Rootzone storage capacity reveals drought coping strategies along rainforest-savanna transitions

Climate change and deforestation have increased the risk of drought-induced forest-to-savanna transitions across the tropics and subtropics. However, the present understanding of forest-savanna transitions is generally focused on the influence of rainfall and fire regime changes, but does not take into account the adaptability of vegetation to droughts by utilizing subsoil moisture in a quantifiable metric. Using rootzone storage capacity (Sr), which is a novel metric to represent the vegetation's ability to utilize subsoil moisture storage and tree cover (TC), we analyze and quantify the occurrence of these forest-savanna transitions along transects in South America and Africa. We found forest-savanna transition thresholds to occur around a Sr of 550–750 mm for South America and 400–600 mm for Africa in the range of 30%–40% TC. Analysis of empirical and statistical patterns allowed us to classify the ecosystem's adaptability to droughts into four classes of drought coping strategies: lowly water-stressed forest (shallow roots, high TC), moderately water-stressed forest (investing in Sr, high TC), highly water-stressed forest (trade-off between investments in Sr and TC) and savanna-grassland regime (competitive rooting strategy, low TC). The insights from this study are useful for improved understanding of tropical eco-hydrological adaptation, drought coping strategies, and forest ecosystem regime shifts under future climate change

Moisture sources for East Asian precipitation: mean seasonal cycle and interannual variability

This study investigates the moisture sources that supply East Asian (EA) precipitation and their interannual variability. Moisture sources are tracked using theWater Accounting Model-2layers (WAM-2layers), based on the Eulerian framework. WAM-2layers is applied to five subregions over EA, driven by the ERA-Interim reanalysis from 1979 to 2015. Due to differences in regional atmospheric circulation and in hydrological and topographic features, the mean moisture sources vary among EA subregions. The tropical oceanic source dominates southeastern EA, while the extratropical continental source dominates other EA subregions. The moisture sources experience large seasonal variations, due to the seasonal cycle of the EA monsoon, the freeze-thaw cycle of the Eurasian continent and local moisture recycling over the Tibetan Plateau. The interannual variability of moisture sources is linked to interannual modes of the coupled ocean-atmosphere system. The negative phase of the North Atlantic Oscillation increases moisture transport to northwestern EA in winter by driving a southward shift in the mid-latitude westerly jet over theMediterranean Sea, the Black Sea and the Caspian Sea. Atmospheric moisture lifetime is also reduced due to the enhanced westerlies. In summers following El Ni ˜nos, an anti-cyclonic anomaly over the western North Pacific increases moisture supplied from the South China Sea to the southeastern EA and shortens the travelling distance. A stronger Somali Jet in summer increases moisture to the Tibetan Plateau and therefore increases precipitation over the eastern Tibetan Plateau. The methods and findings in this study can be used to evaluate hydrological features in climate simulations

Dietary supplementation with multiple micronutrients: No beneficial effects in pediatric cystic fibrosis patients

AbstractBackgroundCystic fibrosis (CF) patients are subjected to increased oxidative stress due to chronic pulmonary inflammation and recurrent infections. Additionally, these patients have diminished skeletal muscle performance and exercise capacity. We hypothesize that a mixture of multiple micronutrients could have beneficial effects on pulmonary function and muscle performance.MethodsA double-blind, randomized, placebo controlled, cross-over trial with a mixture of multiple micronutrients (ML1) was performed in 22 CF patients (12.9±2.5 yrs) with predominantly mild lung disease. Anthropometric measures, pulmonary function, exercise performance by bicycle ergometry, muscular strength and vitamins A and E were determined.ResultsAnalysis was performed using the paired Student t-test comparing the change in each parameter during ML1 and placebo. Plasma vitamin E and A levels increased during ML1 when compared to placebo. However, no significant difference between the effect of the ML1 or placebo was observed neither for FEV1, FVC, anthropometry, nor for the parameters for muscle performance.ConclusionsThe micronutrient mixture was not superior to placebo with respect to changes in pulmonary function or muscle performance in pediatric CF patients, despite a significant increase in plasma vitamin E concentrations

Dry seasons and dry years amplify the Amazon and Congo forests’ rainfall self-reliance

