Clayton L. Hanson

Stochastic Weather Simulation: Overview and Analysis of Two Commonly Used Models

Abstract Two stochastic weather simulation models (USCLIMATE and CLIGEN) were compared for their performance in replicating observed precipitation, temperature, and solar radiation variables at six locations in the United States. Statistical tests of significance were performed on means and standard deviations of a variety of standard and derived daily weather variables over monthly and annual time periods. Model replication of extreme events also was evaluated. In general, mean monthly and annual values were well replicated by both models, but variance replication of temperature and solar radiation were found superior in USCLIMATE. Extreme-value replication, especially over short (24-h) time intervals, was highly a function of climatic element, location, and time of year but, in general, was judged only fair in both models. Suggestions for model improvement and enhancement are given, as are suggestions for model applications.

Modeling Evapotranspiration and Surface Energy Budgets Across a Watershed

Transport of mass and energy between and within soils, canopies, and the atmosphere is an area of increasing interest in hydrology and meteorology. On arid and semiarid rangelands, evapotranspiration (ET) can account for over 90% of the precipitation, making accurate knowledge of the surface energy balance particularly critical. Recent advances in measurement and modeling have made the accurate estimate of ET and the entire surface energy balance possible. The Simultaneous Heat and Water (SHAW) model, a detailed physical process model capable of simulating the effects of a multispecies plant canopy on heat and water transfer, was applied to 2 years of data collected for three vegetation types (low sagebrush, mountain big sagebrush, and aspen) on a semiarid watershed. Timing and magnitude of ET from the three sites differed considerably. Measured and simulated ET for approximately 26 days of measurement in 1990 were 41 and 44 mm, respectively, for the low sagebrush, 74 and 69 mm for the mountain big sagebrush, and 85 and 89 mm for the aspen. Simulated and measured cumulative ET for up to 85 days of measurement at the three sites in 1993 differed by 3–5%. Simulated diurnal variation in each of the surface energy balance components compared well with measured values. Model results were used to estimate total ET from the watershed as a basis for a complete water budget of the watershed.

Quantification of precipitation measurement discontinuity induced by wind shields on national gauges

Various combinations of wind shields and national precipitation gauges commonly used in countries of the northern hemisphere have been studied in this paper, using the combined intercomparison data collected at 14 sites during the World Meteorological Organizations (WMO) Solid Precipitation Measurement Intercomparison Project. The results show that wind shields improve gauge catch of precipitation, particularly for snow. Shielded gauges, on average, measure 20–70% more snow than unshielded gauges. Without a doubt, the use of wind shields on precipitation gauges has introduced a significant discontinuity into precipitation records, particularly in cold and windy regions. This discontinuity is not constant and it varies with wind speed, temperature, and precipitation type. Adjustment for this discontinuity is necessary to obtain homogenous precipitation data for climate change and hydrological studies. The relation of the relative catch ratio (RCR, ratio of measurements of shielded gauge to unshielded gauge) versus wind speed and temperature has been developed for Alter and Tretyakov wind shields. Strong linear relations between measurements of shielded gauge and unshielded gauge have also been found for different precipitation types. The linear relation does not fully take into account the varying effect of wind and temperature on gauge catch. Overadjustment by the linear relation may occur at those sites with lower wind speeds, and underadjustment may occur at those stations with higher wind speeds. The RCR technique is anticipated to be more applicable in a wide range of climate conditions. The RCR technique and the linear relation have been tested at selected WMO intercomparison stations, and reasonable agreement between the adjusted amounts and the shielded gauge measurements was obtained at most of the sites. Test application of the developed methodologies to a regional or national network is therefore recommended to further evaluate their applicability in different climate conditions. Significant increase of precipitation is expected due to the adjustment particularly in high latitudes and other cold regions. This will have a meaningful impact on climate variation and change analyses.

Water Intake and Runoff as Affected by Intensity of Grazing.

bilize after one summer’s rainfall. Soit Movement on the PZots.Generally, the lower half of the 12-ft-long plots underwent more erosion than the upper half, possibly owing to increased velocity and quantity of surface flow on the lower half. The cleared, pitted, and seeded plots were the only ones showing distinctly greater erosion from the upper half than from the lower half. The cleared and pitted plots, the cleared and seeded plots, and the pitted and seeded plots, showed equal amounts of erosion in the upper and lower halves. Effects of Treatments on Surface Runoff. There was little correlation between treatments RAINFALL EFFECTS

Spatial Variability and Interpolation of Stochastic Weather Simulation Model Parameters

Abstract The spatial variability of 58 precipitation and temperature parameters from the “generation of weather elements for multiple applications” (GEM) weather generator has been investigated over a region of significant complexity in topography and climate. GEM parameters were derived for 80 climate stations in southern Idaho and southeastern Oregon. A technique was developed and used to determine the GEM parameters from high-elevation snowpack telemetry stations that report precipitation in nonstandard 2.5-mm (versus 0.25 mm) increments. Important dependencies were noted between most of these parameters and elevation (both domainwide and local), location, and other factors. The “parameter-elevation regressions on independent slopes model” (PRISM) spatial modeling system was used to develop approximate 4-km gridded data fields of each of these parameters. A feature was developed in PRISM that models temperatures above and below mean inversions differently. Examples of the spatial fields derived from th...

