Hydroclimatic regimes: a distributed water-balance framework for hydrologic assessment and classification

Abstract

Abstract. Runoff-based indicators of terrestrial water availability are appropriate for humid regions, but have tended to limit our basic hydrologic understanding of drylands – the dry-sub-humid, semi-arid, and arid regions which presently cover nearly half of the global land surface. In response, we introduce an indicator framework that gives equal weight to humid and dryland regions, accounting fully for both vertical (precipitation + evapotranspiration) and horizontal (groundwater + surface-water) components of the hydrologic cycle in any given location – as well as fluxes into and out of landscape storage. We apply the framework to a diverse hydroclimatic region (the conterminous USA), using a distributed water-balance model consisting of 53 400 networked landscape hydrologic units. Our model simulations indicate that about 21% of the conterminous USA either generated no runoff or consumed runoff from upgradient sources on a mean-annual basis during the 20th century. Vertical fluxes exceeded horizontal fluxes across 76% of the conterminous area. Long-term average total water availability (TWA) during the 20th century, defined here as the total influx to a landscape hydrologic unit from precipitation, groundwater, and surface water, varied spatially by about 400 000-fold, a range of variation ~100 times larger than that for mean-annual runoff across the same area. The framework includes, but is not limited to classical, runoff-based approaches to water-resource assessment. It also incorporates and re-interprets the green-blue water perspective now gaining international acceptance. Implications of the new framework for hydrologic assessment and classification are explored.

Climatic and terrestrial storage control on evapotranspiration temporal variability: Analysis of river basins around the world

“…Under this situation, the impact of anthropogenic-related terrestrial storage change (such as irrigation) will have a major contribution to ET variance [Scanlon et al, 2012;Wada and Bierkens, 2014]. Further research is needed to characterize the anthropogenic impacts, such as land use change irrigation, water storage, and groundwater pumping [Vogel et al, 2015;Weiskel et al, 2014], on ET variance for regions with out-of-phase PET and P seasonality. On the other hand, future research is also needed to understand how intra-annual and interannual ET variance change affects water resources management under changing climate, especially to match crop ET requirement [Cai et al, 2015a].…”