Evaluation Of Hydrological Models Research Articles

Spatial Variation of Rainfall over a Large Watershed in Central Iowa

Rainfall amounts and the distribution across the landscape are critical to decision-making and evaluation of hydrological models. Spatial variation in rainfall has been observed through anecdotal evidence and limited studies; however, there is little quantitative evidence that can be used to assess rainfall variation within a watershed on a daily, monthly, or yearly temporal scale. This study was conducted to quantify the spatial variation within a watershed in central Iowa and to determine if there were consistent differences among rain gages for the period from 1991 through 1998. The study was conducted within Walnut Creek watershed located south of Ames, Iowa on the Des Moines Lobe Landform region. The topography of this 5130 ha watershed is characterized by gently rolling fields with a narrow area of steeper land along the stream in the lower part of the watershed. Twenty-two tipping bucket rain gages were placed throughout the watershed and rainfall was recorded as 5 minute totals and then aggregated into daily totals. Accumulation of errors of the 5 minute values into the daily totals were considered to be random. There was a large coefficient of variation in the average daily totals; however, there was no consistent pattern of variation among rain gages, and coefficient of variation decreased with amount of rain. Each rain gage had an equal chance of receiving the lowest or highest rainfall total for any given storm event. When the daily average was computed over the year, there were no differences among rain gages. Monthly and yearly totals showed a decreased coefficient of variation compared to daily totals. There was no consistent pattern of spottiness within the watershed and if daily rainfall amounts are required for a decision, then direct measurements may be required.

Point evaluation of a surface hydrology model for BOREAS

Detailed observations of moisture and energy fluxes made at the Boreal Ecosystem‐Atmosphere Study (BOREAS) tower flux sites offer a unique opportunity for the evaluation of hydrological models, since model process representations can be compared with observations. The distributed hydrology‐soil‐vegetation model (DHSVM) was used to simulate the latent and sensible heat fluxes at the old black spruce and old jack pine tower flux sites in the southern study area and the old black spruce tower in the northern study area during the summer of 1994. The model did a reasonable job of simulating both the seasonal average fluxes and the diurnal cycle of the surface heat fluxes. However, a lag was observed in the simulation of the sensible heat flux, which was attributed to an inadequate representation of the ground heat flux and ground heat storage. It was also noted that direct soil evaporation forms an important part of the latent heat flux simulated by the model. Incorporation of a more complete soil thermal model, and further field work in 1996 to evaluate the importance of the moss layer and the direct evaporation from the soil, is expected to lead to further improvements.

Closure to “ Evaluation of Hydrologic Models Used to Quantify Major Land‐Use Change Effects ” by the Task Committee on Quantifying Land‐Use Change Effects of the Watershed Management and Surface‐Water Committees of the Irrigation and Drainage Division (March, 1985, Vol. 111, No. 1)

Closure to “ <i>Evaluation of Hydrologic Models Used to Quantify Major Land‐Use Change Effects</i> ” by the Task Committee on Quantifying Land‐Use Change Effects of the Watershed Management and Surface‐Water Committees of the Irrigation and Drainage Division (March, 1985, Vol. 111, No. 1)

Discussion of “ Evaluation of Hydrologic Models Used to Quantify Major Land‐Use Change Effects ” by the Task Committee on Quantifying Land‐Use Change Effects of the Watershed Management and Surface‐Water Committees of the Irrigation and Drainage Division (March, 1985, Vol. 111, No. 1)

Discussion of “ <i>Evaluation of Hydrologic Models Used to Quantify Major Land‐Use Change Effects</i> ” by the Task Committee on Quantifying Land‐Use Change Effects of the Watershed Management and Surface‐Water Committees of the Irrigation and Drainage Division (March, 1985, Vol. 111, No. 1)

Discussion of “ Evaluation of Hydrologic Models Used to Quantify Major Land‐Use Change Effects ” by the Task Committee on Quantifying Land‐Use Change Effects of the Watershed Management and Surface‐Water Committees of the Irrigation and Drainage Division (March, 1985, Vol. 111, No. 1)

Discussion of “ <i>Evaluation of Hydrologic Models Used to Quantify Major Land‐Use Change Effects</i> ” by the Task Committee on Quantifying Land‐Use Change Effects of the Watershed Management and Surface‐Water Committees of the Irrigation and Drainage Division (March, 1985, Vol. 111, No. 1)

Entropy as a measure of hydrologic data uncertainty and model performance

This paper extends the original use of entropy by Amorocho and Espildora as a measure of uncertainty in hydrologic data and the reduction in that uncertainty due to application of a model. In many situations calculations of entropy are better based on a proportional rather than a fixed class interval. General equations are given for the proportional class interval, are solved for assumed log-normal and gamma distributions, and extended to data series with zero values. The solutions are shown to be independent of the units of measurement of the original data. The results are applied to comparative evaluation of hydrologic models using the same and different data sets, and a new criterion of model performance is suggested for the latter case.