Semi-arid City Research Articles

Application of HEC-HMS Model for Evaluation of Rainwater Harvesting Potential in a Semi-arid City

Application of HEC-HMS Model for Evaluation of Rainwater Harvesting Potential in a Semi-arid City

Local Meteoric Water Lines in a Semi-Arid Setting of Northwest China Using Multiple Methods

The local meteoric water lines (LMWLs) reflect water sources and the degree of sub-cloud evaporation at a specific location. Lanzhou is a semi-arid city located at the margin of the Asian monsoon, and the isotope composition in precipitation around this region has aroused attention in hydrological and paleoclimate studies. Based on an observation network of stable isotopes in precipitation in Lanzhou, LMWLs at four stations (Anning, Yuzhong, Gaolan and Yongdeng) are calculated using the event-based/monthly data and six regression methods (i.e., ordinary least squares, reduced major axis, major axis regressions, and their counterparts weighted using precipitation amount). Compared with the global meteoric water line, the slope and intercept of LMWL in Lanzhou are smaller. The slopes and intercepts calculated using different methods are slightly different. Among these methods, precipitation-weighted least squares regression (PWLSR) usually had the minimum average value of root mean sum of squared error (rmSSEav), indicating that the result of the precipitation weighted method is relatively stable. Higher precipitation amount and lower air temperature result in larger slopes and intercepts on an annual scale, which is out of accordance with the summertime.

Modeling the response of ecological service value to land use change through deep learning simulation in Lanzhou, China

Land use (LU) changes caused by urbanization, climate, and anthropogenic activities alter the supply of ecosystem services (ES), which affects the ecological service value (ESV) of a given region. Existing LU simulation models extract neighborhood effects with only one data time slice, which ignores long-term dependence in neighborhood interactions. Previous studies on the dynamic relationship between LU change and ES in semi-arid areas is rare than that in humid coastal areas. Here, we selected a semi-arid city, Lanzhou, in Northwest China as the study area, to simulate LU changes in 2030 under natural growth (NG), ecological protection (EP), economic development (EP), and ecological protection-economic development (EPD) scenarios, using a novel deep learning method, named CL-CA. Convolutional neural network and long short term memory (CNN-LSTM) with cellular automata (CA) were utilized to extract the spatiotemporal neighborhood features. The overall simulation performance of the proposed model was larger than 0.92, which is surpassed that of LSTM-CA, artificial neural network (ANN)-CA, and recursive neural network (RNN)-CA. Ultimately, we utilized LU and ES to quantitatively evaluate the ESV changes. The results indicated that: (1) The variable trend of ESV in arid area is different from that in coastal humid areas. (2) Forest land and water were the main factors that affect the ESV change. (3) The EPD scenario was more suitable for sustainable urban development.

Heating events drive the seasonal patterns of volatile organic compounds in a typical semi-arid city

The emission characteristics, source apportionment and chemical behavior of volatile organic compounds (VOCs) are important for strategy-making on ozone (O3) and fine particulate matter (PM2.5) control. Based on the continuous observation during four seasons, the seasonal characteristics, chemical reactivity and source apportionment of 116 VOCs species were studied in a typical semi-arid city with no relevant research. The results showed that the annual average concentrations of total volatile organic compounds (TVOCs) in Hohhot was 44.67 ± 46.59 ppbv with the predominant of alkanes and oxygenated volatile organic compounds (OVOCs). The sharp increment of TVOCs were explained by the elevating OVOCs and alkanes in autumn, while alkanes and alkenes in winter. The levels of alkenes presented negative and positive correlations with solar radiation and PM10, respectively. The mixing ratios accounted for 30% (alkanes) and 23% (alkenes and aromatics) of the TVOCs, respectively; while their ozone formation potential (OFP) ~15% and nearly 50% (even 75% in winter), respectively, indicating that the OFP of different VOCs species depends not only on their concentrations but more importantly on their chemical activity in atmosphere. According to the seasonal source apportionment, both the high levels of short-chain alkanes, alkenes and aromatics and the increasing coal sales volume suggested that the combustion sources were the predominant in heating seasons, while solvent uses was extracted as the most predominant during non-heating seasons. In non-heating seasons, the biogenic emission sources, ranking as the second contributor, were significantly higher than heating seasons. Isoprene was the most active biogenic VOCs species, bagging test results showed that deciduous trees were the predominant contributors for isoprene (~99%), while coniferous trees and shrub for monoterpenes (>95%). It will be helpful for understanding the characteristics of VOCs in Chinese national key development areas and informing policy to control semi-arid regional VOCs air pollution.

