On inclusion of water resource management in Earth system models – Part 1: Problem definition and representation of water demand

Abstract

Abstract. Human activities have caused various changes to the Earth system, and hence the interconnections between human activities and the Earth system should be recognized and reflected in models that simulate Earth system processes. One key anthropogenic activity is water resource management, which determines the dynamics of human-water interactions in time and space and controls human livelihoods and economy, including energy and food production. There are immediate needs to include water resource management in Earth system models. First, the extent of human water requirements is increasing rapidly at the global scale and it is crucial to analyze the possible imbalance between water demands and supply under various scenarios of climate change and across various temporal and spatial scales. Second, recent observations show that human-water interactions, manifested through water resource management, can substantially alter the terrestrial water cycle, affect land-atmospheric feedbacks and may further interact with climate and contribute to sea-level change. Due to the importance of water resource management in determining the future of the global water and climate cycles, the World Climate Research Program's Global Energy and Water Exchanges project (WRCP-GEWEX) has recently identified gaps in describing humanwater interactions as one of the grand challenges in Earth system modeling (GEWEX, 2012). Here, we divide water resource management into two interdependent elements, related firstly to water demand and secondly to water supply and allocation. In this paper, we survey the current literature on how various components of water demand have been included in large-scale models, in particular land surface and global hydrological models. Issues of water supply and allocation are addressed in a companion paper. The available algorithms to represent the dominant demands are classified based on the demand type, mode of simulation and underlying modeling assumptions. We discuss the pros and cons of available algorithms, address various sources of uncertainty and highlight limitations in current applications. We conclude that current capability of large-scale models to represent human water demands is rather limited, particularly with respect to future projections and coupled landatmospheric simulations. To fill these gaps, the available models, algorithms and data for representing various water demands should be systematically tested, intercompared and improved. In particular, human water demands should be considered in conjunction with water supply and allocation, particularly in the face of water scarcity and unknown future climate. Background and scope Large-scale modeling -an introduction to land-surface and global hydrological modelsThe Earth system is an integrated system that unifies the physical processes at the Earth's surface. These processes include a wide range of feedbacks and interactions between and within the atmosphere, land and oceans and cover the global cycles of climate, water and carbon that sup...

Sensitivity of future U.S. Water shortages to socioeconomic and climate drivers: a case study in Georgia using an integrated human-earth system modeling framework

“…Subsequent studies could then develop approaches to derive the full probability distributions to the isolated key variables resulting from the sensitivity analysis, greatly reducing the dimensionality and cost of the stochastic analysis. This approach is consistent with standard sensitivity analysis methods employed in the decision sciences literature (Lempert et al 1996;Groves et al 2008;Morgan et al 2009;Means III et al 2010), but here the methods are applied to a new class of high resolution, integrated modeling frameworks. Figure 1 is a diagram of the integrated modeling framework used for this research.…”

“…GCAM-USA was then used to generate water demand scenarios for the 21st century using combinations of high, low, and reference water demand parameter values. An exhaustive set of possible combinations would have resulted in 6,561 GCAM downscaled model runs, but we used a fractional factorial design that required only 2,187 runs and still identified the combinations of parameter values that would bound the highest and lowest water demand (Montgomery 2012). We then had only to downscale the highest, lowest, and reference cases for the sensitivity analysis.…”

On inclusion of water resource management in Earth system models – Part 2: Representation of water supply and allocation and opportunities for improved modeling

“…However, as noted in our companion paper (hereafter referred to as Nazemi and Wheater, 2015), the current scale of human activities significantly perturbs the terrestrial water cycle, with local, regional and global implications. Such disturbances affect both hydrological functioning and land-atmospheric interactions, and therefore should be explicitly represented in large-scale models.…”

“…These latter areas are beyond the scope of this paper, but highlight the need to represent human water allocation in large-scale models for regional and global impact assessments. For instance, the most densely populated parts of the globe suffer from extremely fragile water supply conditions (e.g., Grey et al, 2013;Falkenmark, 2013;Nazemi and Wheater, 2015) and this will be amplified under future climate change and population growth (e.g., Arnell, 2004;Wada et al, 2013;Rosenzweig et al, 2014;Schiermeier, 2014;Haddeland et al, 2014). While population growth directly affects water demand, indirect effects include changing land and water management, with associated impacts on the aquatic environment.…”

“…Nazemi and H. S. Wheater: On inclusion of water resource management in Earth system models -Part 2 large-scale models and focus on water quantity rather than water quality. We note that while historically the effects of water management have largely been neglected in LSMs and GHMs, there has been increasing interest in recent years in their inclusion and a common first step is to estimate the demand for water, in particular associated with irrigation (see Nazemi and Wheater, 2015). However, in practice water resource systems are often complex, and associated infrastructure may have competing functional requirements and constraints (e.g., flood protection, water supply, environmental flows), exacerbated during drought.…”