Numerous global and regional validation studies have examined MODIS snow mapping accuracy by using measurements at climate stations, which are mainly at open sites. MODIS accuracy in alpine and ...forested regions is, however, still not well understood. The main objective of this study is to evaluate MODIS (MOD10A1 and MYD10A1) snow cover products in a small experimental catchment by using extensive snow course measurements at open and forest sites. The MODIS accuracy is tested in the Jalovecky creek catchment (northern Slovakia) in the period 2000–2011. The results show that the combined Terra and Aqua images enable snow mapping at an overall accuracy of 91.5%. The accuracies at forested, open and mixed land uses at the Červenec sites are 92.7%, 98.3% and 81.8%, respectively. The use of a 2-day temporal filter enables a significant reduction in the number of days with cloud coverage and an increase in overall snow mapping accuracy. In total, the 2-day temporal filter decreases the number of cloudy days from 61% to 26% and increases the snow mapping accuracy to 94%. The results indicate three possible factors leading to misclassification of snow as land: patchy snow cover, limited MODIS geolocation accuracy and mapping algorithm errors. Out of a total of 27 misclassification cases, patchy snow cover, geolocation issues and mapping errors occur in 12, 12 and 3 cases, respectively.
Vegetation cover has a major effect on water flow in soils. Two sites, separated by distance of about 50 m, were selected to quantify the influence of grass cover on hydrophysical parameters and ...heterogeneity of water flow in a sandy soil emerging during a heavy rain following a long hot, dry period. A control soil （pure sand） with limited impact of vegetation or organic matter was obtained by sampling at 50 cm depth beneath a glade area, and a grassland soil was covered in a 10 cm thick humic layer and colonised by grasses. The persistence of water repellency was measured using the water drop penetration time test, sorptivity and unsaturated hydraulic conductivity using a mini disk infiltrometer, and saturated hydraulic conductivity using a double-ring infiltrometer. Dye tracer experiments were used to assess the heterogeneity of water flow, and both the modified method for estimating effective cross section and an original method for assessing the degree of preferential flow were used to quantify this heterogeneity from the images of dyed soil profiles. Most hydrophysical parameters were substantially different between the two surfaces. The grassland soil had an index of water repellency about 10 times that of pure sand and the persistence of water repellency almost 350 times that of pure sand. Water and ethanol sorptivities in the grassland soil were 7% and 43%, respectively, of those of the pure sand. Hydraulic conductivity and saturated hydraulic conductivities in the grassland soil were 5% and 16% of those of the pure sand, respectively. Dye tracer experiments revealed a stable flow with ＂air-draining＂ condition in pure sand and well-developed preferential flow in grassland soil, corresponding to individual grass tussocks and sinai! micro-depressions. The grassland soil was substantially more water repellent and had 3 times the degree of preferential flow compared to pure sand. The results of this study reinforce our view that the consequences of any change in climate, which will ultimately influence hydrology, will be markedly different between grasslands and bare soils.
Snow water equivalents (SWE) produced by the National Centers for Environmental Prediction–U.S. Department of Energy (NCEP–DOE) and 40-yr European Centre for Medium-Range Weather Forecasts (ERA-40) ...reanalyses and snow depths (SD) produced by the 25-yr Japanese “JRA-25” reanalysis over the main Russian river basins for 1979–2000 were examined against measured data. The analysis included comparisons of mean basin values and correlation of anomalies, as well as seasonal and interannual variabilities and trends. ERA-40 generally provided better estimates of mean SWE values for river basins than did the NCEP–DOE reanalysis. Mean SD values from the JRA-25 reanalysis were systematically underestimated. The best correlations among the anomalies were given by ERA-40, followed by JRA-25. All reanalyses reproduced seasonal variability well, although the differences in absolute values varied substantially. The highest differences were typically connected with the snowmelt period (April and May). Interannual variability confirmed the errors of ERA-40 and JRA-25 in 1992–94 and 1979–83, respectively. Otherwise, the reproduction of the interannual variability of SWE and SD was reasonable. Strong biases in SD data from JRA-25 that decrease with time induce artificial positive trends. Significant underestimations of SWE data by ERA-40 for 1991–94 influenced the values of the trends. NCEP–DOE reasonably represented the trend found in measured data. In general, the highest discrepancies between measured and reanalysis data were found for the northern European and eastern Asian rivers (Pechora, Lena, and Amur). The assessment of the quality of SWE and SD reanalysis data can help potential users in the selection of a particular reanalysis as being appropriate to the purpose of their studies.