Solar potential of urban forms of a cold semi-arid city in Algeria in the present and future climate

Realizing the potential of renewable energies in existing and new urban areas can reduce the fossil energy consumption of cities and the corresponding greenhouse emissions. In this paper, four different urban forms in the city of Constantine, a cold semi-arid city in Algeria, are analysed. Using the Citysim model, calibrated against local electricity and gas demand, and weather data taken from Meteonorm7.0, for both present and future climates, the study shows a significant difference between the energy demands of the urban forms due to their typo-morphological indicators. It is also shown that a small area of photovoltaics on rooftops can supply building demand, highlighting the favorable solar potential for the location. Future climate projections, for 2050, within the lifetime of many buildings, are expected to lead to higher energy demand, particularly in the summer. The increase in photovoltaic capacity to address that higher demand will open the opportunity to replace a significant fraction of gas usage with solar-powered heat pumps in the heating season.

Investigation of feedstuff contaminated with aflatoxigenic fungi species in the semi-arid region in northeast of Iran.

There is a close relationship between human health and the quality of the ration used by domestic animals. Also, molds, like genus of Aspergillus, infect animal and human food products with dangerous toxic substances, i.e., aflatoxins that are causing primary and secondary mycotoxicosis in animals and human. The aim of this study was to compare fungal species that contaminated and produced aflatoxin in livestock and poultry feed in Gonabad that is a semi-arid city in northeast of Iran. Sampling was randomly performed three times from two livestock feed mills and two poultry feed mills during summer and autumn. Samples were cultured in two forms of solid and suspension in Sabouraud dextrose agar with chloramphenicol medium (SC) for 5days in 28°C. Microscopic diagnostic test and also molecular diagnostic test were used to determine fungal species in culture based on β-tubulin gene sequencing. A total of 27.25% and 31.7% of two livestock feed and two poultry feed samples were contaminated with Aspergillus, respectively. Aspergillus flavus (n = 4), Aspergillus Fumigatus (n = 2), Aspergillus versicolor (n = 2), Aspergillus niger (n = 2), Aspergillus parasiticus (n = 1), Aspergillus ochraceus (n = 1), and Aspergillus terreus (n = 1) were detected by molecular PCR test. The rate of contamination to genus of Aspergillus in autumn was higher than summer (P value = 0.008). Poultry feed sample showed more contamination to Aspergillus species compared with livestock feed.

When Small Is Not Beautiful: The Unexpected Impacts of Trees and Parcel Size on Metered Water-Use in a Semi-Arid City

Colorado’s water supply is under threat due to climate change pressures and population growth, however Colorado has been recognized to have some of the most progressive water conservation programs in the country. Limiting outdoor water consumption is an increasingly popular approach to conserving water in semi-arid cities, yet in order to implement effective water reduction and conservation policies, more utilities and city managers need a firm understanding of the local drivers of outdoor water consumption. This research explores the drivers of outdoor water consumption in a semi-arid, medium-sized Colorado city that is projected to undergo significant population growth. We used a combination of correlation and linear regression analyses to identify the key descriptive variables that predict greater water consumption at the household scale. Some results were specific to the development patterns of this medium-sized city, where outdoor water use increased 7% for each additional mile (1.6 km) a household was located from the historic urban center. Similarly, more expensive homes used more water as well. Surprisingly, households with a higher ratio of vegetation cover to parcel size tended toward less water consumption. This result could be because parcels that are shaded by their tree canopy require less irrigation. We discuss these results to assist city managers and policymakers in creating water-efficient landscapes and provide information that can be leveraged to increase awareness for water conservation in a growing, semi-arid city.

