Global maps of soil temperature.

Research in global change ecology relies heavily on global climatic grids derived from estimates of air temperature in open areas at around 2 m above the ground. These climatic grids do not reflect conditions below vegetation canopies and near the ground surface, where critical ecosystem functions occur and most terrestrial species reside. Here, we provide global maps of soil temperature and bioclimatic variables at a 1-km <sup>2</sup> resolution for 0-5 and 5-15 cm soil depth. These maps were created by calculating the difference (i.e. offset) between in situ soil temperature measurements, based on time series from over 1200 1-km <sup>2</sup> pixels (summarized from 8519 unique temperature sensors) across all the world's major terrestrial biomes, and coarse-grained air temperature estimates from ERA5-Land (an atmospheric reanalysis by the European Centre for Medium-Range Weather Forecasts). We show that mean annual soil temperature differs markedly from the corresponding gridded air temperature, by up to 10°C (mean = 3.0 ± 2.1°C), with substantial variation across biomes and seasons. Over the year, soils in cold and/or dry biomes are substantially warmer (+3.6 ± 2.3°C) than gridded air temperature, whereas soils in warm and humid environments are on average slightly cooler (-0.7 ± 2.3°C). The observed substantial and biome-specific offsets emphasize that the projected impacts of climate and climate change on near-surface biodiversity and ecosystem functioning are inaccurately assessed when air rather than soil temperature is used, especially in cold environments. The global soil-related bioclimatic variables provided here are an important step forward for any application in ecology and related disciplines. Nevertheless, we highlight the need to fill remaining geographic gaps by collecting more in situ measurements of microclimate conditions to further enhance the spatiotemporal resolution of global soil temperature products for ecological applications

Interactive effects of water-table depth, rainfall variation, and sowing date on maize production in the Western Pampas

tShallow water-tables strongly influence agro-ecosystems and pose difficult management challenges tofarmers trying to minimize their negative effects on crops and maximize their benefits. In this paper, weevaluated how the water-table depth interacts with rainfall and sowing date to shape maize performancein the Western Pampas of Argentina. For this purpose, we analyzed the influence of water-table depthon the yields of 44 maize plots sown in early and late dates along eight growing seasons (2004–2012)that we rated as dry or wet. In addition, we characterized the influence of the water-table depth onintercepted radiation and crop water status by analyzing MODIS and Landsat images, respectively. Thefour conditions we evaluated (early sown-dry growing season, early-wet, late-dry, late-wet) showedsimilar yield response curves to water-table depth, with an optimum depth range (1.5–2.5 m) whereyields were highest and stable (∼11.6 Mg ha−1on average). With water-table above this range, yieldsdeclined in all conditions at similar rates (p > 0.1), as well as the crop water status, as suggested bythe Crop Water Stress Index, evidencing the negative effects of waterlogging. Water-tables deeper thanthe optimum range also caused declines of yield, intercepted radiation and crop water status, beingthese declines remarkably higher in early maize during dry seasons, evidencing a greater reliance of thiscondition on groundwater supply. Yield in areas with deep water-tables (>4 m) was significantly reducedto between a quarter and a half of yields observed in areas with optimum water-tables. Rainfall occurredaround flowering had a strong impact on maize yield in areas with deep water-tables, but not in areaswith optimum depth, where yields showed high temporal stability and independence from rainfall in thatperiod. Our study confirmed the strong influence of water-table on rainfed maize and provides severalguidelines to help farmers to take better decisions oriented to minimize hydrological risks and maximizethe benefits of shallow water-tables

Hydrologic consequences of land cover change in central Argentina

Vegetation exerts a strong control on water balance and key hydrological variables like evapotranspiration. water yield or even the flooded area may result severely affected by vegetation changes. Particularly, transitions between tree- and herbaceous-dominated covers, which are taking place at increasing rates in South America, may have the greates.t impact on the water balance. Based on Landsat imagery analysis, soil sampling and hydrological modeling, we evaluated vapor and liquid ecosystem water fluxes and soil moisture changes in temperate Argentina and provided a useful framework to assess potential hydrological impacts of vegetation cover changes. Two types of native vegetation (grasslands and forests) and three modified covers (eucalyptus plantations. single soybean crop and wheat/soybean rotation) were considered in the analysis. Despite contrasting structural differences, native forests and eucalyptus plantations displayed evapotranspiration values remarkably similar ( -1100 mm y- 1) and significantly higher than herbaceous vegetation covers ( -780, - 670 and - 800 mm y-1 for grasslands, soybean and wheat/soybean (Triticum aestivum L, Glycine max L.) system, respectively. In agreement with evapotranspiration estimates, soil profiles to a depth of 3m were significantly drier in woody covers (31m3 m-3) compared to native grasslands (39m3 m-3 ). soybean (38.5 m3 m- 3) and wheat/soybean rotation (35m3 m-3 ). Liquid water fluxes (deep drainage+ surface runoff) were at least doubied in herbaceous covers. as suggested by modeling( - 170 mmy-1 and -357 mm y- 1. for woody and herbaceous covers. respectively). Our analysis revealed the hydrological outcomes of different vegetation changes trajectories and provided valuable tools that will help to anticipate likely impacts, minimize uncertainties and provide a solid base for sustainable land use planning

Higher water-table levels and flooding risk under grain vs. livestock production systems in the subhumid plains of the Pampas

