Millennium Ecosystem Assessment Scenario drivers (1970-2050): Climate and hydrological alterations

This study was carried out to support and enhance a series of global studies assessing contemporary and future changes in nutrient export from watersheds (Global Nutrient Export from Watersheds (NEWS)). Because hydrography is one of the most important drivers in nutrient transport, it was essential to establish how climatic changes and direct human activities (primarily irrigation and reservoir operations) affect the hydrological cycle. Contemporary and future hydrography was established by applying a modified version of a global water balance and transport model (WBMplus) driven by present and future climate forcing, as described in the Millennium Ecosystem Assessment scenarios (1970-2050). WBMplus represents a major upgrade to previous WBM implementations by incorporating irrigational water uptake and reservoir operations in a single modeling framework. Contemporary simulations were carried out by using both observed climate forcings from the Climate Research Unit of East Anglia (CRU) data sets and from Global Circulation Model (GCM) simulations that are comparable to the future simulations from the same GCM forcings. Future trends in three key human activities (land use, irrigation, and reservoirs operation for hydropower) were taken from the Integrated Model to Assess the Global Environment (IMAGE). The reservoir operation required establishing a realistic distribution of future reservoirs since the IMAGE model provided only the hydropower potentials for the different future scenarios

EPA Program Review: Consequences of Global Climate Change: Water Quality Impacts, Ecological Impacts & Nonlinear Responses

A presentation that overviews existing modeling frameworks to analyze water system sensitivity to climate change and other stress factors

Human-water interface in hydrological modeling: Current status and future directions

Over the last decades, the global population has been rapidly increasing and human activities have altered terrestrial water fluxes at an unprecedented scale. The phenomenal growth of the human footprint has significantly modified hydrological processes in various ways (e.g., irrigation, artificial dams, and water diversion) and at various scales (from a watershed to the globe). During the early 1990s, awareness of the potential water scarcity led to the first detailed global water resource assessments. Shortly thereafter, in order to analyse the human perturbation on terrestrial water resources, the first generation of large-scale hydrological models (LHMs) was produced. However, at this early stage few models considered the interaction between terrestrial water fluxes and human activities, including water use and reservoir regulation, and even fewer models distinguished water use from surface water and groundwater resources. Since the early 2000s, a growing number of LHMs are incorporating human impacts on hydrological cycle, yet human representations in hydrological models remain challenging. In this paper we provide a synthesis of progress in the development and application of human impact modeling in LHMs. We highlight a number of key challenges and discuss possible improvements in order to better represent the human-water interface in hydrological models

Human–water interface in hydrological modelling: current status and future directions

Over recent decades, the global population has been rapidly increasing and human activities have altered terrestrial water fluxes to an unprecedented extent. The phenomenal growth of the human footprint has significantly modified hydrological processes in various ways (e.g. irrigation, artificial dams, and water diversion) and at various scales (from a watershed to the globe). During the early 1990s, awareness of the potential for increased water scarcity led to the first detailed global water resource assessments. Shortly thereafter, in order to analyse the human perturbation on terrestrial water resources, the first generation of largescale hydrological models (LHMs) was produced. However, at this early stage few models considered the interaction between terrestrial water fluxes and human activities, including water use and reservoir regulation, and even fewer models distinguished water use from surface water and groundwater resources. Since the early 2000s, a growing number of LHMs have incorporated human impacts on the hydrological cycle, yet the representation of human activities in hydrological models remains challenging. In this paper we provide a synthesis of progress in the development and application of human impact modelling in LHMs. We highlight a number of key challenges and discuss possible improvements in order to better represent the human-water interface in hydrological models

A green-gray path to global water security and sustainable infrastructure

Sustainable development demands reliable water resources, yet traditional water management has broadly failed to avoid environmental degradation and contain infrastructure costs. We explore the global-scale feasibility of combining natural capital with engineering-based (green-gray) approaches to meet water security threats over the 21st century. Threats to water resource systems are projected to rise throughout this period, together with a significant expansion in engineering deployments and progressive loss of natural capital. In many parts of the world, strong path dependencies are projected to arise from the legacy of prior environmental degradation that constrains future water management to a heavy reliance on engineering-based approaches. Elsewhere, retaining existing stocks of natural capital creates opportunities to employ blended green-gray water infrastructure. By 2050, annual engineering expenditures are projected to triple to $2.3 trillion, invested mainly in developing economies. In contrast, preserving natural capital for threat suppression represents a potential$3.0 trillion in avoided replacement costs by mid-century. Society pays a premium whenever these nature-based assets are lost, as the engineering costs necessary to achieve an equivalent level of threat management are, on average, twice as expensive. Countries projected to rapidly expand their engineering investments while losing natural capital will be most constrained in realizing green-gray water management. The situation is expected to be most restrictive across the developing world, where the economic, technical, and governance capacities to overcome such challenges remain limited. Our results demonstrate that policies that support blended green-gray approaches offer a pathway to future global water security but will require a strategic commitment to preserving natural capital. Absent such stewardship, the costs of water resource infrastructure and services will likely rise substantially and frustrate efforts to attain universal and sustainable water security

Urbanisation affects ecosystem functioning more than structure in tropical streams

Urbanisation poses a clear threat to tropical freshwater streams, yet fundamental knowledge gaps hinder our ability to effectively conserve stream biodiversity and preserve ecosystem functioning. Here, we studied the impact of urbanisation on structural and functional ecosystem responses in low-order streams in Singapore, a tropical city with a mosaic landscape of protected natural forests, managed buffer zones (between forest and open-country habitats), and built-up urban areas. We quantified an urbanisation gradient based on landscape, in-stream, and riparian conditions, and found an association between urbanisation and pollution-tolerant macroinvertebrates (e.g. freshwater snail and worm species) in litter bags. We also found greater macroinvertebrate abundance (mean individuals bag−1; forest: 30.3, buffer: 70.1, urban: 109.0) and richness (mean taxa bag−1; forest: 4.53, buffer: 4.75, urban: 7.50) in urban streams, but similar diversity across habitats. Higher levels of primary productivity (measured from algal accrual on ceramic tiles) and microbial decomposition (measured from litter-mass loss in mesh bags) at urban sites indicate rapid microbial activity at higher light, temperature, and nutrient levels. We found that urbanisation affected function 32% more than structure in the studied tropical streams, likely driven by greater algal growth in urban streams. These changes in ecological processes (i.e. ecosystem functioning) possibly lead to a loss of ecosystem services, which would negatively affect ecology, society, and economy. Our results point to possible management strategies (e.g. increasing vegetation density through buffer park creation) to reduce the impacts of urbanisation, restore vital ecosystem functions in tropical streams, and create habitat niches for native species