Hydrology Seminar – Monday 16 July, 2pm

Dr Taufique Mahmood, of the Global Institute of Water Security and Centre for Hydrology, will present a seminar on
Hydrologic Spatial Patterns in a semiarid Ponderosa Pine hillslopes
on Monday 16 July, 2012, at 2:00pm, in Room 146 Kirk Hall
Ponderosa pine forests are a dominant land cover type in semiarid montane areas. Water supplies in major rivers of the southwestern United States depend on ponderosa pine forests as these ecosystems:
(1) receive a significant amount of rainfall and snowfall,
(2) intercept precipitation and transpire water, and
(3) indirectly influence runoff by impacting the infiltration rate.
However, the hydrologic patterns in these ecosystems with strong seasonality are poorly understood. In this study, we use a distributed hydrologic model to understand hydrologic patterns in a patchy ponderosa pine landscape. Our modeling effort is focused on the hydrologic responses during North American Monsoon (NAM) and winter to summer transitional period.
Our findings indicate that vegetation patterns primarily influence the hillslope hydrologic response during dry summer periods leading to patchiness related to the ponderosa pine stands. The spatial response patterns switch to fine-scale terrain curvature controls during persistently wet NAM periods. Thus, a climatic threshold involving rainfall and weather conditions during the NAM is identified in the hillslope response when sufficient lateral soil moisture fluxes are activated by high rainfall amounts and the lower evapotranspiration induced by cloud cover.
Our findings on the winter to summer transitional period indicate the importance of the relative wetness of each season. For a sequence with a wet winter and a dry summer, a robust snowpack results in abundant soil moisture in the hillslope that persists until the summer season when evapotranspiration consumes it. Under these conditions, the hillslope lateral transport becomes disconnected during the spring transition. We observe an opposite sequence of events when a dry winter is followed by a wet summer period. For each case, the spatial controls on hillslope hydrologic patterns are assessed relative to the terrain and vegetation distributions.
Results from this work have implications on the design of hillslope experiments, the resolution of hillslope scale models, and the prediction of hydrologic conditions in ponderosa pine landscapes. Further, the proposed methodology can be useful for predicting responses to climate and land cover changes that are anticipated for the southwestern United States.