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    Tropical deforestation causes large reductions in observed precipitation
    (Springer Nature, 2023-03-01) Smith, C.; Baker, J. C. A.; Spracklen, D. V.
    Tropical forests play a critical role in the hydrological cycle and can influence local and regional precipitation. Previous work has assessed the impacts of tropical deforestation on precipitation, but these efforts have been largely limited to case studies. A wider analysis of interactions between deforestation and precipitation—and especially how any such interactions might vary across spatial scales—is lacking. Here we show reduced precipitation over deforested regions across the tropics. Our results arise from a pan-tropical assessment of the impacts of 2003–2017 forest loss on precipitation using satellite, station-based and reanalysis datasets. The effect of deforestation on precipitation increased at larger scales, with satellite datasets showing that forest loss caused robust reductions in precipitation at scales greater than 50 km. The greatest declines in precipitation occurred at 200 km, the largest scale we explored, for which 1 percentage point of forest loss reduced precipitation by 0.25 ± 0.1 mm per month. Reanalysis and station-based products disagree on the direction of precipitation responses to forest loss, which we attribute to sparse in situ tropical measurements. We estimate that future deforestation in the Congo will reduce local precipitation by 8–10% in 2100. Our findings provide a compelling argument for tropical forest conservation to support regional climate resilience.
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    Oceanic climate changes threaten the sustainability of Asia’s water tower
    (Springer Nature, 2023-03-01) Zhang, Qiang; Shen, Zexi; Pokhel, Yadu; Farinotti, Daniel; Singh, Vijay P.; Xu, Chong-Yu; Wu, Wenhuan; Wang, Gang
    Water resources sustainability in High Mountain Asia (HMA) surrounding the Tibetan Plateau (TP)—known as Asia’s water tower—has triggered widespread concerns because HMA protects millions of people against water stress. However, the mechanisms behind the heterogeneous trends observed in terrestrial water storage (TWS) over the TP remain poorly understood. Here we use a Lagrangian particle dispersion model and satellite observations to attribute about 1 Gt of monthly TWS decline in the southern TP during 2003–2016 to westerlies-carried deficit in precipitation minus evaporation (PME) from the southeast North Atlantic. We further show that HMA blocks the propagation of PME deficit into the central TP, causing a monthly TWS increase by about 0.5 Gt. Furthermore, warming-induced snow and glacial melt as well as drying-induced TWS depletion in HMA weaken the blocking of HMA’s mountains, causing persistent northward expansion of the TP’s TWS deficit since 2009. Future projections under two emissions scenarios verified by satellite observations during 2020–2021 indicate that, by the end of the twenty-first century, up to 84% (for scenario SSP245) and 97% (for scenario SSP585) of the TP could be afflicted by TWS deficits. Our findings indicate a trajectory towards unsustainable water systems in HMA that could exacerbate downstream water stress.
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    Proper management of irrigation and nitrogen-application increases crop N-uptake efficiency and reduces nitrate leaching
    (Taylor & Francis Group - Informa UK Limited, 2022-09-28) ten Damme, Loraine; Jing, Shuxuan; Montcalm, Ashley Marie; Jepson, Maisie; Andersen, Mathias Neumann; Hansen, Elly Møller
    Irrigation is, on one hand, expected to increase the risk of nitrate leaching through increased rates of percolation, but, on the other hand, enhances plant nutrient uptake and growth, thereby limiting the risk of leaching. To investigate this dichotomy, we analysed the effects of irrigation at three nitrogen (N)-application rates in spring barley (Hordeum distichum L., two experiments with 50, 100, and 150 kg N ha−1) and winter oilseed rape (Brassica napus L., one experiment with 50, 150, and 250 kg N ha−1) on a coarse sandy soil in Denmark in a humid climate, which facilitates nitrate leaching. Analyses comprised grain/seed dry matter yield, N-uptake, nitrogen use efficiency (partial nitrogen budget, PNB, and partial-factor productivity, PFP) and nitrate leaching. For both crops, increasing N-application without consideration of the crops’ drought stress responses lead to a relatively lower N-uptake in grain, lower yield, lower PNB and PFP and higher nitrate leaching, although responses were not proportionally to increasing N-application. The effect of irrigation at the lowest N-rates was limited. The non-irrigated treatments with the highest N-rates had a grain/seed yield of 3.2, 2.3 and 0.7 t ha−1 and nitrate leaching rates of 64, 72 and 127 kg N ha−1 compared to a grain/seed yield of 5.3, 5.0 and 2.6 kg N ha−1 and nitrate leaching rates of 61, 42 and 85 kg N ha−1 (for spring barley, spring barley and winter oilseed rape, respectively). These results show that synchronised management of both irrigation and N-application are essential for reducing the risk of nitrate leaching and to promote efficient crop N-uptake in periods of droughts.