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Mark R. Jury

Abstract

The concentration of trace gases and aerosols in Ethiopia is poorly characterized due to a limited history of surface measurements. Here, satellite measurements and model estimates of atmospheric composition are employed to understand space–time distributions in the period 2000–16. Methane (CH4) and carbon monoxide (CO) display high concentrations over the highlands and provide a focus for analysis of monthly and daily data. CH4 emissions from livestock peak at the beginning of the dry season, while CO from biomass burning rises at the end of the dry season. The seasonal cycle of dust, aerosol optical depth (AOD), and CO2 is inversely related with CH4, while CO closely follows sensible heat flux, thus linking drying and rural biomass burning. Stable easterly flow in the dry season accumulates local emissions, so near-surface concentrations of CO and CH4 are high then. The weather pattern underlying an episode of high nitrogen dioxide (NO2) concentrations was studied. In addition to a stable lapse rate and dry anticyclonic weather, midtropospheric subsidence was related to intrusion of the northern subtropical jet stream on 24–26 December 2010. The wind shadow was cast by the Rift Escarpment limited dispersion, particularly with the dry, stable weather conditions. A key outcome of this work is that CH4 concentrations over Ethiopia are high in global context and have increased >0.1 ppm from 2002 to 2016; hence, there is a need to improve livestock management and production efficiency.

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Saumya Sarkar, Jonathan B. Butcher, Thomas E. Johnson, and Christopher M. Clark

Abstract

Climate change is likely to alter the quantity and quality of urban stormwater, presenting a risk to water quality and public health. How might stormwater management practices need to change to address future climate? Answering requires understanding how management practices respond to climate forcing. Traditional “gray” stormwater design employs engineered structures, sized based on assumptions about future rainfall, which have limited flexibility once built. Green infrastructure (GI) uses vegetation, soil, and distributed structures to manage rainwater where it falls and may provide greater flexibility for adaptation. There is, however, uncertainty about how a warmer climate may affect performance of different types of GI. This study uses the hydrologic and biogeochemical watershed model, Regional Hydro-Ecologic Simulation System (RHESSys), to investigate sensitivity of different GI practices to climate. Simulations examine 36 urban “archetypes” representing different development patterns (at the city block scale) of typical U.S. cities, 11 regional climatic settings, and a range of mid-twenty-first-century scenarios based on downscaled climate model output. Results suggest regionally variable effects of climate change on the performance of GI practices for water quantity, water quality, and carbon sequestration. GI is able to mitigate most projected future increases in surface runoff, while bioretention can mitigate increased nitrogen yield at nine of 11 sites. Simulated changes in carbon balance are small, while local evaporative cooling can be substantial. Given uncertainty in the local expression of future climate, infrastructure design should emphasize flexibility and robustness to a range of future conditions.

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Andrew R. Bock, Lauren E. Hay, Gregory J. McCabe, Steven L. Markstrom, and R. Dwight Atkinson

Abstract

The accuracy of statistically downscaled (SD) general circulation model (GCM) simulations of monthly surface climate for historical conditions (1950–2005) was assessed for the conterminous United States (CONUS). The SD monthly precipitation (PPT) and temperature (TAVE) from 95 GCMs from phases 3 and 5 of the Coupled Model Intercomparison Project (CMIP3 and CMIP5) were used as inputs to a monthly water balance model (MWBM). Distributions of MWBM input (PPT and TAVE) and output [runoff (RUN)] variables derived from gridded station data (GSD) and historical SD climate were compared using the Kolmogorov–Smirnov (KS) test For all three variables considered, the KS test results showed that variables simulated using CMIP5 generally are more reliable than those derived from CMIP3, likely due to improvements in PPT simulations. At most locations across the CONUS, the largest differences between GSD and SD PPT and RUN occurred in the lowest part of the distributions (i.e., low-flow RUN and low-magnitude PPT). Results indicate that for the majority of the CONUS, there are downscaled GCMs that can reliably simulate historical climatic conditions. But, in some geographic locations, none of the SD GCMs replicated historical conditions for two of the three variables (PPT and RUN) based on the KS test, with a significance level of 0.05. In these locations, improved GCM simulations of PPT are needed to more reliably estimate components of the hydrologic cycle. Simple metrics and statistical tests, such as those described here, can provide an initial set of criteria to help simplify GCM selection.

