Impervious Land Research Articles

Inconsistent using FLOOD and Flooding Development of EPA SWMM for Assessing Flood Occurrences in Vulnerable Urban Watershed Considering Extreme Rainfall Events

Urban flood, commonly known as urban water congestion, is a type of water hazard that poses significant challenges for urban residents and water management experts. Chittagong, an essential economic hub in Bangladesh, renowned for its role as a port city, comprises a diverse range of land use, including residential, industrial, and commercial sectors. The Chaktai canal, an important element of Chittagong drainage system, is connected to the Karnaphuli river, playing a vital role in managing drainage by handling a substantial portion of the city water. Therefore, this research evaluated the operational efficiency of a specific drainage network under the influence of altered rainfall events using the Storm Water Management Model (SWMM). Using ArcGIS 10.4, the land use pattern of the area was researched, incorporating data from field surveys and secondary sources. SWMM 5.1 integrated watershed data, and further simulation was carried out to estimate runoff in various sub-catchments and drainage network limitations during heavy rain. During the intense monsoon period, the tool determined the average runoff depth, considering backwater effects and robust tidal surges, resulting in a depth of 3.3m compared to 2.6m in the dry season. This research evaluated the influence of impervious land use changes on urban drainage systems. While meteorological factors alone render drainage network sufficient in dry periods, the outfall shows vulnerability during the rainy season, with an allowance of only 0.7m, jeopardizing the catchment through flood. It contributed a schematic sub-catchment representation, emphasizing that flood events depend on volume runoff and peak flow in urban drainage system. SWMM model was used to illustrate the catchment surface runoff and interconnected node depths via conduits, as well as the current catchment scenario comprehensively.

Stormwater Treatment Using Natural and Engineered Options in an Urban Growth Area: A Case Study in the West of Melbourne

The expected increase in urbanization and population in coming years is going to increase the impervious land area, leading to substantial increases in stormwater runoff and hydrological challenges, and presents significant challenges for urban potable water supply. These are worldwide challenges that can potentially be ameliorated by harvesting stormwater for potable use or for other uses that can reduce the pressure on potable water supply. This study sought to assist the local water authority in planning for future potable water supply through a review of the scientific literature to determine the likely chemical and microbial characteristics of stormwater, the treatment train (TT) requirements, and the likely costs of treatment to achieve potable standards for the high-growth metropolitan region of Melbourne, Australia. Literature stormwater quality statistical data and treatment process performance data were used to model the expected product water microbial and chemical quality after treatment using a number of advanced TT options. The results of the modelling were compared with literature microbial log reduction targets (LRTs) for the potable use of stormwater and with the Australian Drinking Water Guidelines (ADWG). It was found that a reverse osmosis (RO)-based TT with microfiltration pre-treatment and post-RO advanced oxidation and chlorination in storage reservoirs is a conservative stormwater potable use treatment option. A less conservative and less expensive ozone-and-biologically active filtration (O3/BAF)-based TT option is also proposed if RO concentrate disposal is deemed to be too challenging. These results could be useful in climate change adaptation involving the evaluation of options for the mitigation of future population-growth- and climate-change-driven water supply challenges, as well as urbanization-driven stormwater hydrology and receiving water pollution challenges.

Increasing actual evapotranspiration on the Loess Plateau of China: An insight from anthropologic activities and climate change

Actual evapotranspiration (ETa) is an important element of water circulation, and susceptible to environmental change. Precise estimation of ETa and identifying its key influence factors are of great importance. Loess Plateau has been largely affected by human activities and climate change, and the dynamics of ETa and its key influencing factors remain unknown in this region. The spatio-temporal variations of ETa over Loess Plateau from 2000 to 2020 were depicted on the basis of the ETWatch model. Then the individual contributions of climatic factors and human activities to ETa variation were quantified by applying generalized additive model. Results indicated that the annual average ETa during the period of 2000–2020 displayed a fluctuating increasing pattern from 386.67 mm in 2000 to 544.73 mm in 2020, with a growth rate of 6.25 mm⋅yr−1. Spatially, the ETa displays a downward pattern from southeast to northwest, which is highly similar to vegetation coverage with the coefficients of 0.766–0.832. The ETa of forest, grassland, cropland, shrub, barren land and impervious land exhibited positive or negative significantly correlations with their corresponding land cover area at the 0.05 or 0.01 level. Sunshine duration, temperature and precipitation are the top three factors showing high correlations with ETa. The results of contribution analysis suggested that the variations in ETa were largely controlled by LUCC in the Loess Plateau, where the LUCC accounted for 52.89% of the total ETa. The impacts of LUCC on ETa were greater than that of climate change on ETa, although climate change was dominant in a few years. These results could contribute to optimizing water resource management and developing various water-saving tactics in the Loess Plateau.