Rainfall is a key determinant of tropical rainforest resilience in South America and Africa, of which a substantial amount originates from terrestrial and forest evaporation through moisture recycling. Both continents face deforestation that reduces evaporation and thus dampens the water cycle, and climate change that increases the risk of water-stress induced forest loss. Hence, it is important to understand the influence of forest moisture supply for forest rainfall during dry periods. Here, we analyze mean-years and dry-years dry-season anomalies of moisture recycling in the South American (Amazon) and African rainforests (Congo) over the years 1980-2013. Annual average reliance of forest rainfall on their own moisture supply (ρfor) is 26 % in the Amazon and 28% in the Congo forest. In dry seasons, this ratio increases by 7% (or ~2 percentage points) in the Amazon and up to 30 % (or ~8 percentage points) in Congo. Dry years further amplify dry season ρfor in both regions by 4-5 %. In both Amazon and Congo, dry season amplification of ρfor are strongest in regions with a high mean annual ρfor. In the Amazon, forest rainfall self-reliance has declined over time, and in both Amazon and Congo, the fraction of forest evaporation that recycles as forest rainfall has declined over time. At country scale, dry season ρfor can differ drastically from mean annual ρfor (e.g., in Bolivia and Gabon, mean annual ρfor is ~30% while dry season ρfor is ~50 %). Dry period amplification of ρfor illuminates additional risks of deforestation as well as opportunities from forest conservation and restoration, and is essential to consider for understanding upwind forest change impacts on downwind rainfall at both regional and national scales

Effects of horizontal resolution and air-sea coupling on simulated moisture source for East Asian precipitation

Precipitation over East Asia in six MetUM simulations are compared with observation and ERA-Interim reanalysis. These simulations include three different horizontal resolutions, from low, medium to high, and including atmosphere-only version (GA6.0) and air-sea coupling version (GC2.0). Precipitations in simulations are systematically different from that of observation and reanalysis. Increasing horizontal resolution and including air-sea coupling improve simulated precipitation but cannot eliminate bias. % Moisture sources of East Asian precipitations are identified using the WAM-2layers - a moisture tracking model that traces moisture source using collective information of evaporation, atmospheric moisture and circulation. Similar to precipitation, moisture sources in simulations are systematically different from that of ERA-Interim. Major differences in moisture sources include underestimated moisture contribution from tropical Indian Ocean and overestimate contribution from Eurasian continent. % By increasing horizontal resolution, precipitation bias over the Tibetan Plateau is improved. From the moisture source point of view, this is achieved by reducing contribution from remote moisture source and enhancing local contribution over its eastern part. % Although including air-sea coupling does not necessarily change East Asian precipitation, moisture sources show differences between coupled and atmospheric-only simulations. These differences in moisture sources indicate different types of models biases caused by surface flux or/and atmospheric circulation on different locations. These information can be used to target model biases on specified locations and due to different mechanisms

Notable shifts beyond pre-industrial streamflow and soil moisture conditions transgress the planetary boundary for freshwater change

Human actions compromise the many life-supporting functions provided by the freshwater cycle. Yet, scientific understanding of anthropogenic freshwater change and its long-term evolution is limited. Here, using a multi-model ensemble of global hydrological models, we estimate how, over a 145-year industrial period (1861–2005), streamflow and soil moisture have deviated from pre-industrial baseline conditions (defined by 5th–95th percentiles, at 0.5° grid level and monthly timestep over 1661–1860). Comparing the two periods, we find an increased frequency of local deviations on ~45% of land area, mainly in regions under heavy direct or indirect human pressures. To estimate humanity’s aggregate impact on these two important elements of the freshwater cycle, we present the evolution of deviation occurrence at regional to global scales. Annually, local streamflow and soil moisture deviations now occur on 18.2% and 15.8% of global land area, respectively, which is 8.0 and 4.7 percentage points beyond the ~3 percentage point wide pre-industrial variability envelope. Our results signify a substantial shift from pre-industrial streamflow and soil moisture reference conditions to persistently increasing change. This indicates a transgression of the new planetary boundary for freshwater change, which is defined and quantified using our approach, calling for urgent actions to reduce human disturbance of the freshwater cycle

Quantifying Earth system interactions for sustainable food production via expert elicitation

Several safe boundaries of critical Earth system processes have already been crossed due to human perturbations; not accounting for their interactions may further narrow the safe operating space for humanity. Using expert knowledge elicitation, we explored interactions among seven variables representing Earth system processes relevant to food production, identifying many interactions little explored in Earth system literature. We found that green water and land system change affect other Earth system processes strongly, while land, freshwater and ocean components of biosphere integrity are the most impacted by other Earth system processes, most notably blue water and biogeochemical flows. We also mapped a complex network of mechanisms mediating these interactions and created a future research prioritization scheme based on interaction strengths and existing knowledge gaps. Our study improves the understanding of Earth system interactions, with sustainability implications including improved Earth system modelling and more explicit biophysical limits for future food production

