Improving the representation of hydrologic processes in Earth System Models

Abstract

Many of the scientific and societal challenges in understanding and preparing for global environmental change rest upon our ability to understand and predict the water cycle change at large river basin, continent, and global scales. However, current large-scale land models (as a component of Earth System Models, or ESMs) do not yet reflect the best hydrologic process understanding or utilize the large amount of hydrologic observations for model testing. This paper discusses the opportunities and key challenges to improve hydrologic process representations and benchmarking in ESM land models, suggesting that (1) land model development can benefit from recent advances in hydrology, both through incorporating key processes (e.g., groundwater-surface water interactions) and new approaches to describe multiscale spatial variability and hydrologic connectivity; (2) accelerating model advances requires comprehensive hydrologic benchmarking in order to systematically evaluate competing alternatives, understand model weaknesses, and prioritize model development needs, and (3) stronger collaboration is needed between the hydrology and ESM modeling communities, both through greater engagement of hydrologists in ESM land model development, and through rigorous evaluation of ESM hydrology performance in research watersheds or Critical Zone Observatories. Such coordinated efforts in advancing hydrology in ESMs have the potential to substantially impact energy, carbon, and nutrient cycle prediction capabilities through the fundamental role hydrologic processes play in regulating these cycles.

The evolution of process-based hydrologic models: historical challenges and the collective quest for physical realism

“…Addressing this challenge requires shifting focus from traditional approaches at short timescales where "properties define processes" towards approaches on longer timescales that focus on predicting how "processes define properties" (Rodríguez-Iturbe et al, 1992;Eagleson, 2002;Harman and Troch, 2014). Importantly, it requires the treatment of humans as an endogenous component of the Earth system Clark et al, 2015a).…”

Planning for climate change impacts on hydropower in the Far North

“…Heat and moisture tend to flow along this gradient, poleward. Projected rates of hydroclimate change in globalor low-latitude studies may underestimate the true rates of change for high latitudes in the future because of the imperfect representation of these processes in models (Clark et al, 2015;Christensen et al, 2013).…”

“…Traditional water supply projections lead to different conclusions than projections that take into account climate change, including the range of plausible futures, or "uncertainty" around the model projections Hamlet, 2011). The following general techniques are used in recent work to predict future hydrologic regimes (Clark et al, 2015;Hagemann et al, 2013;Chen et al, 2012Chen et al, , 2014Balsamo et al, 2009Balsamo et al, , 2011Brekke et al, 2011;Koutsoyiannis et al, 2009;Lawrence and Hisdal, 2011;Frigon et al, 2007;Hagg et al, 2006;Bergstrom et al, 2001):…”

“…Because getting to detailed, precise information at the watershed scale requires intensive effort and significant computing power, these methods have mostly been applied to case studies of particular basins (Bennett et al, 2012;Shrestha et al, 2012 in the Far North). Land surface models within GCMs and regional climate models (RCMs) are another class of model that have been tested and compared for hydrologic applications, and are designed for global domains, but challenges of river routing (Li et al, 2013) and other local processes cause these tools to have large uncertainties at the watershed scale (Clark et al, 2015). The hydrologic modeling should also be used to drive models of sediment load for projecting reservoir in-filling and wear and tear on turbines (Toniolo and Schultz, 2005).…”

Monthly streamflow forecasting at varying spatial scales in the Rhine basin

“…Since the land surface component of ESMs often represents groundwater dynamics and the river routing in a simplified way (Clark et al, 2015), the simulated runoff might be fed to a routing model as e.g. in Pappenberger et al (2010).…”