Influence of road network expansion on the landscape ecological risk in the Yangtze River Delta region over the past two decades

One of China's regions with the finest foundations for urbanization, the Yangtze River Delta (YRD), has experienced tremendous urbanization growth over the past 20 years. It is crucial to assess how the region's rapidly expanding road network may affect the landscape ecological risk (LER) by using landscape analysis, kernel density estimation and statistical analysis. The findings concluded that 1) The LER, which was significantly affected by the landscape pattern and topography was unevenly distributed throughout the YRD region, exhibiting obvious characteristics of high LER values in the north and low LER values in the south. From 2005 to 2020, the medium and sublow LER zones showed increasing trends, with increases of 7101 and 3186 km2, respectively. The decreased areas reached 5310, 2583, and 2394 km2 for the low, subhigh, and high LER zones, respectively. 2) There were obvious spatial differences in the impact of road networks on the LER’s geographical distribution in the YRD region. Significantly negative correlation areas were mainly distributed along and around the minimum spanning tree (MST) generated by the city centers of provinces, which had dense road networks. Significantly positive correlation areas were far away from the MST. 3) From 2005 to 2020, road network expansion in the YRD region impacted the interannual changes in both the LER index and each component index. As the road network expands, the fragmentation, splitting and disturbance indices of shrubs, grasslands and impervious land patches decrease, while those of croplands, forestlands, and water bodies increase. This study can serve as a scientific foundation and point of reference for planning the road network expansion and assessing the regional ecological risk in the YRD region.

Evaluation of total infiltration and storage capacities for different soil types in Sarawak using SWMM

Climate change and irresponsible urbanization practices are anticipated to further exacerbate flood risk. The different soil types’ physical, chemical, and biological characteristics significantly impact surface water movement, porosity, permeability, and infiltration potential. Therefore, soil infiltration is perhaps the most challenging and crucial process to characterize on a field scale. Various methods have been developed to measure the infiltration rate empirically and theoretically. However, the relationship between different soil types and infiltration rates in Sarawak remains unknown as no previous study has been conducted. This study uses the Storm Water Management Model (SWMM) to evaluate the infiltration rates for five different soil types: clay, clay loam, loam, sandy loam, and sand. 30 samples of various types and soil depths were examined at intervals of 0.5 m, 1.0 m, 1.5 m, 2.0 m, 2.5 m, and 3 m. The study was carried out using a standardized slope of 0.7% and an impervious land of 25% with a catchment size of 2 acres. Extreme rainfall data on the 5th and 6th of December 2021 was input into the infiltration model. Results showed that the difference between initial and final water storage of all the investigated soil depths for clay, clay loam, loam, sandy loam, and sand was found to be 48.42 mm, 51.20 mm, 58.01 mm, 66.96 mm, and 115.54 mm, respectively. The findings demonstrated that clay has the lowest water storage capability, followed by clay loam, loam, and sandy loam. Sand could store a comparatively large amount of rainwater. In contrast, sand has the highest infiltration rate with 2.541 mm/h, followed by sandy loam with 1.835 mm/h, loam with 1.432 mm/h, clay loam with 1.039 mm/h. Clay has the lowest infiltration rate, with 0.852 mm/h. This research concluded that sandy soil could significantly reduce surface runoff and help reduce flood risk in urban regions.