Twenty-three unsolved problems in hydrology (UPH) – a community perspective

This paper is the outcome of a community initiative to identify major unsolved scientific problems in hydrology motivated by a need for stronger harmonisation of research efforts. The procedure involved a public consultation through on-line media, followed by two workshops through which a large number of potential science questions were collated, prioritised, and synthesised. In spite of the diversity of the participants (230 scientists in total), the process revealed much about community priorities and the state of our science: a preference for continuity in research questions rather than radical departures or redirections from past and current work. Questions remain focussed on process-based understanding of hydrological variability and causality at all space and time scales. Increased attention to environmental change drives a new emphasis on understanding how change propagates across interfaces within the hydrological system and across disciplinary boundaries. In particular, the expansion of the human footprint raises a new set of questions related to human interactions with nature and water cycle feedbacks in the context of complex water management problems. We hope that this reflection and synthesis of the 23 unsolved problems in hydrology will help guide research efforts for some years to come

The residence time of water in the atmosphere revisited

This paper revisits the knowledge on the residence time of water in the atmosphere. Based on state-of-the-art data of the hydrological cycle we derive a global average residence time of 8.9 ± 0.4 days (uncertainty given as 1 standard deviation). We use two different atmospheric moisture tracking models (WAM-2layers and 3D-T) to obtain atmospheric residence time characteristics in time and space. The tracking models estimate the global average residence time to be around 8.5 days based on ERA-Interim data. We conclude that the statement of a recent study that the global average residence time of water in the atmosphere is 4-5 days, is not correct. We derive spatial maps of residence time, attributed to evaporation and precipitation, and age of atmospheric water, showing that there are different ways of looking at temporal characteristics of atmospheric water. Longer evaporation residence times often indicate larger distances towards areas of high precipitation. From our analysis we find that the residence time over the ocean is about 2 days less than over land. It can be seen that in winter, the age of atmospheric moisture tends to be much lower than in summer. In the Northern Hemisphere, due to the contrast in ocean-to-land temperature and associated evaporation rates, the age of atmospheric moisture increases following atmospheric moisture flow inland in winter, and decreases in summer. Looking at the probability density functions of atmospheric residence time for precipitation and evaporation, we find long-tailed distributions with the median around 5 days. Overall, our research confirms the 8–10-day traditional estimate for the global mean residence time of atmospheric water, and our research contributes to a more complete view of the characteristics of the turnover of water in the atmosphere in time and space

The fate of land evaporation – a global dataset

Various studies investigated the fate of evaporation and the origin of precipitation. The more recent studies among them were often carried out with the help of numerical moisture tracking. Many research questions could be answered within this context, such as dependencies of atmospheric moisture transfers between different regions, impacts of land cover changes on the hydrological cycle, sustainability-related questions, and questions regarding the seasonal and interannual variability of precipitation. In order to facilitate future applications, global datasets on the fate of evaporation and the sources of precipitation are needed. Since most studies are on a regional level and focus more on the sources of precipitation, the goal of this study is to provide a readily available global dataset on the fate of evaporation for a fine-meshed grid of source and receptor cells. The dataset was created through a global run of the numerical moisture tracking model Water Accounting Model-2layers (WAM-2layers) and focused on the fate of land evaporation. The tracking was conducted on a 1.5∘×1.5∘ grid and was based on reanalysis data from the ERA-Interim database. Climatic input data were incorporated in 3- to 6-hourly time steps and represent the time period from 2001 to 2018. Atmospheric moisture was tracked forward in time and the geographical borders of the model were located at ±79.5∘ latitude. As a result of the model run, the annual, the monthly and the interannual average fate of evaporation were determined for 8684 land grid cells (all land cells except those located within Greenland and Antarctica) and provided via source–receptor matrices. The gained dataset was complemented via an aggregation to country and basin scales in order to highlight possible usages for areas of interest larger than grid cells. This resulted in data for 265 countries and 8223 basins. Finally, five types of source–receptor matrices for average moisture transfers were chosen to build the core of the dataset: land grid cell to grid cell, country to grid cell, basin to grid cell, country to country, basin to basin. The dataset is, to our knowledge, the first ready-to-download dataset providing the overall fate of evaporation for land cells of a global fine-meshed grid in monthly resolution. At the same time, information on the sources of precipitation can be extracted from it. It could be used for investigations into average annual, seasonal, and interannual sink and source regions of atmospheric moisture from land masses for most of the regions in the world and shows various application possibilities for studying interactions between people and water, such as land cover changes or human water consumption patterns. The dataset is accessible under https://doi.org/10.1594/PANGAEA.908705 (Link et al., 2019a) and comes along with example scripts for reading and plotting the data.publishedVersio