High Potential Evapotranspiration Research Articles

Seasonality and Drivers of Low Flows Across Europe and the United States

AbstractLow river flows can negatively impact society and the riverine environment. Thus, it is useful to predict their seasonal timing and reveal their main drivers. The typical timing of low flows varies between regions, yet systematic overviews across Europe and the United States are rare. Here, we identify regional patterns of the seasonal timing of annual minimum flows, and the consistency of that timing, across 1860 European and US catchments. Catchments where low flows typically occur during late summer or winter tend to have more consistent low‐flow timings. We compare the timing of annual low flows with that of potential climatic drivers. Low flows in 89% of the European and 86% of the US catchments exhibit a statistically significant (p < 0.05) overlap in timing with at least one potential climatic driver. In most catchments, low flows tend to occur during the warm season, reflecting a period of high potential evapotranspiration exceeding precipitation. In the higher elevation European Alps, Scandinavia, the Rocky Mountains, and the Upper Midwest and Plains states, low flows mostly occur during winter as a result of freezing temperatures which inhibit snowmelt. Binomial statistics also enabled us to statistically exclude individual climatic drivers for certain regions. The regional patterns of timings and drivers of low flows across Europe and the contiguous US can inform low‐flow management, provide context for the evolution of low flows under climate change, and point to processes that require attention in future low‐flow research.

Climatic water balance in Hamelmalo, Eritrea

Agricultural production is an important sector for peoples to live, but it is highly affected by climate change. To have a good production we need to understand the climatic parameters which adversely affect production. Hamelmalo, which is located in the semi-arid area of Eritrea, is vulnerable to climate change and this is realised in the total production loss. Nevertheless, there is no concrete reference about the climate of the region due to lack of data for a long time. Changes in precipitation (P), evapotranspiration (ET) and, implicitly, in the climatic water balance (CWB), are imminent effects of climate change. However, changes in the CWB, as a response to changes in P and ET, have not yet been analysed thoroughly enough in many parts of the world, including Eritrea. This study also explores the changes of the CWB in the Hamelmalo region, based on a wide range of climatic data (P, relative air humidity and evaporation pan necessary for computing potential evapotranspiration (PET) with the pan evaporation method) recorded at Hamelmalo from 2015-2019. This analysis shows that the annual cumulative CWB for Hamelmalo is negative in 67% of the years. The dry season without precipitation leads to negative CWB and the change in CWB only starts from the raining or crop season. Based on this recent study, 2015 had the highest PET and lowest P, and this resulted in the lowest CWB in the investigated period. Opposite to this, 2019 had lower PET and highest P, which led to the highest CWB. However, the monthly values of CWB did not correlate with the annual P or ET. On the base of our study, it can be concluded that PET and P were very variable in the investigated years and P was the most influential elements of CWB.

Verifying the applicability of SWAT to simulate fecal contamination for watershed management of Selangor River, Malaysia

The Soil and Water Assessment Tool (SWAT) ecohydrological model was utilized to simulate fecal contamination in the 1937 km2 Selangor River Watershed in Malaysia. The watershed conditions posed considerable challenges owing to data scarcity and tropical climate conditions, which are very different from the original conditions that SWAT was developed and tested for. Insufficient data were compensated by publicly available data (e.g., land cover, soil, and weather) to run SWAT. In addition, field monitoring and interviews clarified representative situations of pollution sources and loads, which were used as input for the model. Model parameters determined by empirical analyses in the USA (e.g., surface runoff, evapotranspiration, and temperature adjustment for bacteria die-off) are thoroughly discussed. In particular, due consideration was given to tropical climate characteristics such as intense rainfall, high potential evapotranspiration, and high temperatures throughout the year. As a result, the developed SWAT successfully simulated fecal contamination ranging several orders of magnitude along with its spatial distribution (i.e., Nash-Sutcliffe Efficiency (NSE) = 0.64, Root Mean Square Error–Observations Standard Deviation Ratio (RSR) = 0.64 at six mainstem sites, and NSE = 0.67 and RSR = 0.57 at 12 major tributaries). Moreover, mitigation countermeasures for future worsening of fecal contamination (i.e., E.coli concentration > 20,000 CFU/100 mL for 690 days during nine years at a raw water intake point for Kuala Lumpur [KL] residents) were analyzed through scenario simulations, thereby contributing to discussing effective watershed management. The results propose improving decentralized sewage treatment systems and treating chicken manure with effective microorganisms in order to guarantee water safety for KL residents (i.e., E.coli concentrations <20,000 CFU/100 mL throughout the period, considering Malaysian standards). Accordingly, this study verified the applicability of SWAT to simulate fecal contamination in areas that are difficult to model and suggests solutions for watershed management based on quantitative evidence.