Beyond Phosphorus: Salinization as a driver of eutrophication symptoms in North American lakes

The acceleration of global urbanization continues to fuel concerns surrounding water quality impairments in urban lakes, particularly eutrophication. Eutrophication of freshwater environments is generally assumed to be driven by increased anthropogenic phosphorus (P) supplies which can alleviate limitations on primary production. Salinization is also recognized as a stressor on urban freshwater quality, particularly in cold temperate climate regions where salts are applied to road surfaces as de-icing agents. While the ecological damages caused by P enrichment and salinization to freshwaters are both well established, thus far, their impacts on water quality have only been considered independently. Although improvements to the management of urban stormwater and wastewater have decreased P inputs to freshwater systems in recent decades, many lakes worldwide remain eutrophic, as indicated by declining dissolved oxygen (DO) concentrations and rising dissolved inorganic P (DIP) concentrations in the hypolimnion. Our previous study of an urban freshwater lake in Ontario, Canada, showed that persistent eutrophication symptoms are linked to salinization associated with impervious land cover expansion, rather than increased external P loading. In this research, we present a multiple decade of water chemistry data analyses for several other urban lakes in Ontario, Wisconsin, and Minnesota to determine how increased lake salinization rates intersect with water temperature and morphometry to alter water column stratification, thus, increasing eutrophication symptoms. Our trend analysis shows progressive salinization (observed through significant increases in chloride or electrical conductivity) of all the lakes investigated. Calculations of lakes mixing indices over time show that, on average, lake stratification is becoming more stable with increased salinity playing a crucial role in enhancing lake stratification. Overall, salinity is becoming a stronger regulator of water density than temperature in the cold temperate urban freshwater lakes of North America. The increasing salinity trends are accompanied by increasing hypolimnion hypoxia and increasing DIP to total P (TP) ratios in all lakes, thereby demonstrating the mechanistic link between salinization and internal P loading. Rising salinity intensifies water column stratification, in turn, reducing the oxygenation of the hypolimnion and enhancing internal P loading from the sediments. These results highlight that stricter management of de-icing salt application rates should be considered to control lake eutrophication symptoms in cold climate regions.

Impervious Land Expansion as a Control Parameter for Climate-Resilient Planning on the Mediterranean Coast: Evidence from Greece

Impervious land expansion is linked to ecosystem fragmentation and degradation, posing threats to nature conservation and multiplying climate change impacts. This is particularly true on the Mediterranean coast, where persistent urbanization is coupled with tourism development, further intensifying coastal erosion, flood risk, heat stress and biodiversity loss, while decreasing carbon sequestration. In this research, high-resolution imperviousness data were analyzed through a geospatial methodology to detect patterns and processes in a heavily burdened Mediterranean coastal area, namely Greece. The methodology was structured on a set of GIS tools, analyzing the distribution of new impervious cover between 2006 and 2018, to evaluate pressures exerted on coastal territories and on the environmental protection network. The results revealed relatively slow rates of impervious land expansion at a nationwide scale, mostly attributed to the economic recession period in Greece. However, certain locations exhibited continuing artificialization of land even within Natura 2000 areas, while future pressures on coastal territories are expected to increase due to the restarting of construction activity and the continuing dynamic of the mass tourism sector. The conclusions imply that controlling for imperviousness is important in order to develop spatial planning policies for climate resilience, which should be decisively enforced in the Mediterranean to prevent a business-as-usual scenario.

High summer land surface temperatures in a temperate city are mitigated by tree canopy cover

As climate warms, the impact of existing urban heat islands on the health of residents in towns and cities will worsen. A reduction in impervious in cities may help to reduce temperatures, but the relationship between tree canopy coverage and land surface temperature (LST) is not well characterised. Here, we quantified the summer LST of the temperate city of Leeds, UK using Landsat 8 TIRS remote sensing image and explored the spatial relationships between LST and impervious land cover, greenspace coverage, type of greenspace and canopy cover. We found a strong relationship between LST and canopy coverage across the built-up region of Leeds and use this relationship to project the impact of future canopy cover expansion. We found that of the nine main types of greenspaces in Leeds, private gardens occupied the greatest fraction of the total greenspace area and offered most potential for canopy cover expansion. Results suggest that a doubling of canopy coverage across the city, could reduce the mean LST by around 2.5 °C during the warmest summer months. Such a temperature reduction adds further weight to efforts by cities and countries globally to increase tree cover to both mitigate for and adapt to climate change.