Priority Areas for Developing Green Infrastructure in Semi-arid Cities: A Case Study of Tehran

Urban green infrastructure (GI) approach supports building resilience, mitigating greenhouse gases emissions and adapting to the impacts of climate change. However, the development and maintenance of GI in semi-arid cities can be hindered by limitations such as available water resources. In this article, we study priority areas for GI development schemes at the neighbourhood scale through a seasonal vulnerability framework with the case study of two urban districts in the semi-arid city of Tehran, Iran. Heat mitigation and stormwater runoff control are considered as the main objectives of GI development. The results show that priority areas have high levels of land surface temperature, impervious surfaces and population density, with a low proportion of vegetation land cover. The necessary GI services vary in different local climate zones (LCZ) during the year. Although heat mitigation is required in both compact and open LCZs, the runoff control service of GI is also needed for neighbourhoods with compact midrise settings. To promote sustainability at the neighbourhood scale, the findings of the study can be used for initiating nature-based solutions and GI development projects.

The impact of impervious surface, vegetation, and soil areas on land surface temperatures in a semi-arid region using Landsat satellite images enriched with Ndaisi method data.

Impervious surfaces are a significant issue of both urbanization and environmental assessment. However, it is a problem to classify impervious surface (IS) and soil areas as separate classes in land cover classification. The objectives of this study are to obtain impervious surface, vegetation, and soil areas clearly of an urban complex with a semi-arid climate and to better determine the relationships of IS, vegetation, and soil areas with land surface temperatures (LSTs). For this purpose, IS, vegetation, and soil areas in a semi-arid city of Turkey-Kayseri city were identified by using Normalized Difference Anthropogenic Impervious Surface Index (NDAISI) data and support vector machine (SVM) method together in the classification of different areas. Landsat 5, 7, and 8 satellite images of 1987, 2000, and 2013 were used, respectively, in this study. Afterward, the effects of these areas on LSTs were analyzed. Regression analysis was used to determine the relationships between land cover areas and surface temperatures. To better demonstrate these relationships, besides common pixel-based and classical regional-based approaches, a new density-based regional analysis approach was proposed. This study is an innovative one in terms of detecting IS and indicating relationships between land cover areas and surface temperatures in semi-arid regions. Another innovation of the study is related to the results produced. The results showed that decreasing LST values were observed with increasing IS and vegetation cover values and increasing LST values were observed with increasing soil areas. The present findings may provide significant contributions to the literature and will facilitate the development of urban planning strategies in semi-arid regions.

Socioeconomic Drought in a Mexican Semi-arid City: Monterrey Metropolitan Area, a Case Study

The Monterrey Metropolitan Area (MMA) is located in northeastern Mexico in a semi-arid region. As in other areas of the world, prolonged and severe meteorological droughts are recurrent. Meteorological droughts affect the level of dam reservoirs, rivers, and groundwater (aquifers) in the region to the extent they become hydrological droughts which in turn may contribute to socioeconomic droughts. The recent dry event (2011–2013) in northern Mexico severely affected various socioeconomic sectors and may serve as an example of future climatic and hydrologic conditions in this region. Meteorological droughts in northeastern Mexico, mostly induced by anomalously intense subsidence, frequently result in hydrological droughts and intense pressure in the water resources services of the Monterrey Metropolitan Area (MMA), one of the largest cities in Mexico. Landfalling tropical cyclones entering northeastern Mexico historically have alleviated water crises during prolonged droughts. In 2013, the rains from tropical cyclone Ingrid helped to recover water levels in the system of dam reservoirs that provides water to the MMA. However, water management is only one part of a complex socioeconomic system that must respond to the growing demands for water in a region where aquifers are already overexploited. Trends in the atmospheric circulation indicate that droughts in the region may become more severe in the coming decades. Improved water management programs and protocols should be considered in addition to closer reviews of the hydraulic infrastructure. Water transfers from one region to another should be carefully planned because solving a problem in one place may adversely affect another. The use of climate information may be critical to avoidance of water conflicts in the future.

Seasonal impact of urban parks on land surface temperature (LST) in semi-arid city of Tehran

ABSTRACT This paper studies the impact of parks as an element of urban green infrastructure on regulating surface temperature in the semi-arid city of Tehran, Iran. Land surface temperature (LST) of parks and their immediate surroundings, derived from Landsat images of winter to autumn 2017, are analysed in two urban districts with different local climate zones and population density levels. The results show that the highest levels of cooling impact are observed in spring and summer for parks larger than 1 ha in the compact midrise setting. Although area and vegetation cover influence the impact of parks in all sizes, parks shape becomes important in parks larger than 1 ha in open built zones. To benefit from LST regulating services of park vegetation cover and facilitate achieving sustainable urban landscapes, it is recommended to opt for 1–10 ha parks, where possible, and improve vegetation cover inside parks, particularly in parks smaller than 1 ha.