EHSMu: a New Ecohydrological Streamflow Model to Estimate Runoff in Urban Areas

A conceptual lumped ecohydrological streamflow model (EHSMu) is presented as a promising tool to simulate runoff in urban catchments. The model, based on the interaction between a soil bucket and two linear reservoirs, enables also evapotranspiration and aquifer recharge to be estimated. Notwithstanding its minimalism, EHSMu describes interactions among soil moisture dynamics, hydrological fluxes and ecological processes. The model was calibrated and validated within two densely urbanized sub-basins in Charlotte (US). A Monte Carlo procedure is used to investigate the efficiency of random sets of 8 model parameters. Results show the high model performance (NSE = 0.72). The influence of land use change is evaluated, by varying the imperviousness and crop coefficients. Synthetic experiments show that increasing urbanization triggers a linear decrease in evapotranspiration and aquifer recharge, while it increases the fast runoff. An opposite response is achieved by installing vegetation with higher potential evapotranspiration, which would contribute to the actual evapotranspiration making up 50–55% of the total water balance.

White‐faced darter distribution is associated with coniferous forests in Great Britain

Abstract Understanding of dragonfly distributions is often geographically comprehensive but less so in ecological terms. White‐faced darter (Leucorhinnia dubia) is a lowland peatbog specialist dragonfly which has experienced population declines in Great Britain. White‐faced darter is thought to rely on peat‐rich pool complexes within woodland, but this has not yet been empirically tested. We used dragonfly recording data collected by volunteers of the British Dragonfly Society from 2005 to 2018 to model habitat preference for white‐faced darter using species distribution models across Great Britain and, with a more detailed landcover data set, specifically in the North of Scotland. Across the whole of Great Britain, our models used the proportion of coniferous forest within 1 km as the most important predictor of habitat suitability but were not able to predict all current populations in England. In the North of Scotland, our models were more successful and suggest that habitats characterised by native coniferous forest and areas with high potential evapotranspiration represent the most suitable habitat for white‐faced darter. We recommend that future white‐faced darter monitoring should be expanded to include areas currently poorly surveyed but with high suitability in the North of Scotland. Our results also suggest that white‐faced darter management should concentrate on maintaining Sphagnum rich‐pool complexes and the maintenance and restoration of native forests in which these pool complexes occur.

Drought Trends and the Extreme Drought Frequency and Characteristics under Climate Change Based on SPI and HI in the Upper and Middle Reaches of the Huai River Basin, China

The Huai River Basin (HRB) is an important grain and industrial production area in eastern China with frequent droughts. Under the background of current climate change, the hydrological and meteorological characteristics of the basin may be changed, which may lead to the changes of regional drought characteristics. It should be paid more attention on the drought research under climate change and the difference between different drought indices. Coupled Model Intercomparison Project phase 5 (CMIP5) as an important tool for climate change research has been used in the study and the study chosen three global circulation models (GCMs)—such as CNRM-CM5 (CNR), HadGEM2-ES (Had), and MIROC5 (MIR)—to gather an ensemble model (EnM) for providing the future climate information. The Standardized Precipitation Index (SPI) and Humidity Index (HI) were used to evaluate and compare the drought situations in the past and the future periods with two representative concentration path scenarios (RCP4.5 &amp; RCP8.5). Some sequence statistics methods, such as Mann–Kendall test and run theory, were carried out to analyze the trend and the changes of extreme drought frequency and characteristics values. The research showed that the simulation accuracy of the EnM would better. SPI and HI take different factors into count and thus lead to differences in describing drought trend, extreme drought frequency, and characteristic values, such as drought severity, drought duration, mean drought severity, and max drought intensity. The research showed that both SPI and HI showed the same wetting or drying trend in the same timescales (except winter) as in the historical data. However, the future annual and seasonal drought trend reflected by SPI shows a wetting trend while HI shows a drying trend. Both in the past and the future, extreme drought frequency and characteristic values reflected by HI are higher than SPI. The drought trend is greater, and the extreme drought frequency and characteristics tend to be strengthened under RCP8.5. Low precipitation and high potential evapotranspiration (PET), especially the PET caused by temperature rise, are the main influencing factors of drought in the future. Therefore, the influence of the PET should not be ignored in drought analysis and we should strengthen the comparative study of different drought indices in future drought analysis under climate change.

