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Catchments with response time shorter than a day require simulations at sub-daily resolution for flood forecasting. Long-term hydrological data with sub-daily time resolution is lacking for many catchments and, thus, it is worthwhile to investigate the potential in using hydrological model parameters calibrated at a daily temporal resolution to simulate sub-daily runoff. This study investigates the potential of directly transferring the parameters from the one-day Hydrological Predictions for the Environment (HYPE) model for Sweden to a one-hour time step version. A sensitivity analysis and calibration of the one-hour model were also performed to explore the possibility of achieving improved model performance through an additive and multiplicative scaling of the parameters. Directly transferring the parameters led to a negligible loss in performance for all 147 catchments evaluated here. Scaling of the parameters did not lead to improvement for slow-responding catchments, while the increase in performance was negligible for catchments with sub-daily response time. [ABSTRACT FROM AUTHOR]

Both monitoring and model simulation are useful for understanding and detecting changes in the environment. To understand and simulate leaching in small forested catchments, it is important to have knowledge of soil processes. Here, we describe recent development of the Hydrological Predictions for the Environment (HYPE) model for forested catchments. HYPE includes an organic carbon (OC) variable in addition to previously published nitrogen (N), phosphorus (P), and water flow models. The aspects addressed in the current study included P concentrations under low-flow conditions and high concentrations of inorganic N. HYPE was further developed based on nine small forested catchments (0.5-200 ha) in Sweden, which were calibrated separately using local data. The model (excluding the OC variable) was tested on a larger set of forest catchments from the operational HYPE model of Sweden (S-HYPE). We observed the following: (1) dissolved organic P could make a significant contribution to the total P concentration in a stream during low-flow periods, (2) the inorganic N concentration simulated in a stream improved when part of the atmospheric N was retained in the soil, (3) the soil flow path formulation was critical for simulating concentration dynamics, and (4) evaluating an additional variable (OC) further elucidated the soil runoff processes in the model. Copyright © 2016 Swedish Meteorological and Hydrological Institute. Hydrological Processes published by John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: Since the early 1970s operational flood forecasts in Sweden have been based on the hydrological HBV model. However, the model is only one component in a chain of processes for production of hydrological forecasts. During the last 35years there has been considerable work on improving different parts of the forecast procedure and results from specific studies have been reported frequently. Yet, the results have not been compared in any overall assessment of potential for improvements. Therefore we formulated and applied a method for translating results from different studies to a common criterion of error reduction. The aim was to quantify potential improvements in a systems perspective and to identify in which part of the production chain efforts would result in significantly better forecasts. The most sensitive (>20% error reduction) components were identified for three different operational-forecast types. From the analyses of historical efforts to minimise the errors in the Swedish flood-forecasting system, it was concluded that 1) general runoff simulations and predictions could be significantly improved by model structure and calibration, model equations (e.g. evapotranspiration expression), and new precipitation input using radar data as a complement to station gauges; 2) annual spring-flood forecasts could be significantly improved by better seasonal meteorological forecast, fresh re-calibration of the hydrological model based on long time-series, and data assimilation of snow-pack measurements using georadar or gamma-ray technique; 3) short-term (2days) forecasts could be significantly improved by up-dating using an auto-regressive method for discharge, and by ensembles of meteorological forecasts using the median at occasions when the deterministic forecast is out of the ensemble range. The study emphasises the importance of continuously evaluating the entire production chain to search for potential improvements of hydrological forecasts in the operational environment. [Copyright &y& Elsevier]

The article presents a study on the new theory on runoff spectrum relative to the hydro-morphological and hydraulic properties of watersheds in Sweden. It shows an increased steepness of runoff Fourier spectrum each year, which suggests a predictable intra-annula runoff pattern. The study employs Fourier analysis and wavelet analysis to determine the coherence and dominant trends of a long-time series of discharge and precipitation in several watersheds.

A system for ensemble stresmflow prediction, ESP, has been operational at SMHI since July 2004, based on 50 meteorologicsl ensemble forecasts from ECMWF. Hydrologicsl ensemble forecasts are produced daily for 51 basins in Sweden. All ensemble members, as well as statistics (minimum, 255/o quartile, median, 75% quartile and maximum), are stored in a database. This paper presents an evaluation of the first 18 months of ESP median forecasts from this system, and in particular their performance in comparison with today's categorical forecast. The evaluation was made in terms of three statistical measures: bias B, root mean square error RMSE and absolute peak flow error PE. For ESP forecasts the bias ranged between -20% and 80% with a systematic overestimation for Sweden as a whole. A comparison between bias in input precipitation and ESP output, respectively, revealed only a weak relationship, but streamflow overestimation is likely related mainly to model properties. The results from the streamflow forecast comparison showed that the ESP median in deterministic terms performs overall as well as the presently used categorical forecast. Further, ESP has the advantage of providing at least a qualitative measure of the uncertainty in the forecasts, with probability forecasts being the ultimate goal. [ABSTRACT FROM AUTHOR]

Recent mild and wet years in Sweden were compared with long observation series of temperature, precipitation and runoff. Spatial average series for northern and southern Sweden were constructed and analyzed for the period 1901-2002. Precipitation increased considerably during the period, whereas temperature and runoff increases were weaker. On average, for the whole country, the differences between the period 1991-2002 and 1901-1990 were + 0.7°C for temperature, + 11% in precipitation and + 7% in runoff. The differences in temperature and precipitation, but not runoff, were significant at the 5% level. However, the 1930s were equally mild, and the runoff was almost as high in the 1920s. The characteristic feature of the past decade is the combination of high temperature, precipitation and runoff. The deviation between the most recent decade and the preceding years is consistent with climate scenario projections for Sweden, but there are also differences in the seasonal pattern. [ABSTRACT FROM AUTHOR]

The effect of soil frost on runoff was investigated using a comprehensive data set collected at the Svartberget Experimental Forest, near Vindeln, Västerbotten in northern Sweden. Measurements of snow depth, soil temperature, frost depth and other climate parameters have been made at three sites since 1981, as part of a long-term climate monitoring programme. Simulation residuals from the HBV rainfall-runoff model, in which no effect of soil frost is assumed, were compared with 16 years of measured soil frost conditions. A simple model for simulation of soil frost depth was developed and incorporated into the HBV model. The model parameters were calibrated to observations of snow depth, soil frost depth, groundwater levels and runoff, by use of a simple weighted optimization criterion. No clear effect of soil frost could be seen on the timing and magnitude of runoff in this analysis, or when analysing data on the conservative oxygen isotope [sup18]O. The soil at the forested site froze in only slightly more than half the years, despite the high latitude and low winter temperatures. Furthermore, the soil had often thawed before the start of the spring flood. Almost all spring floods, therefore, occurred when the soil was unfrozen. Snow depth and soil frost depths were inversely related, with the deepest soil frost during winters with little snow. Soil frost therefore is unlikely to aggravate the very high floods in forested basins of this type, except perhaps under exceptional circumstances such as large rain events on frozen ground. [ABSTRACT FROM AUTHOR]