Abstract
Data collected by gauges represent a fundamental force in most hydrological studies. On the basis of sensor type and recording system, such records are characterized by different aggregation time, ta. In this review paper, a comprehensive rainfall database of rain gauge networks operative worldwide is used to determine the temporal evolution of ta. As a second step, issues related to the limited and heterogeneous temporal resolution of rainfall data are discussed with regard to avoiding possible errors in the analysis of historical series. Particular attention is focused on quantifying the effects on the estimation of extreme rainfalls that play a crucial role in designing hydraulic structures. To this aim, algebraic relations for improving a correct determination of extreme rainfall are also provided.
Highlights
As is widely recognized, rainfall data is necessary for the mathematical modelling of extreme hydrological events, such as droughts or floods [1], as well as for evaluating surface and subsurface water resources and their quality.The phase, quantity, and elevation of generic hydrometeors in the atmosphere [2,3,4,5,6]can be estimated by ground-based radars
When rainfall records are characterized by coarse time resolution, the underestimation error in the determination of the annual maximum rainfall depth for a fixed d can be considered as a random variable following an exponential probability distribution with entity inversely correlated to Hd [42]
Rainfall observations are available with different time resolutions, with typical values between 1 min and 1 day, due to the development of recording systems over time
Summary
Rainfall data is necessary for the mathematical modelling of extreme hydrological events, such as droughts or floods [1], as well as for evaluating surface and subsurface water resources and their quality. Long series of Hd values typically include a relevant number of possible underestimated values deriving from rainfall data with coarse ta , grouped with elements obtained from high-time-resolution data recorded in the last two to three decades This issue, together with other crucial elements (relocation of stations, use of different rain gauge types, and change of station surroundings), may determine relevant effects on many related investigations, such as those related to the determination of rainfall depth–duration–. Independently of the main objective of this paper, we note that well-known measurement errors (e.g., the amount of rainwater lost during the tipping movement of the bucket, wind influence on precipitation measurements due to interaction between the gauge body and the airflow, debris in the bucket, inappropriate location of the sensor) remain mostly ignored, and the historic information contained in the archived rainfall series continues to be affected by significant biases and uncertainties Such errors propagate in the derivation of rainfall statistics related to the expected frequency of rainfall events, the calculation of design rainfall for engineering works, and other hydrological applications. The same is true in the field of climatology, where the quality and homogeneity of historic rainfall records is imperative to ensure that the assessment of possible climatic trends is correctly substantiated
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