Threats to soil and water resources in South Africa

South Africa has always been subject to an arid climate, receiving only slightly more than half of the world's average precipitation. This precarious situation is further exacerbated by very high potential evapotranspiration and an extremely rapid population growth. This paper aims to evaluate the threats to the soil and water resources of South Africa. These resources are vital in ensuring sustainable food production. Physically, wind and water erosion, structural decay, subsoil compaction and soil surface crusting are of great concern. Chemically, acidification, salinization, and pollution are the main concerns; with acidification mainly limited to the humid eastern parts and salinization to the arid western parts of South Africa. Biological degradation is mainly driven by organic matter decline, reducing the already low soil organic carbon content of South African soils. The extent of organism decline and the concomitant pathogen increase is not that well-known. Water resources in South Africa are very limited and of variable certainty. Water use efficiency, especially in agriculture and forestry, should receive urgent attention, since these are the main consumers of this valuable resource. Sedimentation, salinization, and pollution constitute the main impacts on water quality. Water pollution arises mainly from point sources such as municipal effluent, with smaller impacts from industry and feedlots. Given the varied nature of institutions and role-players involved in soil and water degradation, it is vital that one or more national institutions take responsibility to monitor and at least attempt to rectify and/or manage the degradation of South Africa's soil and water resources. In this regard substantial financial support from the private sector would also be imperative.

VAZÃO E TRATAMENTO SECUNDÁRIO DE ESGOTO DOMÉSTICO EM ESTAÇÃO DE PEQUENO PORTE COM SISTEMA DE ZONA DE RAÍZES

VAZÃO E TRATAMENTO SECUNDÁRIO DE ESGOTO DOMÉSTICO EM ESTAÇÃO DE PEQUENO PORTE COM SISTEMA DE ZONA DE RAÍZES&#x0D; &#x0D; &#x0D; ANA CLÁUDIA OLIVEIRA SÉRVULO1; JEANE DA SILVA TAVARES2RODRIGO MOURA PEREIRA3E DELVIO SANDRI4&#x0D; &#x0D; 1Doutoranda, Programa de Pós Graduação em Agronomia, Universidade de Brasília (UnB),Faculdade de Agronomia e Medicina Veterinária (FAV), Campus Universitário Darcy Ribeiro, ICC Centro,Asa Norte CEP 70.910-900 – Brasília, Brasil, e-mail: anaclaudiaoservulo@hotmail.com.&#x0D; 2Aluna de graduação, Universidade de Brasília (UnB),Faculdade de Agronomia e Medicina Veterinária (FAV), Campus Universitário Darcy Ribeiro, ICC Centro,Asa Norte CEP 70.910-900 – Brasília, Brasil, e-mail:jeanesilva2512@hotmail.com.&#x0D; 3Doutorando, Universidade de Brasília (UnB),Faculdade de Agronomia e Medicina Veterinária (FAV), Campus Universitário Darcy Ribeiro, ICC Centro,Asa Norte CEP 70.910-900 – Brasília, Brasil, e-mail: rodrigomoura@agricola.eng.br.&#x0D; 4Prof. Associado 1, Universidade de Brasília (UnB),Faculdade de Agronomia e Medicina Veterinária (FAV), Campus Universitário Darcy Ribeiro, ICC Centro,Asa Norte CEP 70.910-900 – Brasília, Brasil, e-mail: sandri@unb.br.&#x0D; &#x0D; &#x0D; 1 RESUMO&#x0D; &#x0D; O sistema de zona de raízes (SZR) é uma alternativa para tratamento de esgotos, cuja eficiência depende do material de suporte, composição do esgoto, espécie de macrófita e tempo de detenção hidráulica (TDH). Objetivou-se avaliar a medição de vazões de afluente e efluente de esgoto dos SZR com o uso de hidrômetro e método direto volumétrico(MDV) e a eficiência de diferentes espécies de macrófitas na remoção de atributos físicos e químicos do efluente. O esgoto bruto é gerado nos sanitários e restaurante universitário da Fazenda Água Limpa -UnB. Quatro leitos de tratamento foram utilizados: não cultivado, SZR com C. giganteus, Typha sppe H. rostrata. As avaliações ocorreram em quatro dias distintos. A evapotranspiração potencial (ETP) dos leitos foi obtida pela razão entre a diferença de volumes de afluente e efluente e a área superficial dos leitos. O hidrômetro não foi adequado na medida do volume de afluente, recomendando-se o MDV. A maior ETP ocorreu no SZR com Typha spp (9,98 mm dia-1)seguido do C. giganteus(9,37 mm dia-1).O maior valor de TDH foi de 9,49 dias e o menor de 4,68 dias. O oxigênio dissolvido, pH, turbidez e sólidos totais atendem aos limites para lançamento em corpos hídricos de classe 2.&#x0D; &#x0D; Palavras-chaves: macrófita, água residuária, leito cultivado.&#x0D; &#x0D; &#x0D; SÉRVULO, A.C.O.; TAVARES, J.S.; PEREIRA, R.M.; SANDRI, D. &#x0D; FLOW RATES AND SECONDARY TREATMENT OF WASTEWATER IN SMALL-SCALE TREATMENT PLANT WITH ROOT ZONE SYSTEM&#x0D; &#x0D; &#x0D; 2 ABSTRACT&#x0D; &#x0D; The root treatment wetland (RTW) is a low cost option to wastewater treatment, which efficiency depends on support material, wastewater composition, macrophyte specie and hydraulic detention time (HDT). This paper aimed to test the performance of the hydrometer and the volumetric method (VM)on measurement of effluentflow, and the removal efficiency of different macrophyte species over physical and chemical effluent attributes. The wastewater was from the bathrooms and restaurant in the experimental farm of the University of Brasília. Four constructed wetlands were used: free water system (FWS), RTW with Cyperus giganteus, with Typha spp and with Heliconia rostrata. The evaluation occurred in four days isolated. The systems’ potential evapotranspiration (PET) was determinate by the quocient of affluent-effluent volumes balance and the wetland surface area. The hydrometer didn’t measure affluent flow properly, recommending the VM. The highest PET was on RTW-Typha spp (9.98 mm day-1), followed by C. giganteus (9.37 mm day-1). The highest HDT was 9,49 days and the lowest was 4.68 days. The dissolved oxygen, pH, turbidity and total solids content are fit the Brazilian legal requirements for release into class 2 receiving bodies.&#x0D; &#x0D; Keywords: macrophytes, sewage, wetland.

