Observed Trends in Hydrologic Cycle Components

Abstract

Documentation of change in the Earth's climate is accomplished by assessing the rates, magnitude, and distribution of changes in various elements of the climate system, such as the components of the hydrologic cycle. The present section reviews the general character of changes in precipitation, streamflow, and evaporation as determined using systematically collected data through the end of the twentieth century. Precipitation over global land areas increased about 2% during the century, and streamflow also exhibited widespread increases. There was good agreement regionally between the observed precipitation and streamflow increases. The precipitation increases appear to have occurred most commonly in higher intensity categories (>50 mm per day), while the streamflow increases were overwhelmingly observed in the low to moderate range of flows. No systematic increases were observed in peak streamflows. These findings indicate that a general intensification of the hydrologic cycle occurred during the twentieth century, but that this intensification did not result in increased hydrologic extremes.

Stationarity: Wanted Dead or Alive?1

“…If one looks at the p ‐values associated with the trends (Figures 4c and 4d), one sees no evidence of widespread trends. This example is consistent with the results of nearly every study of trends in annual maximum streamflow published during the past decade (for a review of flood trend studies see Lins, 2005). The findings of Hamed (2008) are, perhaps, of greater relevance as he notes that LTP “may offer an explanation for inconsistencies in the results from several trend studies, known as ‘regional inconsistency,’ or ‘spatial nonuniformity,’ where neighboring stations may have significant, yet opposite trends.” Lacking both accurate physical understanding and statistical evidence, it is hard to justify admitting nonstationarity into rigorous analyses.…”

Weather noise impact on the uncertainty of simulated water balance components of river basins

“…Houghton et al 1990, IPCC 1996, Bates et al 2008) is accompanied by considerable changes of the hydrological cycle on different spatial and temporal scales (e.g. Barnett et al 2004, Lins 2005, Huntington 2006, Bates et al 2008, Kundzewicz et al 2008, Shiklomanov and Georgievski 2008, Sivakumar 2011, Motovilov and Gelfan 2013, Shepherd 2014. In comparison with surface temperature, the changes of the hydrological cycle are characterized by higher spatial inhomogeneity and stronger uncertainties when estimating from different empirical data and climate models (Shiklomanov 1994, Georgievskii et al 1996, Shiklomanov et al 2000.…”

Large-basin hydrological response to climate model outputs: uncertainty caused by internal atmospheric variability

“…The first group of empirical (data-based) approaches is based on treatment of available hydrometeorological records and includes, for instance, time series analysis of runoff characteristics (see reviews presented by Lins, 2005;Bates et al, 2008), analysis of these characteristics' sensitivity to climate variations, particularly by using "elasticity" indices (Sankarasubramanian et al, 2001;Vano and Lettenmaier, 2014), analysis of relationships between spatial and temporal runoff variations ("trading space for time") (Peel and Blöschl, 2011;Singh et al, 2011), etc. The second group includes approaches that are based on hydrological models forced by assigned scenarios of hydrometeorological inputs.…”