Although the strong influence of vegetation shaping the hydrological cycle is increasingly recognized, the effects of land-use changes in very flat regions (i.e. hyperplains, regional slope < 0.1%) are less understood in spite of their potentially large magnitude. In hyperplains with sub-humid climates, long-lasting flooding episodes associated to water-table raises are a distinctive ecohydrological feature and a critical environmental concern. We evaluated the hydrological impacts caused by the replacement of livestock systems, dominated by perennial alfalfa pastures, by grain production systems, dominated by annual crops, that has been taking place in the Pampas (Argentina). For this purpose, we combined remote sensing estimates of vegetation transpiration and surface water coverage with long-term (1970-2009) hydrological modeling (HYDRUS 1D), and water-table depth and soil moisture measurements. The NDVI derived from MODIS imagery was 15% higher in dairy systems than in grain production ones, suggesting higher transpiration capacity in the former (852 vs. 724 mm y-1). Even higher contrasts were found among individual cover types, with perennial pastures having the highest NDVI and transpiration potential rates (0.66 and 1075 mm y-1), followed by double winter/summer crops (0.55 and 778 mm y-1) and single summer crop (0.45 and 679 mm y-1). Significantly deeper long-term average water-table levels in dairy system compared to single and double cropping (4 m, 2.1 m and 1.5 m, respectively) were suggested by the hydrological modeling and confirmed by field observations at nine paired sites (pasture vs. cropland, p<0.05) and two transects. At two additional paired sites, continuous water-table depth monitoring with pressure transducers, provided insights about the mechanisms behind these contrasts, which included enhanced groundwater recharge in the cropland and direct groundwater discharge by the pasture. Soil profiles, being notably drier under pastures (316 vs. 552 mm stored at 0-3 m depth, p<0.05), prevented the recharge episodes experienced by agricultural plots after an extraordinary rainy period. Our study highlights the key role of land-use on the hydrology of subhumid hyperplains, supporting the linkage of groundwater level raises and flood frequency and severity increases with the expansion of grain production systems in the Pampas. Given the spatial connectivity imposed by the hydrologic system and the strong association observed between the plot water balance and regional flooding, it is highly relevant to improve the quantification of the hydrological responsibility and interdependence of land use decision across plots and farms. This further step should support territorial policies that optimize the hydrological services of the region

Regional patterns and controls of ecosystem salinization with grassland afforestation along a rainfall gradient

In this study, salinization occurred rapidly where rainfall was insufficient to meet the water requirements of tree plantations, and where groundwater use compensated for this deficit, it was the driving factor for salt accumulation in the ecosystem. Vegetation change affects water fluxes, and influences the direction and intensity of salt exchange between ecosystems and groundwater. It can lead to an intense accumulation of salts in soils and aquifers, as evidenced in conversion from native grassland to tree plantation. An understanding of the vegetation-groundwater relationship helps predict and manage the consequences of groundwater use from stand to regional levels of analysis

Reciprocal influence of crops and shallow ground water in sandy landscapes of the Inland Pampas

The analysis shows that in flat humid landscapes such as the Pampas, crops and shallow ground water are closely connected and influence each other. An optimum groundwater depth range where crop yields were highest was observed for all three crop species analyzed (wheat, maize, and soybean). The areas within these optimum bands had yields that were respectively, 3.7, 3 and 1.8 times larger than those where the water table was below 4 m. As groundwater levels become shallower crop yields declined sharply. Understanding complex interactions and simultaneous occurrences could provide keys to regulating the labile hydrology of these plains

Water subsidies from mountains to deserts : their role in sustaining groundwater-fed oases in a sandy landscape

The study indicates a reliance of ecosystem productivity on Andean snowmelt, which is increasingly being diverted to one of the largest irrigated regions of the continent. Deep soil coring, plant measurements, direct water-table observations, and stable isotopic analyses (2H and 18O) of meteoric, surface, and ground waters, were used to compare woodland stands, bare dunes, and surrounding shrublands. The isotopic composition of phreatic groundwaters closely matched the signature of water brought to the region by the Mendoza River, suggesting that mountain-river infiltration, rather than in situ rainfall deep drainage was the dominant mechanism of groundwater recharge

Global maps of soil temperature

Research in global change ecology relies heavily on global climatic grids derived from estimates of air temperature in open areas at around 2 m above the ground. These climatic grids do not reflect conditions below vegetation canopies and near the ground surface, where critical ecosystem functions occur and most terrestrial species reside. Here, we provide global maps of soil temperature and bioclimatic variables at a 1-km2 resolution for 0–5 and 5–15 cm soil depth. These maps were created by calculating the difference (i.e. offset) between in situ soil temperature measurements, based on time series from over 1200 1-km2 pixels (summarized from 8519 unique temperature sensors) across all the world's major terrestrial biomes, and coarse-grained air temperature estimates from ERA5-Land (an atmospheric reanalysis by the European Centre for Medium-Range Weather Forecasts). We show that mean annual soil temperature differs markedly from the corresponding gridded air temperature, by up to 10°C (mean = 3.0 ± 2.1°C), with substantial variation across biomes and seasons. Over the year, soils in cold and/or dry biomes are substantially warmer (+3.6 ± 2.3°C) than gridded air temperature, whereas soils in warm and humid environments are on average slightly cooler (−0.7 ± 2.3°C). The observed substantial and biome-specific offsets emphasize that the projected impacts of climate and climate change on near-surface biodiversity and ecosystem functioning are inaccurately assessed when air rather than soil temperature is used, especially in cold environments. The global soil-related bioclimatic variables provided here are an important step forward for any application in ecology and related disciplines. Nevertheless, we highlight the need to fill remaining geographic gaps by collecting more in situ measurements of microclimate conditions to further enhance the spatiotemporal resolution of global soil temperature products for ecological application