Special issue «environmental change on the Mongolian plateau: atmosphere, forests, soils and water»

The Mongolian Plateau forms a part of the Central Asian Plateau and covers an area of approximately 3,200,000 square kilometers in Mongolia and adjacent areas in China and Southern Siberia. It contains one of the world’s largest grassland areas, with the Gobi desert in the south and a transition via steppe and forest steppe to the taiga and mountain tundra in the North (Dulamsuren et al. 2005; Miao et al. 2015). Due to its location, the Plateau's climate is continental and semi-arid to arid, characterized by low precipitation (about 250 mm on average), high potential evapotranspiration (almost 1000 mm on average), large temperature amplitudes, long and harsh winters and recurrent droughts (Dorjgotov 2009; Liu et al. 2019). The Mongolian Plateau mostly drains into the Arctic Ocean basin, including the system of the Selenga River and Lake Baikal, which is not only the world's largest freshwater lake but also a natural heritage of global importance (Kasimov et al. 2017). Hydrologically, parts of the plateau also belong to the Pacific Ocean and Central Asian internal drainage basins.

Reconstruction of potential evapotranspiration over western Himalaya in India based on tree ring-width records

Tree-ring chronologies from different sites of western Himalaya have been used in this study to examine the climate variability/change over the region. The 1st principal component (PC1) which has been computed by multi species tree ring chronologies of western Himalaya is negatively correlated with heat index (HT), temperature (TM) and potential evapotranspiration (PET) but positively with the rainfall of the region during spring season. However, HT and PET showed the stronger influence on tree growth than temperature which has been used to reconstruct the spring season PET back to A.D. 1779. The extended periods of low PET have been found at ending phase of Little Ice Age (LIA) during 1827–1845. The reconstructed PET showed that the advance of the glaciers over the western Himalaya might have influence on reduction of downward shortwave radiation on the earth's surface; which may in turn cause low temperature and low PET over the region. The result indicates that longer tree ring chronologies from the western Himalaya are very useful to get valuable information on PET and glacier fluctuation during the last few centuries. The highest PET in the entire reconstruction was noticed during the year 1921 in the 20th century, which has been associated with lowest trees growth in the entire western Himalaya.

