FORCING, INTERMITTENCY, AND LAND-SURFACE HYDROLOGIC PARTITIONING

Because of sampling problems, the precipitation estimates from satelli te remote sensing are aggregated over time (typically monthly) and ove r space. Since land surface hydrologic processes have threshold and no nlinear dependencies on precipitation, coarse-resolution precipitation observations may not be directly used in hydrologic models. Differenc es in the character of intermittency of precipitation, the averaged va lues remaining the same, can in fact yield large differences in the hy drologic partitioning and therefore in the resulting climate. In this paper an equilibrium hydrologic model is used to Study the influence o f,intermittency on the way precipitation is partitioned into different hydrological quantities. The parameters defining intensity and durati on of storms are varied (keeping total precipitation volume constant), and the resulting effects on the partitioning into runoff, evaporatio n, recharge, and soil moisture storage are determined. It is found tha t the character of intermittency in storm arrivals has a large impact on the hydrologic partitioning. Furthermore, investigations on the sen sitivity of hydrologic partitioning on soil type and water table depth show that rainfall intermittency plays a major role irrespective of t hese other factors. Runoff generation, evaporation, and groundwater re charge are the three main components of the water balance. Depending o n the soil type and climate, the main competition is between different combinations of these three loss mechanisms. It is concluded that the temporal structure of storms has a strong influence on the long-term equilibrium state of the hydrological system.