Spatio-Temporal Variation of Carbon Sources and Sinks in the Loess Plateau under Different Climatic Conditions and Land Use Types

The carbon balance of terrestrial ecosystems is intertwined with climate and changes in land use. Over the past 30 years, the Loess Plateau (LP) has experienced temperature increases and an expansion of forest and grassland. The net ecosystem productivity (NEP) underlying these changes is worth investigating. Using three periods (i.e., 1990–2000, 2000–2010, and 2010–2019) of annual average NEP and climatic, topographic, and land use data, we analyzed changes in the spatial distribution of carbon sources and sinks of the LP. Using an optimal parameter-based geographical detector model to discuss the driving factors of carbon sources and sinks, we found that: (1) The area of carbon sinks has been increasing continuously, and that the distributions of both of these elements are zonal. The carbon sinks show a downward trend from south to north, which is mainly driven by climate and land use type. (2) Carbon sources are mainly concentrated in the middle temperate zone, and they are mainly linked to impervious land, unused land, and grassland. The carbon sinks are mainly concentrated in the south temperate zone and plateau climatic zone, and they are mainly linked to forest, grassland, and cultivated land. Additionally, the southern temperate zone has been the most green, due to its superior hydrothermal conditions that sustain carbon sinks. (3) It is not uncommon for some forests, grasslands, and cultivated land to transition between being carbon sources and carbon sinks, especially when affected by human intervention and inadequate management measures. (4) NEP was primarily influenced by CO2 concentration, temperature, and precipitation, and the interaction of these factors greatly influenced the dynamics of carbon sources and sinks, while terrain exerted insignificant impacts on the NEP. This study highlights the importance of the carbon balance in terrestrial ecosystems and can be used to guide the creation of vegetation-based carbon sequestration policies.

Water Deficit Caused by Land Use Changes and Its Implications on the Ecological Protection of the Endorheic Dalinor Lake Watershed in Inner Mongolia, China

Dalinor Lake, the second-largest endorheic salt lake in Inner Mongolia, has shown a shrinking trend given the lack of a significant decrease in precipitation (PRE). Based on high-spatial-resolution datasets, we employed a linear regression model, Theil–Sen median trend analysis, the Mann–Kendall test, and a land use transfer matrix to identify the spatio-temporal distribution and trends of PRE and actual evapotranspiration (AET) at the watershed scale during 2001–2019; then, the water deficit (WD) caused by land use changes in different surface lithology zones was analyzed. The results showed that the annual PRE and WD of the Dalinor Lake watershed showed insignificant upward trends, while the annual AET showed a significant upward trend. Spatially, about 89% of the watershed showed a significant upward trend for AET, while 12% showed a weak significant upward trend for PRE. The WDs of the aeolian sand zone and the sand, gravel, and silt accumulation zone were most heavily affected by the new increased land use from 2001 to 2019, accounting for 43.14% and 25.56% of the total WD of the watershed, respectively. Specifically, the WD of the aeolian sand zone caused by the new increased grassland and farmland in 2019 accounted for 41.92% and 18.52% of the total WD of the zone, respectively. The WD of the sand, gravel, and silt accumulation zone caused by the new increased grassland and farmland in 2019 accounted for 37.07% and 35.59% of the total WD of the zone, respectively. The WD caused by the new increased land use was increased by 7.78 million m3 in 2019 compared with the corresponding land use type in 2001, which would decrease the water yield. It is necessary to strengthen the protection of regional forest ecosystems in the granite and terrigenous clastic rock zone; standardize pasture management and reduce farmland reclamation in the sand, gravel, and silt accumulation zone, the aeolian sand zone, and the basalt platform zone; and reduce unnecessary impervious land construction in the aeolian sand zone.

