Field assessment of metal and base cation accumulation in green stormwater infrastructure soils.

Green stormwater infrastructure (GSI) is adopted to reduce the impact of stormwater on urban flooding and water quality issues. This study assessed the performance of GSI, like bioretention basins, in accumulating metals. Twenty one GSI basins were considered for this study, which were located in New York and Pennsylvania, USA. Shallow (0-5 cm) soil samples were collected from each site at inlet, pool, and adjacent reference locations. The study analyzed 3 base cations (Ca, Mg, Na) and 6 metals (Cd, Cr, Cu, Ni, Pb, and Zn), some of which are toxic to ecosystem and human health. The accumulation of cations/metals at the inlet and pool differed between the selected basins. However, accumulation was consistently higher at the inlet or the pool of the basin as compared to the reference location. Contrary to prior research, this study did not find significant accumulation with age, suggesting that other factors such as site characteristics (e.g., loading rate) might be confounding. GSI basins that receive water only from parking lots or parking lots and building roofs combined showed higher metals and Na accumulation as compared to the basins that received stormwater only from building roofs. Cu, Mg and Zn accumulation showed a positive relationship with the organic matter content in soil, indicating likely sorption of metals on organic matter. Ca and Cu accumulation was greater in GSI basins with larger drainage areas. A negative relationship between Cu and Na implies that Na loading from de-icers may reduce Cu retention. Overall, the study found that the GSI basins are successfully accumulating metals and some base cations, with highest accumulation at the inlet. Additionally, this study provided evidence of GSI effectiveness in accumulating metals using a more cost efficient and time averaged approach compared to traditional means of stormwater inflow and outflow monitoring.

More accurate specification of water supply shows its importance for global crop production.

Warming temperatures tend to damage crop yields, yet the influence of water supply on global yields and its relation to temperature stress remains unclear. Here we use satellite-based measurements to provide empirical estimates of how root zone soil moisture and surface air temperature jointly influence the global productivity of maize, soybeans, millet and sorghum. Relative to empirical models using precipitation as a proxy for water supply, we find that models using soil moisture explain 30-120% more of the interannual yield variation across crops. Models using soil moisture also better separate water-supply stress from correlated heat stress and show that soil moisture and temperature contribute roughly equally to historical variations in yield. Globally, our models project yield damages of -9% to -32% across crops by end-of-century under Shared Socioeconomic Pathway 5-8.5 from changes in temperature and soil moisture. By contrast, projections using temperature and precipitation overestimate damages by 28% to 320% across crops both because they confound stresses from dryness and heat and because changes in soil moisture and temperature diverge from their historical association due to climate change. Our results demonstrate the importance of accurately representing water supply for predicting changes in global agricultural productivity and for designing effective adaptation strategies.

Climate impacts and adaptation in US dairy systems 1981-2018.

Animal-level responses to weather variability in US dairy systems are well described, but the potential of housing and other farm management practices (for example, fans and sprinklers) to moderate the impacts of weather remains uncertain. Here we assess the influence of historical variation in the temperature-humidity index (THI) on milk yields using monthly state-level yield data and high-resolution daily weather data over 1981-2018. We find that milk yields are compromised by exposure to both extreme heat (>79 THI) and cold (<39 THI), causing average daily yield decreases of around 3.7% and 6.1%, respectively, relative to optimal conditions (65-69 THI). Colder regions are more sensitive to heat extremes, and warm regions are more sensitive to cold extremes. Sensitivity to THI has reduced dramatically over time. Climate trends contributed modestly (around 0.1% over 38 years) to rising yields in most states via alleviating cold stress, although more extreme future conditions may negate these benefits.

Urban heat island: Aerodynamics or imperviousness?

More than half of the world's population now live in cities, which are known to be heat islands. While daytime urban heat islands (UHIs) are traditionally thought to be the consequence of less evaporative cooling in cities, recent work sparks new debate, showing that geographic variations of daytime UHI intensity were largely explained by variations in the efficiency with which urban and rural areas convect heat from the land surface to the lower atmosphere. Here, we reconcile this debate by demonstrating that the difference between the recent finding and the traditional paradigm can be explained by the difference in the attribution methods. Using a new attribution method, we find that spatial variations of daytime UHI intensity are more controlled by variations in the capacity of urban and rural areas to evaporate water, suggesting that strategies enhancing the evaporation capability such as green infrastructure are effective ways to mitigate urban heat.

Stomatal response to humidity and CO2 implicated in recent decline in US evaporation.

Evapotranspiration, defined as the total flux of water from the land surface to the atmosphere, is a major component of the hydrologic cycle and surface energy balance. Although evapotranspiration is expected to intensify with increasing temperatures, long-term, regional trends in evapotranspiration remain uncertain due to spatially and temporally limited direct measurements. In this study, we utilize an emergent relation between the land surface and atmospheric boundary layer to infer daily evapotranspiration from historical meteorological data collected at 236 weather stations across the United States. Our results suggest a statistically significant (α = 0.05) decrease in evapotranspiration of approximately 6% from 1961 to 2014, with a significant (α = 0.05) sharp decline of 13% from 1998 to 2014. We attribute the decrease in evapotranspiration mostly to declines in surface conductance, but also to offsetting changes in longwave radiation, wind speed, and incoming solar radiation. Using an established stomatal conductance model, we explain the changes in inferred surface conductance as a response to increases in carbon dioxide and, more recently, to an abrupt decrease in atmospheric humidity.

Changes in autumn senescence in northern hemisphere deciduous trees: a meta-analysis of autumn phenology studies.

BACKGROUND AND AIMS: Many individual studies have shown that the timing of leaf senescence in boreal and temperate deciduous forests in the northern hemisphere is influenced by rising temperatures, but there is limited consensus on the magnitude, direction and spatial extent of this relationship. METHODS: A meta-analysis was conducted of published studies from the peer-reviewed literature that reported autumn senescence dates for deciduous trees in the northern hemisphere, encompassing 64 publications with observations ranging from 1931 to 2010. KEY RESULTS: Among the meteorological measurements examined, October temperatures were the strongest predictors of date of senescence, followed by cooling degree-days, latitude, photoperiod and, lastly, total monthly precipitation, although the strength of the relationships differed between high- and low-latitude sites. Autumn leaf senescence has been significantly more delayed at low (25° to 49°N) than high (50° to 70°N) latitudes across the northern hemisphere, with senescence across high-latitude sites more sensitive to the effects of photoperiod and low-latitude sites more sensitive to the effects of temperature. Delays in leaf senescence over time were stronger in North America compared with Europe and Asia. CONCLUSIONS: The results indicate that leaf senescence has been delayed over time and in response to temperature, although low-latitude sites show significantly stronger delays in senescence over time than high-latitude sites. While temperature alone may be a reasonable predictor of the date of leaf senescence when examining a broad suite of sites, it is important to consider that temperature-induced changes in senescence at high-latitude sites are likely to be constrained by the influence of photoperiod. Ecosystem-level differences in the mechanisms that control the timing of leaf senescence may affect both plant community interactions and ecosystem carbon storage as global temperatures increase over the next century.