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1. Past warm intervals inform the future South Asian summer monsoon

   https://doi.org/10.1038/s41586-025-08956-6  

   He, Linqiang; Zhou, Tianjun; Guo, Zhun (May 2025, Nature)

   In the future, monsoon rainfall over densely populated South Asia is expected to increase, even as monsoon circulation weakens1,2,3. By contrast, past warm intervals were marked by both increased rainfall and a strengthening of monsoon circulation4,5,6, posing a challenge to understanding the response of the South Asian summer monsoon to warming. Here we show consistent South Asian summer monsoon changes in the mid-Pliocene, Last Interglacial, mid-Holocene and future scenarios, characterized by an overall increase in monsoon rainfall, a weakening of the monsoon trough-like circulation over the Bay of Bengal and a strengthening of the monsoon circulation over the northern Arabian Sea, as revealed by a compilation of proxy records and climate simulations. Increased monsoon rainfall is thermodynamically dominated by atmospheric moisture following the rich-get-richer paradigm, and dynamically dominated by the monsoon circulation driven by the enhanced land warming in subtropical western Eurasia and northern Africa. The coherent response of monsoon dynamics across warm climates reconciles past strengthening with future weakening, reinforcing confidence in future projections. Further prediction of South Asian summer monsoon circulation and rainfall by physics-based regression models using past information agrees well with climate model projections, with spatial correlation coefficients of approximately 0.8 and 0.7 under the high-emissions scenario. These findings underscore the promising potential of past analogues, bolstered by palaeoclimate reconstruction, in improving future South Asian summer monsoon projections. 

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2. California margin temperatures modulate regional circulation and extreme summer precipitation in the desert Southwest

   https://doi.org/10.1088/1748-9326/acfd43  

   Bhattacharya, Tripti; Feng, Ran; Maupin, Christopher R.; Coats, Sloan; Brennan, Peter R.; Carter, Elizabeth (October 2023, Environmental Research Letters)

   Abstract In August 2022, Death Valley, the driest place in North America, experienced record flooding from summertime rainfall associated with the North American monsoon (NAM). Given the socioeconomic cost of these type of events, there is a dire need to understand their drivers and future statistics. Existing theory predicts that increases in the intensity of precipitation is a robust response to anthropogenic warming. Paleoclimatic evidence suggests that northeast Pacific (NEP) sea surface temperature (SST) variability could further intensify summertime NAM rainfall over the desert southwest. Drawing on this paleoclimatic evidence, we use historical observations and reanalyzes to test the hypothesis that warm SSTs on the southern California margin are linked to more frequent extreme precipitation events in the NAM domain. We find that summers with above-average coastal SSTs are more favorable to moist convection in the northern edge of the NAM domain (southern California, Arizona, New Mexico, and the southern Great Basin). This is because warmer SSTs drive circulation changes that increase moisture flux into the desert southwest, driving more frequent precipitation extremes and increases in seasonal rainfall totals. These results, which are robust across observational products, establish a linkage between marine and terrestrial extremes, since summers with anomalously warm SSTs on the California margin have been linked to seasonal or multi-year NEP marine heatwaves. However, current generation earth system models (ESMs) struggle to reproduce the observed relationship between coastal SSTs and NAM precipitation. Across models, there is a strong negative relationship between the magnitude of an ESM’s warm SST bias on the California margin and its skill at reproducing the correlation with desert southwest rainfall. Given persistent NEP SST biases in ESMs, our results suggest that efforts to improve representation of climatological SSTs are crucial for accurately predicting future changes in hydroclimate extremes in the desert southwest. 

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3. Belowground responses to altered precipitation regimes in two semi-arid grasslands

   https://doi.org/10.6073/pasta/2d233f4ba9af3a13b564a1c6364704c7  

   Holguin, Jennifer; Collins, Scott L; McLaren, Jennie R (January 2022, Environmental Data Initiative)

   Predicted climate change extremes, such as severe and prolonged drought, may profoundly impact biogeochemical processes like carbon and nitrogen cycling in water-limited ecosystems. To increase our understanding of how extreme climate events impact belowground ecosystem processes, we investigated the effects of five years of severe growing season drought and two-month delay in monsoon precipitation on belowground productivity and biogeochemical processes in two semi-arid grasslands. This experiment takes place during the fifth year of the Extreme Drought in Grassland Experiment (EDGE) at the Sevilleta National Wildlife Refuge (SNWR), a Long-Term Ecological Research in central New Mexico, USA. The two grassland sites a Chihuahuan Desert grassland dominated by Bouteloua eriopoda and Great Plains grassland dominated by B. gracilis are ~5km apart in the SWNR. The EDGE platform was established in the spring of 2012 (pre-treatment). Each site contains three treatments (ten replicates): ambient rainfall, extreme growing season drought, and delayed monsoon. The extreme drought treatment reduces growing season rainfall (April through September) each year by 66%, which equates to a 50% reduction of annual precipitation while maintaining natural precipitation patterns. There are 10 replicates per treatment within each site. All plots are 3 x 4 m in size and are paired spatially into blocks with treatments assigned randomly within a block. We measured an array of belowground and biogeochemical variables. Each variable was measured either once, twice, or three times (specific information on sampling scheme for each measured variable in methods section). Belowground net primary productivity, standing crop root biomass, total organic carbon, and total nitrogen were measured once. Extractable organic carbon, extractable total nitrogen, microbial biomass carbon, microbial biomass nitrogen and extracellular enzymes were measured twice. Available soil nitrate, available soil ammonium, and available soil phosphate were measured three times. 