Comparison of Hydrology of Two Atlantic Coastal Plain Forests

Abstract. This article compares the short-term and long-term hydrology of two typical forests in the humid Atlantic Coastal Plain, including a relatively undisturbed forest with natural drainage in South Carolina (SC) and a drained pine plantation in North Carolina (NC), using monitoring and modeling approaches. Highly dynamic outflow (O) from both of these systems is driven by the water table (WT) position, as influenced by rainfall (R) and evapotranspiration (ET). The annual runoff coefficient (ROC) varied from 5% in dry years to 56% in wet years, depending on the soil water storage (SWS), with a significantly higher average value for the NC site despite its deeper WT, on average, than the SC site. Although both sites behaved similarly in extreme climate conditions, the change in SWS above the WT influenced the annual RO, ROC, and ET. The 17-year average annual ET of 1114 mm (R – O, assuming annual balanced SWS) for the SC site was significantly higher (p = 0.014) than the ET of the drained NC site (997 mm) despite the SC site’s lower mean annual R of 1370 mm, compared to 1520 mm for the NC site. This may be due to both the higher potential ET (PET) and soil water-holding capacity of the SC site. The SC site had higher frequency and duration of WT near the surface during winter, deeper summer WT, and higher correlation of annual ET to annual R (r2 = 0.90 vs. 0.15), suggesting that the SC site was often moisture-limited, particularly during the growing season. Most of the streamflow in these systems occurred during winter, with low ET demands. However, summer periods with tropical storms also resulted in large RO events, generally with higher frequency and longer durations at the drained NC site. These results are similar to an earlier short-term comparison with an unstable behavior period at the SC site after Hurricane Hugo (1989). This study highlighted (1) the differences in hydrology between coastal forests drained for silvicultural production and undrained natural forests managed only for restoration, (2) the importance of long-term monitoring and the effects of regeneration as well as vegetation management on flow regime, and (3) the application and limitations of two widely used models (MIKESHE and DRAINMOD) in describing the hydrology of these forests. Long-term studies can be a basis for testing new hypotheses on water yield, stormwater management, wetland hydrology, vegetation restoration, bioenergy production, and climate change, in addition to applications of proper models for assessing the eco-hydrologic impacts of land use and climate change on freshwater coastal forests linked with downstream riparian rivers and estuaries affected by tidal fluxes and sea level rise.HighlightsOutflow, driven by water table position on these forest systems, is highly variable, depending on its soil water storage.The hydrologic responses of both forest sites were similar during extreme climatic events or disturbances.Effect of forestry drainage on runoff was obscured by its large interannual differences.Long-term monitoring provides better insights on climate and vegetation management effects on flow regime and model validation Keywords: Drainage, Evapotranspiration, Hydrologic models, Pine forest, Poorly drained soils, Runoff coefficient, Water table.

ESTIMATING THE POTENTIAL EVAPOTRANSPIRATION (PET) USING SATELLITE IMAGERY IN ARID LANDS

Evapotranspiration is one of the main sources of water loss in arid regions. Although FAO Penman-Monteith (FAO-PM) method is one of the accurate method to estimate potential evapotranspiration (PET). Nevertheless, it is a point-based method and requires several weather data such as radiation, wind speed, air humidity and temperature, which is not available in all regions. Therefore, this study is aimed to estimate PET equivalent to FAO-PM model using satellite data and Priestly-Taylor (PT) model in Yazd province, located in Central Iran. Daily net radiation and soil heat flux, which are used in PT method, were calculated using Landsat 5 data. Then, the net radiation data were integrated with ground data to estimate PET through PT equation. Although similarity between ground-based Priestly-Taylor (PT land) and satellite-based Priestly-Taylor (PT image) was observed, FAO-PM had higher PET values (RMSE=4.74 mmd-1) compared to other methods in all climatic zones of the study area. Therefore, results of PT image method can be replaced with PT land results to estimate potential evapotranspiration, in regions with limitation or lack of weather data. Finally, linear regression model were used for presenting relationship between ground-based FAO-PM and PT land. For this purpose, 70% and 30% of ground data were used for modeling and testing, respectively at different Selianinov climatic zones of the study area. Maximu RMSE for modeled and test data were 4.6 and 2.93, respectively. The model output was applied on PT image to get the FAO-PM image with maximum RMSE of 3.67. It can be concluded that the defined regression equations for each climate zones in this study, can be used to convert values of satellite- based Priestly Taylor method (PT image) as independent variable (X) to equivalent of FAO-PM PET.

Warmer temperatures reduce net carbon uptake, but do not affect water use, in a mature southern Appalachian forest

Increasing air temperature is expected to extend growing season length in temperate, broadleaf forests, leading to potential increases in evapotranspiration and net carbon uptake. However, other key processes affecting water and carbon cycles are also highly temperature-dependent. Warmer temperatures may result in higher ecosystem carbon loss through respiration and higher potential evapotranspiration through increased atmospheric demand for water. Thus, the net effects of a warming planet are uncertain and highly dependent on local climate and vegetation. We analyzed five years of data from the Coweeta eddy covariance tower in the southern Appalachian Mountains of western North Carolina, USA, a highly productive region that has historically been underrepresented in flux observation networks. We examined how leaf phenology and climate affect water and carbon cycling in a mature forest in one of the wettest biomes in North America. Warm temperatures in early 2012 caused leaf-out to occur two weeks earlier than in cooler years and led to higher seasonal carbon uptake. However, these warmer temperatures also drove higher winter ecosystem respiration, offsetting much of the springtime carbon gain. Interannual variability in net carbon uptake was high (147 to 364 g C m−2 y−1), but unrelated to growing season length. Instead, years with warmer growing seasons had 10% higher respiration and sequestered ∼40% less carbon than cooler years. In contrast, annual evapotranspiration was relatively consistent among years (coefficient of variation = 4%) despite large differences in precipitation (17%, range = 800 mm). Transpiration by the evergreen understory likely helped to compensate for phenologically-driven differences in canopy transpiration. The increasing frequency of high summer temperatures is expected to have a greater effect on respiration than growing season length, reducing forest carbon storage.

