Using bias-corrected Nexrad precipitation estimates and spatial statistics of rainfall intensity, we examine the influence of irrigation on summer precipitation in the Texas High Plains. In this region, human alteration of the surface water and energy balance has been extreme. Irrigation enhances precipitation downwind, yielding storms of greater duration, length, and accumulation. Irrigation water is not a significant source of moisture feeding precipitation; rather, the cool, wet surface increases low-level instability, triggering storms. We estimate that an additional 6% to 18% of summer precipitation attributable to irrigation falls ~90 km downwind of the irrigated region.