Recharge estimation and soil moisture dynamics in a Mediterranean, semi-arid karst region

Abstract

Abstract. Knowledge of soil moisture dynamics in the unsaturated soil zone provides valuable information on the temporal and spatial variability of groundwater recharge. This is especially true for the Mediterranean region, where a substantial fraction of long-term groundwater recharge is expected to occur during high magnitude precipitation events of aboveaverage wet winters. To elucidate process understanding of infiltration processes during these extreme events, a monitoring network of precipitation gauges, meteorological stations, and soil moisture plots was installed in an area with a steep climatic gradient in the Jordan Valley region. In three soil moisture plots, Hydrus-1D was used to simulate water movement in the unsaturated soil zone with soil hydraulic parameters estimated by the Shuffled Complex Evolution Metropolis algorithm. To generalize our results, we modified soil depth and rainfall input to simulate the effect of the pronounced climatic gradient and soil depth variability on percolation fluxes and applied the calibrated model to a time series with 62 years of meteorological data.Soil moisture measurements showed a pronounced seasonality and suggested rapid infiltration during heavy rainstorms. Hydrus-1D successfully simulated short and longterm soil moisture patterns, with the majority of simulated deep percolation occurring during a few intensive rainfall events. Temperature drops in a nearby groundwater well were observed synchronously with simulated percolation pulses, indicating rapid groundwater recharge mechanisms. The 62-year model run yielded annual percolation fluxes of up to 66 % of precipitation depths during wet years and of 0 % during dry years. Furthermore, a dependence of recharge on the temporal rainfall distribution could be shown. Strong correlations between depth of recharge and soil depth were also observed.

Seasonal changes in the soil moisture distribution around bare rock outcrops within a karst rocky desertification area (Fuyuan County, Yunnan Province, China)

“…3). A similar seasonality is reported in more detail by Ries et al (2015) for a semiarid karst area in the Jordan Rift Valley. Throughout the dry season, their records show low soil moisture values similar to those observed here.…”

“…At the beginning of the wet season, the soil profiles were found to be wetted from the top to the bottom; yet after heavy rainfall events within the wet season, saturated conditions started to develop at the rock-soil interface, suggesting rapid infiltration into deeper portions of the soil. According to Ries et al (2015), the saturated conditions persisted at maximum two days. As our measurements were taken after three days without rain, the observed water contents in the wet season are expected to represent values close to field capacity rather than saturation.…”

Effects of juniper removal and rainfall variation on tree transpiration in a semi-arid karst: evidence of complex water storage dynamics

“…Intense summer drought conditions, by reducing the water transport capacity of trees, set the stage for a subsequent wet fall and winter to saturate the rhizosphere and increase the chance of deep drainage by bypass flow, further reducing the hydrological differences between intact and cleared woodlands. In this light, the global trend towards more extreme precipitation patterns, combined with warming, may ultimately have a pronounced impact on groundwater recharge in karst and other regions where focused recharge is important (Ries et al, 2015;Meixner et al, 2016;Thomas et al, 2016). Additional effects imposed by spatially and temporally confined reductions of woody plant cover may be small in comparison.…”

Usefulness of Soil Moisture and Actual Evapotranspiration Data for Constraining Potential Groundwater Recharge in Semiarid Regions

“…Soil moisture has been widely used for estimating groundwater recharge usually through constraining localscale numerical models (Andreasen et al, 2013;Chen et al, 2014;Emerman, 1995;Jiménez-Martínez et al, 2009;Kendy et al, 2003;Lu et al, 2011;Mathias et al, 2017;Min et al, 2015;Ragab et al, 1997;Ries et al, 2015;Sorensen et al, 2014;Wang et al, 2016;Xie et al, 2018). These studies are mostly at the scale of 1-D vertical soil column and often utilize multiple depths of soil moisture measurements (e.g., Chen et al, 2014;Min et al, 2015).…”