Orbitally-paced variations of water availability in the SE Asian Monsoon region following the Miocene Climate Transition

Middle Miocene Earth had several boundary conditions similar to those predicted for future Earth including similar atmospheric pCO2 and substantial Antarctic ice cover but no northern hemisphere ice sheets. We describe a 12 m outcrop of the terrestrial Yanwan Section in the Tianshui Basin, Gansu, China, following the Miocene Climate Transition (13.9–13.7 Ma). It consists of ∼25 cm thick CaCO3-cemented horizons that overprint siltstones every ∼1 m. We suggest that stacked soils developed in siltstones under a seasonal climate with a fluctuating water table, evidenced by roots, clay films, mottling, presence of CaCO3 nodules, and stacked carbonate nodule δ13C and δ18O profiles that mimic modern soils. We suggest that the CaCO3-cemented horizons are capillary-fringe carbonates that formed in an arid climate with a steady water table and high potential evapotranspiration rates (PET), evidenced by sharp upper and basal contacts, micrite, sparite, and root-pore cements. The CaCO3 of the cemented horizons and the carbonate nodules have similar mean δ18O and δ13C values but the cements have significantly smaller variance in δ13C and δ18O values and a different δ18O versus δ13C slope, supporting the conclusion that these carbonates are from different populations. The magneto-stratigraphic age model indicates obliquity pacing of the arid conditions required to form the CaCO3-cemented horizons suggesting an orbital control on water availability. We suggest two possible drivers for the obliquity pacing of arid conditions: 1) variability in the cross-equatorial pressure gradient that controls summer monsoon (ASM) strength and is influenced by obliquity-paced variations of Antarctic ice volume and 2) variability in Western Pacific Ocean–East Asian continent pressure gradient controlled by the 25–45°N meridional insolation gradient. We also suggest that variations in aridity were influenced by variations in PET and sensible heating of the regional land surface which are both influenced by precession-controlled 35°N summer insolation. We then use orbital configurations to predict lithology. Coincidence of obliquity minima (strong ASM) and 35°N summer insolation maxima (strong ASM) drives strong ASM and high PET, resulting in soil formation in an environment with relatively large seasonal changes in water availability. Coincidence of obliquity maxima (weak ASM) and 35°N summer insolation maxima (strong ASM) moderates the ASM, results in high PET, and thus drives overprinting of soils by capillary fringe carbonates above a deepened and relatively stable water table. Coincidence of obliquity and insolation minima also moderates the ASM but results in low PET and thus a high water table, which explains the previously documented occurrence of aquatic plants in this section. This context allows us to assign an orbital configuration to atmospheric pCO2 determined from the paleosols. Our best estimate of pCO2 during the times of intermediate ice volume is 475+650/−230 ppmV (median value with error reported as 84th–16th percentile values). Southern hemisphere control of ASM variability during the Middle Miocene may have resulted in larger orbital scale water availability variations compared with the Pleistocene.

Response of deep groundwater to land use change in desert basins of the Trans‐Pecos region, Texas, USA: Effects on infiltration, recharge, and nitrogen fluxes

AbstractQuantifying the effects of anthropogenic processes on groundwater in arid regions can be complicated by thick unsaturated zones with long transit times. Human activities can alter water and nutrient fluxes, but their impact on groundwater is not always clear. This study of basins in the Trans‐Pecos region of Texas links anthropogenic land use and vegetation change with alterations to unsaturated zone fluxes and regional increases in basin groundwater NO3− concentrations. Median increases in groundwater NO3− (by 0.7–0.9 mg‐N/l over periods ranging from 10 to 50+ years) occurred despite low precipitation (220–360 mm/year), high potential evapotranspiration (~1570 mm/year), and thick unsaturated zones (10–150+ m). Recent model simulations indicate net infiltration and groundwater recharge can occur beneath Trans‐Pecos basin floors, and may have increased due to irrigation and vegetation change. These processes were investigated further with chemical and isotopic data from groundwater and unsaturated zone cores. Some unsaturated zone solute profiles indicate flushing of natural salt accumulations has occurred. Results are consistent with human‐influenced flushing of naturally accumulated unsaturated zone nitrogen as an important source of NO3− to the groundwater. Regional mass balance calculations indicate the mass of natural unsaturated zone NO3− (122–910 kg‐N/ha) was sufficient to cause the observed groundwater NO3− increases, especially if augmented locally with the addition of fertilizer N. Groundwater NO3− trends can be explained by small volumes of high NO3− modern recharge mixed with larger volumes of older groundwater in wells. This study illustrates the importance of combining long‐term monitoring and targeted process studies to improve understanding of human impacts on recharge and nutrient cycling in arid regions, which are vulnerable to the effects of climate change and increasing human reliance on dryland ecosystems.

