underlying the saturation response of ANPP to increasing N addition. The results showed that ANPP increased linearly with N addition rates in 2015, while converted to a saturation response with N addition rates in 2016–2017. With increasing N addition rate, species richness and soil pH significantly reduced while standing litter, light limitation, and NH₄⁺‐N content significantly increased. Under low N addition rate (N0 to N4), increases in N availability significantly improved ANPP although it was partly offset by the indirect N effect via increasing litter accumulation and thus light competition. Under high N addition rate (N8–N32), the decreases in species richness mostly explained the N‐induced reduction in ANPP, leading to a saturation response. This study provides empirical evidences on interpreting N saturation response of ANPP in the alpine meadow. The findings will advance our current understanding of N enrichment effects on ANPP and benefit biogeochemical models in parameterization and benchmark analysis.