Interpretation of hydrologic trends from a water balance perspective: The role of groundwater storage in the Budyko hypothesis

Abstract

[1] We investigate the observed positive trends in annual runoff in several basins in central Nebraska using the Budyko hypothesis as a diagnostic tool. In basins where runoff is dominated by base flow we found that the estimated annual evapotranspiration (ET a ) to precipitation (P) ratio (ET a /P) from data is negatively related to the aridity index (ET p /P, where ET p is potential annual evapotranspiration). This observation is inconsistent with the Budyko hypothesis. We hypothesized that the observed negative trend results from significant interannual changes in basin water storage. This hypothesis is tested using data from groundwater monitoring wells in the Sand Hills region of Nebraska. Plots of the yearly changes in groundwater storage versus the annual aridity index revealed the mean annual aridity index as a critical climatological variable that controls basin storage gain-loss dynamics. For the same absolute deviation from the mean climate, we found that a wetter year leads to a larger gain in groundwater storage than the net loss in a drier year. We argue that this storage gain-loss behavior builds a climate memory in the hydrologic system, causing persistence and statistically significant trends in annual runoff. A parsimonious model was developed that couples the Budyko hypothesis with a linear reservoir equation for base flow and was used to examine the possible causes of observed positive trends of annual runoff. We found that subtle, statistically insignificant, increases in annual P have led to positive and statistically insignificant trends in annual ET a and P À ET a . Annual runoff, on the other hand, was predicted to have high persistence and statistical significance, consistent with observations. Further model sensitivity analyses showed that increasing the size of the groundwater reservoir is associated with increased long-term (multidecadal) persistence in annual runoff and translates high-frequency, high-amplitude variation in climate to low-frequency, low-amplitude runoff response. Our results underscore the importance of evaluating apparent trends in any system variable in a complete water budget context.

New interpretation of the role of water balance in an extended Budyko hypothesis in arid regions

“…Recently, the BH has been widely used to investigate the interannual variability of precipitation partitioning (Gerrits et al, 2009), separation of runoff trends (H.-Y. Xiong et al, 2015), evapotranspiration change (Savenije, 1997) and water storage change (Istanbulluoglu et al, 2012;Gao et al, 2014). These studies show that hydrological processes have been greatly affected by the climate change and intensive change of land cover owing to human activities.…”

Systematic shifts in Budyko relationships caused by groundwater storage changes

“…However, poor performance in some locations, especially over annual or seasonal time periods, has been attributed to the influence of storage changes that violate the steady-state assumption (Milly and Dunne, 2002;Zhang et al, 2008). Istanbulluoglu et al (2012) and Wang et al (2009) showed interannual storage changes can produce a negative correlation between the evapotranspiration ratio and aridity that is counter to the Budyko curve for baseflowdominated basins in the Nebraska Sand Hills. Wang (2012) evaluated inter-annual storage changes for twelve watersheds in Illinois and showed that, on an annual timescale, variability in runoff and storage is larger than evapotranspiration, and accounting for storage can improve the performance of Budyko predictions.…”

Comparison of future runoff projections using Budyko framework and global hydrologic model: conceptual simplicity vs process complexity

“…Most of these studies have been applied at single basins (Donohue et al, 2011;Jiang et al, 2015;Liang and Liu, 2014;Liu and McVicar, 2012;Roderick and Farquhar, 2011;Xu et al, 2014;Zhang X. et al, 2014) or multiple basins within a single region: USA (Chen et al, 2013;Wang and Hejazi, 2011;Carmona et al, 2014;Istanbulluoglu et al, 2012), Australia (Donohue et al, 2010(Donohue et al, , 2012Teng et al, 2012), China (Yang D. et al, 2007(Yang D. et al, , 2009Yang and Yang, 2011;Yang H. et al, 2014;Cong et al, 2015;Xiong and Guo, 2012;Yu et al, 2013) and Europe (Velde et al, 2014;Oudin et al, 2008). The global scale studies have also been conducted but mainly focusing on the development of the Budyko functional forms (Koster and Suarez, 1999;Zhang L. et al, 2001;Arora, 2002) and their parameters (Li et al, 2013;Williams et al, 2012).…”