Toward Sustainable Development Trajectories? Estimating Urban Footprints from High-Resolution Copernicus Layers in Athens, Greece

Land imperviousness reflects settlement growth and urban sprawl. Grounded on a comparative approach, a set of multidimensional statistical techniques were adopted here to quantify the evolution of land imperviousness from Copernicus High-Resolution Layers (HRLs) in a representative case study of Southern Europe (Athens, Greece). A two-way data matrix reporting the percent share of the surface land exposed to different sealing levels (101 classes ranging continuously from 0% to 100%) in the total municipal area was computed for two years (2006 and 2018) individually for 115 municipalities in metropolitan Athens. This matrix represented the information base needed to derive place-specific urban footprints and a comprehensive (global) profile of land imperviousness. Results of a Detrended Correspondence Analysis (DCA) delineated a metropolitan structure still organized along the density gradient, moving from dense settlements in central locations with dominant land classes sealed for more than 90% of their surface area to completely pervious land (0%) typical of rural locations. While the density gradient became less steep between 2006 and 2018, it continued to aliment a socioeconomic polarization in urban and rural districts with distinctive profiles of land imperviousness. Intermediate locations had more mixed imperviousness profiles as a result of urban sprawl. Differential profiles reflect place-specific urban footprints with distinctive land take rates.

An Event-Based Resilience Index to Assess the Impacts of Land Imperviousness and Climate Changes on Flooding Risks in Urban Drainage Systems

Assessing the resilience of urban drainage systems requires the consideration of future disturbances that will disrupt the system’s performance and trigger urban flooding failures. However, most existing resilience assessments of urban drainage systems rarely consider the uncertain threats from future urban redevelopment and climate change, which leads to the underestimation of future disturbances toward system performance. This paper fills in the gap of assessing the combined and relative impacts of future impervious land cover and rainfall changes on flooding resilience in the context of a densely infilled urban catchment served by an urban drainage system in Salt Lake City, Utah, USA. An event-based resilience index is proposed to measure climate change and urbanization impacts on urban floods. Compared with the traditional resilience metric, the event-based resilience index can consider climatic and urbanized impacts on each urban flooding event; the new resilience index assist engineers in harvesting high-resolution infrastructure adaptation strategies at vulnerable spots from the system level to the junction level. Impact comparison for the case study shows that impervious urban surface changes induce greater effects on the system performance curves by magnifying the maximum failure level, lengthening the recovery duration, and aggravating the flooding severity than rainfall intensity changes. A nonlinear logarithmic resilience correlation is found; this finding shows that flooding resilience is more sensitive to the land imperviousness change due to urban redevelopment than rainfall intensity changes in the case study. This research work predicts the system response to the disturbances induced by climate change and urban redevelopment, improving the understanding of impact analysis, and contributes to the advancement of resilient urban drainage systems in changing environments.

Modeling Alex Hurricane: flood map simulation applying Multisensor grid precipitation, Monterrey, Mexico

A simulation was carried out in the Santa Catarina River watershed, located in the State of Nuevo Leon, Mexico, to study flood patterns and velocity maps during the occurrence of Hurricane Alex in June-July 2010. To conduct this simulation, a two-dimensional model of the Santa Catarina River Watershed was employed using the HEC-RAS software. The model was driven by Multisensor grid precipitation data as input. Land cover and soil layers were utilized in order to obtain various parameters within the watershed, such as Curve Number, Manning Number, Abstraction Ratio, Infiltration Rate, and Percent of Impervious Land. The simulated water levels were calibrated by comparing them with observed values at the Cadereyta Hydrometric Station, which is located near the city of Monterrey. The utilization of the HEC-RAS two-dimensional model combined with Multisensor grid precipitation demonstrates that this particular model is easy to set up and is user-friendly. Moreover, the model exhibits stability and possesses the ability to accurately simulate flood patterns and velocity maps within the watershed.
 Keywords: Floodmap, HEC-RAS 2D, Mexico, Monterrey, MRMS-QPE.

The Impacts of Land Use Changes on Water Yield and Water Conservation Services in Zhangjiakou, Beijing’s Upstream Watershed, China