Estimation of Optimum Water Requirement and Frequency of Watering for Different Tree Seedlings at Bako Agricultural Research Center Nursery Site

Determining water requirement and application frequency of tree seedlings is crucial to use available water effectively. This study estimated the Optimum water requirement and application frequency of tree seedlings: Grevillea robusta, Moringa olifera and Cordia africana at nursery site for the two consecutive years. The experiment was implemented during off-season; because of the objective of the study was to determine amount of water and frequency required for normal growth tree seedlings at nursery stage. Three different water application (1, 1.5, and 2 liters) and two irrigation frequencies (watering twice daily and watering twice after one day) and the control (Local practices) were combined with tree species. Seeds were sown directly into polythene bags in the traditional nursery site. Different growth parameters were collected and evaluated to estimate the optimum water requirement and watering frequency of different tree seedlings at nursery site. Growth parameters: root collar diameter (cm), height (cm), root depth (cm) and survival rate (%) were assessed during the nursery stage. The growth parameters measured were subjected to Analysis of Variance (ANOVA). The means were separated by Least Significant Difference (LSD; P ≤ 0.05). The result reveals that significant difference (P≤0.05) was observed among the three tree species growth parameters; root collar diameter, height and survival rate under different watering applications and irrigation frequencies. The average potential evapotranspiration of study area over the two consecutive years were 47 mm/month. The result indicated that, the growth performance of Moringa olifera and Grevillea robusta were better when watered twice daily with 1.5 liters of per a given plot. The growth performance of Cordia africana was good performed when watered twice after one day with 2 liters of water per a given plot. Also the result showed that Moringa olifera watered twice daily with 1.5 liters had the highest height of 50.74 cm followed by Moringa olifera watered twice after one day with 2 liters had height of 45.35 cm and while Grevillea robusta watered twice after one day with 1 liters had the least height 10.73 cm. The study therefore recommends that Moringa olifera and Grevillea robusta seedlings watered twice daily with 1.5 liters and Cordia Africana seedlings watered twice after one day with 2 liters per plot of water availability should be adopted in the area where warm humid climate and high potential evapotranspiration, since it ensures good growth performance of those tree seedlings species.

Evaporation fractionation in a peatland drainage network affects stream water isotope composition

AbstractThere is increasing interest in improving understanding of evaporation within a catchment for an enhanced representation of dominant processes in hydrological models. We used a dual‐isotope approach within a nested experimental design in a boreal catchment in the Scottish Highlands (Bruntland Burn) to quantify the spatiotemporal dynamics of evaporation fractionation in a peatland drainage network and its effect on stream water isotopes. We conducted spatially distributed water sampling within the saturated peatland under different wetness conditions. We used the lc‐excess—which describes the offset of a water sample from the local meteoric water line in the dual‐isotope space—to understand the development of kinetic fractionation during runoff in a peatland network. The evaporation fractionation signal correlated positively with the potential evapotranspiration and negatively with the discharge. The variability of the isotopic enrichment within the peatland drainage network was higher with higher potential evapotranspiration and lower with higher discharge. We found an increased evaporation fractionation toward the center of the peatland, while groundwater seepage from minerogenic soils influenced the isotopic signal at the edge of the peatland. The evaporation signal was imprinted on the stream water, as the discharge from a peatland dominated subcatchment showed a more intense deviation from the local meteoric water line than the discharge from the Bruntland Burn. The findings underline that evaporation fractionation within peatland drainage networks affects the isotopic signal of headwater catchments, which questions the common assumption in hydrological modeling that the isotopic composition of stream waters did not undergo fractionation processes.

Root traits of cup plant, maize and lucerne grass grown under different soil and soil moisture conditions

AbstractThe cup plant (Silphium perfoliatum L.) is presently discussed as a promising alternative to silage maize for biomethane production in Germany. It is assumed that the cup plant develops a profound root system, contributing decisively to the drought tolerance of this crop. This study is aimed at providing the first experimental data on root growth and water uptake of this novel biogas crop. Root morphological characteristics of the cup plant were studied at six sites differing in soil type. Root samplings were made at the time of maximum root expansion (flowering). In a 2‐year field experiment at an additional location, continuous measurements of root development and soil water acquisition during the growth cycle were taken under contrasting water supply, together with maize (Zea mays L.) and lucerne grass (mixture of Medicago sativa L. with Festuca pratensis Huds. and Phleum pratense L.) as reference crops. The cup plant attained maximum rooting depths of 80–240 cm. The root length density was comparable to that of maize, but markedly lower than that of lucerne grass. Despite the cup plant's higher potential evapotranspiration and similar water‐use efficiency, its soil water extraction ability was significantly lower than that of lucerne grass. Compared with maize and lucerne grass, the cup plant showed no outstanding ability to cope with drought stress by means of its root system. Because of its high potential evapotranspiration, the cup plant can attain biomass yields comparable to those of maize only at sites with high water supply.