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Hongshou Li

Abstract

Because of Earth’s motion, periodic temperature fluctuations occur in soil on daily and yearly time scales, which inevitably lead to pulsation of the air pressure in the soil. The Earth–air pressure monitoring technique called “hou-qi” is the basis of a calendar formulated by the ancient Chinese. However, the daily/yearly variation of air pressure in the soil is very weak, according to practical monitoring experiments, so hou-qi has long been considered a pseudoscience. To determine the potential maximum change of Earth–air pressure, identify what is causing the underlying Earth–air pressure variation, and reveal the mechanism, we use a closed system, which is a more appropriate system test of the possible validity of hou-qi, to monitor Earth–air pressure variation in this paper. The results show that there are potential air pressure fluctuations of about 120–190 hPa in closed soil over the daily/yearly temperature range of 5°–40°C. This provides ample magnitude for hou-qi. The largest contribution made to Earth–air pressure variation was pressurization due to air warming, with vapor due to water evaporation and desorbed gas having smaller effects. The soil’s water content has a significant effect on Earth–air pressure amplitude. Dry soil contributes almost no water vapor, but the adsorbed gases from dry soil have up to a 38-hPa influence on air pressure. The soil’s salt content also has an important regulating role on Earth–air pressure and can reduce the influence of vapor pressure. This paper provides a scientific basis for the ancient Earth–air monitoring system of hou-qi and also has important significance for hydrometeorology and research on the ancient Chinese civilization.

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Youyue Wen, Xiaoping Liu, and Guoming Du

Abstract

Climate warming exhibits asymmetric patterns over a diel time, with the trend of nighttime warming exceeding that of daytime warming, a phenomenon commonly known as asymmetric warming. Recently, increasing studies have documented the significant instantaneous impacts of asymmetric warming on terrestrial vegetation growth, but the indirect effects of asymmetric warming carrying over vegetation growth (referred to here as time-lag effects) remain unknown. Here, we quantitatively studied the time-lag effects (within 1 year) of asymmetric warming on global plant biomes by using terrestrial vegetation net primary production (NPP) derived by the Carnegie–Ames–Stanford Approach (CASA) model and accumulated daytime and nighttime temperature (ATmax and ATmin) from 1982 to 2013. Partial correlation and time-lag analyses were conducted at a monthly scale to obtain the partial correlation coefficients between NPP and ATmax/ATmin and the lagged durations of NPP responses to ATmax/ATmin. The results showed that (i) asymmetric warming has nonuniform time-lag effects on single plant biomes, and distinguishing correlations exist in different vegetation biomes’ associations to asymmetric warming; (ii) terrestrial biomes respond to ATmax (4.63 ± 3.92 months) with a shorter protracted duration than to ATmin (6.06 ± 4.27 months); (iii) forest biomes exhibit longer prolonged duration in responding to asymmetric warming than nonforest biomes do; (iv) mosses and lichens (Mosses), evergreen needleleaf forests (ENF), deciduous needleleaf forests (DNF), and mixed forests (MF) tend to positively correlate with ATmax, whereas the other biomes associate with ATmax with near-equal splits of positive and negative correlation; and (v) ATmin has a predominantly positive influence on terrestrial biomes, except for Mosses and DNF. This study provides a new perspective on terrestrial ecosystem responses to asymmetric warming and highlights the importance of including such nonuniform time-lag effects into currently used terrestrial ecosystem models during future investigations of vegetation–climate interactions.

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Jinyun Tang and William J. Riley

Abstract

While coupling carbon and nitrogen processes is critical for Earth system models to accurately predict future climate and land biogeochemistry feedbacks, it has not yet been analyzed how numerical methods that land biogeochemical models apply to couple soil mineral nitrogen mobilizing and immobilizing processes affect predicted ecosystem carbon and nitrogen cycling. These effects were investigated here by using the E3SM land model and an evaluation of three plausible and widely used numerical couplings: 1) the mineral nitrogen–based limitation scheme, 2) the net uptake–based limitation scheme, and 3) the proportional nitrogen flux–based limitation scheme. It was found that these three schemes resulted in large differences (with a range of 316 PgC) in predicted cumulative land–atmosphere carbon exchanges under the RCP4.5 atmospheric CO2 simulations. This large uncertainty is without accounting for the different representations of the many land biogeochemical processes, but is about 73% of the range (434 PgC) reported for CMIP5 RCP4.5 simulations. These results help explain the large uncertainty found in various model intercomparison experiments and suggest that more robust numerical implementations are needed to improve carbon–nutrient cycle coupling in terrestrial ecosystem models.

