Decadal-Scale Changes in the Seasonal Surface Water Balance of the Central United States from 1984 to 2007

Abstract

Variations in climate have important influences on the hydrologic cycle. Observations over the continental U.S. in recent decades show substantial changes in hydrologically significant variables, such as decreases in cloud cover and increases in solar radiation (i.e., “solar brightening”), as well as increases in air temperature, changes in wind speed, and seasonal shifts in precipitation rate and rain/snow ratio. Impacts of these changes on the regional water cycle from 1984-2007 are evaluated using a terrestrial ecosystem/land surface hydrologic model (Agro-IBIS). Results show an acceleration of various components of the surface water balance in the Upper Mississippi, Missouri, Ohio, and Great Lakes basins over the 24-year period, but with significant seasonal and spatial complexity. Evapotranspiration (ET) has increased across most of our study domain and seasons. The largest increase is found in fall, when solar brightening trends are also particularly significant. Changes in runoff are characterized by distinct spatial and seasonal variations, with the impact of precipitation often being muted by changes in ET and soil-water storage rate. In snow-dominated regions, such as the northern Great Lakes basin, spring runoff has declined significantly due to warmer air temperatures and an associated decreasing ratio of snow in total precipitation during the cold season. In the northern Missouri basin, runoff shows large increases in all seasons, primarily due to increases in precipitation. The responses to these changes in the regional hydrologic cycle depend on the underlying land cover type (i.e., maize, soybean, and natural vegetation), and comparisons are also made with other hydroclimatic timeseries to place the decadal-scale variability in a longer-term context.

Evaluation of Northern Hemisphere snow water equivalent in CMIP6 models during 1982–2014

“…Due to the global warming, the melting season begins earlier, with the timing of streamflow peaks also becoming earlier (Kundzewicz et al, 2008). In addition, changes in snow cover affect the intensity of spring streamflow, as an increasing proportion of winter precipitation is rain instead of snow (Callaghan et al, 2011;Cohen et al, 2015;Dong et al, 2020; Published by Copernicus Publications on behalf of the European Geosciences Union. 1008 K. Kouki et al: Evaluation of Northern Hemisphere snow water equivalent Kundzewicz et al, 2008).…”

Water and Energy budgets over hydrological basins on short and long timescales

“…Despite the fundamental importance to our understanding of climate and climate change, there remain some key challenges to quantifying the regional water and energy cycling rates. In particular observations of the flux and storage terms tend to have large uncertainties and are inconsistent with budget considerations, while model estimates are internally consistent but usually show some mismatches to observations (e.g., Dong et al, 2020). Rosenzweig et al (2021) focused on human impacts on the water cycle and produced a remotely sensed ensemble of the terrestrial water budget (REESEN) containing 60 unique realisations of the water budget for basins between 50 • S and 50 • N, over Oct 2002-Dec 2014.…”

Development and evaluation of 0.05° terrestrial water storage estimates using CABLE land surface model and GRACE data assimilation

“…The approach sequentially updates the model's states using an optimal value computed by combining model simulations with observations. A variety of satellite observations reflecting different TWS components can be assimilated into the system (e.g., Kumar et al, 2014;Dong and Crow, 2018). TWS observations from the Gravity Recovery And Climate Experiment (GRACE) satellite mission (Tapley et al, 2004) offer integrated water column information that can be used to constrain multiple water storage components simultaneously (e.g., Zaitchik et al, 2008;Forman et al, 2012;Tangdamrongsub et al, 2015).…”