Semiarid regions exhibit large temporal and spatial variability in surface conditions and, therefore, pose a challenge for estimating components of the surface energy budget. In particular, it is difficult to estimate the evapotranspiration component of the hydrological cycle. Because evapotranspiration is strongly controlled by absorbed solar radiation, an attempt has been made here to evaluate the accuracy at which the downward shortwave irradiance (SW↓) can be estimated from satellites on basin scale. It was demonstrated that even under highly variable cloud conditions, satellite estimates of SW↓ daily means were within 10% of measured values, while 5-day means were within 3% of measured values. Such accuracies are of relevance for hydrological modeling at watershed and basin scales. ¿ American Geophysical Union 1994