The Water Conservation Functional Zone and Ecological Environmental Supporting Zone (the Capital Two Zones in China), Zhangjiakou (ZJK) City, situated in China, has played a key role in mitigating water scarcity pressure on Beijing via delivering sustainable and high-quality water yield, as well as water conservation services aimed at maintaining the ecological functions of the Capital Two Zones. However, the changing mechanism for both water yield and water conservation services instigated by the combined impacts of human activities and climate change remains poorly understood. In this study, we used the Integrated Valuation of Ecosystem Services and Trade-offs Tools (InVEST) model to analyze the changes in water yield and water conservation services, revealing the impacts of different land use scenarios. The results showed significant forest and impervious land area increment, while the water surface area decreased sharply from 1990 to 2020, with obvious urbanization expansion in ZJK during the period. Average annual water yield and water conservation from 1990 to 2020 were recorded at 48.98 mm and 2.35 mm, respectively. Precipitation emerged as the primary driver of water yield and conservation service changes, while the south of ZJK generally exhibited higher water yield and conservation service than the north of ZJK. Results also indicate that grassland had the highest water yield, with an average of 56.60 mm, followed by forest (55.66 mm) and shrub (55.07 mm). Further, the forest had the highest water conservation value (3.73 mm), followed by shrub (2.56 mm), and grassland (2.37 mm), respectively. The return of cropland to forest scenario had the most substantial decrease in water yield. Findings suggest that precipitation has a direct impact on water yield and conservation services via the amount of atmospheric water input, while land use alteration contributes to changes in regional-scale water.

Assessing the effects of land cover change in runoff processes with RHESSys: a case study in the Waterford River Watershed, Newfoundland and Labrador, Canada

Evaluating the current state of hydrologic processes in urban and semi-urban areas is an essential part of ensuring the sustainable management of water and preventing emergencies of extreme events. This study evaluated the effects of land use and land cover (LULC) change on runoff processes in the Waterford River Watershed (WRW), located in the eastern part of the province of Newfoundland and Labrador (NL), Canada. The Regional Hydro – Ecological Simulation System (RHESSys), a GIS-based hydro-ecological model, was used in a new urbanistic approach to simulate the effects of increasing impervious land as well as reducing urban green areas. The increase in hypothetical peak flows had a direct relationship with the reduction of pervious areas in the watershed. The most sizeable flow increases were observed in the periods of April to May and October to December. This study emphasizes the importance of using a prominent network of green and pervious structures or water retention areas when allocation for residential and commercial land increase.

Urbanization reduces soil microbial network complexity and stability in the megacity of Shanghai

Urbanization is altering the co-occurrence networks of ecological communities that are critical to maintaining ecosystem functions and services. Soil microbial communities play key roles in various ecosystem processes, but how soil microbial co-occurrence networks respond to urbanization is unclear. Here we analyzed co-occurrence networks in soil archaeal, bacterial, and fungal communities from 258 soil sampling sites across the megacity of Shanghai along large urbanization gradients. We found that topological features of microbial co-occurrence networks were strongly altered by urbanization. In particular, microbial communities in more urbanized land-use and highly impervious land cover had less connected and more isolated network structures. These structural variations were accompanied by the dominance of connectors and module hubs affiliated with the Ascomycota in fungi and Chloroflexi in bacteria, and there were greater losses in efficiency and connectivity in urbanized than in remnant land-use in simulated disturbances. Furthermore, even though soil properties (especially soil pH and organic carbon) were major factors shaping topological features of the microbial networks, urbanization still uniquely explained a proportion of the variability, particularly those describing network connections. These results demonstrate that urbanization has clear direct and indirect effects on microbial networks and provide novel insights into how urbanization alters soil microbial communities.

Impact of land use land cover change on the land surface temperature: A case study of Shillong

Shillong has been experiencing changes in land use land cover over the past years especially in the town areas where a lot of built-ups are emerging. In response to this, there has been some impacts in the distribution of temperature. In this study, remote sensing techniques have been used. The maximum likelihood method has been used for supervised classification of land use land cover from false color composite images. Landsat 5 TM and Landsat 8 OLI/ TIRS has been used in this study. The study period is 30 years from 1992 - 2022 with an interval of 15 years. The emergence and increase of more built-up and impervious land cover type surfaces has made the land surface temperature to increase. The correlation between NDVI and LST shows a negative relationship while that of NDBI and LST shows a positive relationship. The temperature has been increasing with an average of 2° C each interval of study. The hotspot analysis has been used to demarcate the heat zones. The highest temperature is found in the crowded and high built-up areas while the lowest temperature is found in the vegetated lands which further cause heat island effect in these highly built-up areas. Key Words: Land use land cover, Land surface temperature, Change detection, Hotspot analysis, Correlation analysis, Heat-island effect.

