Hydrology, Volume 2, Issue 2 (June 2015) – 3 articles , Pages 48-111

Most models evaluated by the Intergovernmental Panel for Climate change estimate projected increases in temperature and precipitation with rising atmospheric CO₂ levels. Researchers have suggested that increases in CO₂ and associated increases in temperature and precipitation may stimulate vegetation growth and increase evapotranspiration (ET), which acts as a cooling mechanism, and on a global scale, may slow the climate-warming trend. This hypothesis has been modeled under increased CO₂ conditions with models of different vegetation-climate dynamics. The significance of this vegetation negative feedback, however, has varied between models. Here we conduct a century-scale observational analysis of the Eastern US water balance to determine historical evapotranspiration trends and whether vegetation greening has affected these trends. We show that precipitation has increased significantly over the twentieth century while runoff has not. We also show that ET has increased and vegetation growth is partially responsible. Full article

It is always a dream of hydrologists to model the mystery of complex hydrological processes in a precise way. If parameterized correctly, a simple hydrological model can represent nature very accurately. In this study, a simple and effective optimization algorithm, sequential replacement of weak parameters (SRWP), is introduced for automatic calibration of hydrological models. In the SRWP algorithm, a weak parameter set is sequentially replaced with another deeper and good parameter set. The SRWP algorithm is tested on several theoretical test functions, as well as with a hydrological model. The SRWP algorithm result is compared with the shuffled complex evolution-University of Arizona (SCE-UA) algorithm and the robust parameter estimation (ROPE) algorithm. The result shows that the SRWP algorithm easily overcomes the local minima and converges to the optimal parameter space. The SRWP algorithm does not converge to a single optima; instead, it gives a convex hull of an optimal space. An ensemble of results can be generated from the optimal space for prediction purpose. The ensemble spread will account for the parameter estimation uncertainty. The methodology was demonstrated using the hydrological model (HYMOD) conceptual model on upper Neckar catchments of southwest Germany. The results show that the parameters estimated by this stepwise calibration are robust and comparable to commonly-used optimization algorithms. SRWP can be an alternative to other optimization algorithms for model calibration. Full article

Karst springs of the Makook anticline were investigated to get more insight into the hydrogeologic, hydraulic, and hydrodynamic behavior of this complex karst system. Eight springs were studied in terms of hydrogeochemical constituents as well as δ¹⁸O and δ²H during September 2011 to November 2012. For the first time, the local meteoric water line was plotted for the area based on precipitation data from the period November 2011 to April 2012. The regional meteoric line plots between the global and Mediterranean meteoric water lines. The majority of the spring samples plot between the local and Mediterranean meteoric water lines implying influences by Mediterranean air masses, rapid infiltration of rainfall through the karst system and a short residence time (shallow karst aquifers). The correlation of d-excess and saturation index of halite was used to evaluate the evaporation process in karst waters of the area. The temporal variation in isotopic composition of karst springs was observed making it possible to distinguish between different origins for springs and indicate a possible connection between the aquifers and depending on this, the karst system can be classified into three aquifers: Behkme aquifer, Kometan aquifer, and Shiranish aquifer. Full article