Water loss from a shortgrass steppe

Abstract

Daily and hourly water loss from a shortgrass steppe in northeastern Colorado was determined for four years (1972–1975) with a weighing lysimeter. Daily potential evapotranspiration rates were also calculated, and canopy resistance was evaluated on an hourly basis for selected days. The results show that on a monthly basis water loss was generally equal to the water input, while actual water loss was substantially lower than the potential evapotranspiration rate. The daily water loss data show that water loss is approximately equal to the potential evapotranspiration rate immediately after large precipitation events, then decreases very rapidly for four days after the event. The precipitation data show that large events (> 15 mm day −1) contribute most of the annual total precipitation, with most of the annual water loss from the system occurring during the period (2–14 days) immediately following the large precipitation events. The hourly water loss data show that when the soil was wet, water loss was maintained at the maximum rate; however, as the soil dried out, the water loss rate fell below the potential rate during the middle of the day, with the rate falling below the potential rate at early morning hours with drier soils. The canopy resistance is fairly low (2–5 s cm −1) when the soil is wet and does not change throughout the daytime; however, as the soil dries, the resistance increases throughout the day with the greatest increase observed on the driest soils.