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Summary The purpose of this paper is to contribute to the understanding of the importance of the initial soil moisture state for flash flood magnitudes. Four extreme events that occurred in different case study regions were analysed, one winter and one autumn flash flood in the Giofiros and Almirida catchments in Crete, and two summer floods in the Rastenberg catchment in Austria. The hydrological processes were simulated by the spatially distributed flash flood model Kampus. For the Crete cases Kampus model was calibrated against remotely sensed soil moisture while for the Austrian case the model was calibrated against observed runoff. Kampus model was then used to estimate the sensitivity of the stream flow peak to initial soil moisture. The largest of the events analysed (in terms of specific peak discharge) was found to have a sensitivity of less than 0.2% flood peak change per % soil moisture change while the smallest event had a sensitivity of more than 3% flood peak change per % soil moisture change. This suggests that initial soil moisture effects on the flash flood response probably depend on event magnitude rather than on the climate or region. Moreover, the Austrian catchment was found to exhibit a more nonlinear relationship between antecedent soil moisture and the peak discharge than the Cretan catchments which was explained by differences in the soil type. [ABSTRACT FROM AUTHOR]

Summary: Time dependent observations of the gravity field are carried out to gain a better understanding about the dynamics of the Earth. Terrestrial measurements are made with gravimeters which monitor temporal changes in the vertical component of the Earth’s gravity field. At present, superconducting gravimeters (SG) are the most precise instruments for long-term stationary continuous observations. Such an instrument, as part of a worldwide gravimeter network, is located at the Geodynamic Observatory Moxa, Germany. The measurements of the SG are affected among other environmental influences by hydrological mass balance changes. The temporal and spatial variability of water distribution in the surrounding of the SG makes a quantification and reduction of such effects a challenging task. For further investigations of these influences an interdisciplinary research project which comprises scientists from hydrology, hydrogeology, geophysics and soil sciences has been launched in the surrounding of the observatory. For this project, the small (≈2km2) catchment which surrounds the observatory has been instrumented with soil moisture and groundwater probes at various locations as well as additional precipitation gauges and a climate measurement station for monitoring of climatological and hydrological parameters in high spatial and temporal resolution. Secondly, a distributed and spatially high resolution hydrological model, based on the modelling system J2000, has been set up for continuous simulation of the hydrological processes in the catchment using daily and hourly time steps. The main purpose of the project is to explore the types and magnitudes of hydrological influence on gravity monitored by the very sensitive superconducting gravimeter. Preliminary assessment showed that the gravimeter records contain noticeable influence due to variations of groundwater, soil water content and snow coverage. These influences interfere with the geodynamic signals, but the observed gravity changes carry interesting information from a hydrological point of view, in that a method for direct, integrative and non-invasive measurement of soil water contents and groundwater variations would be available if the hydrological influence on the response of the gravimeter records is extracted and utilised. This paper concentrates on the measurement and spatially distributed simulation of soil water contents and their effect on the signal of the SG. This is done by qualitative comparison of the volumetric soil water content with the observed gravity variations. Additionally, examples of how the modelled water volumes can be translated into gravity variations by means of a 3D gravimetric model is demonstrated and briefly discussed towards the end of the paper. [Copyright &y& Elsevier]

Summary: The knowledge of soil moisture spatial variability is an important issue for hydrological and climatic studies. This paper investigates the soil moisture spatial pattern obtained from spot measurements carried out in different experimental plots located in small basins of Central Italy. The near-surface volumetric soil moisture content was measured using a portable time domain reflectometer (TDR) over regular grids whose areas ranging in extension from 9 to 8800m2. The sampling in each site was periodically repeated in order to investigate the moisture pattern as function of wetness conditions. The statistical properties of the measurements and the relation of the statistical parameters with the field-mean soil moisture content were analyzed. The results states that the probability distribution can be assumed normal for soil moisture in flat areas and for normalized soil moisture in gentle slope areas. A general decreasing trend of variance with increasing mean moisture content was observed. Moreover, considering the relationship between the field-mean water content and the coefficient of variation an optimal measurements number ranging from 15 to 35, in the worse case, was found for the study areas. The higher number was required for the site with more significant relief. These results were also confirmed through the geostatistical analysis and the correlation with the topographical attributes. Specifically, the correlation lengths were found increasing with the mean areal slope and the mean drainage direction and ranging between 10 and 15m. This is corroborated through geostatistical analysis showing that the natural logarithm of the specific upslope area was the best spatial predictor for near-surface soil moisture when the water volume in the soil is higher. On this basis, the surface and subsurface lateral redistribution of water can be surmised fundamental in spatial organization of soil moisture. [Copyright &y& Elsevier]