The construction of flood loss ratio function in cities lacking loss data based on dynamic proportional substitution and hierarchical Bayesian model

A reliable flood loss assessment in city is the basis of efficient flood risk management. However, it is difficult to fit empirical functions with typical case data for most of the world's arid or semi-arid cities that lack or even have no historical flood loss data. Under the background of frequent global extreme weather events and high-speed urbanization, urban flood loss assessment has become increasingly important to support urban flood risk management. At present, few researches have focused on the modeling of Flood Loss Ratio Function (FLRF ) for cities lacking loss data. Therefore, based on the improved analogy principle, a Dynamic Proportional Substitution (DPS) method in this paper was proposed to transfer large sample data from multiple quoted cities into a sample matrix of loss ratios in the study city to address the lack of data. Then, according to the hierarchical data structure characteristics of the loss ratio matrix, a Hierarchical Bayesian Model (HBM) of FLRF with unknown parameters was constructed based on the prior distribution of parameters . Finally, taking the city lacking data—Zhengzhou, China as the study area, the water depth – loss ratio functions of four land types (industry, commerce, residence, and public utilities) were calculated. The results showed that: 1. The combined feature schemes achieved dynamic selectivity; 2. The parameters gradually converged after a certain number of iterations; 3. The error of FLRF solved by HBM was less than that of the least square method (LSM); 4. The DPS-HBM model had good performance in transplantation verification. This study is expected to provide a reference for the establishment of flood loss functions in cities lacking data.

Association of airborne particulate matter with pollen, fungal spores, and allergic symptoms in an arid urbanized area.

Studies focused on the seasonal distribution of pollen and spores in semiarid cities are scarce. At these sites, climate change potentiates the emission and transport of fine (PM10) to ultrafine particles (PM2.5), easily attached to pollen surfaces, causing allergen's release. This study examines the potential correlation of seasonal variations of pollen, fungal spores, PM10, and meteorological parameters with allergic reactions of 150 people living in a Sonoran desert city. We collected PM10, airborne pollen, and spores during a year. We also studied topsoil and road dust samples as potential PM-emission sources. We obtained dust-mineralogy, chemistry, and particle size attached to pollen by X-ray diffraction and scanning electron microscope. Results show that seasonal high PM-loading in the urban atmosphere coincides with aeroallergens promoting micro- to nanoparticles' attachment to pollen's surface. A collapsed membrane was observed in several samples after individual grains show the following maximum wall coverage: Poaceae 28%, Asteraceae 40%, Chenopodiaceae-Amaranthacea 29%, Fabaceae 18%. Most of the particles covering pollen's surface have a geogenic origin mixed with metals linked to traffic (bromide, chlorine, and antimony). Mineralogical, granulometric analysis, and main wind-direction show that two local soil-types are the main contributors to PM. A high frequency of positive sensitization to pollen with high particle loading was detected. These results suggest that climate-driven dust emissions may alter pollen and spore surfaces' physicochemical characteristics with the further consequences in their allergenic potential.

Curbing the Summer Surge: Permanent Outdoor Water Use Restrictions in Humid and Semiarid Cities

AbstractAs urban droughts make headlines across the globe, it is increasingly relevant to critically evaluate the long‐term sustainability of both water supply and demand in the world's cities. This is the case even in water‐rich regions, where upward swings in water demands during periods of hot, dry weather can aggravate already strained water supplies and increase cities' vulnerability to water shortage. Summer spikes in water demand have motivated several cities to impose permanent restrictions on outdoor water uses; however, little is yet known about their effectiveness. This paper examines daily water production data from 15 Canadian cities to (1) quantify how overall and seasonal demands are evolving over time across humid and semiarid settings and (2) determine whether permanent water use restrictions have been effective in curbing summer water demands both seasonally and during specific hot and dry periods. Results show that while per‐capita water demand is declining in all cities studied, the seasonal distribution of that demand has remained largely stable in all but a few cases. While average demands in the summer months remain largely unaffected by the imposition of permanent restrictions, cities that enforce stringent limits on outdoor water use have seen a reduction in the variability of daily demands and a decline in peak demands following their implementation. During short‐term periods of exceptionally hot and dry weather when vulnerability to water shortage is most acute, cities with strict restrictions also see smaller surges in demand than those with weaker or no restrictions in place.