Research gaps in understanding flood changes at the catchment scale caused by changes in forest management, agricultural practices, artificial drainage, and terracing are identified. Potential ...strategies in addressing these gaps are proposed, such as complex systems approaches to link processes across time scales, long‐term experiments on physical‐chemical‐biological process interactions, and a focus on connectivity and patterns across spatial scales. It is suggested that these strategies will stimulate new research that coherently addresses the issues across hydrology, soil and agricultural sciences, forest engineering, forest ecology, and geomorphology.
Plain Language Summary
This commentary explores research gaps in the field of land use change impacts on floods at the catchment scale and proposes possible ways forward for addressing these gaps. Specifically the impacts of forest management, agricultural practices, artificial drainage, and terracing on flood generation at the catchment scale are explored. Potential strategies in addressing research gaps in these fields are complex systems approaches to link processes across time scales, long‐term experiments on physical‐chemical‐biological process interactions, and a focus on connectivity and patterns across spatial scales. It is suggested that these strategies will stimulate new research that coherently addresses the issues across hydrology, soil and agricultural sciences, forest engineering, forest ecology, and geomorphology.
Key Points
Land use change impacts on floods are poorly understood at the catchment scale
Numerous synergies are identified in exploring the effects of changed agricultural practices, artif. drainage, terracing, and forest cover
A cross‐disciplinary systems approach aided by long‐term field studies and a focus on flow connectivity are needed to make major advances
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•Catchment transforms chemical and isotopic signals of precipitation.•Water flow redistribution in weathered rocks determines elements transport.•Isotopic stratification in the lake ...reflected the location of the subsurface inlets.•Water transit time impact water composition of surface and subsurface flows.
Understanding water flow paths and chemical inputs from the catchment to downstream water bodies is essential for determining sensitivity and response of water resources to climatic, land use and environmental changes. Multivariate analysis of hydrochemical data and estimation of water balance using chloride as a chemical tracer, and oxygen and hydrogen stable isotopes in water as physical tracers were applied to explore surface and subsurface hydrological pathways of water, organic and inorganic solutes in the unmanaged mountain catchment of Plešné Lake (Czech Republic). Nitrate 18O and 15N data were used to support hydrochemical data and hydrological pathways identification. Our results showed that even small variations of water transit time had an important influence on chemical composition in surface and subsurface flows. Water flowing through the subsurface weathered granite had mean transit time of about 11 months and a higher content of geogenic ions due to longer contact with bedrock materials. In contrast, surface flows with a transit time of about 5 months had higher concentrations of dissolved organic carbon, total phosphorus and organic nitrogen due to a higher proportion of water originating from the upper, organic-rich soil horizon. Stratification of oxygen isotopes in the water column of the lake were related to subsurface inlets into the lake. Our results were used to describe the transformation of chemical and isotopic signals by surface and subsurface hydrological pathways in the sensitive headwater catchment.