Monitoring Drought Trends Induced Climate Variability over Egypt Using MODIS NDVI Satellite Data and Drought Indices

The Drought is considered as a regional phenomenon because the main causes that can produce it are linked to the regional scale. Empirical studies showed that drought is never the result of a single cause. It is the result of many causes, often synergistic in nature (Magana et al. 1997, Estrada, 2001, Contreras, 2003, Vicente-Serrano et al., 2012, Rita Man Sze Yu, 2013, Joan Ramon, 2013 and Vicente-Serrano et al., 2014). Climatological events over the past three decades have prompted many researchers to pay closer attention to drought across the arid and semi-arid regions such as Egypt. Climate variability leads to more intense and more frequent droughts in the arid regions especially in Egypt. Drought is a recurring extreme climate event over land characterized by below normal precipitation over a period of several months to several years or even a few decades. The main aim of this research is to monitor the drought trends and classification induced by climate variability over Egypt using Terra-MODIS/ NDVI satellite data in companion with Drought Indices. To achieve the aim of the study the climate variability over Egypt is described by the analysis of temperature and rainfall at annual and seasonal time-scale. The drought trends and classifications, which are approached by the application of the most widely, used drought indices Self-Calibrated of Palmer’s Drought Severity Index (Sc-PDSI) which improves the “original” PDSI, Standardized Precipitation Evapotranspiration Index (SPEI) which is based on the difference between the precipitation and the reference evapotranspiration, and Standardized Precipitation Index (SPI) which is based on precipitation data over Egypt 1940-2014. These climatic indices based on rainfall and temperature data, and it has the advantage of combining multi-scalar character with the capacity to include the effects of the temperature variability on drought monitoring. A trend analysis is carried out on drought time-series in order to understand the behavior of drought conditions. Furthermore, the research was depended on the analysis of temperature and rainfall variability from 1940 to 2014 at annual and seasonal time-scale. Moreover, the trends and their statistical significance are also analyzed. This analysis provides relevant information related to the behavior of the main climate variables of Egypt under the current climate change conditions. Remote sensing NDVI data provided by Moderate Resolution Imaging Spectroradiometer (MODIS) Sensor, and Terra-MODIS/NDVI data available from 2000 until 2016, it was used to monitor drought in Egypt. The results accentuated that SPEI drought index does not work properly in all stations of Egypt due to the lack of rainfall compared to really high potential evapotranspiration causes an optimal calibration of the index and, in consequence, SPEI will not be a good tool to monitor and analysis dry events in Egypt. In a country like Egypt where reliable data are difficult to obtain continuous, remote sensing data proved to be a significant tool in monitoring and detecting drought components.

Weed Management in Dryland Agriculture in India for Enhanced Resource Use Efficiency and Livelihood Security

As per FAO, the regions receiving rainfall less than potential moisture loss through evaporation and transpiration with aridity index <0.65 are considered as drylands. These lands are characterized by low and erratic rainfall, water scarcity, high temperature, high potential evapo-transpiration, low humidity, high wind velocity coupled with unique bio-physic and socio-economic characteristics. Drylands occupy nearly 40 % earth land surface which is inhabited by nearly 35 % population of the world. But it has the highest level of poverty (around 47 %). In India, dryland accounts for about 57 % of total cultivated area that supports 40 % human and 60 % livestock population, but crop production is not stable. Therefore stable crop production is of prime importance to achieve sustainable livelihoods in drylands. Conservation of precipitation, nutrients, natural resources and increasing resource use efficiency can play vital role to achieve stable crop production and livelihood security. Among many factors that adversely influence resource use efficiency and crop production, severe weed infestation is most important. Weeds have the ability to survive under adverse condition, as they extract more water and nutrients from the soil, thereby reduce crop yield by 37 to 79 % in dryland agriculture. Weeds being more aggressive, adaptive and persistent pose serious threat to crop production and are difficult to control below economic threshold level with single weed management practice. Hence, more emphasis is needed to develop multiple and integrated weed control strategies in a holistic manner for sustainable crop production and livelihood security in drylands.