Research on the anti-interference capability of the tourism environment system for the core stakeholders of semi-arid valley-type cities: analysis based on the multi-scenario and time series diversity perspectives.

Given the relatively harsh natural environment in semi-arid valley areas, the attraction and radiation functions of semi-arid valley cities have become the foci of further development in Western China. This study takes Lanzhou City (a semi-arid river valley city) as an example and uses the theoretical framework of pressure-state-response to optimize the response strategies of the tourism environmental needs of the City's core stakeholders from the multi-scenario and time series diversity perspectives. Based on the index system of the tourism environment system (TES) in semi-arid valley cities, the system dynamics model is used to forecast the index system of the tourism environment from multi-scenario perspectives. Based on the evolutionary optimization algorithm NSGA-II, the core stakeholders are optimized to meet the tourism environment needs, and the optimal solution set is selected based on the decision makers' preferences. Finally, several measures to improve the anti-interference ability of semi-arid valley cities' TES are proposed, namely standardizing the preferences of decision makers, improving the resilience of the destination TES, carrying out the safety management of valley cities' TES, and adjusting the seasonality of such cities to improve their tourism environment and promote the welfare of various stakeholders.

A comparative analysis of day and night land surface temperature in two semi-arid cities using satellite images sampled in different seasons

Urban heat island (UHI) refers to the occurrence of very high temperature patches in urban areas with respect to surrounding rural areas. The behaviour of Land Surface Temperature (LST) with different land covers varies for day and night time in a given urban area. Therefore, an attempt has been made for the comparative analysis of the day and night LST in two semi-arid cities in India i.e. Ahmedabad and Gandhinagar using two Landsat 8 images (one for day and one for night time) for each city. The relations of day and night LST with three independent variables such as Normalized Difference Vegetation Index (NDVI), Normalized Difference Built-up Index (NDBI) and impervious surface fraction (ISF) were established using Landsat 8 data. Based on the relation of LST with indices, the combinations of indices were used for developing the models to improve the correlation of day and night LST with the land cover. The developed models improved the correlation of day and night LST with the combinations of indices as compared to the relation of LST with individual variables in semi-arid urban landscapes with reasonably good coefficient of determination (R2) values of 0.63 in Ahmedabad and 0.79 in Gandhinagar for day time. The reasonably good values of R2 were found to be 0.81 and 0.75 for Ahmedabad and Gandhinagar, respectively, for night time. The developed model was also evaluated using 12 MODIS satellite images i.e. six images of each city for the summer, post-monsoon and winter seasons (one for day and one for night time in each season). The results of the developed models showed high capability to explain LST in heterogeneous semi-arid urban area for both day and night time in the summer, post-monsoon and winter seasons in a year. However, the relations established in this study can further be investigated for other months and years to understand its significance for other dates in semi-arid urban areas.

Finding new sources of water for semi-arid cities in unlikely places.

Determining alternative water sources to meet municipal water demands is important when availability is limited. The purpose of this study was to demonstrate a means for water planners to estimate the amount of combined sanitary wastewater and storm water that they might already be capturing through open air oxidation ponds. Increased understanding of the quantity of water that is already available could help water planners to better envision optimal water reuse scenarios. Using water and climate data on oxidation ponds in these three cities within the Texas Panhandle from 2010 to 2014, we evaluated water quantities which would be available for potential reuse. From the net monthly wastewater volumes values, the study also considered if per capita demand could have been met by reusing the wastewater. The study found wastewater volumes were lower in fall and winter months and much higher in spring and summer months. If a city considers reusing wastewater, blue water (groundwater) extraction could be reduced by as low as 45-50% in one city to as high as 100% in another. Water planners in similar environments and wastewater treatment systems may find this demonstration of potential reuse water quantity encouraging for better meeting their own water demands and enhancing water supply resiliency.

Ecohydrology of urban trees under passive and active irrigation in a semiarid city.