Abstract: This paper deals with the effects of land levelling on soil hydrological properties and spatial variability of soil moisture at different depths in bare vineyard fields under different rainfall distributions over the year. The research was carried out in a levelled vineyard in the Penedès region (NE Spain), which is representative of the land management practices in that area. Twelve locations were instrumented in the selected plot to control soil moisture periodically at different depths (0–20, 20–40, 40–60cm, using a TDR tube probe), and runoff (using Gerlach collectors located at the same positions) during the period April 2002–March 2004. Rainfalls were recorded at one-minute intervals in the experimental field using a pluviometer linked to a data-logger. The vine yield and its relationship with the rainfall distribution over the year was evaluated in this levelled vineyard vs. a less transformed vineyard. The land levelling works carried out in the plot before the establishment of the vineyard led to major differences in soil depth (ranging from 50 to 110cm) and in soil layer characteristics along and across the plot. This helps to generate different soil moisture conditions at the same depth at different positions of the plot. The areas located at the top of the plot showed soil moisture conditions in the surface layer that were up to 5% lower than down slope, although with high variability across the plot. Soil moisture in the whole profile depends on the intensity of rainfall more than total rainfall. At high intensities, soil moisture increases only occur in the surface layer, but no significant increases are observed in deeper layers, where vines have most of their roots. On the other hand, under low intensity rainfalls the soil water content increases in the whole profile. Levelled plots showed a yield reduction in comparison with those undergoing less transformation, which was exacerbated by a very irregular rainfall distribution: for a similar total rainfall, but with dry periods during the stages in which the water requirement for vines is higher, grape production was up to 50% lower in areas with high land transformation, where Chardonnay was planted, and up to 16% lower at the bottom areas, where Macabeo was planted. [Copyright &y& Elsevier]

• Two geographically multiple regression models inspect the TWS " spatial" drivers. • The OLS retains the TWS basin-wide drivers, and GWR explains the local drivers. • The GWR highlights the importance of the spatial domain in the TWS investigation. GRACE (Gravity Recovery and Climate Experiment) long-term terrestrial water storage anomaly (TWSA) is attributed to the complex interaction of climatic, physical and anthropogenic drivers. This paper, therefore, explores how different hydroclimatic and anthropogenic processes interact and combine over " space " to produce the mass variations that GRACE-TWSA detects. Using the Nile River Basin (NRB) as a case study, it explicitly analyzes nine hydroclimatic and anthropogenic processes, as well as their relationship to the TWSA in different climatic zones. The analytic method employed the long-term trends derived for both the dependent (TWSA) and independent (explanatory) variables via applying two geographically multiple regression (GMR) approaches: (i) an ordinary least square regression (OLS) model in which the contributions of all variables to TWSA variability are deemed equal at all locations; and (ii) a geographically weighted regression (GWR) which assigns a weight to each variable at different locations based on clustering occurrences. The models' efficacy was investigated using standard goodness of fit diagnostics. The OLS explains that the basin at large TWSA spatial variability significantly attributed to five variables, i.e., precipitation, runoff, surface water storage, soil moisture storage, and population density, (p < 0.0001). The OLS model, however, produced an R2 value of 0.14 with skewed standardized residuals. In contrast, the GWR model retained varying explanatory variables by different climate zone. For instance, the results showed that all nine variables contribute significantly, with varying ranking, to the trend in TWSA in the tropical zone. The evapotranspiration (ET) and population density are the only significant variables in the semiarid zone; population density contributes significantly to TWSA variability in all zones. The GWR model yielded R2 values with a median of 0.71 and normally distributed standard residuals. To evaluate the robustness of the GWR approach, the basin-wide TWSA pattern was simulated using the GWR model outputs. Herein, the GWR highlights the importance of the spatial locations to attribute the spatial variability in GRACE TSWA long-term trends. This spatial information, therefore, is critical for developing robust statistical models for reconstructing time series of proxy GRACE anomalies that predate the launch of the GRACE and for gap-filling between GRACE and GRACE Follow-On (GRACE-FO) mission. [ABSTRACT FROM AUTHOR]