Effect of direction of thunderstorm movement on peak discharge in a long narrow southeastern Arizona watershed

Abstract

Thunderstorms in the southwestern United States move significant distances during their life cycle. Due to regional geologic characteristics, small watersheds in southeastern Arizona valleys are typically long and narrow, and direction of thunderstorm movement across such watersheds may have a significant effect on peak discharge rate. Recording rain gage data from thunderstorms occurring over a long narrow watershed near Tombstone, Arizona was analyzed to verify that they can move appreciable distances. A conceptual distributed rainfall-runoff model was modified-to simulate hydrologic processes in a semi-arid area, and calibrated and checked using data from 17 major events. Actual movement direction was estimated for five major thunderstorms. Data from these storms was recentered over five points along the length of the watershed and rotated in eight different directions, and results were passed to the rainfall-runoff model to demonstrate the effect of direction of thunderstorm movement on peak discharge rate. When the storms were centered over the watershed centroid, simulated peak flows were significantly higher for downbasin movement of two storms, slightly higher for downbasin movement of one storm, and slightly higher for upbasin movement of two storms. Possible reasons for these findings were investigated.