Kenneth G. Renard

Using monthly precipitation data to estimate the R-factor in the revised USLE

The methods used to calculate both the Revised Universal Soil Loss Equation (RUSLE) erosivity factor (R) and the 10 year frequency storm erosion index value (EI10) are presented. As the calculation methods require long-term rainfall intensity data, and such data are not available for all application sites, an approach used to estimate the R-factor is described. Examples illustrating applications of the estimation technique in Africa, Asia, and other parts of the world are summarized. The method, which establishes correlations between measured R-values and more readily available precipitation data, is used to develop relations for estimating R-values in the USA. Correlations based on average monthly precipitation data and the R-factor values for 155 US stations were initially used to develop estimation relations. The 155 stations were segregated based on the annual distribution of monthly precipitation and the correlations improved. Exclusion of 23 stations with both ‘winter-type’ precipitation distributions and modified Fournier index values greater than 100 mm improved the relations for the remaining 132 stations (r2 = 0.81). An estimation relation for the EI10 is also presented. The R-factor and EI10 estimation relations should facilitate the use of RUSLE for locations with only monthly precipitation data.

Correction to “Sediment yields from unit‐source semiarid watersheds at Walnut Gulch”

[1] This study reports sediment yields from seven small (0.18–5.42 ha) watersheds in Southern Arizona measured from 1995 to 2005. Sediment concentrations and total event sediment yields were related to storm-runoff characteristics, and statistical relationships were developed to estimate sediment yields for events with missing data. Precipitation ranged from 263 to 298 mm yr , runoff ranged from 8.2 to 26.4 mm yr , and sediment yields ranged from 0.07 to 5.7 t ha 1 yr , with an areal average of 2.2 t ha 1 yr . For six of the seven watersheds, between 6 and 10 events produced 50% of the total sediment yields over the 11-year period. On the seventh watershed, two storms produced 66% of the sediment because of differences in the geomorphology and vegetation characteristics of that area. Differences between sediment yields from all watersheds were attributable to instrumentation, watershed morphology, degree of channel incision, and vegetation.

Quantifying Extreme Rainfall Events and Their Hydrologic Response in Southeastern Arizona

AbstractHydrologists are concerned with high-intensity rainfall and peak runoff rates for stormwater infrastructure designs, post-event assessments, and mitigation of environmental impacts. In the southwestern United States the need for accurate information about these rates is increasingly important as population growth and associated development are projected to exceed national averages. Design storm totals for various durations and return period frequencies are routinely derived from the National Oceanic and Atmospheric Administration (NOAA) Atlas 14 and are commonly used as input to hydrologic models to estimate peak runoff rates and runoff volumes. For the southwestern United States during the North American Monsoon, NOAA relies on sparse rain gauge networks to measure rainfall from limited area convective storms primarily at daily time steps and estimates of subdaily event intensities are derived by temporal downscaling from a few point locations. The USDA, Agricultural Research Service, Southwest W...