Hydraulic conductivity spatiotemporal variability in watersheds

Saturated hydraulic conductivity (Ks) is a key parameter in hydrology, though its variability in space and time is far from being completely understood up to now (Rienzner and Gandolfi 2014). Ks varies extensively across spatial and temporal scales due to heterogeneities in soil, vegetation, and cover characteristics. The spatial variability of Ks is a function of both the method and the scale of measurement (Kargas et al. 2017). Accordingly, field estimated values of Ks are fully representative only of the point and the time at which the measurement is taken (Rienzner and Gandolfi 2014). Furthermore, relationships between Ks and other soil characteristics are not strong enough to provide sufficiently accurate predictions of its value (Chirico et al. 2007). The fact that soil properties vary on a scale of a few meters, complicates hydrological processes modeling in larger areas such as watersheds (Dingman 2002). Thus, the small-scale values that it is possible to measure and the effective values required in models are actually different quantities (Beven 2012). Apart of the heterogeneities related to soil and cover properties, disturbances such as wildfires, floods etc. that are also part of natural ecosystems dynamics may influence Ks spatial and temporal variability (Zimmermann and Elsenbeer 2008; Kargas et al. 2016; Soulis 2018). Human induced changes may play a significant role in altering hydrologic response in natural watersheds as well (Soulis et al. 2015). Forest fires cause widespread and abrupt changes that may have a marked effect on hydrological response. The impacts of forest fires on the hydrological cycle can be direct, due to the destruction of the vegetation cover, as well as indirect by altering the hydraulic properties of the soil (Soulis et al. 2012; Zhou et al. 2015). In order to investigate the spatial and temporal variability of Ks at multiple scales in natural watersheds, six measurement campaigns covering a 14 years period were performed in a small-scale experimental watershed in Greece. The watershed was also affected by a major forest fire that provided the additional opportunity to investigate as well the effect of major disturbances in spatial and temporal variability of Ks.