Compatibility evaluation of national precipitation gage measurements

Compatibility of precipitation measurements of various national gages commonly used in the Northern Hemisphere countries has been evaluated, based on the gage intercomparison data collected at 10 stations during the World Meteorological Organization (WMO) Solid Precipitation Measurement Intercomparison Project. Little difference (less than 5%) is found between national rainfall data, but a significant discrepancy (up to 110%) exists between national snowfall records. This difference is not constant and it varies with wind speed and temperature. It is certain that use of different precipitation gages in neighboring countries has introduced a significant discontinuity into precipitation records, particularly in cold and windy regions. Strong linear relations among daily national gage measurements have been defined for several national gages commonly used in the Northern Hemisphere. These linear relations provide a useful technique to adjust gage records when wind speed and temperature data are not available. The linear relations have been tested at selected WMO intercomparison stations, and good agreements of the adjusted amounts to other gage measurements are obtained at most of the test sites, indicating that the linear relations perform reasonably well at the selected WMO sites. Use of the proposed adjustment procedure will reduce inconsistency between precipitation measurements of national gages.

Topographic and Atmospheric Influences on Precipitation Variability over a Mountainous Watershed

Abstract Using rotated principal component analysis (PCA), unique, orthogonal spatial patterns of daily and monthlyprecipitation on a well-instrumented, mountainous watershed in Idaho are examined for their relationship totopography, geographic location, and atmospheric variability. Precipitation pattern and homogeneous precipitationregion differences between daily and monthly timescales and between winter and summer Seasons were identifiedusing the rotated PCA procedure. In general, monthly data produced regional boundaries more closely alignedwith topography, reflecting the integration of many storm events on monthly timescales. Spatial fields, derivedfrom mapping rotated component loadings at 46 precipitation stations on a 234-kmz watershed, were found tobe highly correlated with topography and geographic location. The eight-year time series of the components forspecific watershed regions were found to be moderately related to linear combinations of meteorological variablesderived from a single radioso...

The Spatial and Temporal Influence of Vegetation on Surface Soil Factors in Semiarid Rangelands

Technology for modeling runoff and erosion on rangelands has improved, but improvements in simulation accuracy are often lost in techniques used to estimate model parameters. This is particularly true on semiarid rangelands which have significant spatial and temporal variations in runoff and erosion processes. The spatial distribution of the amount and kind of vegetation is an important factor controlling infiltration and erosion rates on rangelands. Improvements in model parameter estimation techniques and in our understanding of vegetation and soil induced variability are needed to increase our hydrologic and erosion predictive capabilities for rangelands. The role vegetation performs in controlling the spatial and temporal variability of surface soil properties that influence infiltration and erosion on semiarid rangelands was investigated using data representing a northwest sagebrush plant community and a southern great plains bunchgrass/sodgrass plant community. Vegetation was found to be the primary factor influencing the spatial and temporal variability of surface soil processes controlling infiltration and interrill erosion rates on semiarid rangeland. On sagebrush dominated landscapes, vegetation growth form (e.g., bunchgrass, sodgrass, shrub) is the primary factor influencing surface soil factors that control infiltration and erosion rates. On grass dominated landscapes the temporal response of surface soil factors induced by normal variations in climate, plant cover and biomass is greater than the spatial variability induced by grass growth form. To improve the utility of models for use on rangeland we must fully recognize that the rangeland system is spatially and temporally influenced by the amount and growth form of native vegetation.

An evaluation of the Wyoming Gauge System for snowfall measurement

The Wyoming snow fence (shield) has been widely used with precipitation gauges for snowfall measurement at more than 25 locations in Alaska since the late 1970s. This gauges measurements have been taken as the reference for correcting wind-induced gauge undercatch of snowfall in Alaska. Recently, this fence (shield) was tested in the World Meteorological Organization Solid Precipitation Measurement Intercomparison Project at four locations in the United States of America and Canada for six winter seasons. At the Intercomparison sites an octagonal vertical Double Fence with a Russian Tretyakov gauge or a Universal Belfort recording gauge was installed and used as the Intercomparison Reference (DFIR) to provide true snowfall amounts for this Intercomparison experiment. The Intercomparison data collected were compiled at the four sites that represent a variety of climate, terrain, and exposure. On the basis of these data sets the performance of the Wyoming gauge system for snowfall observations was carefully evaluated against the DFIR and snow cover data. The results show that (1) the mean snow catch efficiency of the Wyoming gauge compared with the DFIR is about 80–90%, (2) there exists a close linear relation between the measurements of the two gauge systems and this relation may serve as a transfer function to adjust the Wyoming gauge records to obtain an estimate of the true snowfall amount, (3) catch efficiency of the Wyoming gauge does not change with wind speed and temperature, and (4) Wyoming gauge measurements are generally compatible to the snowpack water equivalent at selected locations in northern Alaska. These results are important to our effort of determining true snowfall amounts in the high latitudes, and they are also useful for regional hydrologic and climatic analyses.

Long‐Term Soil Water Content Database, Reynolds Creek Experimental Watershed, Idaho, United States

We describe long-term soil water data collected at the Reynolds Creek Experimental Watershed (RCEW). Data were collected for 10 -25 years at 18 sites representing different climatic regimes and soils in the RCEW. Soil profile data are also available. High correlation between neutron probe and lysimeter measurements are the basis for assessing the accuracy of neutron probe-measured changes in soil water content. These data are available to the public via the U.S. Department of Agriculture, Agricultural Research Service, Northwest Watershed Research Center anonymous ftp site ftp.nwrc.ars.usda.gov.