Characterizing Times Between Storms in Mountainous Areas

Authors: Bonta, James - Jim; NAYAK, ANURAG - UNIVERSITY OF IDAHO

Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/17/2008
Publication Date: 10/31/2008
Citation: Bonta, J.V., Nayak, A. 2008. Characterizing Times Between Storms in Mountainous Areas. Transactions of the ASABE. 51(6):1-16.

Interpretive Summary: An exploratory investigation was conducted on how two parameters that characterize dry times between storms (average time between storms, ATBS, and minimum dry time between storms, MTBS) vary with elevation in mountainous areas, and how these two parameters may be estimated in areas without detailed precipitation data. 16 rain gauges with hourly data spanning an elevation change of 982 m, from 1188 m to 2170 m, in Idaho were used. Dry times between storms could be modeled using the exponential frequency distribution for nearly all gages at all elevations, but extreme dry times may follow another distribution and requires further study. Both ATBS and MTBS varied from about 11 hr to 98 hr (~ 4 days) for all months. ATBS varied with elevation, with shorter ATBS values at higher elevations. There was no consistent variation with elevation for MTBS. ATBS could be modeled well with a semilog equation for individual gauges as elevation changes. ATBS could be estimated well if average annual precipitation, average monthly precipitation, and elevation were known, but MTBS could be estimated using ATBS for individual gauges. The results of the study suggest that ATBS must be estimated first using the 3 variables above, and then MTBS estimated from ATBS. This study adds to our body of knowledge of how these 2 parameters vary horizontally and with elevation, and the relationships will be useful for characterizing dry times in an existing storm-based precipitation model. The results will benefit researchers and practitioners interested in assessing the impacts of land management practices, urbanization, drought studies, and engineering design.

Technical Abstract: An exploratory investigation was conducted on how two parameters that characterize dry times between storms (average time between storms, ATBS, and minimum dry time between storms, MTBS) vary with elevation, and how these two parameters may be estimated for areas without data. 16 rain gauges with hourly data spanning an elevation change of 982 m, from 1188 m to 2170 m, in Idaho were used. The exponential frequency distribution fitted the data well for nearly all gages at all elevations, but extreme dry times may follow another distribution. Both ATBS and MTBS varied from 11 hr to 98 hr. ATBS varied with elevation, with shorter ATBS at higher elevations. There was no consistent variation with elevation for MTBS. ATBS could be modeled with a semilog equation well for individual gauges as a function of elevation. ATBS could be estimated well as a function of average annual precipitation, average monthly precipitation, and elevation, but MTBS could be estimated only as a function of ATBS for individual gauges. The results of the study suggest that ATBS must be estimated first using the 3 variables, and then MTBS estimated from ATBS. This study adds to our body of knowledge of how these 2 parameters vary horizontally and with elevation, and the relationships will be useful for characterizing dry times in an existing storm-based precipitation model. The results will benefit researchers and practitioners interested in assessing the impacts of land management practices, urbanization, drought studies, and engineering design.