Divergent urbanization-induced impacts on global surface urban heat island trends since 1980s

Urbanization experiences different speeds and forms under diverse development stages across the globe. However, urbanization-induced impacts on long-term surface urban heat island intensity (Is) trends across global cities and the regulators of such impacts remain understudied Here we estimate interannual trends in daytime Is (i.e., urban-rural differences in surface temperatures) across 511 major cities for 1985–2020 using annual averages calculated using reconstructed land surface temperature data derived from >250,000 Landsat thermal images. Our study reveals that the global mean Is growth rate is 0.156 °C/decade. We further examine Is change associated with per 1% impervious land growth (denoted as β) in each city throughout the research period and during different periods. The global mean β is 0.018 ± 0.025 °C/% (mean ± 1 standard deviation) for the whole period, with greater values in humid than in arid climates; and the β may change during different periods, e.g., it has more than tripled when urban impervious land exceeds 30%, indicating the spatiotemporally divergent impacts of urbanization on Is trends across global cities. The spatial variations in β across global cities are well correlated with rural vegetation abundance and precipitation but not with urban population. Among these three factors, rural vegetation abundance possesses the greatest standardized regression coefficient of partial least-squares model, signifying the critical role of biome background in regulating β. The finding implies that future urbanization over densely vegetated regions should be more carefully and strategically planned due to the greater urbanization-induced surface warming effect.

Climatic Control on Mean Annual Groundwater Evapotranspiration in a Three‐Stage Precipitation Partitioning Framework

AbstractA three‐stage precipitation partitioning framework is proposed to study the climate controls on mean annual groundwater evapotranspiration (GWET) for 33 gauged watersheds in west‐central Florida. Daily GWET, total evapotranspiration (ET), groundwater recharge, base flow, and total runoff are simulated by the Integrated Hydrologic Model, which dynamically couples a surface water model (HSPF) and a groundwater flow model (MODFLOW). The roles of GWET on long‐term water balance are quantified by four ratios. The ratios of GWET to total available water, watershed wetting, ET, and recharge decrease exponentially with watershed aridity index (WAI), which is defined as the ratio of potential evapotranspiration to total available water. In the one‐stage precipitation partitioning framework, the contribution of GWET to the ratio between total ET and available water for ET (i.e., the y‐axis of Budyko curve) decreases with WAI. In the two‐stage precipitation partitioning framework, the contribution of GWET to the ratio between total ET and watershed wetting (i.e., Horton index) decreases with WAI. The changes in GWET caused by intra‐monthly (IM) climate variability are the highest among the temporal scales of climate variability investigated to understand controls on GWET. The inter‐annual, intra‐annual, and IM climate variabilities lead to increase of GWET; but the sub‐daily climate variability results in decrease of GWET. For the third stage of partitioning, given the same ratio of potential GWET to available water for GWET, higher percentage of forest and wetland and lower percentage of impervious land contribute to higher ratio of GWET to available water for GWET.

When impervious cover doesn't predict urban runoff: Lessons from distributed overland flow modeling

We used the distributed hydrologic model GSSHA to simulate overland runoff from impervious and semi-pervious (low vegetation) land covers in a 0.3 km2 urban catchment. The model is hypothetical, which allowed us to test alternative land use configurations and better understand the effects of urban heterogeneity. To track the arrival of water to a stormwater basin inlet from distinct parts of the catchment, we applied a conservative solute tracer to portions of the gridded model area, a new application for GSSHA’s ‘contaminant transport’ module. We rearranged the positions of pervious and impervious land uses over the catchment during four storm events and found that the portion of total runoff volume from impervious areas varied from 50 to 75% while the relative proportion of impervious cover remained constant at 54%. We also applied solute to equal-sized zones with different slopes and land uses and found that percent imperviousness did not predict solute mobilization. Furthermore, variation in total runoff volume and peak discharge for different land use arrangements and storm sizes showed that percent imperviousness could not be used to estimate a runoff-rainfall ratio. Fluctuating solute proportions over time suggested that grab samples might not be adequate for capturing average overland runoff chemistry. We quantified factors contributing to non-linearity in rainfall-runoff responses from an urban watershed with stormwater infrastructure and determined that using models to find hotspots for stormwater infiltration and to explore resilience to future storm events can improve design and function of stormwater control measures.