The infiltration of stormwater runoff for use by urban trees is a major co-benefit of green infrastructure for desert cities with limited water resources. However, the effects of this passive irrigation versus regular, controlled moisture inputs, or active irrigation, is largely unquantified. We monitored the ecohydrology of urban mesquite trees (Prosopis spp.) under these contrasting irrigation regimes in semiarid Tucson, AZ. Measurements included soil moisture, sap velocity, canopy greenness, and leaf-area index. We expected both irrigation types to provide additional deep (>20 cm) soil moisture compared to natural conditions, and that trees would depend on this deep moisture for transpiration and phenological activity. Results show that active irrigation supported higher soil moisture throughout the study than passive irrigation. Passive irrigation only provided additional deep moisture when green infrastructure features received impervious runoff from a city street. Sap velocity and greenness were similar under both irrigation types, outside of isolated periods of time. These differences occurred during the extremely wet summer 2017 when passively irrigated trees exhibited a greenness peak, and the dry conditions of spring when actively irrigated trees had higher sap flow and relative greenness. Finally, it was not determined that deep soil moisture had a stronger relationship with mesquite productivity than shallow moisture, but both relationships were stronger in the spring, before summer rains. This study aims to contribute empirical observations of green infrastructure performance for urban watershed management.

Phthalate esters in atmospheric PM2.5 and PM10 in the semi-arid city of Xi'an, Northwest China: Pollution characteristics, sources, health risks, and relationships with meteorological factors.

PM2.5 and PM10 samples were collected in the semi-arid city of Xi'an in Northwest China from November 2016 to November 2017 and analyzed to assess pollution characteristics, sources, health risks, and influencing factors of 6 priority phthalate esters (PAEs). The results showed that the sum of the 6 PAEs (Σ6PAEs) was 85.5 ng m-3 in PM2.5 and 94.5 ng m-3 in PM10, being higher at the suburban site than the urban site and winter > spring > summer > autumn. The most abundant PAE was bis(2-ethylhexyl phthalate) (DEHP). PM2.5- and PM10-bound PAEs were associated mainly with the use of plasticizers plus the uses of cosmetics and personal care products, construction materials, and home furnishings. Temperature, relative humidity, and visibility had stronger influences on the concentrations of PM and PM-bound PAEs than pressure and wind speed. Pressure and relative humidity were positively correlated with the concentrations of PM and most of the PM-bound PAEs, while temperature, visibility and wind speed had negative correlations with the concentrations of PM and PM-bound PAEs. The non-carcinogenic risks of human inhalation exposure to PM-bound PAEs were in the range of 10-7 to 10-3, suggesting low non-cancer risks, which were higher at the suburban site than the urban site and higher to children than adults. The cancer risks of human inhalation exposure to PM-bound DEHP and butyl benzyl phthalate (BBP) were in the range of 10-12 to 10-10, suggesting low carcinogenic risks, being in the order of the suburban site > the urban site and DEHP > BBP. Special attention should be paid to long-term low dose exposure to PAEs in the suburb, especially in winter and spring.

Spatiotemporal variability in water sources of urban soils and trees in the semiarid, irrigated Salt Lake Valley

AbstractPlant transpiration is a critical process in ecohydrology and urban water budgets. Urban forests in the semiarid cities of the western United States are composed largely of non‐native species sustained by irrigation. Given that the major end use of water in these cities is usually landscape irrigation, the efficiency of irrigation practices is essential in future water conservation measures. The dependence of urban trees on irrigation is driven not only by the availability of alternative water sources (e.g., precipitation) but also by patterns of infiltration and mobility of soil water. We used hydrogen and oxygen stable isotopes to identify spatiotemporal dynamics of trees, of varied sizes and species, and shallow soil water apportioning of irrigation versus winter snowmelt in urban parks in the semiarid Salt Lake Valley. We estimate for this ecosystem that, on average, >70% of tree transpiration and soil moisture during the summer originate from irrigation, with lower proportions of snowmelt (<30%) from the preceding winter. This implies that a fraction of summer transpiration is originated from out of phase precipitation inputs. Irrigation fractions are dominant throughout the growing season for soil and stem water, but snowmelt fractions increase in stem water towards the end of summer. Tree size, location, and species were not strongly associated with water sources under well‐irrigated conditions. These results show that urban tree management practices should consider the impact of both irrigation practices and residual precipitation inputs, highlighting the importance of examining interannual time scales when calculating the local water budget.