The consequences of large-scale disturbances magnified by climate extremes and land-use changes in Norway spruce forests in the Tatra Mountains (Slovakia) are assessed in this study. The study area ...is part of the territory of Tatra National Park (TANAP). The driver−pressure−state−impact−response (DPSIR) framework was applied to evaluate how the ecosystem and its services are affected. The state of the ecosystem and its potential for provisioning ecosystem services before and after disturbances is expressed by a set of indicators derived mostly from long-term ecological research conducted in TANAP. The differences are classified by a standardised change index (CI). Ten years after the major windthrow disturbance in 2004, all ecosystem services were still below the pre-disturbance state. The most pronounced declines were found in cultural (average CI = 0.69) and provisioning (average CI = 0.86) ecosystem services. Regulating services are recovering faster (average CI = 0.97), with some indicators exceeding the state before the disturbances. Significant changes took place at the tree line, which is a new phenomenon not known from previous disturbances. Despite a gradual recovery of the ecosystem state and functioning, this analysis confirms that there is a serious risk of decline in forest ecosystem benefits according to regional climate change projections. It also indicates the increasing importance of sustainable forest management for safeguarding ecosystem services under changing conditions.
► We examine the Richards-Baker’s flashiness indices in 122 mountain catchment in Austria and Slovakia in period 1976–2005. ► Trends in flashiness indices were often caused by human hydrotechnical ...activities. ► Among catchment attributes, geology has an important influence on the flashiness index. ► Multivariate regression can describe the main spatial patterns of the flashiness index. ► Statistically significant relationships between the flashiness index and two discharge characteristics were found.
This article evaluates the spatial and temporal changes in streamflow flashiness in 122 mountain catchments in Slovakia and Austria. The flashiness is quantified by the Richards–Baker flashiness index (
FI), which is the ratio of absolute day-to-day fluctuations of streamflow relative to total flow in a year. The analysis is based on daily streamflow data from the period 1976 to 2005. The results show that the average day-to-day fluctuations of streamflow vary from 6% to 43%, depending on the catchment. The spatial pattern of the
FI reflects the variations in the main geological units and generally shows a trend of decreasing flashiness with increasing size of the catchment. Statistically significant temporal trends in flashiness are found in 7 Slovak and 22 Austrian catchments. Most of these trends are related to anthropogenic effects, while, in a few catchments, the change in annual flashiness appears to be caused by changes in precipitation seasonality. A multivariate statistical analysis of
FI indicates negative correlations with catchment area, mean catchment elevation, percents of forest cover, agricultural land and Quaternary geology. Positive correlations are found between
FI and Tertiary and Calcareous geologies. Extrapolating the regression models beyond the observed range of catchment attributes used in the estimation leads to significant prediction errors. In order to better interpret the
FI values, a statistically significant relationship was found between the
FI and the frequency of peak flows exceeding the long-term mean as well as between the
FI and the 5% quantile of daily streamflow.
The snow water equivalent (SWE) and snow depth (SD) in the Aral Sea Basin from the NCEP/DOE, ERA-40 and JRA-25 reanalyses were examined against the measured data. The SWE data from the ERA-40 and SD ...from the JRA-25 reanalyses demonstrated good agreement with the measured data in the plain part of the Aral Sea Basin in the terms of the mean values (1979–2000) and the correlation coefficients. For the mountain part of the basin, however, the agreement was less consistent, and all the reanalyses tended to underestimate the SWE and SD. The interannual variability of the snow cover area (SCA) from satellite data in the Aral Sea Basin (1971–2006) was also analyzed. The biggest fluctuations of the SCA were observed between 1971 and 1982, and between 1995 and 2005, and the lowest ones during 1983 through 1993. The analysis of the long-term variability of the SD revealed a positive trend during the period from 1930 through 1965 in the upper and middle reaches of the Amudarya and Syrdarya rivers. After 1965, a tendency towards a decrease of the SD in the southern part of the Aral Sea Basin was identified. The analysis of the long-term trends of the SD and the river runoffs in the Amudarya and Syrdarya basins showed that the runoffs of Amudarya and, especially, Syrdarya rivers were increasing, while the SD was mostly decreasing. The SCA in the Aral Sea Basin also exhibited a statistically significant decreasing trend.
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