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David M. Schultz, Timothy M. DelSole, Robert M. Rauber, and Walter A. Robinson
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Gretchen Keppel-Aleks, Samantha J. Basile, and Forrest M. Hoffman

Abstract

Earth system models (ESMs) simulate a large spread in carbon cycle feedbacks to climate change, particularly in their prediction of cumulative changes in terrestrial carbon storage. Evaluating the performance of ESMs against observations and assessing the likelihood of long-term climate predictions are crucial for model development. Here, we assessed the use of atmospheric growth rate variations to evaluate the sensitivity of tropical ecosystem carbon fluxes to interannual temperature variations. We found that the temperature sensitivity of the observed growth rate depended on the time scales over which atmospheric observations were averaged. The temperature sensitivity of the growth rate during Northern Hemisphere winter is most directly related to the tropical carbon flux sensitivity since winter variations in Northern Hemisphere carbon fluxes are relatively small. This metric can be used to test the fidelity of interactions between the physical climate system and terrestrial ecosystems within ESMs, which is especially important since the short-term relationship between ecosystem fluxes and temperature stress may be related to the long-term feedbacks between ecosystems and climate. If the interannual temperature sensitivity is used to constrain long-term temperature responses, the inferred sensitivity may be biased by 20%, unless the seasonality of the relationship between the observed growth rate and tropical fluxes is taken into account. These results suggest that atmospheric data can be used directly to evaluate regional land fluxes from ESMs, but underscore that the interaction between the time scales for land surface processes and those for atmospheric processes must be considered.

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Farhat Abbas, Nida Sarwar, Muhammad Ibrahim, Muhammad Adrees, Shafaqat Ali, Farhan Saleem, and Hafiz Mohkum Hammad

Abstract

Climatic extremes have direct and indirect effects on an ecosystem, whereby thermal variations bring warm and cold weather, and hydrological anomalies cause droughts and floods. Changing patterns of 13 temperature and 11 precipitation extreme indices for a 36-yr period (1980–2015) for four cities of the Balochistan province of Pakistan (Pasni, Jiwani, Khuzdar, and Dalbadin) were computed using RClimdex. A nonparametric Mann–Kendall test and Sen’s slope estimates were used to determine the statistical significance and magnitude of a trend, respectively. Most of the indices calculated for temperature extremes show statistically significant changes in their historic pattern, depicting a clear picture of warming in the regions. The indices calculated for precipitation extremes show statistically significant as well as nonsignificant results, depicting asymmetrical droughts in the region. If the patterns of humid weather with hot and wet extremes in the coastal cities of Balochistan continue for a couple of future decades, there will be challenges in implementing the multibillion-dollar Balochistan coastal development projects of the Pakistani port of Gwadar—a doorway to the Middle East for Chinese-planned business endeavors through Pakistan.

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Virnei Silva Moreira, Luiz Antonio Candido, Debora Regina Roberti, Geovane Webler, Marcelo Bortoluzzi Diaz, Luis Gustavo Gonçalves de Gonçalves, Raphael Pousa, and Gervásio Annes Degrazia

Abstract

The water balance in agricultural cropping systems is dependent on the physical and hydraulic characteristics of the soil and the type of farming, both of which are sensitive to the soil management. Most models that describe the interaction between the surface and the atmosphere do not efficiently represent the physical differences across different soil management areas. In this study, the authors analyzed the dynamics of the water exchange in the agricultural version of the Integrated Biosphere Simulator (IBIS) model (Agro-IBIS) in the presence of different physical soil properties because of the different long-term soil management systems. The experimental soil properties were obtained from two management systems, no tillage (NT) and conventional tillage (CT) in a long-term experiment in southern Brazil in the soybean growing season of 2009/10. To simulate NT management, this study modified the top soil layer in the model to represent the residual layer. Moreover, a mathematical adjustment to the computation of leaf area index (LAI) is suggested to obtain a better representation of the grain fill to the physiological maturity period. The water exchange dynamics simulated using Agro-IBIS were compared against experimental data collected from both tillage systems. The results show that the model well represented the water dynamics in the soil and the evapotranspiration (ET) in both management systems, in particular during the wet periods. Better results were found for the conventional tillage management system for the water balance. However, with the incorporation of a residual layer and soil properties in NT, the model improved the estimation of evapotranspiration by 6%. The ability of the Agro-IBIS model to estimate ET indicates its potential application in future climate scenarios.

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