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4. Distinct Features of Atmospheric Rivers in the Early Versus Late East Asian Summer Monsoon and Their Impacts on Monsoon Rainfall

   https://doi.org/10.1029/2020JD033537  

   Park, Chanil; Son, Seok‐Woo; Kim, Hyemi (March 2021, Journal of Geophysical Research: Atmospheres)

   Abstract Atmospheric river (AR) and its impact on monsoon rainfall in East Asia are investigated by considering their month‐to‐month variations during the East Asian summer monsoon (EASM). The AR in the EASM, defined as an anomalously enhanced plume‐like water vapor transport, frequently forms over eastern China, Korea and western Japan. However, its characteristics vary from the early (June‐July) to the late (August‐September) period of the EASM. In the early EASM, AR is typically characterized by a quasi‐stationary monsoon southwesterly along the northern boundary of the western North Pacific subtropical high (WNPSH), which is further intensified by a migrating extratropical cyclone in the north. In contrast, the late‐EASM AR, which is less frequent than the early EASM AR, is primarily organized by a migrating extratropical cyclone. The quasi‐stationary monsoon southwesterly is less influential as the northern boundary of the WNPSH shifts northward, being decoupled from the subtropical ocean. Both the early‐ and late‐EASM ARs contribute substantially to monsoon rainfall, especially to heavy rainfall events. In the early EASM, 35%–70% of total rainfall amount and 60%–80% of heavy rainfall events in eastern China, Korea and western Japan are associated with AR. Although weakened, AR‐related rainfall is still significant in the late EASM in Korea and western Japan. These results indicate that AR is a key ingredient of EASM precipitation and its subseasonal variations should be taken into account to better understand and predict AR‐related extreme precipitation in East Asia. 

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5. SEV-LTER quadrat plant species cover and height all sites and experiments

   https://doi.org/10.6073/pasta/de4f0ae6a2d304db6a8033a6340501e7  

   Baur, Lauren; Collins, Scott; Muldavin, Esteban; Rudgers, Jennifer A; Pockman, William T. (January 2021, Environmental Data Initiative)

   {"Abstract":["This dataset includes plant species cover and height data measured\n in 1 m x 1 m quadrats at several sites and experiments under the\n Sevilleta LTER program. Quadrat locations span four distinct\n ecosystems and their ecotones: creosotebush dominated Chihuahuan\n Desert shrubland (est. winter 1999), black grama-dominated\n Chihuahuan Desert grassland (est. winter 1999), blue grama-dominated\n Plains grassland (est. winter 2002), and pinon-juniper woodland\n (est. winter 2003). Data on plant cover and height for each plant\n species are collected per individual plant or patch (for clonal\n plants) within 1 m x 1 m quadrats. These data inform population\n dynamics of foundational and rare plant species. In addition, using\n plant allometries, these non-destructive measurements of plant cover\n and height can be used to calculate net primary production (NPP), a\n fundamental ecosystem variable that quantifies rates of carbon\n consumption and fixation. Estimates of plant species cover, total\n plant biomass, or NPP can inform understanding of biodiversity,\n species composition, and energy flow at the community scale of\n biological organization, as well as spatial and temporal responses\n of plants to a range of ecological processes and direct experimental\n manipulations. The cover and height of individual plants or patches\n are sampled twice yearly (spring and fall) in permanent 1m x 1m\n plots within each site or experiment. This dataset includes core\n site monitoring data (CORE, GRIDS, ISOWEB, TOWER), observations in\n response to wildfire (BURN), and experimental treatments of extreme\n drought and delayed monsoon rainfall (EDGE), physical disturbance to\n biological soil crusts on the soil surface (CRUST), interannual\n variability in precipitation (MEANVAR), intra-annual variability via\n additions of monsoon rainfall (MRME), additions of nitrogen as\n ammonium nitrate (FERTILIZER), additions of nitrogen x phosphorus x\n potassium (NutNet), and interacting effects of nighttime warming,\n nitrogen addition, and El Niño winter rainfall (WENNDEx). To build\n allometric equations that relate biomass to plant cover or volume, a\n separate dataset of selectively harvested plant species is provided\n in "SEV-LTER Plant species mass data for allometry."\n Together, these datasets produce \u201cSEV-LTER Plant biomass all sites\n and experiments\u201d using the scripts posted with that dataset. Data\n from the CORE sites in this dataset were designated as NA-US-011 in\n the Global Index of Vegetation-Plot Databases (GIVD). Data from the\n TOWER sites in this dataset are linked to Ameriflux sites:\n ameriflux.lbl.gov/doi/AmeriFlux/US-Seg and\n ameriflux.lbl.gov/sites/siteinfo/US-Ses."]} 

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