PNNL

Abstract

Hydrologic modeling depends on having quality meteorological input available at the simulation timestep. Often two needs arise, disaggregation from daily to subdaily, and extending the available subdaily record. Simple techniques were tested for generating hourly air temperature, precipitation, solar radiation, relative humidity, and wind speed from limited daily data at the H.J. Andrews Experimental Forest, Oregon. Skill of the daily-to-hourly methods ranged from poor to very good. The best method for each variable had bias 0.5, with the exception of wind speed, which had a bias problem related to change in measurement height. Significance of the disaggregation assumptions for simulated hydrology was evaluated by driving the watershed model DHSVM with alternative meteorological inputs. The largest differences in streamflow simulation efficiency were related to differences in precipitation phase, which followed from the air temperature method used. The largest differences in annual water balance were related to the humidity model used; the common assumption that daily dewpoint temperature equals minimum air temperature caused sharply higher evapotranspiration. Hourly streamflow and annual water balance were less sensitive to uniform distribution of precipitation throughout the day and parameterization of solar radiation. The set of best methods and daily data from a nearby station were used to extend the hourly meteorological record of the target station back in time, facilitating hydrologic and ecologic modeling over the entire experimental period at HJA.