ABSTRACT
Monitoring is the foundation stone for sound development and protection, for both water resources and the environment. Recent decades have seen increasing attention to the costs of running hydrological monitoring schemes and the accuracy of assessment. The high costs of maintaining ground-based monitoring stations have led to widespread rationalization of station networks. This highlights one of the many conflicts between standard meteorological procedure and the requirements of hydrology, and means that some of the under-measurement problems could be significantly reduced if measurements were being taken solely for hydrological purposes. More recent developments include direct measurement of vapour fluxes in the air using ultrasonic waves or infrared radiometry, but these are restricted to experimental applications. Alternatively, field estimates of soil moisture combines with precipitation, river discharge and groundwater monitoring to calculate evapotranspiration losses.
